A design method for reducing underwater exhaust noise nozzle and contraction lobe nozzle

Abstract

The present invention discloses a design method for reducing underwater exhaust noise nozzle and a contraction lobe nozzle. The method includes: selecting parameters of the lobe nozzle section and the contraction section; establishing a physical model of the lobe nozzle structure; establishing physical assumptions and simulation; determining the final nozzle parameters; the exhaust process of underwater equipment belongs to submerged exhaust; the exhaust noise includes upstream noise in the exhaust pipeline and downstream noise outside the exhaust pipe; the silencer structure in the exhaust pipeline can effectively suppress the upstream noise, but it is difficult to act on the downstream noise outside the pipe; and the downstream noise is precisely the part with the strongest amplitude. If targeted measures are not taken to suppress the downstream noise, the total sound pressure level is difficult to reduce; the present invention analyzes the influence of nozzle flow, pressure pulsation in the pipe and exhaust noise by means of numerical simulation and experiments; analyzes the noise reduction mechanism of the lobe nozzle, designs a nozzle to reduce underwater exhaust noise, and provides a reference for the engineering design of exhaust noise reduction of underwater equipment.

Description

Technical Field

[0001] The present invention relates to the field of underwater exhaust technology, and in particular to a design method for a nozzle that reduces underwater exhaust noise and a contraction lobe nozzle. Background Art

[0002] The underwater exhaust process is widely present in the underwater navigation process, and this process often produces strong exhaust noise. With the continuous development of underwater equipment, the requirements for noise control are getting higher and higher. How to reduce underwater noise has become an urgent problem to be solved. In the existing technical approach, the method of reducing the exhaust noise of underwater equipment is mainly an underwater exhaust noise reduction device, but similar underwater noise reduction devices are often large in size, complex in structure, high in cost, and limited in practical application scope. Fig.14 This is an exploded view of the existing underwater exhaust noise reduction device.

[0003] In existing public reports, the main method to reduce the exhaust noise of underwater equipment is to install a silencer structure in the exhaust pipe. Since the exhaust pipe mainly has single-phase gas flow, the design theory of single-phase exhaust silencer can be used for reference in the design of the silencer structure. However, the exhaust process of underwater equipment belongs to submerged exhaust. The submerged exhaust noise includes the upstream noise in the exhaust pipeline (single-phase exhaust noise) and the downstream noise outside the exhaust pipe (bubble noise and boundary noise). The silencer structure in the exhaust pipeline can effectively suppress the upstream noise, but it is difficult to act on the downstream noise outside the pipe. The downstream noise happens to be the part with the strongest amplitude. If targeted measures are not taken to suppress the downstream noise, the total sound pressure level is still difficult to reduce. Therefore, the applicant proposed a design method for a nozzle that reduces underwater exhaust noise and a contracting lobe nozzle. Summary of the invention

[0004] In view of this, one aspect of the present invention is to propose a design method for reducing underwater exhaust noise nozzles, and to analyze the influence of nozzle flow, pressure pulsation in the tube, and exhaust noise by means of numerical simulation and experiments; on this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle for reducing underwater exhaust noise is designed, providing a reference for the engineering design of exhaust noise reduction of underwater equipment. Another aspect of the present invention is to propose a contraction lobe nozzle, which can enhance the continuity of flow, alleviate the pressure surge caused by necking, and has a good noise reduction effect in the medium and low frequency bands, with a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz.

[0005] According to one aspect of the present invention, a design method for a nozzle that reduces underwater exhaust noise is provided. The nozzle flow, the pressure pulsation in the pipe, and the influence of exhaust noise are analyzed by means of numerical simulation and experiments. On this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle that reduces underwater exhaust noise is designed, which provides a reference for the engineering design of exhaust noise reduction of underwater equipment. The nozzle includes a lobe nozzle section and a contraction section; the method includes:

[0006] Selection of parameters for the lobe nozzle section and the contraction section;

[0007] A physical model of the lobe nozzle structure is established according to the lobe nozzle section and contraction section parameters;

[0008] According to the physical model of the lobe nozzle structure, physical assumptions are established and simulation is performed;

[0009] The final nozzle parameters are determined based on the simulation results.

