Design method of truncated cone type supercavitation projectile

Abstract

The invention belongs to the technical field of supercavitation projectile design, and particularly discloses a truncated-cone-shaped supercavitation projectile design method which comprises the specific steps that a cavitation contour line is calculated and verified; calculating a projectile speed attenuation rule and solving projectile quality according to a target range; designing a preliminary outline of the supercavitation projectile; according to the cavitation contour line, the initial shape contour of the projectile is optimized; and according to the quality requirement, the projectile shape contour of the projectile cone section is adjusted, and then projectile contour design is completed. Compared with the prior art, cavitation bubbles generated by the cavitator can completely wrap the projectile, so that the underwater trajectory of the projectile is stable, and the effective firing range of the projectile is increased; meanwhile, a large amount of CFD simulation in the design process is avoided, and the design work and time are saved to a greater extent.

Description

Technical Field

[0001] The invention belongs to the technical field of supercavitation projectile design, in particular to a truncated cone supercavitation projectile design method. Background Art

[0002] Supercavitating projectiles are high-speed ammunition developed using the supercavitation principle and fired by artillery to attack underwater targets. They can be used to perform a variety of tasks such as intercepting torpedoes, destroying mines, and countering frogmen. When moving underwater at high speed, supercavitating projectiles travel at high speed in the supercavitation generated by the cavitator on their heads, which can achieve a drag reduction effect of more than 90%. Supercavitating projectiles are expected to optimize the design process to ensure that the projectile maintains stable motion, and at the same time, have enough kinetic energy to destroy the target after flying underwater for a long distance without power and control.

[0003] Usually, when designing a supercavitating projectile, it is necessary to use CFD simulation software to calculate and determine the cavitator diameter and projectile line shape. When the projectile does not meet the overall damage requirements, range requirements, motion stability requirements, or the damage effect faces new mission requirements, it is necessary to redesign the projectile shape and perform simulation analysis. It often takes a lot of CFD simulation work and time to get an effective design solution.

[0004] Therefore, a new truncated cone supercavitating projectile design method is needed to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a design method for a truncated cone supercavitating projectile to solve the problem that a large amount of CFD simulation calculations are required in the design process and the projectile design time is long.

[0006] The technical solution to achieve the purpose of the present invention is: a method for designing a truncated cone supercavitating projectile, the specific steps are:

[0007] Step 1, calculate and verify the cavitation contour line;

[0008] Step 2, calculate the projectile velocity attenuation law curve and solve the projectile mass according to the target range;

[0009] Step 3, designing the preliminary shape of the supercavitating projectile;

[0010] Step 4: Optimize the initial shape of the projectile based on the cavitation contour line;

[0011] Step 5: According to the quality requirements, adjust the projectile profile of the projectile cone section to complete the projectile profile design.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The present invention designs the projectile shape by calculating the cavitation contour line under the condition of attack angle, optimizes the external contour of the projectile, and can make the center of mass of the designed projectile move forward and the tail get wet during movement, so as to better achieve underwater trajectory stability and increase the effective range;

[0014] (2) The present invention solves the cavitator diameter and the cavitation bubble profile curve generated by the cavitator according to the initial conditions, and designs the preliminary shape profile of the super-controlled projectile; thus avoiding a large number of CFD simulation calculations required in the design process, and effectively shortening the projectile design time;

[0015] (3) The present invention provides a basis for calculating the projectile velocity attenuation law and projectile mass according to the range, and for the design of the materials of each part of the projectile and the distribution of the mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of a design method for a truncated cone type supercavitating projectile of the present invention;

[0017] Figure 2 It is a curve diagram of the projectile velocity attenuation law in the present invention;

[0018] Figure 3 It is the cavitation profile curve diagram at different speeds in the present invention;

[0019] Figure 4 It is a schematic diagram of the projectile cone section being changed into two truncated cone sections in the present invention;

[0020] Figure 5 Schematic diagram of a model of a truncated cone supercavitating projectile in the present invention;

[0021] Figure 6 It is a curve diagram of the pitch angle variation during the tail shot of the truncated cone-type supercavitation projectile in the present invention;

[0022] Figure 7 It is a curve diagram of the change of head moment during the tail shot of the truncated cone-type supercavitation projectile in the present invention. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0024] The present invention proposes a design method for a truncated cone supercavitating projectile. In this embodiment, the supercavitating projectile can effectively damage underwater targets at a speed of about 100m / s. The projectile designed by the design method of the present invention can maintain a stable cavitation shape and completely wrap the projectile at 100m / s. According to the range requirements and the calculation of the cavitation contour line, a reasonable shape and counterweight layout are designed to achieve the stability of the underwater trajectory and increase the effective range of the projectile. At the same time, a large number of CFD simulations are avoided in the process, which can save design work and time to a greater extent. Figure 1 Shown is a flow chart of the present invention, from Figure 1 It can be known that the specific steps of the present invention are as follows:

[0025] Step 1, calculate and verify the cavitation profile curve;

[0026] Determine the cavitator radius based on the projectile diameter and length, calculate the cavitation profile curve and verify; the specific process is as follows:

[0027] Step 1.1, set the initial conditions; the initial conditions include the projectile tail radius R, the total length of the projectile L, and the far-field pressure p ∞ , water saturated vapor pressure p v , fluid density ρ, projectile velocity v, and the Savchenko empirical formula are used to calculate the cavitation radius of the projectile tail under different disc-shaped cavitator radii according to the initial parameters to ensure that the projectile can still maintain a stable cavitation shape and completely wrap the projectile when v = 100m / s;

[0028] Step 1.2, calculate the cavitator radius according to Savchenko's empirical formula;

[0029] According to Savchenko's empirical formula:

[0030]

[0031] In formula (1), σ is the cavitation number, p ∞ is the far-field pressure, p v is the saturated vapor pressure of water, ρ is the fluid density, v is the projectile velocity, R c is the maximum cross-sectional radius of the cavitation bubble, R n is the radius of the disc-shaped cavitator, L is the total length of the projectile, L c is the total length of the cavitation bubble, R(L) is the radius of the cavitation bubble at the tail of the projectile;

[0032] To ensure that the cavitation bubble at the tail of the projectile completely wraps the projectile at 100m / s, the following conditions should be met:

[0033] R(L)≥R (2)

[0034] In formula (2), R is the radius of the tail of the projectile, that is, the radius of the cavitation bubble at the tail of the projectile is greater than or equal to the radius of the projectile;

[0035] Combining equations (1) and (2), we can get the radius R of the disk cavitator: n The minimum relationship of is:

[0036]

[0037] Solve for the minimum value R n0 , which is taken as the radius of the supercavitating projectile cavitator;

[0038] Step 1.3, calculating the cavitation contours at different speeds according to the cavitator radius;

[0039] Replacing the total length of the projectile L in equation (3) with any set axial position x, the cavitation contour expression is obtained as follows:

[0040]

[0041] According to the cavitation number calculation formula in formula (1) and formula (4), a coordinate system is established with the center of the projectile cavitator as the origin. By setting the initial parameters: fluid density, far-field pressure, water saturated vapor pressure and different speeds, the initial time i = 0 is set, and it is iterated i = i + 1 to calculate the size of the cavitation bubble R [x (i)] generated by the cavitator when it moves 1 mm of space. The cavitation contour curves at different speeds are plotted as follows: Figure 3 As shown;

[0042] Step 1.4: Calculate the cavitation profile curve at the effective damage speed, and then verify that the cavitation generated by the cavitator radius determined in step 1.2 can remain stable and completely wrap the projectile at the effective damage speed. The effective damage speed calculated in this embodiment is 100m / s.

[0043] Step 2, calculate the projectile velocity attenuation law curve and solve the projectile mass according to the target range;

[0044] The specific process is:

[0045] Step 2.1, calculate the projectile velocity attenuation curve; from Newton's second law and the resistance formula, we get

[0046]

[0047] In formula (5), c xn =1.1c x0 (1+σ) is the cavitation drag coefficient, where c x0 =0.827 is the zero cavitation number drag coefficient, where A0 = πR n 2 is the cross-sectional area of ​​the cavitator, m is the mass of the projectile, and a is the acceleration of the projectile motion;

[0048] Integrate the acceleration a to get the velocity expression:

[0049]

[0050] In formula (6), v0 is the initial velocity of the projectile, and t is the projectile motion time;

[0051] Integrating the velocity v gives the range expression:

[0052]

[0053] In formula (7), s is the projectile range;

[0054] Set the initial parameters: projectile initial velocity, final velocity, projectile mass, fluid density, far-field pressure and water saturated vapor pressure, and calculate the projectile velocity attenuation law curve by integrating equations (5), (6) and (7), as shown in Figure 2 As shown;

[0055] Step 2.2, according to the target range requirement of the initial condition, reversely solve to determine the mass of the projectile, and verify it through the projectile velocity attenuation law curve;

[0056] The expression for projectile velocity is obtained by differentiating the range:

[0057]

[0058] The expression for the acceleration of the projectile is obtained by differentiating the velocity:

[0059]

[0060] Solving for the mass of the projectile:

[0061]

[0062] Step 3: Design the preliminary outline of the supercavitating projectile: including the combination of the cone section and the cylindrical section;

[0063] A properly designed projectile shape should make the tail wetted area relatively far back when the projectile tail moves, generating a rotational moment that reduces the value of the angle of attack and ensures the stability of the projectile trajectory.

