Numerical simulation method for high-back-pressure internal and external flow of air inlet channel and computer program product

Abstract

The invention relates to an air inlet high back pressure internal and external flow numerical simulation method and a computer program product, which can realize numerical simulation of an aircraft three-dimensional air inlet in a high back pressure limit state, and the method comprises the following steps: (1) deducing back pressure boundary conditions through a Riemannian invariant feature theory; (2) dividing a proper structural grid according to the real appearance of the air inlet channel; and (3) setting a certain number of flow field monitoring points in the air inlet channel. And (4) giving an initial back pressure condition, solving the three-dimensional NS equation, and increasing the back pressure value according to a certain strategy in the calculation process, so that the back pressure value gradually reaches the limit back pressure value under the real condition. And (5) monitoring a flow field monitoring point arranged in the air inlet channel, and judging whether a convergence calculation result is obtained or not. And (6) outputting all flow field information. The method has the advantages of being convenient to operate, high in calculation efficiency, capable of stably converging complex shapes, high in robustness and the like.

Description

Technical Field

[0001] The present invention relates to the field of computational fluid and flow display, and in particular to a numerical simulation method for high back pressure internal and external flows of an air inlet based on a structured grid and a computer program product. Background Art

[0002] With the development of computational fluid dynamics (CFD), numerical simulation has been used in complex flow mechanism research, aerodynamic characteristics analysis and other aspects.

[0003] For supersonic or hypersonic inlets, in order to enable the inlet to ignite and start smoothly, the high-speed incoming flow is usually reduced to subsonic speed at the front of the combustion chamber. At this time, the pressure in the combustion chamber is dozens or even hundreds of times the pressure value at the inlet inlet. In view of this engineering problem, it was found in the numerical simulation process that directly using commercial software and numerical simulation calculations with a given back pressure usually cannot obtain a normal convergence solution. There are two main solutions: one is to first give a lower back pressure to obtain preliminary results, and then gradually increase the back pressure to obtain the convergence results under each back pressure condition. In this way, once there is a problem with the calculation result under a certain back pressure condition in the middle, the whole process must be restarted, which is time-consuming and laborious; there is also an alternative way to add an extension section at the outlet of the inlet and use a porous medium model. This method obtains the convergence result under a given back pressure condition by modifying the friction coefficient of the porous medium model and monitoring the pressure value at the outlet. This method also relies on the given friction coefficient method and requires repeated calculations and multiple approximations to obtain the convergence result under a given back pressure condition. This method is also cumbersome in engineering. Summary of the invention

[0004] The technical problem solved by the present application is: to overcome the deficiencies of the prior art and to provide a method for numerical simulation of high back pressure internal and external flows in an inlet duct based on a structured grid, which can obtain the convergence results of numerical simulation of such problems through a more convenient and efficient calculation method.

[0005] The present application discloses a numerical simulation method for high back pressure internal and external flows in an inlet based on a structured grid. Based on the CFD method, a subsonic outflow back pressure boundary condition is developed on the basis of a common laboratory research procedure. At the same time, the simulation strategy can realize real-time monitoring during the calculation process, timely discover whether the strategy for a given back pressure is appropriate, and can make judgments and adjustments more quickly.

[0006] The technical solutions provided by this application are as follows:

[0007] A numerical simulation method for internal and external flows of an inlet with high back pressure, comprising:

[0008] S1: Establish the coordinate system and determine the calculation domain according to the conditions and size of the aircraft; divide the structural grid according to the actual aircraft and air inlet shape;

[0009] S2: The outer boundary of the computational domain includes the high back pressure far field outer boundary. When calculating the high back pressure inlet flow problem, the high back pressure far field outer boundary conditions that need to be supplemented are derived through the Riemann invariant characteristic theory. The supplemented high back pressure far field outer boundary conditions are the back pressure or temperature of the far field outer boundary.