[0010] According to another aspect of the present invention, a contraction-type lobe nozzle is provided; the lobe nozzle comprises a lobe section and a contraction section;

[0011] The lobe segment is cylindrical, one end of the lobe segment spreads outward to form a plurality of lobes, and the other end of the lobe segment is connected to the contraction segment;

[0012] The contraction section is in the shape of a diffusion tube, and the end not connected to the lobe section diffuses outwards to form a trumpet shape;

[0013] The lobe section and the contraction section are combined to form a Laval nozzle-like nozzle.

[0014] The beneficial effects of the present invention are concentrated in the following two aspects:

[0015] (1) The exhaust process of underwater equipment belongs to submerged exhaust. Submerged exhaust noise includes upstream noise (single-phase exhaust noise) in the exhaust pipe and downstream noise (bubble noise and boundary noise) outside the exhaust pipe. The silencer structure in the exhaust pipe can effectively suppress the upstream noise, but it is difficult to act on the downstream noise outside the pipe. The downstream noise is precisely the part with the strongest amplitude. If targeted measures are not taken to suppress the downstream noise, the total sound pressure level is still difficult to reduce. The downstream noise is closely related to the flow state near the nozzle. Based on the control of downstream noise, a nozzle design method for reducing underwater exhaust noise is proposed. The influence of nozzle flow, pressure pulsation in the pipe and exhaust noise is analyzed by numerical simulation and experimental means. On this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle for reducing underwater exhaust noise is designed, which provides a reference for the engineering design of exhaust noise reduction of underwater equipment.

[0016] (2) The lobe nozzle can enhance the continuity of the flow, alleviate the pressure surge caused by the necking phenomenon, and has a good noise reduction effect in the medium and low frequency bands, with a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz. The lobe nozzle improves the gas velocity distribution at the nozzle, forms a local high-speed area in the jet, and thus enhances the jet penetration; the diffusion area of ​​the nozzle can induce the primary and secondary fluids to flow in the radial direction, thereby strengthening the gas-liquid mixing near the nozzle and improving the jet penetration; the necking phenomenon is further alleviated, and the pressure pulsation and low-frequency noise related to it are effectively suppressed; the increased contact area accelerates the attenuation of the boundary gas velocity, thereby effectively reducing the boundary noise mainly distributed in the medium frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a flow chart of an embodiment of a design method for reducing underwater exhaust noise nozzle of the present invention;

[0019] Figure 2 1 is a schematic diagram of a nozzle according to an embodiment of a method for designing a nozzle to reduce underwater exhaust noise according to the present invention;

[0020] Figure 3 1 is a schematic diagram of a specific flow chart of S100 in an embodiment of a method for designing a nozzle for reducing underwater exhaust noise according to the present invention;

[0021] Figure 4 Schematic diagram of various parameters in an embodiment of a design method for reducing underwater exhaust noise nozzle according to the present invention;

[0022] Figure 5 Schematic diagram of various parameters in an embodiment of a design method for reducing underwater exhaust noise nozzle according to the present invention;

[0023] Figure 6 It is a schematic flow chart of a further development of an embodiment of a design method for reducing underwater exhaust noise nozzle according to the present invention;

[0024] Figure 7 is the shape of the contraction curve of the contraction section in the first embodiment of the design method for reducing underwater exhaust noise nozzle of the present invention;

[0025] Figure 8The velocity distribution of the contraction curve of the contraction section at the Y0 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention;

[0026] Fig. 9 The velocity distribution of the contraction curve of the contraction section at the Y1 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention;

[0027] Fig.10 The velocity distribution of the contraction curve of the contraction section at the Y2 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention;

[0028] Fig.11 The velocity distribution of the contraction curve of the contraction section at the Y3 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention;

[0029] Fig.12 2 is a schematic diagram of an apparatus of an embodiment of a contraction-type lobe nozzle of the present invention;

[0030] Fig.13 2 is a schematic diagram of an apparatus of an embodiment of a contraction-type lobe nozzle of the present invention;

