RU65019U1 - BLOW SCREW BLADE - Google Patents

Abstract

The utility model “Propeller blade” refers to the field of hydrodynamics, and can be used for modern high-speed apparatuses, moving in water in whole or in part, high-speed blade devices that are used in various sectors of the economy, mainly in shipbuilding, namely for propellers. The purpose of the utility model is to reduce the destructive phenomenon - cavitation, which destroys the ship's propeller blades and increase the propulsion capabilities of the blade. This is achieved by special profiling of the surface of the blade with swirlers made in the form of scalloped recesses with parameters t and h, which are in the ratio h / t = 2-4, installed in rows at an angle α = 20-60 ° to the radial axis of the blade, while the relative area of the blade swirlers is 0.8 ÷ 0.95 of the original blade area. Using the optimal ratio of the parameters of the swirls obtained experimentally and in a mathematical experiment, the increase in traction characteristics reached 16-18% without cavitation phenomena.

Description

The utility model relates to the field of hydrodynamics, and can be applied to modern high-speed devices moving in whole or in part of water, high-speed blade devices that are used in various sectors of the economy, mainly in shipbuilding, namely, propellers. The purpose of the utility model is to reduce the destructive phenomenon - cavitation, which destroys the ship's propeller blades and increase the propulsion capabilities of the blade.

Annually, about 25 thousand tons of metal enclosed in the propeller blades goes for remelting due to erosion of the blades. The service life of the screws is reduced to 2-3 years. In practice, there are cases of failure of the screws due to erosion within 2-3 months (Figure 1).

The seemingly harmless “boiling” of water, arising on the blades in the zones of minimum pressure, in the form of an abundant zone of bubbles, is the main cause of erosion of the blade and a decrease in its traction characteristics. This well-studied phenomenon shows how a bubble filled with vapors or gases exits the “boiling” zone into the high-pressure zone and disappears. The disappearance of the bubble occurs almost instantly and is accompanied by the supersonic speed of the all-round aspiration of the water flow into the resulting empty space. If the collapse of the bubble occurs on the surface of the structure, then in this place an instant increase in pressure reaches one million atmospheres. This microexplosion destroys the most durable structural materials. First, microcracks form on the surface of the structure, which quickly pass into areas of random erosion. Theoretical profiling violated

blades, its geometry and weight parameters. The propeller balancing as a whole is disturbed, and, as a result, the whole ship is shaking.

Cavitation has another problem, namely, a decrease in the traction characteristics of the blade. Thus, the power of the marine engine is used only by 60-70%, after which cavitation occurs, and the inadmissibility of increasing the speed of the screw or its size is inadmissible.

Known "Ship propeller" according to patent RU 2090440 from 09/20/1997, the design of which provides for the installation of a bulb-shaped thickening with a step to the main surface of the blade on the suction side of the propeller blade. The use of the invention reduces cavitation of the propeller blades. It is known that the suction side of the blade (with the flow path it is the upper part of the blade profile), due to the greater curvature and greater rarefaction, creates a greater (about 70%) percentage of thrust, compared with the lower plane on which pressure is created. In this patent, reducing cavitation due to the relatively large (about 60%) non-core zone (without curvature), the traction characteristics of the blade decrease (approximately in the same ratio), which significantly reduces its efficiency.

Known "Propeller" with means for reducing cavitation damage according to patent RU 2137674 from 09.20.1999. The propeller has an axial channel for supplying air to the tail of the blade (to the trailing edges), the edges are made in the form of rubber lips. A control check valve is installed in the air supply channel in the rear of the hub. At certain critical rotational speeds, fluid flows closing the screw generate cavitation phenomena. The automatic air supply system in the area of the propeller blades, when the pressure on the blades drops to the saturated vapor pressure, really reduces the formation of cavitating bubbles. However, as tests of this kind of device have shown, suction

air spreads in the form of an “air bubble” to the lower pressing surface, which leads to a sharp increase in the rotations of the screw in this “bubble” and a decrease in its thrust.

Known "Propeller ship screw" according to patent RU 2094304 from 10.27.1997. The blades contain through holes or slots with a total area of 4-20% of the surface area of the blade. The use of the invention reduces cavitation on the propeller blades and thereby increases their efficiency. Indeed, the effect of cavitation decreases on the blades, but at the same time it increases in the areas of through holes due to high flow rates from the high pressure region to the low region; moreover, the flow around the suction surface is disturbed, which is accompanied by turbulence and loss of thrust of the blade.

