Integrated evaluation method for cross-medium static stability margin of supercavitation navigation body

Abstract

The invention discloses a supercavitation navigation body cross-medium static stability margin integrated evaluation method, which comprises the following steps: (1) establishing a fluid domain and solid domain model, dividing grids, requiring good matching of a solid wall surface in contact with a fluid, setting initial and boundary conditions of the fluid domain, setting material attributes of a solid structure and endowing the solid structure with an initial working condition; (2) monitoring a pitching moment and a pitching force value in the air, calculating an aerodynamic center of the supercavitation navigation body in the air, and obtaining a static stability margin of the supercavitation navigation body in a flight state; (3) according to an empirical cavitation contour formula and the underwater characteristics of the supercavitation navigation body, the wetting volume and the equivalent buoyancy center position of the navigation body are obtained, and the static stability margin after complete development of the cavitation in water is calculated; and (4) carrying out weighted average by integrating the air static stability margin and the underwater static stability margin so as to obtain the static stability margin for judging the super-cavitation navigation body in the cross-medium water entry process. And help can be provided for judging the static stability of the navigation map entering water.

Description

Technical Field

[0001] The present invention belongs to the field of cross-medium water entry, and in particular relates to an integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle. Background Art

[0002] Cross-medium water entry research originated from the analysis of the water entry trajectories of weapons such as torpedoes and missiles. For example, submarine-launched missiles must maintain a stable attitude after exiting the water, while torpedoes must avoid deviating from their trajectory due to cavitation collapse or instability during water entry. At this time, research often relied on experimental and empirical formulas, such as water tunnel tests and scaled-down model testing.

[0003] Supercavitating vehicles use a cavitator on their nose to create a gaseous bubble that envelops the vehicle, significantly reducing underwater drag (drag reduction rate can reach over 90%) and enabling high-speed underwater motion (>100m / s). However, the moment the vehicle passes from air to water (the medium-crossing phase), the cavitation bubble morphology changes dramatically, potentially leading to attitude instability or even trajectory deviation.

[0004] At present, there are relatively mature methods for judging the static stability margin of vehicles in the air and underwater, but there is no mature theoretical method for analyzing the static stability of vehicles in the cross-medium water entry stage. The difficulty lies in: (1) Gas-liquid-solid multiphase transient coupling: At the moment of entry into the water, the head of the vehicle hits the water surface, causing cavitation to form, expand and collapse, involving the phase change, turbulence and compressibility effects of the gas-liquid two-phase flow. The interaction between cavitation and the free liquid surface may cause the flow field around the vehicle to be asymmetric, generate longitudinal torque, and destroy static equilibrium. (2) Nonlinear attitude dynamics: When the vehicle enters the water body (high-density medium) from the air (low-density medium), parameters such as buoyancy and additional mass change in a step-like manner, resulting in strong nonlinearity in the dynamic equations. The coupling of pitch, roll and yaw motions requires the establishment of a six-degree-of-freedom (6-DOF) model to analyze the stable equilibrium point. (3) Fluid-solid coupling: The impact load of high-speed water entry may cause the vehicle to vibrate, change the cavitation morphology and fluid load distribution, and form a feedback loop. The local high pressure (up to GPa level) generated by cavitation collapse may damage the surface of the vehicle, and stability analysis is required to avoid structural resonance.

[0005] At present, there is no mature method to quantitatively evaluate the static stability of cross-media vehicles. However, the static stability analysis during the cross-media entry process is of great significance for the performance evaluation of cross-media vehicles. Summary of the Invention

[0006] The purpose of the present invention is to provide an integrated evaluation method for the cross-media static stability margin of a supercavitating vehicle, which can uniformly evaluate the static stability margin of a supercavitating vehicle in the air, in water, and in complex cross-media water entry processes, thereby providing certain assistance for the static stability judgment of a cross-media supercavitating vehicle entering water.