[0031] Fig.14 It is a schematic diagram of the explosion of an existing underwater exhaust noise reduction device. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following examples are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0033] One aspect of the present invention aims to propose a design method for a nozzle that reduces underwater exhaust noise, and analyzes the nozzle flow, the pressure pulsation in the tube, and the influence of exhaust noise by means of numerical simulation and experiments; on this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle that reduces underwater exhaust noise is designed to provide a reference for the engineering design of exhaust noise reduction of underwater equipment. Structural changes in the exhaust nozzle will cause changes in the outlet gas velocity distribution, the shear layer interface area, and the vortex structure. In essence, changes in the nozzle structure regulate the interaction between the jet body and the ambient fluid, thereby changing the flow field and the sound field of the jet. The lobe nozzle is a nozzle structure with a lobe-shaped trailing edge. This special geometric shape achieves the purpose of noise reduction by enhancing the mixing of the jet body and the ambient fluid. Its enhanced mixing mechanism mainly includes the following aspects:

[0034] (1) The spanwise vortex induced by the Kelvin-Helmholtz instability in the free shear layer can entrain the surrounding fluid;

[0035] (2) The streamwise vortex induced by the lobe-shaped outlet structure can destroy the large-scale coherent structure of the shear layer and form a large number of small-scale turbulent vortices to mix the primary and secondary fluids;

[0036] (3) The complex trailing edge curve makes the exit side length of the lobe nozzle much longer than that of a circular nozzle with the same cross-section, which increases the shear action area between the primary and secondary flows, thereby promoting mixing. Relevant experimental studies have shown that under the combined action of multiple mechanisms, the lobe nozzle can achieve a good enhanced mixing effect and has a significant inhibitory effect on jet noise.

[0037] Another object of the present invention is to provide a contraction lobe nozzle, which can enhance the continuity of flow, alleviate the pressure surge caused by necking, have good noise reduction effect in the medium and low frequency bands, and have a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz.

[0038] See also Figure 1 , Figure 2 , Figure 1 It is a flow chart of an embodiment of a method for designing a nozzle to reduce underwater exhaust noise according to the present invention. Figure 2 Schematic diagram of a nozzle according to an embodiment of a nozzle design method for reducing underwater exhaust noise according to the present invention; Figure 2 As shown, the nozzle includes a lobe nozzle section 1 and a contraction section 2; it should be noted that if substantially the same results are achieved, the method of the present invention is not limited to Figure 1 The process sequence shown is limited.

[0039] like Figure 1 As shown, the method comprises the following steps:

[0040] The method comprises:

[0041] S110: Lobe nozzle section and contraction section parameter selection; see Figure 3 , Figure 3 1 is a specific flow chart of S100 in an embodiment of the design method for reducing underwater exhaust noise nozzle of the present invention. It should be noted that if there is substantially the same result, the method of the present invention is not limited to Figure 3 As shown in FIG3 , S110 specifically includes the following steps:

[0042] S111 determines the parameters of the lobe nozzle section and the contraction section;

[0043] S112 determines the length of the lobe nozzle section and the length of the contraction section based on the determined parameters.

[0044] For further information, see Figure 4 , Figure 5 , Figure 4 , Figure 5 1 is a schematic diagram of various parameters in an embodiment of a design method for reducing underwater exhaust noise of the present invention; the lobe nozzle parameters include nozzle length l2, nozzle diameter r1, number of lobes, lobe width l1, lobe height h, outer expansion angle α, inner expansion angle β;

[0045] The contraction section parameters include the contraction section length l3, the inlet diameter r1, and the outlet diameter r2.

[0046] S120: Establishing a physical model of the lobe nozzle structure according to the parameters of the lobe nozzle section and the contraction section; the established physical model can be found in Figure 6 ,The specific design of the physical model is as follows:

[0047] The main design parameters of the lobe nozzle section include the number of lobes, lobe width, lobe height, and internal and external expansion angles. Generally speaking, if the design conditions permit, measures such as increasing the number of lobes, reducing the lobe width, increasing the lobe aspect ratio, and increasing the total expansion angle can improve the performance of the lobe nozzle.