Known "Propeller for surface and underwater vehicles" according to patent RU 2222470 from 01/27/2004. (SU 37506 A, 06/30/1934. US 4253799 A, 03/03/1981. GB 2156298 A, 10/09/1985. FR 2337661 A1, 05/05/1977.). The propeller contains flat-profile blades mounted on the hub, made with end ridges, bent towards the working surface at an angle of 1 ÷ 90 °. The invention improves the efficiency of the screw and provides an increase in traction by 30-50%. Indeed, the tests carried out on the recommendation of the magazine "Modeller-Designer" No. 6, 1989, pp. 28-29; No. 11, 1988, p. 20; No. 6, 1986, p. 6, for plane-profile blades, i.e. for blades of models cut out of tin, with relatively very small sizes of screws (diameter of about 20-30 mm.) and Reynolds number (Re), an increase in thrust with increasing attached mass on the model blade due to end ridges is shown. The installation of such ridges on full-scale water vehicles is accompanied by rapidly advancing cavitation at the tip of the blade in the presence of two mutually inclined

surfaces at the tip of the blade. Efficiency drop on a screw with a diameter of 500-1000 mm. when installing such ridges is 12-15%. Considering that large-capacity vessels have a propeller diameter of 2000 mm or more, cavitating phenomena at the curved ends of such blades are manifested to an even greater extent.

Known "The blade of the hydraulic propulsion device" according to patent RU 2127208 of 03/10/1999. The essence of the invention lies in the fact that in the blade, the suction surface of which has a maximum ordinate at a distance from the outgoing edge of not more than 0.6 lengths of the chord, the injection surface has a convex-concave shape. The use of the invention allows to provide low-cavitation operation of the propulsion device without ventilation of the blades and increases its efficiency. This technical solution is closest to the claimed utility model "Propeller blade" and we have adopted as a prototype.

Indeed, this propeller blade having a low-cavitation profile, for example, a segment one, of the NACA-66, NACA-16 series with an average line a = 0.8, as well as an elliptical profile with an average line a = 0.8, forms a suction and discharge surface, containing and the leading edge (see. "Theory and calculation of propellers" Basin A.M., Minkovich I.Ya., Sudpromgiz, 1965, Leningrad, p. 461-465). At the same time, each blade has optimal ratios between cavitation, hydrodynamic and strength characteristics due to sections with profiles of various series, for example, Troost B series propellers. The advantages of this blade is that its profile provides a fairly uniform distribution of pressure along the suction and discharge surfaces of the blade. At the same time, a small profile resistance is achieved. Its disadvantage is the lack of regulatory capabilities to exclude cavitation on the suction and discharge surfaces in areas of minimal

pressure, which is visible on the diagrams (Figure 2). Such zones take place on the discharge surface in the region of the toe and tail of the profile and on the suction surface in the middle zone of the profile.

In order to exclude cavitation on the propeller blades and increase the traction characteristics of the blades, the suction and discharge surfaces are provided with profiled swirls in the form of scallop recesses that begin in cavitation zones and end on the end and outlet edges of the blade, while the swirls are arranged in rows with a step t, height h, in the ratio h / t = 1-4, and the rows are installed at an angle α = 20-60 ° to the radial axis of the blade, with the total relative surface area of the blade with the relative surface area of the blade zavihriteljami where:

- the relative surface area of the blade with swirls; S _profiled - the area in terms of the surface of the blade with profiled swirls; S _initial - the area in terms of the surface of the blade (suction and discharge).

The utility model "Propeller blade" is illustrated by drawings

Figure 1 Rowing screw of a large vessel with traces of erosion on its surface.

Figure 2 Modern low-cavitation profiles of the propeller blades with pressure plots:

a) elliptical profile A;

b) NASA profile according to US patent No. 4780058 B;

c) an improved profile according to patent RU 2127208 B.

Figure 3 The propeller blade on the subject of a utility model when viewed from the front and top. In remote zones A and B

Photographs of fragments of tested structures and possible swirl profiles are shown.

Figure 4 Applied equipment for optimizing the size of profiled swirlers.

Figure 5 Tested models of propellers to optimize the size of the profiled swirlers at different temperatures and water pressures.

6 The result of mathematical modeling to determine cavitating areas on the profile.

Fig. 7 Graphs of optimization of parameters (t, h, α) of swirls according to the results of experimental and mathematical modeling.