[0010] Given the additional high back pressure far field outer boundary condition, all flow field variables on the high back pressure far field outer boundary are derived according to the additional high back pressure far field outer boundary condition;

[0011] S3: increasing the given additional supplementary high back pressure far field outer boundary condition, and performing step S3;

[0012] S4: Repeat step S3. Each time S3 is performed, the given additional high back pressure far field outer boundary condition is increased relative to the last time S4 ​​was performed, and it is determined whether the flow field variables in the obtained calculation domain have reached calculation convergence. If the calculation does not converge, it can be considered that under the high back pressure far field outer boundary condition, the air inlet is in a non-starting state.

[0013] In S1, the steps of establishing the coordinate system are: using a three-dimensional Cartesian rectangular coordinate system, with the x-axis along the model flow direction, the y-axis along the normal direction, the z-axis along the circumferential direction, and the coordinate origin O selected as the leading edge point of the aircraft.

[0014] The S1 also includes: setting a flow field monitoring point inside the air intake duct to record the flow field information at the monitoring point position in real time.

[0015] In S2, the outer boundary of the computational domain includes the high back pressure far field outer boundary; when calculating the high back pressure inlet flow problem, the high back pressure far field outer boundary condition that needs to be supplemented is derived through the Riemann invariant characteristic theory, and the additional high back pressure far field outer boundary condition is the back pressure value or temperature. Given the additional high back pressure far field outer boundary condition, all flow field variables on the high back pressure far field outer boundary are derived according to the additional high back pressure far field outer boundary condition, including:

[0016] S21. According to the coordinate system, define is the unit external normal vector on the outer boundary of the far field;

[0017] S22. The high back pressure far field outer boundary condition that needs to be supplemented is the back pressure pressure P of the far field outer boundary. b ;

[0018] Given back pressure value P 0 :P b =P 0

[0019] S23, according to the back pressure value P 0 Solve the three-dimensional NS equations to obtain the internal flow field variables;

[0020] S24, Riemann invariants include the left-hand characteristic invariant R on the outer boundary of the far field b- , right row characteristic invariant R b+ , entropy characteristic invariant s b , supplementary tangential velocity characteristic invariant V bτ and the complementary normal velocity characteristic invariant V bσ ;

[0021] According to the Riemann invariant subsonic outflow, the Riemann invariant expression of the far field outer boundary is calculated;

[0022] S25. According to the Riemann invariant expression of the far field outer boundary and the internal flow field variables, calculate and obtain R b+ 、s b 、V bτ 、V bσ ;

[0023] S26. According to entropy s b and back pressure value P 0 , calculate and obtain R-;

[0024] S27, according to R b- , R b+ 、s b 、V bτ 、V bσ The three-direction velocities on the outer boundary of the far field are obtained by using the unit external normal vector on the outer boundary of the far field;

[0025] S28. Calculate the temperature using the gas state equation.

[0026] In the S24, according to the Riemann invariant subsonic outflow condition, the Riemann invariant expression of the far field outer boundary is calculated, including:

[0027] When the far field outer boundary is in subsonic outflow condition, 0≤V n,e ≤c e , V n,e is the characteristic velocity, c e is the speed of sound, so V n,e -c e ≤0;

[0028] R - Determined by the flow field variables of the external flow field, R + ,s,V τ and V σ Determined by the flow field variables of the internal flow field, that is, the Riemann invariant of the outer boundary of the far field is,

[0029]

[0030] V bτ =V τe , V bσ =V σe ;

[0031] Among them, R b+ Corresponding to the characteristic speed V bn +c b , R b- Corresponding to the characteristic speed V bn -c b ,s b Corresponding to the characteristic speed V bn ;

[0032] The speed of sound, p ∞ ,p e are pressure, ρ ∞ ,ρ e is the density, γ is the specific heat ratio of the gas, which is a fixed value of 1.4; ∞ represents the external flow field, and the subscript e represents the internal flow field;

[0033] R +e is the right characteristic invariant of the internal flow field; V n,e is the velocity of the inner flow field along the outer normal line; c e is the local sound speed in the internal flow field;

[0034] R -∞ is the left characteristic invariant of the external flow field; V n,∞ is the velocity of the external flow field along the external normal line; c ∞ is the local sound speed in the external flow field;

[0035] s be Determine the boundary entropy for the internal flow field; p e is the internal flow field pressure; ρ e is the internal flow field density;

[0036] V τe To supplement the tangential velocity of the internal flow field; V σe To supplement the normal velocity of the internal flow field.

