Starting to study the existing propulsion systems of ships, it is necessary to define this concept. Ship propulsion is a device for converting the work of the ship's power plant into thrust, providing it translational motion... The thrust of the propeller is formed due to the reactive forces arising when the working medium is thrown in the direction opposite to the direction of the ship's translational motion. By the nature of the working environment, the propellers are currently conventionally divided into hydraulic (working medium - water), air (air) and gas-jet (water-air mixture). In turn, hydraulic propellers are subdivided into bladed (paddle, propeller, paddle wheel plates, etc.) and non-bladed (gas jet propellers). An intermediate place in this classification is given to a water jet.
Hydraulic propellers are widely used on all displacement type vessels, air propellers - on high-speed SVP type vessels and ekranoplanes. Of the listed propellers, the manual discusses in more detail the propeller (as the main propeller used on ships) and the water jet propulsion. The thrust of the propeller is formed due to the reactive forces arising when the working medium is thrown in the direction opposite to the direction of the ship's translational motion. The nature
of the working medium, movers are currently conventionally divided into hydraulic (working medium - water), air (air) and gas-jet (water-air mixture). In turn, hydraulic propellers are subdivided into blade (paddle, propeller, paddle wheel, etc.) and non-blade (gas jet propulsion). An intermediate place in this classification is given to a water jet. Hydraulic propellers are widely used on all displacement type vessels, air propellers - on high-speed SVP type vessels and ekranoplanes. Of the propellers listed above, the manual discusses the propeller (as the main propeller used on ships) and the water jet.
In the previous paragraph, we said that there are five main types of power plant on a ship, and each of them is characterized by its own shafting scheme, i.e. a mechanical system for transmitting the rotation of the engine crankshaft to the propeller (propeller). Let's consider in order (fig. 107):
1. The ship is equipped with a conventional stationary converted high-speed engine, which is located in the center of the cockpit, in the area of the midship frame. The crankshaft is connected through a gearbox (to reduce the number of revolutions) by a straight propeller shaft with a propeller (linear shafting diagram). The installation is easy to maintain, efficient, simple, and does not require additional design solutions.
2. The same engine is located aft of the vessel. With this arrangement, a number of advantages are lost, new ones appear (space in the cockpit, noise reduction in the cabin). The major drawback is the constant trim aft and the need to use an angle gearbox (V-shaped, or angular shafting scheme).
3. Scheme of shafting with a swing-out column (Z-shaped transmission) combining the advantages of a stationary engine and a PLM (high engine power, good seaworthiness, tilting the column when colliding with an obstacle, ease of working with the screw and servicing the column, exhaust gases into the water etc.) has one major drawback - high cost.
4. The use of a water jet makes life easier for the navigator due to the absence of any parts protruding below the keel of the vessel, but rather complicates it due to a change in the ship's running characteristics and, above all, deterioration of controllability. The engine is installed slightly farther from the stern than in the previous two cases, which reduces the trim at the stern, there is no need for a coupling and reversing clutch
5. The shafting of outboard boat motors has an L-shape, in which the connection between the engine and the propeller (propeller) is carried out through a reducer using an intermediate, so-called. torsion shaft (spring). PLM does not occupy the usable cockpit area, is easy to maintain and quite cheap
In a number of the shafting options under consideration, the gearboxes used allow simultaneously reversing the propellers - changing the direction of rotation to the opposite. In general, reversing is carried out in three ways: by reversing the main engine, engaging the reverse gear and reversing the propeller itself. Main engine reverse- changing the direction of rotation of the engine crankshaft to the opposite, and, accordingly, changing the direction of the propeller thrust. Such a reverse is provided by a reversing device of the engine itself, the main part of which is a movable camshaft, which provides a predetermined sequence of fuel supply to the cylinders, as a result of which the engine crankshaft begins to rotate in the opposite direction. Reverse gear- this is a transmission with the help of which the direction of rotation of the propeller shaft changes (the propeller shaft is called the shaft on which the propeller is fixed) to the opposite with the same direction of rotation of the engine crankshaft
Reversing is achieved by reversing gear reducers, hydraulic transmission or couplings, which allow disconnecting a part of the gearbox with one direction of rotation and connecting it with another. On boats, reverse gearboxes (reversible clutch) are used - a special mechanism that provides a change in the direction of rotation of the ship's propeller shaft while the direction of rotation of the crankshaft of the ship engine remains unchanged with the inclusion of a gearbox in the design to reduce or a multiplier to increase the number of shaft revolutions. The reverse gear is connected to the crankshaft by flange connections by means of an intermediate shaft or directly (see Fig. 108), the driven shaft is connected to the propeller shaft. The cavity of the gearbox is filled with oil, to check the presence and level of which there is a level indicator (scale). Reverse mover- the change in the direction of the stop created by the propeller is provided by turning the blades at the variable pitch propellers (CPP).
Propeller screw- a device that converts the rotation of the engine shaft into an emphasis - the force pushing the vessel forward. It consists of a hub and several (two or more) blades. The blade of a ship's propeller is a hydrodynamic profile that works at a certain angle of inclination to the water stream, throwing it back and thus creating an emphasis. The blade has an in and out edge
Fig. 108. Two types of bevel gear for stationary motors:
a - with a short intermediate cardan shaft;
b - fixed to the engine.
and working (pumping) surface. The physical essence of the propeller's work is quite simple - when rotating on the surface of its blades facing in the direction of the ship's movement, a vacuum is formed, and those facing backward - increased water pressure. The pressure difference creates a force, one of the components of which moves the ship forward. The thrust is largely dependent on the angle of attack of the blade profile. The optimum value for this angle for speed boats is 4 - 8 °.
Basic concepts when considering the topic and characteristics of the propeller:
Screw pitch- geometric displacement (distance) of any point of the blade along the axis for one complete revolution of the propeller, provided that it makes it in a conditionally solid medium.
