A method for suppressing cross-medium water entry interference of a supercavitating projectile based on optimization of keel length

Abstract

The application provides a supercavitation projectile cross-medium water entry interference suppression method based on optimization of a cymbal length, comprising the following steps: S1, establishing a projectile-cymbal parameterized model, and demarcating an optimization interval of the cymbal length; S2, coupling a multiphase flow model, a cavitation model and a dynamic grid method to simulate a separation process of the projectile and the cymbal, and obtaining original data of the projectile; S3, performing comparative simulation of multiple groups of different cymbal lengths, and quantitatively extracting three key performance indexes of a supercavity symmetry, a pitch angle deviation and a speed attenuation rate by using the original data of the projectile; and S4, establishing a multi-target optimization criterion based on an interference index, determining a globally optimal cymbal length parameter, and completing the whole optimization process. The application can solve the problem caused by improper design of the cymbal length when the supercavitation projectile and the cymbal cooperatively enter water.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of underwater weapon design, and particularly relates to a supercavitation projectile cross-medium water entry interference suppression method based on length optimization of a card flap. BACKGROUND

[0002] The principle of supercavitation technology is to form a wrapping air cavity (cavity) around the projectile body by high-speed movement, so that only the head of the projectile body contacts the water body, and the resistance is reduced to 1 / 5-1 / 10 of the traditional underwater weapon. The supercavitation projectile faces the risk of extreme fluid impact and attitude instability in the instant of high-speed water entry. The card flap, as a key auxiliary part, can maintain the initial trajectory, but there is a fundamental contradiction in the length design of the card flap: long card flap (≈1.0-1.5 times the caliber), which prolongs the fluid shielding time, but causes strong vortex shedding interference due to separation lag, resulting in a pitch oscillation of the projectile of >8°; short card flap (≈0.5 times the caliber) accelerates separation to reduce interference, but weakens the protection of the cavity, and the cavity collapses in advance after water entry, and the speed decay is intensified. The existing technology relies on trial and error experience, and cannot quantitatively map the relationship between the length of the card flap and the water entry stability, and the traditional simulation cannot accurately simulate the dynamic separation flow field, resulting in long design cycle, high cost and poor stability. SUMMARY

[0003] The purpose of the present application is to provide a supercavitation projectile cross-medium water entry interference suppression method based on length optimization of a card flap, aiming to solve the problem caused by improper design of the length of the card flap when the supercavitation projectile and the card flap cooperate in water entry.

[0004] A supercavitation projectile cross-medium water entry interference suppression method based on length optimization of a card flap, comprising:

[0005] Step S1: Establish a projectile-card flap parameterized model, and define an optimization interval for the length of the card flap;

[0006] Step S2: Simulate the separation process of the projectile and the card flap by coupling the multiphase flow model with the dynamic grid method and the cavitation model, and obtain the original data of the projectile;

[0007] Step S3: Perform comparative simulation of multiple groups of different card flap lengths, and quantitatively extract three key performance indicators of cavity symmetry, pitch angle deviation and speed decay rate using the original data of the projectile;

[0008] Step S4: Establish a multi-objective optimization criterion based on the interference index, determine the globally optimal card flap length parameter, and complete the entire optimization process.

[0009] Compared with the prior art, the present application has the following advantages:

[0010] (1) Through the establishment of the quantitative mapping model of the length of the card and the stability of the water, the blindness problem caused by the dependence on experience in the traditional design is solved, and the leap from qualitative design to quantitative optimization is realized, which significantly improves the design efficiency and reliability.

[0011] (2) Based on the multi-objective optimization criterion, the three key indicators of cavity symmetry, pitch angle deviation and speed decay rate are optimized, the performance imbalance caused by single parameter optimization is overcome, and the pitch oscillation is suppressed while ensuring good cavity shape and speed retention.