[0037] In S25, R is calculated based on the Riemann invariant expression of the far field outer boundary and the internal flow field variable. b+ 、s b 、V bτ 、V bσ ,include:

[0038] The internal flow field variables include p e, e , S e 、c e 、V τe 、V σe , the velocity V of the internal flow field along the external normal n,e and the velocity value V of the internal flow field e ;

[0039] According to the above internal flow field variables, the following is calculated:

[0040]

[0041] In S27, according to R b- , R b+ 、s b 、V bτ 、V bσ The three-directional velocities on the outer boundary of the far field are obtained by using the unit external normal vector on the outer boundary of the far field, including:

[0042] According to S b and P 0 , to obtain the density on the outer boundary of the far field

[0043] According to b , obtain the speed of sound on the outer boundary of the far field

[0044] When the flow field converges, C on the outer boundary of the far field e =c b =c ∞ ,according to Combined with R b+ ,get

[0045] According to R b+ and R b- , get the characteristic velocity

[0046] According to V bn , the three-dimensional flow field velocities in three directions on the outer boundary of the far field are obtained as follows:

[0047]

[0048] Among them, u b is the axial velocity on the boundary; u e is the axial velocity of the internal flow field; v b is the normal velocity on the boundary; v e is the normal velocity of the internal flow field; w b is the tangential velocity on the boundary; w e is the tangential velocity of the internal flow field; is the boundary unit normal vector; define Ve =(u e , v e , w e ) is the vector of the internal flow velocity.

[0049] In S4, the additional high back pressure far field outer boundary condition is gradually increased from the initial value to the high back pressure far field outer boundary condition under the actual condition; the initial value of the additional high back pressure far field outer boundary condition=1 / 3×the high back pressure far field outer boundary condition under the actual condition.

[0050] A computer program product includes a computer program / instruction, which, when executed by a processor, implements the steps of any of the above-mentioned methods for locating the center of a pulsed laser spot.

[0051] In summary, this application at least includes the following beneficial technical effects:

[0052] (1) The present invention is completely autonomous and controllable.

[0053] (2) Structural grid technology is used for complex shapes, which has good robustness.

[0054] (3) Real-time monitoring can be achieved throughout the entire calculation process, and whether the calculation can be successfully completed can be determined without the need for complete convergence in the intermediate process, which greatly improves the calculation efficiency.

[0055] (4) The pressure adjustment strategy during the calculation process is more convenient to adjust. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow chart of a numerical simulation method of high back pressure internal and external flow of an inlet based on a structured grid provided by an embodiment of the present invention;

[0057] Figure 2 It is a schematic diagram of the numerical simulation results of high back pressure internal flow in a two-dimensional inlet;

[0058] Figure 3 This is a schematic diagram of the numerical simulation results of a simplified three-dimensional air inlet, where Figure a is the simplified three-dimensional aircraft shape; Figure b is the pressure cloud map inside the air inlet; and Figure c is the Mach number cloud map inside the air inlet. DETAILED DESCRIPTION

[0059] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0060] The present application embodiment discloses a numerical simulation method for high back pressure internal and external flow of an inlet based on a structured grid, such as Figure 1 As shown, the method comprises the following steps:

[0061] Step 1: The back pressure boundary conditions that need to be supplemented, such as pressure, are derived through the Riemann invariant characteristic theory. Based on the supplemented back pressure boundary conditions, the flow field variables on all far-field outer boundaries are derived; the flow field variables include temperature, pressure and velocity.

[0062] Specifically, step one includes:

[0063] S11: Establish a coordinate system and determine the calculation domain according to the conditions and size of the aircraft;

[0064] The steps for establishing the coordinate system are as follows: using a three-dimensional Cartesian rectangular coordinate system, the x-axis is along the model flow direction, the y-axis is along the normal direction, the z-axis is along the circumferential direction, and the coordinate origin O is selected as the leading edge point of the aircraft.