Screw diameter- the diameter of the circle into which the straightened propeller blades are inscribed (Fig. 109)
Step ratio- the ratio of the pitch of the screw to the diameter
Disk ratio- the ratio of the area of the straightened blades (without the hub) to the area of the disk, the diameter of which is equal to the diameter of the propeller (Fig. 111). The pitch and disk ratios are the main parameters of the hydrodynamic characteristics of the propeller, on which the degree of use of the engine power and the achievement of the maximum possible speed by the vessel depend. Each propeller of a specific size and fixed pitch has its own propeller characteristic. In principle, an optimal propeller should be selected for each ship's hull and engine. The process of calculating the propeller is complex and is based on the use of existing graphs and diagrams for determining the diameter and pitch of the propeller depending on the shaft power. For low loads and high speeds, a two-blade propeller is usually chosen, for normal loads (on boats) - a three-blade, for high loads and low speeds - a four-blade. The use of a five-blade propeller significantly reduces vibration.
Slip screw- the phenomenon that occurs when the propeller is operating in a water environment under load is the difference between the calculated pitch of the propeller and the actual distance traveled in one revolution. Slip is almost never less than 15% of the propeller pitch, in most cases it is 30%, sometimes about 45-50% of the propeller pitch.
Coefficient of performance (efficiency) of the screw- the ratio of the useful power used to the power expended by the engine depends mainly on the diameter and rotational speed of the propeller. Efficiency is an estimate of the efficiency of the propeller, its maximum value can reach 70-80%, on small ships 45-50%. Knowing the efficiency of the propeller is necessary to calculate the projected speed of the vessel. The efficiency of propellers is also calculated according to numerous graphs and diagrams, which are based on the power factor (load factor) - the ratio of the product of the engine power given to the propeller by its rotational speed to the forward speed of the propeller in the associated flow
Most propellers operate with load factors ranging from 1 to 10. The load factor structure shows that low engine power, low rpm and high speed result in high propeller efficiency. The direction of rotation of the propeller (Fig. 110) in navigation (right - clockwise, left - counterclockwise) set looking from the stern to the bow when the screw is in forward motion and is determined only for forward motion.
Cavitation- the phenomenon of "boiling" of water and the formation of steam bubbles on the suction side of the propeller blade. When the bubbles break down, huge local pressures are created, which causes the blade to spall. With long-term operation, these destruction reaches large values, which negatively affect the operation of the screw. The second stage of cavitation is the formation of a solid cavity on the blade, which can sometimes close even outside of it.
The stop developed by the propeller falls due to a sharp increase in drag and distortion of the shape of the blades. When changing the pitch and diameter of the propeller more or less than the optimal values, moments arise when the engine is either unable to rotate the propeller at a higher speed (does not develop the rated power), or, on the contrary, not only develops, but also easily exceeds the value of the rated crankshaft speed , and since the propeller stop is small, the ship still does not develop high speed. In this case, the concepts come into force light heavy) screw, which are also among the screw characteristics, o. which was mentioned above.
Propellers are made of bronze, brass, stainless and carbon steel, cast iron. For small craft propellers, plastic is used. Metal screws are made cast with subsequent finishing (processing).
The problem of taking into account the changing resistance of the ship's hull when its load changes and more efficient use of the engine under these conditions is quite successfully solved by using a variable pitch propeller (multi-pitch propeller, not to be confused with a variable pitch propeller - VRS). The propeller hub is metal, the interchangeable blades are made of polyamide resins (recently, the propeller hub is also made of them). The blades have rigidly fixed fingers (Fig. 112), which pass into the holes in the end face of the nose of the hub 6 and enter the grooves of the leash 4, which has a measuring scale.
When turning any blade around its axis, all blades turn synchronously in the direction of increasing (decreasing) the pitch of the propeller. Fixing the blades in the selected position is carried out by nut 3. Bushing 5 has an inner diameter equal to the diameter of the propeller shaft of the motor. From axial movement in the bushing, the screw is fixed with a nut 3 and a locking screw 8. The step change operation takes 3-5 minutes with skill and does not require approaching the bank and removing the screw. For PLM "Vikhr" such screws were produced by the Chernomorsk shipyard.
Rowing adjustable pitch screws differ in the complexity of the device, massive hub and high cost, since the blades are turned to change the pitch of the propeller remotely, during operation (rotation). These propellers were discussed when we talked about changing the mode of movement of the vessel from "full forward" to "stop" and "full reverse" only with the help of the propulsion device. The advantages of the CPP: the ability to use the full power of the engine at various modes of vessel motion and obtain the entire speed range without changing the direction and speed of the propeller shaft; saving fuel and increasing the engine life. The disadvantages of the CPP: the complexity of the design, a decrease in the efficiency of the engine due to the increased size of the hub and the distortion of the profile of the blades during their turn in intermediate operating modes, low efficiency in reverse. To increase the efficiency of the propeller on heavy displacement ships, it is often used ring shaped nozzle(Fig. 113), which is a closed ring with a flat-convex profile .. The area of the inlet section of the nozzle is greater than the area of the outlet, the screw is installed in the narrowest place and with a minimum (0.01 D of the screw) clearance between the edge of the blade and the inner surface of the nozzle ... When the screw is operating, the sucked flow increases the speed due to a decrease in the flow area of the nozzle, as a result of which the slip of the screw decreases. An additional emphasis is created on the nozzle itself (due to the flow of water, it is similar to a wing). The action of the jet propulsion unit is based on the well-known Newton's law: the mass of water thrown by the propulsion unit into the stern creates, in the form of a reaction, stubborn pressure that propels the vessel forward.