[0007] The technical solutions for achieving the purpose of the present invention are:

[0008] An integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle is characterized in that the cross-medium static stability margin of the vehicle is used to determine whether a ricochet occurs when the supercavitating vehicle enters the water, wherein the cross-medium static stability margin SM of the supercavitating vehicle is tran for:

[0009] SM tran =ω·SM air +μ·SM water

[0010] SM air =SM air_X +SM air_Z

[0011]

[0012] SM water =SM water_X +SM water_Z

[0013]

[0014] When SM tran Within the interval, it is considered that the supercavitating vehicle will not ricochet when entering the water;

[0015] Among them SM air is the static stability margin of the supercavitating vehicle in the air, SM air_X is the axial static stability margin of the vehicle in air, SM air_Z is the radial static stability margin of the vehicle in air, X AC is the axial coordinate of the aerodynamic center of the vehicle, Z AC is the radial coordinate of the aerodynamic center of the vehicle, L is the length of the vehicle, SM water is the static stability margin of the supercavitating vehicle in water, SM water_X is the axial static stability margin of the navigation body in water, SM water_Z is the radial static stability margin of the navigation body in water, X CBeff is the axial coordinate of the equivalent buoyancy center of the navigation body, Z CBeff is the radial coordinate of the equivalent buoyancy center of the navigation body, X CG is the axial coordinate of the center of mass of the navigation body, Z CG is the radial coordinate of the center of mass of the navigation body, D C is the diameter of the head cavitator; ω and μ are the cross-medium static stability margin values ​​SM tran The linear weighting coefficient satisfies ω+μ=1.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] (1) Compared with physical experiments and cross-medium water entry simulation, only 2D aerodynamic simulation of the vehicle in the air and analysis of the underwater characteristics of the supercavitation vehicle based on the empirical formula of supercavitation can effectively save computing power;

[0018] (2) By unifying the static stability margin (SSM) index, a coordinated analysis of aerodynamic and inertial forces is achieved, which generally reflects the stability changes of the navigation body from water to air (or vice versa). BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the dimensions of a supercavitating vehicle.

[0020] Figure 2 Schematic diagram of the overall process.

[0021] Figure 3 Schematic diagram of supercavitating vehicle aerial simulation.

[0022] Figure 4 Schematic diagram of the pitching moment and pitching force monitoring points.

[0023] Figure 5 Schematic diagram of the tail and shoulder positions of a supercavitating vehicle.

[0024] Figure 6 Flowchart of simulation verification of embodiment.

[0025] Figure 7 Schematic diagram of simulation results of simulation verification of embodiment. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] The following are specific example parameters and a supercavitation vehicle model, which are used to perform an integrated evaluation of the cross-medium static stability margin. The specific flow chart is as follows: Figure 1 As shown in the figure, the authenticity of this method is further verified by cross-medium water entry simulation calculation, which specifically includes the following steps:

[0028] Step 1: Establish the fluid domain and solid domain models respectively, and divide the meshes. The solid wall in contact with the fluid needs to have good matching, that is, the boundary receptor mesh of the overlapping mesh outside the solid domain should be of the same size as the background mesh (i.e., the fluid domain mesh). Set the initial and boundary conditions of the fluid domain, set the material properties of the solid structure, and assign the initial working conditions of the vehicle, such as speed U, angle of attack α, and angle of entry. wait.