[0048] Based on the above principles, a lobe structure is designed at the nozzle mouth of a circular cross-section nozzle with a nozzle diameter r1 = 20 mm. The structure consists of eight lobes, each with a width and height of 4 mm and 10 mm respectively, and the inner and outer expansion angles are both 15°.

[0049] The environmental fluid domain is a cylinder with a diameter of 600mm and a height of 1000mm. The center of the bottom of the cylinder is the coordinate origin, and the direction of gravity is downward along the Z axis. The environmental fluid consists of a 660mm deep water and a 340mm high air area, forming an immersed exhaust environment with a free liquid surface. Among them, the air area plays a buffering role on the liquid splashed on the water surface, so that most of the liquid will fall back before reaching the upper boundary, maintaining the relative stability of the liquid level. The nozzle is located at the bottom of the model, with a tube length of 60mm, a wall thickness of 2mm, and a distance of 600mm between the nozzle plane and the water surface. The gas flows vertically upward through the nozzle and is discharged into the liquid environment, forming an immersed jet. It should be noted that the environmental parameter settings of the above-mentioned physical model can be designed according to different usage environments, and the above-mentioned environmental parameters are not used as the only settings. The above-mentioned environmental parameter settings are only for a clearer explanation of the implementation mode of the present invention.

[0050] S130: Based on the physical model of the lobe nozzle structure, establish physical assumptions and perform simulations; the complex spatial curved surface of the lobe nozzle makes the flow field near the nozzle orifice have a rich three-dimensional structure. Therefore, the submerged exhaust process of the lobe nozzle is a three-dimensional gas-liquid two-phase flow problem. To simplify the calculation, make the following assumptions:

[0051] (1) The mainstream part of the submerged exhaust is a free shear flow and is far away from the solid boundary, so the effect of the wall on the flow can be ignored;

[0052] (2) The gas phase medium is air, the liquid phase medium is water, and the temperature of both phases is taken as the room temperature of 15 °C under experimental conditions, so the mass transfer and heat transfer between the gas and liquid phases can be ignored;

[0053] (3) The nozzle inlet velocity is 53 m / s (corresponding to d = 20 mm, Q = 60 m 3 / h), the corresponding Mach number is 0.16, under which the compressibility of the gas can be ignored.

[0054] It should be noted that the above physical model assumptions can be established according to different usage environments, and the above assumptions are not used as the only assumption establishment method. The above assumptions are only set to explain the implementation of the present invention more clearly.

[0055] Based on the above-mentioned environmental parameters and assumptions, simulations were conducted and it was found that the lobe nozzle can enhance the continuity of the flow, alleviate the pressure surge caused by the necking phenomenon, and has a good noise reduction effect in the medium and low frequency bands, with a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz. The lobe nozzle produces the above effects because:

[0056] (1) The gas velocity distribution at the nozzle is improved, forming a local high-speed zone in the jet, thereby enhancing the jet penetration;

[0057] (2) The wave crests and troughs can induce the primary and secondary fluids to flow in opposite directions in the radial direction, thereby strengthening the gas-liquid mixing near the nozzle and further improving the jet penetration;

[0058] (3) Under the combined effect of the first two points, the necking phenomenon is alleviated, and the pressure pulsation and low-frequency noise associated with it are effectively suppressed;

[0059] (4) The increased contact area accelerates the attenuation of the boundary gas velocity, thereby effectively reducing the boundary noise mainly distributed in the mid-frequency band.

[0060] S140: Determine the final nozzle parameters based on the simulation results. The planning of the lobe nozzle section and the contraction section is obtained based on the simulation results as follows:

[0061] Table 1 Design planning table

[0062]

[0063] It should be further explained that the above-mentioned final optimization results may be different in different usage environments and need to be improved according to the specific usage environment. The above-mentioned embodiments are only for more clear explanation of the implementation mode of the present invention.