Water jet (water cannon) can be imagined as a powerful pump that draws water from under the bottom and ejects it behind the transom from a nozzle above the water. The water cannon differs from the propeller only in that the propeller (pump wheel) is installed in a pipe inside the vessel. In this case, the ship is steered and reversing is carried out in different ways. The most applicable control method for us is by turning the jet in the exhaust nozzle using a double-leaf reversing-steering device, consisting of two flat plates (rudders) connected to each other and hinged to the reversing box. In this case, on the forward course, the rudders are shifted parallel to each other, changing the direction of the ejected jet in one direction or the other; in reverse, the vessel is not controlled. It is possible to use a rotary nozzle and a reversing deflector, as well as a rotary water cannon (Fig. 114), which significantly increases the maneuverability of the vessel. Water cannons are used mainly on light speed boats, where high power is combined with low weight of the boat.
Propellers find very rare application on small vessels due to low efficiency, large size and a large number of other disadvantages and problems that designers encounter when designing a vessel with such a propulsion system. Propellers are indispensable in the manufacture of amphibious ships (Fig. 115, 116), hovercraft, i.e. such vessels for which the underlying surface may be swamp, snow, ice, smooth sand, etc. Most often, two-blade propellers are used. There are corresponding formulas for calculating the propeller thrust, blade width, pitch, diameter and other characteristics of the propeller. Propellers for boats are most often made of wood, glued from rails.
Finishing the topic of propellers and summarizing brief results, it can be argued that the maximum speed, the greatest efficiency and reliability, as well as the greatest thrust of the existing propellers, is created by the propeller. The smallest draft and material losses for the boatmaster when touching the ground are achieved when using water jet propulsion devices, and simplified installation and ease of maintenance are possible when operating outboard motors and sterndrive.
DMITRY KRASNOPEVTSEV, ALEXEY SHAPKIN,
pupils of the 10th grade of school number 1273, Moscow
New types of propellers for watercraft
Student Research Project
It is given in an abridged and edited form. - Ed.
It is now generally accepted that project activity not only becomes educational for the student, gives the skills of research work, but also, most importantly, allows to learn in practice the method of scientific cognition of reality. This is especially important against the background of modern "freedom of speech" with an abundance of dubious "new" theories and pseudo-assessments of natural phenomena. Project activity allows you to see how the results of your own research work can be used to solve very specific socially significant practical problems. Below is one of two student development projects that are a continuation of the research projects "Why Birds Fly" and "Underwater Kite", the content of which is summarized in the article "Flying in air and water" (Physics # 29/2004). The projects were carried out with the technical assistance of Mika-Antikor OJSC and were presented at the “Fair of Ideas in the South-West” competition in April 2005, where they won first place.
Project manager Galina Pavlovna Ustyugina, physics teacher. [email protected]
Scientific consultant Yuri Evgenievich Ustyugin, Ph.D.
Our previous studies led to the conclusion that the reciprocating action of an alternating force on a propeller of a certain shape can lead to the appearance of a traction force transverse to the direction of action, and a highly economical operation of the propeller. We tested these assumptions by the method of physical modeling: we made the appropriate propellers and drives for them, created models of floating facilities with a motor-propulsion system and investigated their work. It turned out that the new propellers offered by us, in terms of economic indicators, are superior to such a propeller, which is widely used for the movement of vehicles in the air, on water and under water.
1. THE PROBLEM OF ECONOMY
Wildlife often baffles researchers by presenting various "technical" riddles. One of them, over which more than one generation of scientists has been puzzled, is how many marine animals, fish and dolphins manage to move in dense water at speeds that are sometimes inaccessible even for flying in the air? The swordfish, for example, can reach speeds of up to 130 km / h; tuna - up to 90 km / h. Calculations show that in order to overcome the water resistance and gain such speed, the fish needs to develop the power of the car engine - about 100 hp. Ukrainian scientists made a model of a sword-fish, hung it on a speedboat and determined the resistance of the environment and the power required for movement. In terms of the speed and size of the fish, the model experienced a resistance of 4000 N (408 kgf) and required 100 hp power for its movement. (73.6 kW)!
Scuba Diving Record - Swordfish
Living things get energy through oxidative processes. But fish are cold-blooded creatures, their temperature is not much higher than the temperature of water, in which oxygen, by the way, is dissolved in a very small amount. Such capacities are unattainable for them! It remains to assume only one thing: fish somehow "know how" to greatly reduce water resistance. A hypothesis explaining this phenomenon was put forward by a professor at the Institute of Theoretical and Applied Mechanics of the SB RAS V. I. Merkulov(Novosibirsk city) .
Traditional propellers for watercraft
There are four main types of ship propellers: jet propulsion, paddle wheel, propeller and vane propeller.
Water jet propulsion device. It is essentially just a piston or centrifugal pump that sucks in water through an opening in the bow or bottom of the ship and throws it out through nozzles in the stern. The created emphasis ( traction force) is determined by the difference in the amount of movement ( impulses) water jets at the outlet and at the inlet of the propeller. Water jet propulsion was first proposed and patented Tugudom and Hayes in England in 1661. Like other later options proposed by various inventors, the design had a low efficiency. A jet propulsion system is used when low efficiency is compensated by advantages in other respects, for example, for sailing on shallow or clogged rivers.
Paddle wheel. It is a wide wheel with peripheral blades. In more advanced designs, the blades can be rotated relative to the wheel so as to create the desired propulsive force with minimal losses. The axis of rotation of the wheel is above the water level, so that only a small part of it is immersed, and at any given time, only a few blades create an emphasis. The efficiency of a paddle wheel, generally speaking, increases with an increase in its diameter, so wheels with a diameter of 6 m or more are not uncommon. The rotation speed of the large wheel is low. Once it corresponded to the capabilities of steam engines, but over time the machines improved, and low speed became a serious obstacle - paddle wheels gave way to propellers.
Propeller screw. The screw was used by the ancient Egyptians to supply water from the Nile. There is evidence that in medieval China a hand propeller was used to move ships. In Europe, the propeller as a ship propulsion system was first proposed R. Hooke(1680) ... ( The following discussion discusses the propeller parameters not used in this work. - Ed.)