[0065] S12: Divide the appropriate structural grid according to the actual aircraft and air inlet shape.

[0066] Specifically, in step 2, in the process of drawing the structural grid, it is necessary to use external software POINTWISE or ICEM and other grid generation tools, other grid generation tools may also be used, and this patent has no rigid requirements for this step.

[0067] S13: The outer boundaries of the computational domain include the high back pressure far field outer boundary, the supersonic inflow and outflow boundary, the aircraft wall boundary, etc. According to the Riemann invariant principle, at the far field outer boundary, the flow control equations have three Riemann invariants, namely and entropy Corresponding to the characteristic speed V n +c、V n -c and V n , where is the speed of sound, p is the pressure, ρ is the density, and γ is the specific heat ratio of the gas. Considering that the governing equations of the actual three-dimensional flow have five equations, the tangential velocity V is added τ and V σ Also known as the Riemann invariant, V τ and V σ Corresponding to V n ;

[0068] Determine the range of characteristic velocity according to the actual flow characteristics in the intake duct;

[0069] According to the range of characteristic velocity, when calculating the Riemann invariant, use the value of the internal flow field or the value of the external flow field to obtain the judgment result; and calculate R + , R - ,s,V τ , V σ ;

[0070] Specifically, the Riemann invariant of the internal flow field is:

[0071]

[0072] The Riemann invariant of the external flow field is:

[0073]

[0074] When calculating high back pressure flow problems, the outer boundary of the back pressure far field is usually in subsonic outflow conditions (0≤V n,e ≤c e ): At this time, the characteristic speed V n,e -c e ≤0, the corresponding Riemann invariant (R - ) is determined by the external flow field; the remaining characteristic velocities are all greater than zero, and the corresponding Riemann invariant (R + ,s,V τ 、V σ ) is still determined by the Riemann invariant of the internal flow field, that is:

[0075] R + =R +,e , R - =R -,∞ , s=s e , V τ =V τ,e , V σ =V σ,e ;

[0076] For the Riemann invariant that needs to be calculated based on the value of the external flow field, an additional flow parameter (i.e., c in R- ∞ It is necessary to calculate based on an additional flow parameter); According to an additional flow parameter, R- is calculated; According to R b- , R b+ 、s b 、V bτ 、V bσ , calculate and obtain the flow field variables on the outer boundary of the far field (i.e., the flow field variables of the outer flow field, including P, T, density and velocity);

[0077] There are many ways to give flow parameters, such as giving pressure, density, temperature, mass flow rate, etc. In this patent, the pressure is given directly. The values ​​on other outer boundaries can be given directly according to the flight conditions, and this patent will not repeat the giving process.

[0078] The following is a detailed description of the solution process for calculating the flow field variables (three-directional velocities) on the outer boundary of the far field.

[0079] According to the coordinate system, we define is the unit external normal vector on the far field outer boundary. The specific steps for solving the velocity parameters of the far field outer boundary under high back pressure conditions are as follows:

[0080] Step 1: Given back pressure value P 0

[0081] P b =P 0

[0082] Among them, P b is the back pressure at the far field outer boundary, P 0 is the given backpressure value.

[0083] And according to the back pressure value P 0 , solve the three-dimensional NS equations to obtain the internal flow field variables;

[0084] Step 2: According to the Riemann invariant subsonic outflow:

[0085] R + =R +,e , R - =R -,∞ , s=s e , V τ =V τe , V σ =V σe

[0086] To calculate the Riemann invariant at the outer boundary of the far field:

[0087] R b+ =R +e , R b- =R -∞ ,s b =s be , V bτ =V τe , V bσ =V σe

[0088] The subscript b indicates the outer boundary of the far field.

[0089] According to the internal flow field variables, R+ and S are obtained. b 、V τ 、V σ ;

[0090] Entropy S on the boundary b Known, back pressure value P 0 Knowing this, we can find the density on the outer boundary of the far field:

[0091]

[0092] Among them, ρb is the density on the outer boundary of the far field.