[0029] Establish the fluid domain and solid domain models separately and divide the mesh. The solid wall in contact with the fluid needs to have good matching. Limit the freedom of the vehicle in the Y direction, that is, the left and right yaw direction of the vehicle. Therefore, the fluid domain only needs to limit the scale in the X and Z directions, which are the roll and pitch directions of the vehicle around the axis respectively. Set the initial boundary of the fluid domain in the X and Z directions with scale H X 、H Z >>Vehicle length L, set H X 、H Z =10L, using the cutting volume grid and prism layer grid division method, the fluid domain is set as the background grid, the solid domain outer layer is nested with overlapping grids, and the overlapping grid boundary receptor grid size is equivalent to the fluid domain grid size. The simulation domain is as follows Figure 2 As shown; in this example, after the supercavitating vehicle is launched, the speed is U = 300m / s, the angle of attack α = 5°, and the angle of entry is When flying in the air, its structure is a rotating body, with an oblique cone at the head and a cylinder at the tail. The length L of the flying body is 100 mm, the diameter D = 12.7 mm, and the diameter of the head cavitator D c is 3.5mm, and the taper angle θ = 5°, such as Figure 3 As shown. Set the X-direction speed of the supercavitation vehicle Z direction speed The solid material of the vehicle body is #75 structural steel, and its specific physical properties are shown in Table 1. The boundary conditions are all set to pressure outlet to simulate infinite airspace;

[0030] Table 1 - Physical parameters of supercavitating vehicle materials

[0031] parameter Numerical Young's modulus / GPa 206 <![CDATA[Density / (kg·m -3 )]]> 7850 Yield stress / MPa 345 Poisson's ratio 0.3

[0032] Step 2: Monitor the pitching moment and pitching force of the vehicle in the air, and calculate the aerodynamic center (X AC ,Z AC ), and thus the static stability margin SM under its flight state is obtained air .

[0033] Pitch force and moment monitoring points P1, P2 and P3 are set at the head, bottom of the cone and bottom of the cylinder of the supercavitating vehicle respectively, as shown in Figure 4 As shown, the measured pitch moment M = 0.051 kN m and the pitch force value L M =0.76kN, using the formula Where (X AC ,Z AC ) is the focal coordinate of the longitudinal plane of the supercavitating vehicle, that is, the XOZ plane, (X, Z) refis the reference point coordinate. In this embodiment, the default reference point is the vertex of the vehicle head, with coordinates (0,0). Then (X,Z) AC =(0.067,0). Center of mass coordinates (X CG ,Z CG )=(0.062,0), according to the formula SM air =SM air_X +SM air_Z , where SM air_X is the static stability margin of the vehicle in the direction of the air axis, SM air_Z is the radial static stability margin of the vehicle in the air. Since the vehicle in the embodiment is a rotational body, the mass in the Z direction is uniformly distributed, so the aerodynamic center formula can be simplified to Obtain the static stability margin value SM of the vehicle in the air air =5.0%.

[0034] Step 3: Based on the empirical cavitation contour formula and the supercavitation vehicle, a supercavitation will be generated that covers the entire body. Only the cavitator plane and the tail beat are wetted. The wetted volume of the vehicle is obtained by comprehensive consideration, and the equivalent center of buoyancy position (X CBeff ,Z CBeff ), the static stability margin SM after the cavitation is fully developed in water is calculated water .