The sizes of modern propellers range from 0.2 to 6 m or more. The power developed by the propeller can be fractions of a kilowatt, or it can exceed 40 MW, respectively, the rotational speed ranges from 2000 rpm for small propellers to 60 rpm for large ones. The efficiency of good propellers can reach 80%, but in practice it is rather difficult to optimize all the main parameters, so on small ships the efficiency is usually about 45%. The maximum efficiency is achieved with a relative slip (the ratio of the ship's speed to the speed of movement of the propeller.) 10–30% and quickly decreases to zero when the propeller is operating both in the mooring mode and at high revs.
Wing propeller. This is a disk, along the periphery of which 4–8 blades are placed perpendicular to the plane of the disk. The disc is installed flush with the bottom of the ship, and only the blades are lowered into the stream. In addition to the fact that the disk with blades rotates about its axis, the blades themselves can rotate about their longitudinal axes. As a result, the water is accelerated in the required direction and an emphasis is created for the movement of the vessel. This type of propeller has an advantage over the propeller and paddle wheel, since the stop can be created in any desired direction: forward, backward and even sideways without changing the direction of rotation of the engine. You do not need the usual rudders to steer a boat with a vane propeller. Vane propellers are very effective in some special applications.
Wing propeller - Vois-Schneider propeller. - with four blades. The blades rotate with the rotor relative to the central point. ABOUT in one direction at a constant speed and are connected by rigid rods, incl. N which does not rotate with the rotor. If this point is displaced relative to m. ABOUT, then the angle of attack of each blade with respect to the tangent to the circle changes as the point of capture of the blade moves along the circumference. The boat is very easy to steer by shifting i.e. N: the more it is removed from the axis of rotation O, the greater the thrust of the propeller (members.surfeu.at/fprossegger/english/vsp-function)
General view of the propeller (www.voith-schiffstechnik.com/media/vohs_marine_01.pdf) and the circulation of the vessel with this propeller (www.voithturbo.de/media/vohs_1810e_VWT.pdf)
Fishtail propulsion system
Nature constantly demonstrates to man one of the best and most effective movers - the tail of a fish, which makes characteristic visually observed oscillatory movements. The corresponding propellers are given a shape close to the shape of the tail of a fish, and forced to make oscillatory movements. One example is the development G.A. Semyonova... As he writes, “... many people know the“ Gray's paradox ”: a dolphin, developing a speed of 10 m / s, must have a power 10 times greater than it has. From this, in my opinion, the following conclusions follow: 1) modern watercraft, with the power they have, should move at speeds, at least several times greater; 2) with a constant fuel supply, a floating craft with the same propulsion system as a dolphin will provide 10 times greater cruising range. " In the model of a catamaran with a fin propeller developed by him ( the figure is shown. - Ed.) the main feature is the wedge, which improves efficiency. However, in our opinion, Semyonov's mover, like other similar ones, is paddle propulsion, fundamentally different from the natural "fish tail" and therefore unable to achieve its efficiency.
2. ELECTROMECHANICAL DRIVE
Known Variants. For experimental research, it is necessary to assemble or manufacture an electromechanical drive, with the help of which it is possible to transfer the energy of the engine to the propeller. Of the well-known drive options ( the original is a drawing. - Ed.) we have chosen gear and belt drives for our models.
Our drive option. A general view of the electromechanical drive is shown in the photo. As a motor, we used an electric motor (angular velocity 75 r / s) from a radio-controlled toy on four batteries of constant (4 1.5 V) voltage type AA. Two gearboxes lowered the angular speed of the engine to 5–7 rpm: one, gear, from the same toy, the other, belt, made by us. A rubber ring was used as a belt. One end of the shaft was there is a pulley, on the other - a crank.
A general view of a model of a floating craft carrying the entire propulsion system is shown in the photo. The system allows quick replacement of the mover, which is fixed on the rod and reciprocates during operation. The stock is a power element that exerts an alternating force effect on the propeller.
General view of the model of the floating craft - surface ship
3. OUR RESEARCH
Hypothesis. During the execution of projects, we identified the rule U = /l= 0.29, which is fulfilled for all flight feathers of birds (feathers of a city pigeon, crow, eagle and seagull were studied). Moreover, it turned out that the choice of the grip point of the underwater kite in accordance with the rule U= 0.29 literally causes the model to fly out from under the water. As a result, a hypothesis was born: if we take a flexible elastic plate and give it an alternating movement in the direction perpendicular to the plane of the plate, then we should expect the appearance of a traction force in the direction perpendicular to the direction of this movement. Such an oscillating plate can be used as ship propulsion.
Fig. 4. Section of the fly feather, ABOUT
Movers. The photo shows propellers of various shapes that we tested in laboratory conditions, being installed on a model of the radio-controlled surface ship described above. First, rectangular propellers were tested, made of a polymer film with a thickness of 0.4 mm ( in) and 0.15 mm ( d). The position of the propeller capture point (round hole - white point in the photo) was determined in accordance with the rule U= 0.29. It turned out that a rectangular plate is deformed in a complex way (Fig. A): when the gripping point moves up, the front corners of the plate, marked with the two upper stars, bend down, as well as the rear part of the plate, and its middle point (the right star) deviates most strongly.
Fig. A. Shape of a rectangular propeller in a free state (top) and under the action of an external force F (down below). The asterisks mark the areas of maximum displacement
Fig. B. To the definition of the internal contour of the mover
Dotted outlines - outer (red) and inner (blue) - limit the part of the propulsion unit, which plays the role of the bird's feather trunk. Therefore, first, in order to outline the propeller, a 0.4 mm thick plastic plate was cut along the outer (red) contour. Then an internal contour was built (Fig. B): from each point, for example C, of the outer contour, the perpendicular was restored to the intersection with the rear cut line (point D) and divided the segment CD into two parts according to the rule U= 0.29. After that, the grip point was drilled as close to the inner contour as possible. A thin (0.015 mm) polymer film (options but, b, r, f on the picture). This is how propellers like but, b on the picture. Propellers type r, f were used to clarify the influence of cuts and load-bearing elements ("stiffening ribs"). Mover e- the simplest imitation of a fish tail.