[0093] Step 3: According to the density, obtain the speed of sound on the outer boundary of the far field:

[0094]

[0095] Among them, C b is the speed of sound at the outer boundary of the far field.

[0096] Step 4

[0097] When the flow field converges, C on the outer boundary of the far field e =c b =C∞, so we can use Combined with R b+ , we can find:

[0098]

[0099] Further use Can be found

[0100]

[0101] Among them, V bn is the characteristic speed;

[0102] After finding the characteristic velocity, use the following formula:

[0103] u b =u e +(V bn ·nV e ·n)n x

[0104] v b =v e +(V bn ·nV e ·n)n y

[0105] w b =w e +(V bn ·nV e ·n)n z

[0106] Get the three-dimensional flow field velocity u in three directions on the outer boundary of the far field b ,v b ,w b Of which V e is the velocity value of the internal flow field; the internal flow field variables include the velocity value of the internal flow field and are known variables during the calculation process.

[0107] Step 5: The temperature can be obtained through the gas state equation. At this point, the flow field parameters on all back pressure boundaries (i.e., the far field outer boundary under high back pressure conditions) have been obtained.

[0108] Step 2: Set a certain number of flow field monitoring points inside the intake duct.

[0109] Specifically, in this step, flow field monitoring points are set at positions inside the flow field that reflect key flow characteristics of the air inlet, such as at the air inlet entrance, throat, air inlet outlet, etc., and the three-dimensional coordinate information of the monitoring points is recorded to monitor the flow field information of the monitoring points during the calculation process.

[0110] Step 3: Given an initial value of the back pressure at the outer boundary of the far field, increase the back pressure at the outer boundary of the far field according to a certain strategy during the calculation process, so that the back pressure at the outer boundary of the far field gradually reaches the back pressure value under actual conditions.

[0111] Specifically, in step 4, when the initial back pressure condition is given, 1 / 3 of the actual back pressure condition is usually selected as the initial back pressure, which can avoid the occurrence of non-physical solutions during the initial iterative calculation process. The numerical simulation method used is to solve the three-dimensional compressible Navier-Stokes equations using the finite volume method;

[0112] The three-dimensional compressible Navier-Stokes equations are

[0113]

[0114] in, is a conserved variable, are the inviscid flux vectors in the x, y, and z directions respectively, are the viscous flux vectors in the x, y, and z directions respectively; t is time, x is the flow direction in the rectangular coordinate system, y is the normal direction in the rectangular coordinate system, and z is the circumferential direction in the rectangular coordinate system;

[0115] In the process of solving the three-dimensional compressible Navier-Stokes equations, the back pressure at the outer boundary of the far field is increased from the initial value 1 / 3×P 0 , gradually increase to the back pressure value P under real conditions 0 , the back pressure at the outer boundary of the far field is taken as the back pressure value P under real conditions 0 The solution result when θ is taken as the final result. The calculation method of the variables on the high back pressure outer boundary of the computational domain has been obtained in step 1. By giving other boundary conditions of the computational domain (such as supersonic inflow and outflow boundary conditions, solid wall boundaries, etc.), the specific values ​​of the flow field variables such as pressure, temperature and velocity in the entire computational domain can be obtained by iteratively solving the NS equations.

[0116] Step 4: Monitor the flow field monitoring points set inside the inlet duct to determine whether the calculation convergence has been achieved.

[0117] Specifically, in step 4, the flow field at the monitoring point is monitored at any time. This patent mainly monitors the pressure value at the monitoring point, and determines whether the convergence state is reached or whether the possible calculation has a non-physical solution through the pressure fluctuation curve.

[0118] Step 5: Output all flow field information.

[0119] Specifically, in step six, output is performed in a certain order according to the converged calculated flow field. This method uses the Tecplot output format for output, and can be displayed using Tecplot post-processing software.

[0120] Example:

[0121] In this example, simplified two-dimensional air intake duct and simplified three-dimensional air intake duct are used as examples to demonstrate the effects achieved by the present invention.