[0064] The advantage of this setting is that the exhaust process of underwater equipment belongs to submerged exhaust. Submerged exhaust noise includes upstream noise (single-phase exhaust noise) in the exhaust pipeline and downstream noise (bubble noise and boundary noise) outside the exhaust pipe. The silencer structure in the exhaust pipeline can effectively suppress the upstream noise, but it is difficult to act on the downstream noise outside the pipe. The downstream noise is precisely the part with the strongest amplitude. If targeted measures are not taken to suppress the downstream noise, the total sound pressure level is still difficult to reduce. The downstream noise is closely related to the flow state near the nozzle. Based on the control of downstream noise, a nozzle design method for reducing underwater exhaust noise is proposed. The nozzle flow, pressure pulsation in the pipe and the influence of exhaust noise are analyzed by numerical simulation and experimental means. On this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle that reduces underwater exhaust noise is designed, which provides a reference for the engineering design of exhaust noise reduction of underwater equipment.

[0065] See also Figure 6 , Figure 6 1 is a flow chart of a further development of an embodiment of the design method for reducing underwater exhaust noise nozzle of the present invention. It should be noted that if there is substantially the same result, the method of the present invention is not limited to Figure 6 The process sequence shown is limited. Figure 6 As shown, the method comprises the following steps:

[0066] The method comprises:

[0067] S210: Selection of parameters for the lobe nozzle section and the contraction section; this may be as described in S110 above and will not be repeated here;

[0068] S220: Determine the optimal contraction curve based on contraction segment parameter simulation;

[0069] The contraction section is an important part of the contraction lobe nozzle. Its main function is to improve the flow quality, that is, to improve the uniformity and stability of the flow field and reduce turbulence.

[0070] With the development of computational fluid dynamics, the study of the contraction section has shifted to optimizing the design of the contraction section according to actual conditions, and there have been many studies in this regard. Regarding the contraction curve, due to the similarity between the contraction lobe nozzle and the low-speed wind tunnel design, the present invention draws on some experience of low-speed wind tunnels in its design. The Witozinsky curve, also known as the Witozinsky curve, is often recommended for domestic wind tunnel design; in recent years, the quintic equation has been often used in American wind tunnel design; Lin Chaoqiang, Su Yaoxi, Hong Liu, etc. have conducted research on the design of rectangular wind tunnels using bicubic curves and provided numerical results on the influence of the ternary properties of the flow on the wall adverse pressure gradient and the uniformity of the outlet velocity. Therefore, S220: Determine the optimal contraction curve based on the contraction section parameter simulation using the following two parts:

[0071] 1. Contraction curve

[0072] According to the design requirements of the water tunnel, three types of shrinkage curves are selected for numerical calculation and comparison.

[0073] (1) Witozinsky curve (abbreviated as Witozinsky curve). Domestic wind tunnel design handouts often recommend the use of Witozinsky curve. The equation is:

[0074]

[0075] It can also be

[0076]

[0077] (2) The quintic curve is often used in wind tunnel design in the United States in recent years. The equation is

[0078]

[0079] It can also be

[0080] D=[1-10(l / L) 3 +15(l / L) 4 -6(l / L) 5 ]·(D1-D2)+D2

[0081] (3) Bicubic curve, the equation is

[0082]

[0083] It can also be

[0084]

[0085] In the formula, D1 is the inlet diameter r1, D2 is the outlet diameter r2, L is the length of the contraction section l3, l is the variable along L, D is the size of a certain section on the contraction section, m is the contraction ratio, lm is the length ratio of the front and back sections in the bicubic curve. By changing the value of lm, a group of bicubic curves were selected, and the values ​​of lm were 0.1, 0.3, 0.5, 0.6, 0.7, and 0.9 respectively.