[0012] (3) The method has clear engineering applicability, through the technical path of parameterized modeling and systematic simulation, not only greatly reduces the test cost, but also the optimization design criteria formed can directly guide the card design of supercavitating projectiles of different sizes, and has good popularization and application value. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a flow chart of the water entry interference suppression method based on the length optimization of the card.

[0014] Figure 2 It is a model diagram of a water entry projectile with a card.

[0015] Figure 3 It is a pressure cloud chart provided by the embodiment of the present application after water entry.

[0016] Figure 4 It is a pitch angle change diagram provided by the embodiment of the present application. DETAILED DESCRIPTION

[0017] In order to enable the personnel in the art to better understand the present application scheme, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the scope of protection of the present application.

[0018] In conjunction with Figures 1-4 , the present application proposes a supercavitating projectile cross-medium water entry interference suppression method based on the length optimization of the card, as shown in Figure 1 , mainly includes:

[0019] Step S1: Establish a projectile-card parameterized model, and define a reasonable card optimization interval;

[0020] A parameterized assembly model of the projectile body and the separable petal was established. The projectile body adopts a standard supercavitating shape design, with a head cone angle of 15° and a length-diameter ratio of the cylindrical section of 5:1. The assembly gap between the projectile body 1 and the petal 2 is controlled within 0.2 mm, which is close to the actual manufacturing tolerance. The opening angle is fixed at 30° to avoid introducing additional disturbance variables. The model diagram is shown in Figure 2 The petal length was taken as a key design variable. Based on engineering experience and preliminary fluid analysis, the optimization interval was defined as 0.6D-1.0D (where D is the projectile diameter). Within this interval, a parameter space containing more than 5 sample points was established (for example, D=100 mm, =60 mm, 70 mm, 80 mm, 90 mm, 100 mm), ensuring design freedom and covering possible optimization areas.

[0021] Step S2: Build a cross-medium water-entry numerical simulation system to accurately simulate the separation process of the projectile and the petal by coupling the multiphase flow model, the cavitation model, and the dynamic grid method.

[0022] A computational fluid dynamics method was used to build a cross-medium water-entry simulation model. The model couples the VOF multiphase flow method and the Schnerr-Sauer cavitation model to accurately simulate the evolution of the cavitation bubble:

[0023] ;

[0024] wherein is the water phase volume fraction, is the gas phase volume fraction, is the water density, is the projectile velocity vector, is the projectile relative velocity vector, is the simulation time, is the gradient, is the cavitation mass source term. The model of the projectile and the petal and the simulation parameter settings are as follows: Projectile body: fixed supercavitating shape (cone head half angle 15°, length-diameter ratio of cylindrical section 5:1). Petal design: length The petal length was taken as the core variable, and the optimization interval was 0.6-1.0 times the projectile diameter D (for example, D=100 mm, = 60 mm, 70 mm, 80 mm, 90 mm, 100 mm); the opening angle is fixed at 30° to avoid introducing additional interference variables; the assembly gap is set to 0.2 mm to simulate the real manufacturing tolerance. Physical model: VOF multiphase flow model coupled with Schnerr-Sauer cavitation model is used; the turbulent flow model is selected as SST k-ω (near-wall y⁺≤1, inlet turbulent intensity 5%). Motion setting: the projectile body is defined as a 6-DOF rigid body driven by fluid dynamics; grid system: overlapping grid is used: the base size of the background domain is 5 mm, and the projectile / valve domain is locally encrypted to 0.3 mm; the dynamic self-adaptive encryption is set for the gas-liquid interface to ensure the resolution of the cavitation interface. By simulating the separation process, the original data of the projectile (pitch angle , projectile velocity , projectile longitudinal section bilateral cavitation area , ) are obtained to prepare for the extraction of performance indicators for post-processing. The simulation results are shown in Figure 3 . Through computational fluid dynamics analysis, it can be seen that when the valve contacts the water surface, an obvious asymmetric pressure field is formed below the valve, and the maximum pressure gradient appears in the edge region of the valve, with a pressure peak of up to 3.5 MPa. This asymmetric pressure distribution produces an additional pitch moment, directly leading to a change in the attack angle of the projectile during water entry, and the cavitation shape also deforms accordingly.