Experiment. Measurements and observations were carried out in the aquarium and bath. First, a twisted rubber cord was used as the engine. However, it turned out that in this case it was only possible to observe the movement of the model, while it was difficult to measure any parameters due to the inconstancy of the potential energy of the unwinding rubber cord. Therefore, in the future, we assembled a model based on a DC motor. To measure the force, we used an ordinary school dynamometer with a full scale of 5 N and a division value of 0.1 N. Time intervals were measured with a timer (in a cell phone - a division value of 0.001 s, which gave reason to talk about measurement errors). To determine the speed of the model, the distance traveled by it at a steady speed of 20 cm (between the marks on the walls of the aquarium) was measured. Time and pulling force were measured three times by three different operators each time. in further calculations, we used the results averaged over these nine measurements.
Measured values
Calculated values
The table shows the results of measurements and calculations for the propeller proposed by us, as well as (for comparison) for a propeller with a diameter of 0.05 m.
Comment. It is known that the efficiency of an aircraft propeller reaches its maximum value (80%) at = 0.25. When close to zero, the aircraft approaches the resting state, and the propeller is in idle mode, i.e. = 0. At large, the aircraft moves at such a speed that the oncoming flow begins to spin * the propeller, ie. a mode similar to the idling mode of the propeller occurs, in this case also = 0. flight of an apparatus with a propeller step close to 1 is generally excluded.
Dependence of efficiency on the propeller step of the aircraft
The table shows that the efficiency of our propulsion unit (76%) is higher than the efficiency of the propeller (45%). The difference in the relative gait is also significant: 1.1 versus 0.855, i.e. more by about 30%. A model with a propeller moves 7.5 times faster, but at the same time its energy losses are much higher: 7.34 / 0.0264 = 282 times! Thus, the “failure” in the environment, which is typical for the rowing propellers, also leads to significant economic losses.
The results obtained by us allow us to expect a significant economic gain in the operation of the proposed unsupported vortex means for exciting the thrust force in front of the rowing means. The use of paired propellers operating in antiphase should exclude vibration of the vessel's hull and allow to convert part of the energy previously spent on this vibration into the kinetic energy of the vessel's translational motion.
_______________________
* When a helicopter's engine fails, it crashes. In this case, the propeller is spun by the oncoming air flow. It is the same with an airplane: if the airplane flies very quickly, then a non-rotating propeller will push the airplane, but on the contrary, the airplane will unscrew the propeller as it moves, which leads to the airplane braking and even to a negative propeller efficiency. - G.U.
Conclusion
1. A new method of creating a thrust force in fluids is proposed, as well as a device - a propulsion device for swimming vehicles, - the development of which is based on the results obtained in the project.
2. It has been shown experimentally how the presence of an alternating force acting on a propeller in a direction transverse to its surface generates a thrust force for a floating craft with such a propeller.
3. Development of a radio-controlled model of a floating vehicle with propellers of various configurations has been completed, but general principle action satisfying the rule
U= 0.29 found for flight feathers of birds.
4. Experimental design development - a radio-controlled model with a new type of propulsion system - tested in laboratory conditions.
5. It is shown that the efficiency of the new propeller is 76% at the relative advance of the propeller 1, where = u /, u- the speed of the forward motion of the floating craft; - the average speed of the propeller movement under the influence of the alternating force. (With this value, the propeller no longer works as a propeller, becoming a windmill-propeller, like a windmill.)
Literature
1. Ruchkin I., Alekseev K., Belykh A... (school number 1273). Why Birds Fly: Research Paper: Leader G.P. Ustyugin.- "Fair of Yuzao Ideas", Moscow, 2004.
2. Krasnopevtsev D., Shapkin A. (school number 1273). Underwater kite: Project work: Head G.P. Ustyugin.- "Fair of Yuzao Ideas", Moscow, 2004.
3. V.I. Merkulov The fish swimming puzzle. nauka.relis.ru/cgi/nauka.pl?05+0112+05112088+HTML.
4. What you need to know about the propeller. www.kater.ru/catalog/links_u_ustroistvo_sudna.htm.
5. Encyclopedia "Krugosvet". www.krugosvet.ru/articles/14/1001453/1001453a6.htm.
6. Semyonov G.A. RF patent No. 2090441 "Propulsion device for ships and surface and underwater navigation devices".
7. Semyonov G.A. Energy costs for transport can be reduced by 10 times. www.eprussia.ru/epr/info/sklad/036/new_tech_1.3.htm.
8. Mazeikin E.M., Shmelev V.E... Design and modeling of technical devices. ...
9. Sakhnovsky B.M. Models of ships of new types. - Shipbuilding, 1987.http: //www.shipmodeling.ru/books/NewTypeShips/newtypeships.pdf.
10. Prandtl L... Hydroaerodynamics: [email protected] Dynamics. - M.-Izhevsk: Research Center "Regular and Chaotic Dynamics", 2002.