[0064] In order to facilitate launching, the minimum length of the cylindrical section at the tail of the projectile is L / 3. Taking this minimum length as the length of the cylindrical section, the length of the conical section is 2L / 3. Since the diameter of the cavitator and the diameter of the tail of the projectile are determined, the two ends are connected and the front end of the projectile is initially designed to be a conical section.

[0065] Step 4: Optimize the initial shape of the projectile based on the cavitation contour line;

[0066] The specific process is:

[0067] Step 4.1, set the angle of attack at different speeds so that the cylindrical section of the projectile is completely wetted, while the shoulder is not wetted;

[0068] Due to the limitation of the projectile structure, the center of mass of the projectile is generally located behind the shoulder. The torque generated when the head and shoulder are wet will promote the increase of the projectile's angle of attack, which is the overturning torque; while the torque generated when the tail is wet will cause the angle of attack to decrease, which is the rotational torque. Therefore, the tail of the projectile should be kept wet while the shoulder is not wet at different speeds;

[0069] Therefore, in the cavitation contour obtained in step 3, a function for rotating the projectile according to the angle of attack is added to rotate the projectile around the zero point by a certain angle to simulate the motion process of the projectile tail and ensure that the cylindrical section at the tail of the projectile is wetted while the shoulder is not wetted.

[0070] Step 4.2, determining the contours of two truncated cone segments according to the cavitation contour line under the condition of attack angle;

[0071] The cone section is divided into two parts, namely the front cone section L1 and the middle cone section L2, which are two truncated cone sections. Under the premise of ensuring that the projectile contour is always wrapped by the cavitation contour, the volume of the front cone section L1 is maximized. Figure 4 As shown;

[0072] This step can move the center of mass forward, increase the tail rotation torque and improve the stability of the projectile.

[0073] Step 5: Determine the materials and proportions of each part of the overall supercavitating projectile and adjust the projectile profile of the projectile cone section according to quality requirements;

[0074] According to the mass of the projectile determined in step 2 and the size of the cylindrical section determined in step 3, the materials of each part of the supercavitating projectile and the total volume of the two cone sections L1 and L2 are determined; then, according to the total volume of the two cone sections L1 and L2, the projectile profile of the cone section is adjusted to determine the final projectile profile.

[0075] The front section of the supercavitating projectile is made of tungsten alloy, and the rear cylindrical section is made of aluminum alloy or steel.

[0076] In summary, given a supercavitating projectile at a water depth of 4m, a fluid density of 1000kg / m, a fluid saturated vapor pressure of 3.54kPa, an initial velocity of 600m / s, a final velocity of 100m / s, a total length of 190mm, a tail diameter of 12.7mm, and a target range of 80m.

[0077] Figure 5 Table 1 and Table 1 give a schematic diagram of the truncated cone projectile model designed according to the present invention and main size parameters. The designed projectile is subjected to CFD simulation to determine the motion stability of the truncated cone supercavitating projectile. Based on the finite volume method, VOF multiphase flow model and k-ε turbulence model, a three-dimensional free tail-beat motion simulation model is constructed in combination with the dynamic mesh technology. The tail-beat motion of the truncated cone supercavitating projectile is simulated to determine that its motion stability meets the design requirements.

[0078] Table 1 Main parameters of truncated cone supercavitating projectile

[0079]

[0080] The tail beat process of the supercavitation projectile is monitored in the Fluent simulation software, such as Figure 6The figure shows the pitch angle variation curve of the supercavitating projectile during the tail slap process. The pitch angle of the projectile fluctuates periodically and symmetrically above and below the central axis, forming a symmetrical "double-sided tail slap" motion. Figure 7 The figure shows the torque variation curve of the supercavitating projectile head. The projectile head generates a small torque, and the projectile crosses the cavitation axis and tail-slaps downward, maintaining stable motion for a long time in the form of "double-sided tail-slapping" motion. At the same time, the simulation calculation shows that the effective range of the projectile when the speed drops to 100m / s is 85.6m, and the projectile trajectory offset is 0.06m at the effective range. It can be seen that the projectile can better meet the target range requirements and has good ballistic stability. The above method avoids a large number of CFD simulation calculations required in the design process, which can effectively shorten the projectile design time.