The device of the utility model "Propeller blade" (Figure 3) consists of a hub 1 with an axis 2, a blade 3 with an incoming edge 4, an end edge 5, an outgoing edge 6, a suction surface 7 and a pumping surface 8.

On the suction 7 and discharge surface 8, profiled swirls are installed in the form of scallop recesses 9, 10, 11. Swirls 9, 10, 11 are located in the corresponding cavitation zones 9, 10, 11, which are installed experimentally, Fig 2 - (9 - profile toe zone on the pumping surface 8; 10 - the middle zone on the suction surface 7; 11 - zone of the tail of the profile on the pumping surface 8). Each of these three zones contains rows of swirlers whose profiles are optimized for their zones with a step t and a height h. Ridge height h. - determines the size of the recess, those depths, measuring it from the contour of the profile (zone A and B of Figure 3). For the convenience of counting the installation angles of the rows of swirlers 9, 10, 11 at an angle α to the radial axis 12 of the blade 3, a radial axis 12 is introduced, which is equidistant from the edges 4 and 6 and passes through the axis 2 of the hub 1.

The swirlers 9, 10 and 11 begin in the zones of reduced pressure determined by the plots of pressure distribution on the blades 3. The plots are determined either experimentally (Figure 2), for example, by the method of drainage, the installation of film micro-pressure sensors, a laser method, etc., or mathematical programs. Swirlers at the end or outgoing edges of the blade end. (Figure 3). Zones A and B show flow patterns and photographs of really tested designs. Flow patterns are used from the monograph “Flow Separation Control” P. Chzhen, ed “Mir” M. 1979, p. 13 (vortex flow in a recess).

The utility model works as follows. As a result of the rotation of the blade 3 in the direction of the circumferential speed 13, the blade flows around the stream 14 with a speed V. As the speed 13 increases and the traction power increases on the suction surface 7 and the discharge surface 8, critical zones appear (according to the diagrams) on the profile nose, on the suction surface and in the tail of the profile. In figure 2, these critical rarefaction values (-Cp) are shown by a thickened line in the diagrams. In figure 3, in critical zones 9, 10, 11, a critical flow velocity is reached at which the saturated water vapor pressure at the calculated depth and temperature in the temperature range from 0 to 30 ° is 0.0063-0.0429 atm. The liquid begins to “boil” with the release of a large number of bubbles of water vapor. A further increase in the flow velocity leads to the formation of an “air bubble” in which the screw rotates with almost complete loss of traction power. In order to exclude the destructive effect of cavitation and obtain maximum traction force of the blade, profiled swirlers located in cavitation zones 9, 10, 11, - due to the peculiarities of the vortex flow, create a vacuum (tornadoes, typhoons) concentrate the boiling liquid into vortex bundles 15, which

located inside the rows of swirls 9, 10, 11 and transport cavitating bubbles outside the blade structure without contact of the cavitating bubbles with the blade structure. The experiments showed the presence of “continuous cavitation” when the bubbles are twisted into vortex bundles located inside the structure, but without contact with it. The indicated continuity allows a further increase in the ω peripheral speed 13, i.e. an increase in the number of revolutions of the propeller and an increase in its thrust in the presence of cavitation zones, but without the formation of an “air bubble”. This result is a confirmation of the solution of the task.

Figures 4 and 5 show the equipment and models of screws on which the optimal ratios t, h, α for swirlers 9, 10, 11 were obtained. Figure 6 shows the result of mathematical modeling to determine the critical zones of cavitation occurrence. 7 shows the results of experimental and mathematical modeling to optimize the parameters of the swirlers.

As a result of the tests, the observed increase in propeller thrust with blades for the subject of a utility model was 16-18%. No signs of erosion of the blade structure were observed using a microscope. The obtained positive effects confirm the feasibility of using the utility model “Propeller blade”.

Claims (1)

A propeller blade containing a profiled suction and discharge surface with inlet, end, and outlet edges, characterized in that, in order to avoid cavitation on the propeller blades and increase the traction characteristics of the blades, the suction and discharge surfaces are provided with profiled swirlers in the form of scallop recesses, which begin in cavitation zones and end on the end and outgoing edges of the blade, while the swirlers are arranged in rows with a step t, height h in the ratio h / t = 1-4, and p poisons are installed at an angle α = 20-60 ° to the radial axis of the blade, with the total surface area of the blade with swirls S _swirls = 0.8 ÷ 0.95 S of the _original .