Dmitry Krasnopevtsev
Galina Pavlovna Ustyugina is a graduate of the Faculty of Physics of the Tashkent State University in 1971, specializing in "Radiation Physics", a physics teacher of the highest qualification category, teaching experience for 33 years, an honorary worker of general education of the Russian Federation. In order to find ways to improve the education system, she took an active part in the work of the creative laboratory of the USSR people's teacher B. I. Vershinina in Tomsk in 1993. Further search led to a system of developmental education D.B. Elkonin–V.V. Davydova... The basic principles of this system are now the basis of the teacher's lessons. Galina Pavlovna
participated in the development of teaching methods of physics. At the invitation of the leadership of the Gorno-Altai Republican Institute for Advanced Studies, she read a course of lectures on the topic "Modeling the educational process in teaching physics." At the republican seminar "Innovations in the process of teaching physics" she presented the author's developments of the methodology for developing teaching physics. In 1998 she became the winner of the Republican competition "Teacher of the Year". In 2002-2004. conducted district seminars for physics teachers in the South-Western Administrative District of Moscow, in 2003, as part of a delegation of educators in Moscow, held one of best lessons physics under the Master-class program in Kiev. She took part in the work of the second (2003), third (2004) and fourth (2005) Moscow marathons of academic subjects, organized by MDO, IIOO and Publishing House "First September". Currently, he is the head and organizer of design and research work at the school. Her students Sergey Panyushkin and Vladimir Apalnov became prize-winners in the nomination "Design and research work" at the competition "Fair of ideas in the South-West-2003" and laureates of the 7th scientific conference of young researchers "Step into the future. Moscow "(2004), which took place at the Moscow State Technical University. NE Bauman, speaking with the work "Modeling the tornado process". Design work of 9th grade students "Why do birds fly" ( Ivan Ruchkin and AndrewWhite) and "Underwater kite" ( and Alexey Shapkin) were awarded 1st degree diplomas in the competition "Fair of Ideas in the South-West-2004". Galina Pavlovna's students regularly win prizes in physics Olympiads. Has publications in the newspaper "Physics", the magazine "Quant", patents for inventions. Galina Pavlovna's irreplaceable assistant is her husband Yuri Evgenievich Ustyugin, with whom she studied together at the Tashkent State University. Yuri Evgenievich - Ph.D., author of a number of publications on the physics of multiple particle formation at high energies, nuclear geophysics, anti-corrosion coatings of oil-containing equipment and structures (magazines "Nuclear Physics", "Reports of the USSR Academy of Sciences", "Izvestiya AN UzSSR "," Pipeline oil transportation ", collections of articles on geology and nuclear geophysics), has copyright certificates and patents for inventions. In 1996, he developed an original technology for the production of a highly anticorrosive pigment “specularit”, mastered its industrial production and implemented it at the enterprises of JSC “Tsentrsibnefteprovod”. In 1998-2000. In 2000, he was invited by the Sodruzhestvo holding to work as Deputy General Director for Finance and Economics at Ugli Kuzbassa OJSC, in 2001 he was transferred to the position of Orsko General Director -Khalilovsky plant "NOSTA". IN last years busy with issues of hydro- and aerodynamics and the training of future physicists. The family of teachers raised two daughters, and now they are raising two granddaughters and a grandson, devoting all their free time to them, which, unfortunately, is so lacking for everyone. Hobby - mountain tourism.
Does this mean that today the possibilities of these propulsion systems, traditional for shipbuilding, have been exhausted? Not at all.
After the propeller completely supplanted the paddle wheel in the last century, it has been constantly improved and gained predominant distribution in all types of vehicles moving under, on and above the surface of the water. And today this type of propulsion device in shipbuilding remains the most effective.
In aviation, with the advent of jet technology in the mid-40s, a propulsion complex consisting of an internal combustion engine (ICE) and an air propeller gave way to a turbojet and a jet propulsion system combining an engine and a propulsion unit in one unit (these PCs are often called not quite correctly air-jet engines - WFD). The propeller in aviation has fully retained its position only on helicopters, on light-engine airplanes, on motorized hang-gliders, and as part of a turboprop propulsion system - on medium-speed and heavy cargo aircraft.
In fig. 1 shows the dependence of the real values of the efficiency on the speed for ship propellers. different types... According to the author's data, the highest experimental efficiency value of 0.915 was achieved for a narrow-bladed aircraft propeller. Marine propellers, due to the wider blades, have large losses due to friction against the water. When testing insulated screws, their efficiency reaches 0.8. However, for propellers installed on real ships, due to the limited diameter due to the draft of the ship, the efficiency rarely exceeds 0.60. In this case, the value of the total propulsive coefficient is about 0.3 (the efficiency of an internal combustion engine is usually in the range of 0.40-0.50).
For turbojet propulsion systems of modern aircraft, the value of the total propulsion coefficient reaches 0.25. For the river SPK "Burevestnik" with an aircraft turboprop engine and a jet propulsion unit, the propulsion coefficient is half as much - 0.121.
Before starting our acquaintance with non-traditional types of propulsion systems, i.e., PCs that exclude the use of a propeller or a vane pump, we will try to classify all known propellers. It is convenient to divide them into two main groups (Fig. 2): they do not have elements moving relative to the body (that is, blades) and a PC with moving elements of the propeller. The second type is the propeller. The main problems associated with the presence of blades are well known. Due to the rotation of the propeller, the speed of the flow around the blades is many times higher than the speed of the vessel. At such speeds, the phenomenon of cavitation () occurs, which negatively affects the efficiency of the propeller, destroying the surface of the blades. To reduce the effect of cavitation, it is necessary to reduce the thickness of the blades and increase their area, but here shipbuilders face the problem of ensuring the strength of heavily loaded blades cantilevered on the propeller hub.
To one degree or another, these problems are inherent in other types of blade propellers - jet propeller, etc. And if you take the propeller, then the problem arises of dealing with noise, which sharply increases at supersonic speeds around the peripheral elements of the blades. Needless to say about the operational inconveniences that are created by the elements of the propulsion system that are movable relative to the body.
However, is it possible at all to create a propulsive complex without moving elements! It turns out that it is possible and quite real. So far, such complexes have not yet found widespread use in shipbuilding, but they have been used successfully in aviation and astronautics for a long time. This is, first of all, ramjet jet aircraft PC and missile PC... In shipbuilding, an analogue of a jet aircraft PC is usually called hydroreactive, although, to be precise, according to the principle of creating thrust and the propeller is also a hydrojet propulsion device.