[0122] (1) For a simplified two-dimensional inlet, the numerical simulation of the density gradient of the flow field along the flow direction inside the inlet is shown, such as Figure 2 Shown

[0123] (2) For the simplified three-dimensional air inlet, the simplified three-dimensional aircraft and air inlet shape, as well as the pressure cloud map and Mach number cloud map of the flow field in the air inlet are displayed, such as Figure 3 Shown

[0124] The contents not described in detail in this application specification belong to the common knowledge of those skilled in the art.

[0125] The present application is described in detail above in conjunction with specific implementation methods and exemplary examples, but these descriptions cannot be understood as limiting the present application. Those skilled in the art understand that, without departing from the spirit and scope of the present application, a variety of equivalent replacements, modifications or improvements can be made to the technical solution of the present application and its implementation methods, all of which fall within the scope of the present application. The scope of protection of the present application shall be subject to the attached claims.

Claims

1. A numerical simulation method for internal and external flow of an inlet with high back pressure, characterized in that: include: S1: Establish the coordinate system and determine the calculation domain according to the conditions and size of the aircraft; divide the structural grid according to the actual aircraft and air inlet shape; S2: The outer boundary of the computational domain includes the high back pressure far field outer boundary. When calculating the high back pressure inlet flow problem, the high back pressure far field outer boundary conditions that need to be supplemented are derived through the Riemann invariant characteristic theory. The supplemented high back pressure far field outer boundary conditions are the back pressure or temperature of the far field outer boundary. Given the additional high back pressure far field outer boundary condition, all flow field variables on the high back pressure far field outer boundary are derived according to the additional high back pressure far field outer boundary condition; S3: increasing the given additional supplementary high back pressure far field outer boundary condition, and performing step S3; S4: Repeat step S3. Each time S3 is performed, the given additional high back pressure far field outer boundary condition is increased relative to the last time S4 ​​was performed, and it is determined whether the flow field variables in the obtained calculation domain have reached calculation convergence. If the calculation does not converge, it can be considered that under the high back pressure far field outer boundary condition, the air inlet is in a non-starting state.

2. The method for numerical simulation of internal and external flow in an inlet with high back pressure according to claim 1, characterized in that: In S1, the steps of establishing the coordinate system are: using a three-dimensional Cartesian rectangular coordinate system, with the x-axis along the model flow direction, the y-axis along the normal direction, the z-axis along the circumferential direction, and the coordinate origin O selected as the leading edge point of the aircraft.

3. The method for numerical simulation of internal and external flow in an inlet with high back pressure according to claim 1, characterized in that: The S1 also includes: setting a flow field monitoring point inside the air intake duct to record the flow field information at the monitoring point position in real time.

4. The method for numerical simulation of internal and external flow in an inlet with high back pressure according to claim 1, characterized in that: In S2, the outer boundary of the computational domain includes the high back pressure far field outer boundary; when calculating the high back pressure inlet flow problem, the high back pressure far field outer boundary condition that needs to be supplemented is derived through the Riemann invariant characteristic theory, and the additional high back pressure far field outer boundary condition is the back pressure value or temperature. Given the additional high back pressure far field outer boundary condition, all flow field variables on the high back pressure far field outer boundary are derived according to the additional high back pressure far field outer boundary condition, including: S21. According to the coordinate system, define is the unit external normal vector on the outer boundary of the far field; S22. The high back pressure far field outer boundary condition that needs to be supplemented is the back pressure pressure P of the far field outer boundary. b ; Given back pressure value P0: P b =P0 S23, solving the three-dimensional NS equation according to the back pressure value P0 to obtain the internal flow field variables; S24, Riemann invariants include the left-hand characteristic invariant R on the outer boundary of the far field b- , right row characteristic invariant R b+ , entropy characteristic invariant s b , supplementary tangential velocity characteristic invariant V bτ and the complementary normal velocity characteristic invariant V bσ ; According to the Riemann invariant subsonic outflow condition, the Riemann invariant expression of the far field outer boundary is calculated; S25. According to the Riemann invariant expression of the far field outer boundary and the internal flow field variables, calculate and obtain R b+ 、s b 、V bτ 、V bσ ; S26. According to entropy s b and back pressure value P0, calculate and obtain R-; S27, according to R b- , R b+ 、s b 、V bτ 、V bσ The three-direction velocities on the outer boundary of the far field are obtained by using the unit external normal vector on the outer boundary of the far field; S28. Calculate the temperature using the gas state equation.