[0086] See also Figure 7 , Figure 7 This is the shape of the contraction curve of the contraction section in an embodiment of the design method for reducing underwater exhaust noise nozzle of the present invention. Figure 7 The shapes of the above three types of curves are given. Assuming that the coordinates of the inlet of the contraction section are A (x1, y1, z1) and the coordinates of the outlet are B (x1, y1, z1), to connect the above three types of curves, according to the interpolation theorem. It can be seen that the equation of the curve is:

[0087]

[0088] 2 Simulation calculation and analysis of contraction section

[0089] right Figure 7 The contraction section constructed by the three types of eight curves is numerically simulated and analyzed, and the results are the velocity distribution diagrams of different sections of the circular working section. All values ​​are normalized, the horizontal axis is the ratio of the position r to the circular section radius R, and the vertical axis is the ratio of the measured velocity u to U*, U* is the average velocity calculated based on the given inlet flow, U = 7.5571m / s, and the average velocity is shown as a straight line of u / U* = 1 in the figure.

[0090] Using different curves will affect the uniformity of velocity distribution. The Vickers curve and the bicubic curve (xm is 0.1, 0.3) shrink sharply in the front section and are very gentle in the back section; the quintic curve and the bicubic curve (xm is 0.5, 0.6) have a relatively uniform and gentle change trend. The quintic curve and the bicubic curve (xm is 0.5) are symmetrical curves, and the bicubic curve (xm is 0.7, 0.9) shrinks gently in the front section and is very sharp in the back section, which directly affects the velocity uniformity at the inlet section Y0.

[0091] According to the law of conservation of mass, the integral area of ​​various curves and the horizontal axis should be equal to the integral area of ​​u / U*=1 about the horizontal axis, so the velocity distribution designed by each curve should be close to the straight line u / U*=1 and change evenly and smoothly. Figure 8 , Figure 8 The velocity distribution of the contraction curve of the contraction section at the Y0 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention. Figure 8The analysis shows that the velocity distribution designed with the Vickers curve has the best uniformity and is closest to the wall at a velocity of 0.99, which means that the velocity boundary layer designed with the Vickers curve has the thinnest thickness.

[0092] See also Figure 9-11 , Figure 9-11 The velocity distribution of the contraction curve of the contraction section at the Y1 / Y2 / Y3 section in the first embodiment of the design method of the nozzle for reducing underwater exhaust noise of the present invention is different from the velocity distribution at the inlet Y0. After a short period of stable flow, the velocity of most curves tends to be stable and uniform on the selected section.

[0093] Table 3 Relative area occupied by velocity boundary layer

[0094]

[0095] Table 4 Ratio of U max to U*

[0096]

[0097] Table 3 shows the relative area occupied by the velocity boundary layer on each section using different curve designs (the ratio of the area occupied by the velocity less than 0.99 times U* to the cross-sectional area); Table 4 shows the ratio of the maximum velocity U max to U*. The above scheme gives the simulation results of three curves, and the appropriate curve can be selected according to different use environments and different parameters.

[0098] S230: establishing a physical model of the lobe nozzle structure according to the lobe nozzle section and the contraction section parameters; this may be as described in S120 above and will not be described in detail here;

[0099] S240: establishing physical assumptions and simulating according to the physical model of the lobe nozzle structure; this may be as described in S130 above and will not be described in detail here;

[0100] S250: Determine the final nozzle parameters according to the simulation results, which can be as described in S140 above and will not be described again here;

[0101] Said

[0102] One aspect of the present invention is to provide a contraction lobe nozzle, which can enhance the continuity of flow, alleviate the pressure surge caused by necking, have good noise reduction effect in the low and medium frequency bands, and have a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz.

[0103] See also Fig.12 , Fig.13 , Fig.11 , Fig.12It is a schematic diagram of an embodiment of a contraction lobe nozzle of the present invention. The lobe nozzle comprises a lobe section 2 and a contraction section 1;

[0104] The lobe segment 2 is cylindrical, one end of the lobe segment 2 spreads outward to form a plurality of lobes 21, and the other end of the lobe segment 2 is connected to the contraction segment 1;

[0105] The contraction section 1 is in the shape of a diffuser tube, and the end 11 not connected to the lobe section 2 diffuses outwards to form a trumpet shape;

[0106] The lobe section 2 and the contraction section 1 are combined to form a Laval nozzle-like nozzle.

[0107] The advantage of this setting is that it can enhance the continuity of the flow, alleviate the sudden pressure rise caused by the necking phenomenon, have a good noise reduction effect in the mid- and low-frequency bands, and have a noise reduction effect of 3.3-8.6dB on the total sound pressure level of 10-4600Hz.