[0035] According to the empirical cavitation contour formula: Where R(x,t) is the radius of the cavitation at time t at a distance x from the head of the vehicle, where x is along the axis of the vehicle, the vertex coordinates at the center of the head are (x,z) = (0,0), and the x coordinates gradually increase from the head to the tail; R0 is the maximum radius of the cavitation, D is the maximum diameter of the navigation body, C d is the cavitation characteristic coefficient, C d ∈(0.8~1.2), in this embodiment, it is taken as 1.2; U is the speed of the vehicle; L cavity is the total length of the cavitation bubble, σ is the cavitation number, Among them, P ∞ is the ambient static pressure, P v is the saturated vapor pressure of the fluid, and ρ is the density of water. ∞ Take atmospheric pressure 101325Pa, P v The saturated vapor pressure of water at room temperature is 3170Pa, and ρ is approximately 1000kg / m 3 , t is taken as 0.0004s, and the cavitation number σ=0.0022, L cavity=0.18m, thus obtaining the tail cavitation radius R(x,t)=R(L,t)=R(0.1,0.0004)=12.44mm; generally, when the angle of attack α≤cone angle θ, the wetted area of ​​the supercavitating vehicle in the water is the tail, and when the angle of attack α>cone angle θ, the shoulder is wetted. The tail shoulder diagram is shown in the figure below. Figure 5 As shown; define the wetted volume ratio: Where V is the volume of the supercavitating vehicle, V wet is the effective wetted volume of the supercavitating vehicle, L1 is the length of the non-oblique cone section of the supercavitating vehicle, L2 is the length of the oblique cone section of the supercavitating vehicle, V = 9 × 10 -6 m 3 , then this embodiment V wet =1.03×10 -6 m 3 , the axial coordinate of the equivalent buoyancy center of the vehicle Radial coordinate of equivalent buoyancy center of navigation body Where X and Z are the discrete coordinates of the effective wetted volume, ρ ω is the multiphase flow density, here the density of water is approximately ρ = 1000 kg / m 3 , g is the acceleration of gravity; since discrete coordinates (x, z) are difficult to capture in actual engineering, we have to make some simplifying assumptions, that is, it is assumed that the wetted area is uniform along the X direction, and the wetted volume of the tail's up and down oscillations in one cycle is consistent, so that the discrete coordinates of the wetted volume can be concentrated on the axis of the supercavitating vehicle, that is, At this time (X,Z) CBeff =(0.0797,0), center of mass (X,Z) CG =(0.062,0), according to the formula SM water =SM water_X +SM water_Z , where SM water_X is the axial static stability margin of the navigation body in water, SM water_Z The radial static stability margin of the navigation body in water is obtained, and the static stability margin value SM of the navigation body in water is obtained. water =22.2%. Since the Z coordinates on the axis of the navigation body are all 0, there is no need to consider the center of mass, focus and equivalent buoyancy center displacement in the Z direction.

[0036] Step 4: Perform the first-order linear weighted algorithm to calculate the static stability margin SM of the vehicle across the medium tran =ω·SM air +μ·SM water, where ω and μ are linear weighting coefficients, satisfying ω+μ=1. In addition, the weight of ω is in the range of (0.1-0.2), and the corresponding weight of μ is in the range of (0.8-0.9). The academic community generally requires that the static stability margin of a vehicle in the air is between 5% and 15%, and the static stability margin of a vehicle in the water is between 15% and 25%. This is because a supercavitating vehicle in the water relies solely on the tail beat for balance. When the static stability margin is too small, the restoring torque generated by the tail beat is insufficient and the vehicle axis stabilizes in the cavitation. In the cross-medium process, the water phase has a high density and thus plays a dominant role in the static stability margin, but the role of the gas phase cannot be ignored, including water vapor, air, etc. It is generally believed that the static stability margin in the cross-medium process should be greater than the minimum static stability margin allowed in the air and less than the maximum static stability margin allowed in water, that is, it is generally believed that SM tran Between 10% and 20%, the cross-medium vehicle has sufficient static stability reserve when entering the water, while also retaining maneuverability. When entering the water at a small angle of attack α, it can be guaranteed that no ricochet occurs. In this embodiment, ω=0.15, that is, the cross-medium static stability margin SM of the vehicle is tran =19.62%, found SM tran <20%, it can be assumed that the supercavitating vehicle will not ricochet when entering the water at a small angle of attack α = 5°. It is worth noting that the present invention is limited to verification under small angles of attack, i.e., α∈(0°~5°), because under large angles of attack, the axial symmetry of the vehicle is destroyed, and the forces and moments exerted by the water on the vehicle are difficult to be equivalent to the axis of the vehicle, resulting in inaccurate calculation of the equivalent center of buoyancy and prediction errors.