With the development of aviation, it was found that the mass of a piston internal combustion engine operating on a propeller is approximately proportional to its power. And since with an increase in the aircraft speed, the required thrust increases in proportion to the square, and the power - to the cube of the speed, then the mass of the piston engine also grows in proportion to the cube of the speed. Thus, for an airplane flying at a speed of 1000 km / h. would require an internal combustion engine, the mass of which would be equal to the total flight mass of the aircraft, leaving nothing for the structure, fuel supply and payload. The mass of a turbojet or jet PC is approximately proportional to their thrust. Therefore, such PCs for the same speed of 1000 km / h have a quite acceptable mass - about 10% of the mass of the aircraft (excluding fuel) and about 35% with fuel.
Such a productive technical idea in aviation "infected" shipbuilders who are conducting serious research on the creation of a direct-flow hydro-jet PC.
Depending on the method of supplying energy to the zone of interaction with the stream flowing around the hull of the ship, a distinction is made between thermal, gas-jet and magnetohydrodynamic(MHD) direct-flow hydroreactive PC.
Of these types, the greatest efficiency has so far been obtained for a gas-jet PC, with a description of which we will begin. Let's get acquainted with the principles of operation of such a PC using the example of the model described in the book by V. A. Bashkatov et al. The mover model had a length of 0.223 m and a diameter of 0.078 m (Fig. 3). It consisted of a water intake. mixing chambers and nozzles. Air compressed to an overpressure of 0.34 kg cm 2 from a compressor installed outside the propeller through the receiver entered the manifold, made in the form of an annular channel between the diffuser and the fairing, from where through 550 holes with a diameter of 0.8. mm was fed into the mixing chamber located immediately behind the diffuser. The flow of water entering the expanding diffuser slows down its movement, as a result of which the static pressure in it increases. In a mixing chamber with a constant cross-section, air compressed to this pressure is mixed with water and the resulting water-air mixture is ejected through a nozzle. If the cross-sections at the inlet (water intake) and outlet (nozzles) have the same area, then due to the lower density of the water-air mixture compared to the density of water, the speed of the jet flowing out of the nozzle turns out to be greater than that at the inlet.
The described model had a nozzle diameter of 0.034 m and developed a thrust of about 0.2 kg in the design mode, having an efficiency of 0.35 in this mode. More complete studies have shown that the efficiency of direct-flow hydro-jet propellants of this type does not exceed 0.4, and their thrust at the mooring (in the absence of progress) is zero, and the ship needs another propulsion device to accelerate. For example, two-stage have been proposed water-jet-gas jet propellers, consisting of an axial pump and a mixing chamber located in one channel. However, such propellers turned out to be worse in efficiency than a water cannon and do not promise any operational advantages.
In 1971, the director of the Dutch experimental basin Van Manen published an analysis of the feasibility of using a gas-jet PC for a hydrofoil vessel having a speed of 40 to 80 knots and a displacement of 20 to 180 tons. PC and PC with supercavitating propeller. Specific reduced costs at a speed of 60 knots for the gas-jet version turned out to be about 1.5 times higher.
Until now, aircrafts remain unacceptable on ships in terms of their economic indicators. turbojet propulsion systems, although over the past 34 years they have been used more than once on speedboats for races to break the absolute speed record on the water. It was the turbojet PC installed on Donald Campbell's Blue Bird III that made it possible to raise the record immediately by 120 km / h, and then to the current 511.11 km / h, which was developed in 1978 by Australian Ken Vorby on the Spirit of Australia speedboat ". But the efficiency of the turbojet PC at normal, not record-breaking speeds is still quite low.
True, the idea of supplying sprayed water to the nozzle of an air-reactive PC opens up certain prospects. As shown by the model experiments carried out in 1973, this technique makes it possible to increase the thrust by 50-80% without changing the fuel consumption and the operating mode of the PC itself. The American specialist Quandt has theoretically calculated that at a speed of 100 knots (185 km / h) such a PC can achieve a fairly high prolulsive coefficient of 0.48. In this case, the mass of the injected water should be about 10% of the mass of the used air, the movement of which can be ensured not only with the help of an aircraft turbojet PC, but also with the help of an air fan PC. In the domestic literature, the last of the indicated type of PC was called a gas jet propulsion unit with a low water flow rate (Fig. 4).
The original type of gas jet is a two-phase air-water PC based on the use of gravity effects. A thorough experimental study of such a PC in 1968 was carried out by the Finnish researcher Kostilainen. The principle of operation and design of the device is extremely simple (Fig. 5). The compressor delivers air through the receiver to the holes located in the lower part of the flat, inclined aft end of the vessel. Air in the form of bubbles floats up under the action of the Archimedean force and. sliding along the inclined plane of the stern and carrying with it the masses of ode up and back, thus creating thrust. Tests of a model 1.6 m long, 0.5 m wide and 0.19 m draft in a test tank showed that the propulsion coefficient for such a PC can reach 0.35 without taking into account losses in the compressor and air ducts. The thrust of the PC reached 2 kg, and the speed of the model was 0.85 m s. In this case, air was supplied through 7 holes 10 mm in diameter. Air supply through 49 holes with a diameter of 5 mm led to a slight decrease in travel speed, but to an increase in the propulsive ratio. However, it was clear to the inventor that the efficiency of the PC was clearly insufficient for its use on ships. Therefore, Kostilainen made an attempt to use his propulsion unit on a vessel with a ventilated bottom (for more details, see "KiYa" No. 129). The researcher hoped that the propeller would be more efficient than the propeller when it was working behind the air cavity. On tests of a three-meter model, it was possible to obtain a maximum value of the propulsion coefficient of 0.55. For transport vessels, such efficiency is clearly low, however, the simplicity and environmental friendliness of the air-water PC can be useful for the creation of sports and research self-propelled watercraft.