[0108] Further, the number of lobes 21 in lobe segment 2 is an even number;

[0109] The distribution of the lobes 21 includes a uniform distribution;

[0110] The expansion angle of the lobe 21 is 15°.

[0111] The trumpet-shaped end 11 of the contraction section 1 is an outlet end;

[0112] The contraction section 1 and one end of the lobe section 2 are inlet ends;

[0113] The diameter of the outlet end is 1.5 times the diameter of the inlet end.

[0114] The advantage of this setting is that the lobe nozzle can enhance the penetration of the jet and make the axial flow smoother. After simulation verification, it has a good noise reduction effect on medium and low frequency noise.

[0115] Furthermore, the ratio of the lobe 21 height to the lobe width may be 3 or 3.21;

[0116] The advantage of this setting is that in the design of turbine engines, when the bypass ratio remains unchanged, within the range of the lobe aspect ratio of 2 to 4.5, at the outlet of the exhaust system, the mixing efficiency shows an increase-decrease-increase trend with the increase of the lobe aspect ratio, where the lobe aspect ratios of 3 and 3.21 are the two inflection points of the curve. As the lobe aspect ratio increases, the total pressure recovery coefficient and thrust coefficient continue to decrease. Drawing on this rule, it can be applied to our lobe nozzles that reduce underwater exhaust noise. Therefore, the height or width can be selected first, and then the other parameter can be determined based on the aspect ratio.

[0117] Furthermore, the trumpet-shaped end 11 of the contraction section 1 is an outlet end;

[0118] One end of the contraction section and the lobe section is an inlet end;

[0119] The diameter of the outlet end is 1-2 times the diameter of the inlet end.

[0120] Furthermore, the outward diffusion amplitude of the contraction section 1 is confirmed by the contraction curve;

[0121] The shrinkage curve adopts the Vickers curve; the simulation and analysis of the curve can refer to the method described in the previous embodiment. Here, the reason for adopting the Vickers curve is explained.

[0122] According to the law of conservation of mass, the integral area of ​​various curves and the horizontal axis should be equal to the integral area of ​​u / U*=1 about the horizontal axis, so the velocity distribution designed by each curve should be close to the straight line u / U*=1 and change evenly and smoothly. Figure 8 The analysis shows that the velocity distribution designed with the Vickers curve has the best uniformity and is closest to the wall at a velocity of 0.99, which means that the velocity boundary layer designed with the Vickers curve has the thinnest thickness. Figures 9 to 11 The velocity distribution diagrams at three different positions Y1, Y2 and Y3 of the working section of the circular tube are intercepted. Different from the velocity distribution at the inlet Y0, after a short period of stable flow, the velocities of most curves tend to be stable and uniform on the selected cross-sections. Except for the unsatisfactory results of the bicubic curve (xm is 0.9), the results of other curves are acceptable. Table 3 shows the relative area occupied by the velocity boundary layer on each cross-section using different curve designs (the ratio of the area occupied by the velocity less than 0.99 times U* to the cross-sectional area); Table 4 shows the ratio of the maximum velocity U max to U*. By comparison, it can be seen that the two values ​​are the smallest on all cross-sections using the Vickers curve design, that is, the velocity distribution is the most uniform, so the Vickers curve is selected as the design curve of the contraction section. When designing the contraction section, in order to reduce the influence of the contraction curve on the uniformity of the velocity of the working section, it should be avoided to select those design curves with gentle contraction in the front section and very sharp contraction in the back section. Therefore, the contraction curve in this embodiment adopts the Vickers curve.

[0123] Furthermore, a rectifier is provided at the connection between the lobe section and the contraction section;

[0124] The rectifier comprises a honeycomb and a guide plate.