[0025] Step S3: Perform comparative simulation of multiple groups of different valve lengths to quantitatively extract three key performance indicators: cavitation symmetry, pitch angle deviation, and velocity decay rate;

[0026] Under the established simulation system, a series of comparative simulations covering the design range are performed. Each simulation simulates the process of the projectile obliquely entering the water at an initial speed of 600 m / s, and the calculation time is 2 ms. Through post-processing, three key performance indicators are quantitatively extracted:

[0027] Cavitation symmetry : ;

[0028] wherein , are the bilateral cavitation areas of the projectile longitudinal section.

[0029] Pitch angle deviation : ;

[0030] wherein is the pitch angle of the projectile entering the water, is the pitch angle of the projectile after = 2 ms.

[0031] Velocity decay rate : ;

[0032] where is the initial velocity of the projectile entering the water, is the velocity of the projectile after =2 ms.

[0033] The complete dynamic response under each set of parameters is recorded, and three key performance indicators, namely, cavity symmetry, pitch angle deviation, and velocity decay rate, are extracted. On this basis, through systematic data analysis, a quantitative mapping model of the flap length and performance indicators is established, with the following specific contents:

[0034] (1) Obtain multiple sets of sample data composed of ;

[0035] (2) Through systematic mathematical processing methods, discrete simulation data is converted into continuous design guidance models; specifically including: normalizing the obtained sample data set to eliminate the influence of dimensions:

[0036] ;

[0037] where is the normalized flap length, is the minimum flap length of the optimization interval, is the maximum flap length of the optimization interval, is the original flap length value, is the normalized cavity symmetry value, is the minimum cavity symmetry value of the optimization interval, is the maximum cavity symmetry value of the optimization interval, is the original cavity symmetry value, is the normalized pitch angle deviation value, is the minimum pitch angle deviation value of the optimization interval, is the maximum pitch angle deviation value of the optimization interval, is the original pitch angle deviation value, is the normalized velocity decay rate, is the minimum velocity decay rate of the optimization interval, is the maximum velocity decay rate of the optimization interval, is the original velocity decay rate.

[0038] A quadratic response surface model is used to establish the mapping relationship between parameters and performance:

[0039] ;

[0040] ;

[0041] ;

[0042] in The length of the cardiopulmonary bypass is 1 / 3. , , , , , , , , For regression coefficients, This is the error term.

[0043] (3) The prediction accuracy of the model is evaluated by leave-one-out cross-validation, requiring a determination coefficient R² ≥ 0.9 to ensure the reliability of the mapping relationship;

[0044] (4) Based on the established mapping relationship, calculate the sensitivity of each performance index to the card lobe length:

[0045] ;

[0046] ;

[0047] ;

[0048] in To find the partial derivative, , , , , , For regression coefficients, The length of the cardiopulmonary bypass is 1 / 3. Due to cavitation symmetry, For pitch angle deviation, This represents the velocity decay rate.

[0049] Firstly, through Confirm the degree of pitch oscillation of the projectile, and then... The root cause of the problem was found to be the asymmetric flow field induced by the cardiopulmonary bypass, which was finally addressed through... Make sure to change While reducing pitch oscillation, it avoids the side effects of losing cavitation protection and drastically reducing velocity. In this example, a slat length of 0.6–1.0 times the projectile diameter is used for simulation, and the pitch angle curve is shown below. Figure 4 As shown, by selecting a reasonable slat length, the maximum pitch angle deviation of the projectile is made less than 5°, thus solving the problem of pitch oscillation of the long slat.

[0050] Step S4: Establish multi-objective optimization criteria, introduce a comprehensive interference evaluation index, determine the globally optimal cardioid length parameter, and complete the entire optimization process.