In 1974, the French researchers P.-J. Balkyu and M. Kurubl tested a barge with a displacement of 600 tons, equipped with a two-phase PS similar to the one described above. For more intensive mixing of air with water, they proposed to install a mixer on the bottom in the form of a wing attachment with slots. During the tests, the speed of the barge was 14 knots, and the highest value of the propulsion coefficient was 0.4, that is, the introduced innovations practically did not affect the efficiency.
Obviously, the pressure in the mixing chamber of the direct-flow hydrojet propulsive device should be greater than the static pressure at the depth of the nozzle and less than the sum of this static pressure and the velocity head. But there were attempts to create propellers with higher pressures in the mixing chamber and a valve system that regulates the pressure on the approach of the working fluid to the inlet port. The outflow from the nozzle in such a propeller becomes pulsating. In 1955 L.A. Yutkin proposed electro-hydraulic pulsating a propulsion device in which the energy of a high-voltage electric discharge in water is used to create an increased pressure in the mixing chamber, and the inlet and outlet are equipped with a valve system. But, despite the great interest of many inventors in this type of propulsion system, the matter did not come to practical application on ships - the effectiveness of gas jet PCs is still too low.
Among the proposed direct-flow hydrojet propulsion systems, there are those in which thermal energy is converted into thrust directly in the mixing chamber - similar to the operation of aircraft jet propulsion systems, where fuel is supplied to the mixing and combustion chamber. Hydroreactive fuel - lithium, sodium, potassium, aluminum, magnesium - can play the role of a fuel that releases thermal energy i to water. (For example, when 1 kg of lithium reacts with seawater, 28,300 kJ of heat is released, which is 10 times more than when 1 kg of kerosene is burned in the air). Such a hydroreactive fuel is a solid, so it becomes problematic to continuously feed it into the mixing and combustion chamber, ensuring complete combustion. Hydroreactive fuels are difficult to store as they readily combine with oxygen and moisture in the air, releasing explosive hydrogen. Partially these problems are solved if, for fuel combustion, not seawater, but a special oxidizer is used. Such PCs are called missile.
Most promising of different types direct-flow hydroreactive PC, admittedly, is magnetohydrodynamic complex (MHD PC). Relatively recently, thanks to increased advertising by Japanese specialists, it became the subject of a number of "sensational" reports (see, for example, Izvestia, March 12 and April 4, 1988). What is this PC?
The idea of an MHD PC appeared in 1961 simultaneously with the idea of an MHD generator capable of converting thermal energy into electrical energy without internal combustion engines or steam turbines. The required efficiency of such devices is achieved only when using the effect of superconductivity.
The principle of operation of the so-called conductive MHD propulsion device is as follows. Let there be a rectangular channel (Fig. 6) through which an electrolyte, say, salty sea water can flow.
The upper and lower walls of the channel are, respectively, opposite magnetic poles, and the side walls, isolated from the rest, are in contact with the electrolyte and are connected to a direct current source. A direct current will flow between the side walls, i.e., the directional movement of ions will begin. The so-called Lorentz force will act on a positively charged ion that moves from the anode to the cathode and is in a vertical magnetic field. Its direction can be found according to the rule of the left hand: if four fingers of the left hand are directed in the direction of the movement of positive ions, and the palm is placed perpendicular to the direction from the north magnetic pole to the south (the inner side of the palm is looking at the north pole of the magnet), then the thumb will indicate the direction the Lorentz force. Under the action of this force, positive ions will deflect, interacting with the atoms and molecules of the electrolyte, and the entire liquid will begin to move in the indicated direction. The magnets that create the magnetic priest will be acted upon by forces opposite in direction to the Lorentz force, as a result of which the stop necessary for the movement of the ship will arise. Unlike all other types of propellers, here the emphasis is created due to the action of volumetric rather than surface forces on the liquid, which makes it possible to accelerate its flow without changing the pressure.
However, in order for the Lorentz force to have a sufficiently high value, it is necessary to have a very high tension magnetic field and, accordingly, magnetic induction. To imagine the orders of magnitude of these values, we point out that after a solenoid, which has 1 million ampere-turns per meter, creates a magnetic induction in the void equal to 1.26 tesla (T). And in order to obtain a high efficiency of the MHD propulsion device, an induction of 7-10 T is required; at the same time, energy losses (mainly for water heating) will amount to about 20%.
The real design, developed by Japanese specialists, should develop a mooring thrust of up to 2500 tons. Tests of two ship models (SEMD-1 and ST-500) with MHD propulsion systems were successful, and it was decided to start designing MHD propulsion devices for five different vessels. with a displacement of 30 to 10,000 tons.
The reality of creating an MHD PC depends primarily on the solution of three problems: the development of large superconducting magnetic systems capable of creating a powerful magnetic field; shielding external magnetic pockets; ensuring the effective operation of the electrodes in the inevitable electrolysis during their operation, i.e., the release of gases.
Recent reports indicate that the Japan Association for the Promotion of Shipbuilding has approved a project to create a model ship with a displacement of 150 tons, equipped with an MHD PK. The design speed of the model is 8 knots, the stop is 800 kg. Experts hope. that this will be the first step towards creating "the silent and ultra-fast vessel of the 21st century at a speed of 100 knots." In some reports, this Japanese program is called the "Revolution in shipbuilding".
However, if we leave aside the advertising hype, we can see that the development and even testing of models equipped with MHD PCs, albeit without the use of superconductivity, have been going on for a long time. For example, in 1966, a three-meter model of the EMS-1 submarine with a displacement of 408 kg with an MHD PC was tested at the Faculty of Mechanics of the University of California (Fig. 7). To create a magnetic field, a current of 110-120 A was passed through the winding of the magnetic system. The case and the magnetic system had a non-conductive lining, on top of which were installed two electrodes (anode and cathode) in contact with sea water. A constant voltage of 27.8 V was applied to the electrodes, while a current of 91.4 A appeared between the electrodes. The power supply was provided by lead-alkaline rechargeable batteries, the capacity of which was sufficient to operate the PC for 20 minutes.
The model developed a speed of 0.5 m / s)