[0125] The beneficial effects of the present invention are concentrated in the following two aspects:

[0126] (1) The exhaust process of underwater equipment belongs to submerged exhaust. Submerged exhaust noise includes upstream noise (single-phase exhaust noise) in the exhaust pipe and downstream noise (bubble noise and boundary noise) outside the exhaust pipe. The silencer structure in the exhaust pipe can effectively suppress the upstream noise, but it is difficult to act on the downstream noise outside the pipe. The downstream noise is precisely the part with the strongest amplitude. If targeted measures are not taken to suppress the downstream noise, the total sound pressure level is still difficult to reduce. The downstream noise is closely related to the flow state near the nozzle. Based on the control of downstream noise, a nozzle design method for reducing underwater exhaust noise is proposed. The influence of nozzle flow, pressure pulsation in the pipe and exhaust noise is analyzed by numerical simulation and experimental means. On this basis, the noise reduction mechanism of the lobe nozzle is analyzed, and a nozzle for reducing underwater exhaust noise is designed, which provides a reference for the engineering design of exhaust noise reduction of underwater equipment.

[0127] (2) The lobe nozzle can enhance the continuity of the flow, alleviate the pressure surge caused by the necking phenomenon, and has a good noise reduction effect in the medium and low frequency bands, with a noise reduction effect of 3.3-8.6dB for the total sound pressure level of 10-4600Hz. The lobe nozzle improves the gas velocity distribution at the nozzle, forms a local high-speed area in the jet, and thus enhances the jet penetration; the diffusion area of ​​the nozzle can induce the primary and secondary fluids to flow in the radial direction, thereby strengthening the gas-liquid mixing near the nozzle and improving the jet penetration; the necking phenomenon is further alleviated, and the pressure pulsation and low-frequency noise related to it are effectively suppressed; the increased contact area accelerates the attenuation of the boundary gas velocity, thereby effectively reducing the boundary noise mainly distributed in the medium frequency band.

[0128] The above descriptions are only some embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent device or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A contraction lobe nozzle, characterized in that: The lobe nozzle comprises a lobe section and a contraction section, wherein the gas flow is discharged directly into the liquid environment through the contraction section and the lobe nozzle section in sequence, forming an immersed jet; The lobe segment is cylindrical, one end of the lobe segment spreads outward to form a plurality of lobes, and the other end of the lobe segment is connected to the contraction segment; The contraction section is in the shape of a diffusion tube, and the end not connected to the lobe section diffuses outwards to form a trumpet shape; The lobe section and the contraction section are combined to form a Laval nozzle-like nozzle; The nozzle includes the following design method: Parameter selection of the lobe nozzle section and the contraction section; the contraction curve of the contraction section adopts the Vickers curve; A physical model of the lobe nozzle structure is established according to the lobe nozzle section and contraction section parameters; According to the physical model of the lobe nozzle structure, physical assumptions are established and simulation is performed; Determine the final nozzle parameters based on the simulation results; The parameter selection of the lobe nozzle section and the contraction section comprises the following steps: Determine the parameters of the lobe nozzle section and the contraction section; Based on the determined parameters, the length of the lobe nozzle section and the length of the contraction section are determined; The lobe nozzle section parameters include nozzle length, nozzle diameter, number of lobes, lobe width, lobe height, and inner and outer expansion angles; The contraction section parameters include contraction section length, inlet diameter, and outlet diameter; After the parameters of the lobe nozzle section and the contraction section are selected, the following steps are also included: The optimal contraction curve is determined based on contraction section parameter simulation.

2. A contracting lobe nozzle as claimed in claim 1, characterized in that: The number of lobes in the lobe segment is an even number, and the distribution of the lobes includes a uniform distribution; The expansion angle of the lobe is 10°-20°.

3. A contracting lobe nozzle as claimed in claim 1, characterized in that: The ratio of the lobe height to the lobe width is 2-4.

5.

4. A contracting lobe nozzle as claimed in claim 1, characterized in that: The trumpet-shaped end of the contraction section is the outlet end; One end of the contraction section and the lobe section is an inlet end; The diameter of the outlet end is 1-2 times the diameter of the inlet end.

5. A convergent lobe nozzle as claimed in claim 1, characterized in that: A rectifier is provided at the connection between the lobe section and the contraction section; The rectifier comprises a honeycomb and a guide plate.

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