[0051] A multi-objective optimization criterion based on the interference index is established:

[0052] (requires ≤1);

[0053] wherein is the pitch angle deviation, is a reference value of the pitch angle deviation, is the cavity symmetry, is a reference value of the cavity symmetry, is the velocity decay rate, is a reference value of the velocity decay rate, , , are weight coefficients of the pitch angle deviation, the cavity symmetry and the velocity decay rate, respectively, and satisfy: .

[0054] In this example, the reference value of the pitch angle deviation is 5°, the reference value of the cavity symmetry is 0.90, the reference value of the velocity decay rate is 15%, and is in the range of 0.4-0.6, is in the range of 0.2-0.4, is in the range of 0.1-0.3. The feasible solution set that satisfies ≥0.90, ≤5° and ≤15% is first screened out, and then the interference index of each feasible solution is calculated. Through analysis, the chine length that makes the value of minimum is selected as the global optimal parameter. Practical application shows that the optimized parameters determined by the method can reduce the pitch angle deviation by more than 30% and improve the velocity decay by more than 15%, effectively improving the water entry stability of the projectile. The method combines parameterized modeling, accurate simulation, performance quantification and multi-objective decision-making, and establishes a complete chine length optimization process, providing reliable technical support for the engineering design of supercavitating projectiles.

[0055] The present application is not only applicable to the 12 mm diameter projectile used in the above-mentioned embodiments, but also can be extended to the design of supercavitating projectiles of different sizes and speeds, and the water entry interference can still be effectively suppressed by adjusting the chine length optimization range and the corresponding simulation parameters in proportion according to the method disclosed in the present application.

Claims

1. A method for suppressing cross-medium water entry interference of a supercavitation projectile based on optimization of the length of a card valve, characterized in that, Comprise: Step S1: Establishing the parameterized model of projectile and sabot, and setting the optimization interval of the length of the sabot; Step S2: Simulating the separation process of the projectile and the sabot by coupling the multiphase flow model with the cavitation model and the dynamic mesh method to obtain the original data of the projectile; Step S3: Performing comparative simulation of multiple groups of different sabot lengths, and quantitatively extracting three key performance indicators of the symmetry of the cavitation, the pitch angle deviation and the speed attenuation rate by using the original data of the projectile; Step S4: Establishing a multi-objective optimization criterion based on the interference index to determine the globally optimal length of the sabot and complete the entire optimization process.

2. The method of claim 1, wherein, The multi-objective optimization criterion based on the interference index is: ， wherein is a pitch angle deviation, is a pitch angle deviation reference value, is a cavitation symmetry, is a cavitation symmetry reference value, is a speed decay rate, is a speed decay rate reference value, , , are weight coefficients of the pitch angle deviation, the cavitation symmetry, and the speed decay rate, respectively, and satisfy: ; The solution set satisfying ≥ 、 ≤ 、 is screened, and the card interval length making the value of minimum is selected as the global optimal parameter.

3. The method of claim 1, wherein, The optimization interval of the length of the sabot is set to 0.6D-1.0D, wherein D is the diameter of the projectile.

4. The method of claim 1, wherein, The multiphase flow model coupled with the cavitation model uses the VOF multiphase flow model coupled with the Schnerr-Sauer cavitation model: ， wherein is the water phase volume fraction, is the gas phase volume fraction, is the water density, is the projectile velocity vector, is the projectile relative velocity vector, is the simulation time, is the gradient, is the cavitation mass source term.

5. The method of claim 1, wherein, The three key performance indicators are: Cavitation symmetry : ; wherein , is the longitudinal cross-sectional two-sided cavitation area of the projectile; Pitch angle deviation : ; wherein is the angle of elevation of the projectile at time is the time of flight of the projectile is the angle of elevation of the projectile at time rate of speed decay : ; wherein is the initial velocity of the projectile into the water, is the velocity of the projectile at time after entering the water.

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