Claims

1. A method for designing a truncated cone supercavitating projectile, characterized in that: The specific steps are: Step 1, calculate and verify the cavitation contour line; Step 2, calculate the projectile velocity attenuation law curve and solve the projectile mass according to the target range; Step 3, designing the preliminary shape of the supercavitating projectile; Step 4: Optimize the initial shape of the projectile based on the cavitation contour line; Step 5: Adjust the projectile profile of the projectile cone according to the quality requirements, and then complete the projectile profile design.

2. The method for designing a truncated cone supercavitating projectile according to claim 1, characterized in that: In step 1, the cavitator radius is determined according to the projectile diameter and length, and the cavitation contour is calculated and verified. The specific steps are as follows: Step 1.1, set initial conditions; Step 1.2, calculate the cavitator radius according to Savchenko's empirical formula; Step 1.3, calculating the cavitation contours at different speeds according to the cavitator radius; Step 1.4: Calculate the cavitation profile curve at the effective damage velocity, and verify that the cavitation produced by the cavitator radius determined in step 1.2 can remain stable and completely wrap the projectile at the effective damage velocity.

3. The method for designing a truncated cone supercavitating projectile according to claim 2, characterized in that: Step 1.2 Hollowing device radius R n The minimum value relationship of is: Where σ is the cavitation number, R n is the radius of the disc-shaped cavitator, L is the total length of the projectile, and R is the radius of the tail of the projectile; Solve for the minimum value R n0 , is the radius of the supercavitating projectile cavitator.

4. The method for designing a truncated cone supercavitating projectile according to claim 3, characterized in that: In step 1.3, the total length L of the projectile is replaced by setting any axial position x, and the expression of the cavitation contour is obtained as follows: Set the initial time i=0, iterate i=i+1 and calculate the size of the bubble R[x(i)] generated by the cavitator every time it moves 1mm of space.

5. The method for designing a truncated cone supercavitating projectile according to claim 1, characterized in that: The details in step 2 are as follows: Step 2.1, calculate the projectile velocity attenuation law curve; Step 2.2, according to the target range requirement in the initial conditions, reversely solve to determine the mass of the projectile; In the formula, c xn =1.1c x0 (1+σ) is the cavitation drag coefficient, c x0 is the zero cavitation number drag coefficient, A0=πR n 2 is the cross-sectional area of ​​the cavitator, m is the mass of the projectile, and a is the acceleration of the projectile.

6. The method for designing a truncated cone supercavitating projectile according to claim 4, characterized in that: In step 3, the minimum length of the cylindrical section at the tail of the projectile is L / 3, and this minimum length is taken as the length of the cylindrical section; then the length of the cone section is 2L / 3. Since the cavitator diameter R is determined in step 1 n , the projectile tail radius R, and then complete the design of the front end cone section of the projectile and then complete the preliminary design of the projectile.

7. The method for designing a truncated cone supercavitating projectile according to claim 1, characterized in that: The specific steps of optimizing the preliminary shape profile of the projectile according to the cavitation contour line in step 4 are as follows: Step 4.1, set the angle of attack at different speeds so that the cylindrical section of the projectile is completely wetted, while the shoulder is not wetted; In the cavitation contour obtained in step 3, add a function that rotates the projectile according to the angle of attack, so that the projectile rotates a certain angle around the zero point to simulate the motion process of the projectile tail, ensuring that the cylindrical section at the tail of the projectile is wetted but the shoulder is not wetted. Step 4.2, determining the contours of two truncated cone segments according to the cavitation contour line under the condition of attack angle; The cone section is divided into two parts, namely the front cone section L1 and the middle cone section L2, which are a combination of two truncated cone sections. The volume of the front cone section L1 is increased to the maximum extent while ensuring that the contour of the projectile is always wrapped by the contour of the cavitation.

8. The method for designing a truncated cone supercavitating projectile according to claim 1, characterized in that: According to the mass of the projectile determined in step 2 and the size of the cylindrical section determined in step 3, the materials of each part of the supercavitating projectile and the total volume of the two cone sections are determined; then, according to the total volume of the two forged cone sections L1 and L2, the projectile profile of the cone section is adjusted to determine the final projectile profile.

9. The method for designing a truncated cone supercavitating projectile according to claim 8, characterized in that: The front cone section of the supercavitating projectile is made of tungsten alloy, and the rear cylindrical section is made of aluminum alloy or steel.

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