[0037] Verification: Use Figure 6 The calculation process in the embodiment is used to simulate the cross-medium entry of the supercavitating vehicle into water. The simulation results further confirm that the method has a certain accuracy in estimating the static stability margin of the supercavitating vehicle into water. The simulation results are as follows: Figure 7 As shown: the vehicle contacts the water surface at 0.01ms, the shoulder of the vehicle completely enters the water at 0.5ms, the vehicle completely enters the water at 1.5ms, and the vehicle has entered the water for nearly 2 times its length L at 2.0ms. At this time, it is considered that the vehicle has achieved safe cross-medium entry into the water.

[0038] Compared to physical experiments and cross-medium water entry simulations, this invention significantly reduces computing power by focusing solely on 2D aerodynamic simulations of the vehicle in the air and analyzing the underwater characteristics of the supercavitating vehicle based on empirical supercavitation formulas. By unifying the static stability margin (SSM) metric, a coordinated analysis of aerodynamic, buoyancy, and inertial forces is achieved, essentially reflecting the overall stability changes of the vehicle from water to air (or vice versa).

[0039] Obviously, the above embodiments of the present invention are only examples to clearly illustrate the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. An integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle, characterized in that: The static stability margin of the vehicle across the medium is used to confirm whether the supercavitating vehicle will bounce when entering the water, where the static stability margin of the supercavitating vehicle across the medium SM tran for: SM tran =ω·SM air +μ·SM water SM air =SM air_X +SM air_Z SM water =SM water_X +SM water_Z When SM tran Within the interval, it is considered that the supercavitating vehicle will not ricochet when entering the water; Among them SM air is the static stability margin of the supercavitating vehicle in the air, SM air_X is the axial static stability margin of the vehicle in air, SM air_Z is the radial static stability margin of the vehicle in air, X AC is the axial coordinate of the aerodynamic center of the vehicle, Z AC is the radial coordinate of the aerodynamic center of the vehicle, L is the length of the vehicle, SM water is the static stability margin of the supercavitating vehicle in water, SM water_X is the axial static stability margin of the navigation body in water, SM water_Z is the radial static stability margin of the navigation body in water, X CBeff is the axial coordinate of the equivalent buoyancy center of the navigation body, Z CBeff is the radial coordinate of the equivalent buoyancy center of the navigation body, X CG is the axial coordinate of the center of mass of the navigation body, Z CG is the radial coordinate of the center of mass of the navigation body, D C is the diameter of the head cavitator; ω and μ are the cross-medium static stability margin values ​​SM tran The linear weighting coefficient satisfies ω+μ=1.

2. The integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle according to claim 1 is characterized in that: Where (X,Z) ref is the coordinate of the reference point, the reference point is the vertex of the vehicle head; < is the pitching moment of the supercavitation vehicle, L M is the pitching force value of the supercavitating vehicle.

3. The integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle according to claim 1 is characterized in that: Where V wet is the effective wetted volume of the supercavitating vehicle, and V is the volume of the supercavitating vehicle.

4. The integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle according to claim 3 is characterized in that: Effective wetted volume V of supercavitating vehicle wet Calculated by the following formula: L1 is the length of the non-oblique cone section of the supercavitating vehicle, L2 is the length of the oblique cone section of the supercavitating vehicle, α is the attack angle of the supercavitating vehicle, θ is the oblique taper of the supercavitating vehicle, and R(L,t) is the cavitation radius at the tail of the supercavitating vehicle.

5. The integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle according to claim 4 is characterized in that: The cavity radius R(L,t) at the tail of the supercavitating vehicle is calculated by the following formula: Where R(x,t) is the cavitation radius at time t at a distance x from the head of the supercavitation vehicle, R0 is the maximum cavitation radius, and L cavity is the total length of the cavity, and U is the speed of the supercavitating vehicle.

6. The integrated evaluation method for the cross-medium static stability margin of a supercavitating vehicle according to claim 5 is characterized in that: Maximum cavitation radius D is the maximum diameter of the navigation body, C d is the cavitator characteristic coefficient; σ is the cavitation number.

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