5. The method for numerical simulation of internal and external flow in an inlet with high back pressure according to claim 4, characterized in that: In the S24, according to the Riemann invariant subsonic outflow condition, the Riemann invariant expression of the far field outer boundary is calculated, including: When the far field outer boundary is in subsonic outflow condition, 0≤V n,e ≤c e , V n,e is the characteristic velocity, c e is the speed of sound, so V n,e -c e ≤0; R - Determined by the flow field variables of the external flow field, R + ,s,V τ and V σ Determined by the flow field variables of the internal flow field, that is, the Riemann invariant of the outer boundary of the far field is, V bτ =V τe ,V bσ =V σe ; Among them, R b+ Corresponding to the characteristic speed V bn +c b , R b- Corresponding to the characteristic speed V bn -c b ,s b Corresponding to the characteristic speed V bn ; The speed of sound, p ∞ ,p e are pressure, ρ ∞ ,ρ e is the density, γ is the specific heat ratio of the gas, which is a fixed value of 1.4; ∞ represents the external flow field, and the subscript e represents the internal flow field; R +e is the right characteristic invariant of the internal flow field; V n,e is the velocity of the inner flow field along the outer normal line; c e is the local sound speed in the internal flow field; R -∞ is the left characteristic invariant of the external flow field; V n,∞ is the velocity of the external flow field along the external normal line; c ∞ is the local sound speed in the external flow field; s be Determine the boundary entropy for the internal flow field; p e is the internal flow field pressure; ρ e is the internal flow field density; V τe To supplement the tangential velocity of the internal flow field; V σe To supplement the normal velocity of the internal flow field.

6. A numerical simulation method for internal and external flow of an inlet with high back pressure according to claim 5, characterized in that: In S25, R is calculated based on the Riemann invariant expression of the far field outer boundary and the internal flow field variable. b+ 、s b 、V bτ 、V bσ ,include: The internal flow field variables include p e , e , S e 、c e 、V τe 、V σe , the velocity V of the internal flow field along the external normal n,e and the velocity value V of the internal flow field e ; According to the above internal flow field variables, the following is calculated:

7. A numerical simulation method for internal and external flow of an inlet with high back pressure according to claim 6, characterized in that: In S27, according to R b- , R b+ 、s b 、V bτ 、V bσ The three-directional velocities on the outer boundary of the far field are obtained by using the unit external normal vector on the outer boundary of the far field, including: According to S b and P0, to obtain the density on the outer boundary of the far field According to ρ b , to obtain the speed of sound on the outer boundary of the far field When the flow field converges, C on the outer boundary of the far field e =c b =c ∞ ,according to Combined with R b+ ,get According to R b+ and R b- , get the characteristic velocity According to V bn , the three-dimensional flow field velocities in three directions on the outer boundary of the far field are obtained as follows: Among them, u b is the axial velocity on the boundary; u e is the axial velocity of the internal flow field; v b is the normal velocity on the boundary; v e is the normal velocity of the internal flow field; w b is the tangential velocity on the boundary; w e is the tangential velocity of the internal flow field; is the boundary unit normal vector; define V e =(u e , v e , w e ) is the vector of the internal flow velocity.

8. The method for numerical simulation of internal and external flow in an inlet with high back pressure according to claim 1, characterized in that: In S4, the additional high back pressure far field outer boundary condition is gradually increased from the initial value to the high back pressure far field outer boundary condition under the actual condition; the initial value of the additional high back pressure far field outer boundary condition=1 / 3×the high back pressure far field outer boundary condition under the actual condition.

9. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of a pulse laser spot center positioning method described in any one of claims 1-8 are implemented.

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