Method for calculating the shock wave of an inlet based on the bursting of a diaphragm in a high-pressure chamber

Abstract

This invention discloses a method for calculating the hammer wave of an air intake based on the diaphragm burst of a high-pressure cavity, belonging to the field of aircraft air intake structural design technology. It solves the problem that traditional air intake hammer wave calculation methods in the prior art struggle to accurately assess the hammer wave load. This invention uses the results of steady-state numerical simulations of the internal and external flow of the air intake as the initial field. Based on the pressure change function over time at the instant of the high-pressure cavity diaphragm burst, calculation code is written and added to the high-pressure cavity calculation module. This module is then added downstream of the internal flow channel in the steady flow field of the air intake. Given input conditions such as the volume of the high-pressure cavity and the burst pressure, unsteady numerical simulations are used to obtain the process of high-pressure gas propagating against the airflow to form a hammer wave and propagating within the air intake, thus completing the air intake hammer wave calculation. This invention effectively improves the efficiency of diaphragm burst simulation tests and can be applied to high-pressure cavity diaphragm burst tests.

Description

Technical Field

[0001] This invention relates to a method for calculating the hammer wave of an air intake, and more particularly to a method for calculating the hammer wave of an air intake based on the rupture mode of a high-pressure cavity diaphragm, belonging to the field of aircraft air intake structural design technology. Background Technology

[0002] Hammer wave load, as the peak load in air intake structural design, is one of the decisive factors in aircraft air intake structural design. The load variations caused by hammer waves must be considered during the initial aircraft design phase. If the hammer wave load cannot be accurately assessed, it is difficult to determine the structural requirements of the air intake, which may lead to increased structural mass or increased flight risks due to underestimating the given load value. To provide load basis for aircraft air intake structural design, it is necessary to conduct research on the impact loads caused by hammer waves during their generation and propagation.

[0003] In existing technologies, the intake hammer wave test method involves fixing a diaphragm in the direction of reverse airflow within a high-pressure cavity, while simultaneously injecting high-pressure gas into the cavity. When a specific pressure is reached, the diaphragm ruptures through a certain mechanism. The high-pressure reverse airflow within the cavity propagates within the intake duct, forming a hammer wave. This process requires realistic simulation of the hammer wave intensity during engine surge or stall. Therefore, developing a calculation method for intake hammer waves based on the diaphragm rupture mechanism within a high-pressure cavity is crucial for simulating the generation and propagation of this type of hammer wave. This not only allows for simulation of test conditions before the hammer wave test, providing guidance for the experiment, but also, after experimental verification, yields results on the impact of intake hammer waves on the intake duct under different high-pressure cavity volumes, different pressure sequences, and different intake duct types. This significantly reduces experimental workload and costs.

[0004] In summary, a calculation method for intake hammer waves based on the high-pressure cavity diaphragm rupture mechanism is needed. Summary of the Invention

[0005] A brief overview of the invention is given below to provide a basic understanding of certain aspects of it. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0006] In view of this, in order to solve the problem that the traditional intake hammer wave calculation method in the prior art is difficult to accurately evaluate the hammer wave load, the present invention provides an intake hammer wave calculation method based on the high-pressure cavity diaphragm explosion mode.

[0007] The technical solution is as follows: A calculation method for intake duct hammer shock waves based on high-pressure cavity diaphragm rupture, including the following steps:

[0008] S1. Perform steady numerical simulation of the flow field inside and outside the intake duct to obtain the calculation results of the steady flow field, and use the calculation results as the initial field;

[0009] S2. Based on the pressure-bearing characteristics of the diaphragm used in the experiment, and combined with the pressure data at the diaphragm before and after the burst test, determine the pressure change function of the high-pressure cavity diaphragm at the moment of burst with time, and design the calculation code to simulate the burst of the diaphragm based on the change function.

[0010] S3. Add the calculation code for simulating diaphragm bursting to the high-pressure cavity calculation module, and use it as the boundary condition for the directional release of high-pressure gas in the high-pressure cavity;

[0011] S4. Solidify the high-pressure cavity calculation module and add it to the downstream flow field of the inner flow channel of the air intake in the steady flow field inside and outside the air intake in step S1. Given the high-pressure cavity volume and the pressure before the explosion, i.e., input conditions, and start using the high-pressure cavity calculation module.

[0012] S5. The process of high-pressure gas propagating forward against the airflow to form a hammer wave and propagating in the intake duct was simulated by an unsteady numerical simulation method. The influence of the hammer wave on the internal and external flow fields of the intake duct and the load on the intake duct wall was obtained.

[0013] S6. Change the high-pressure cavity volume and the pre-explosion pressure (i.e., input conditions) and repeat step S5 to obtain the effects of different intensities of intake hammer waves on the intake internal and external flow and wall load.

[0014] S7. Change the intake duct type, reconstruct the intake duct internal and external flow digital model, repeat steps S1 to S6 to obtain the influence of intake duct hammer waves of different types and intensities on the intake duct internal and external flow and avoidance load, and complete the intake duct hammer wave calculation.

[0015] Furthermore, in step S2, a diaphragm of a certain thickness is selected from the experiment, which can withstand a pressure difference of 4.2 atmospheres. It is planned to burst the diaphragm when the pressure in front of the diaphragm is 220,000 Pa. Based on the pressure change curve measured at the diaphragm, the instantaneous pressure of the high-pressure cavity diaphragm bursting is obtained. Over time The variation function is given in piecewise form, fitted with terms of up to the third degree. The coefficients and expressions of each term are as follows.

[0016] The change function is expressed in piecewise form as follows:

[0017] (0≤) ≤600)

[0018] (600< ≤1300)

[0019] (1300< ≤2000)

[0020] Among them, time The unit is ms;

[0021] Using the user-defined function (udf) in computational fluid dynamics simulation software, the instantaneous pressure of the high-pressure cavity diaphragm rupture was determined. Over time The code for calculating the set of change functions s, i.e., pressure Change is represented by time The function;

[0022] The calculation code is represented as follows:

[0023] face_t f;

[0024] Declare a face identifier variable, which will be used in subsequent loops to iterate over each mesh face f on the boundary;

[0025] real t;

[0026] t = CURRENT_TIME;

[0027] Declare a real number variable time t, and use the CURRENT_TIME macro to get the current physical time of the calculation, and assign it to time t;

[0028] if (t <= 600)

[0029] ;

[0030] When time t is greater than or equal to 600, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function;

[0031] if ((t>600)&&(t<=1300))

[0032] ;

[0033] When time t is greater than 600 and less than or equal to 1300, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function;

[0034] if((t>1300)&&(t<=2000))

[0035] ;

[0036] When time t is greater than 1300 and less than or equal to 2000, the result of the mathematical expression calculated on the right side of the equals sign is assigned to the currently looping mesh surface f by the F_PROFILE assignment function.

[0037] The beneficial effects of this invention are as follows: This invention adopts a calculation method based on the formation of hammer waves by the bursting of a high-pressure cavity diaphragm and their propagation process in the intake duct. It can be used to calculate the influence of hammer waves on the intake duct under different volumes of high-pressure cavities, different pressure sequences, and different intake duct types. This invention improves the efficiency of the experiment. Attached Figure Description

[0038] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0039] Figure 1 This is a flowchart illustrating the calculation method for intake hammer shock waves based on the high-pressure cavity diaphragm rupture mechanism.

[0040] Figure 2 This is a schematic flowchart of an embodiment of the calculation method for intake hammer waves based on the high-pressure cavity diaphragm rupture method;

[0041] Figure 3 This is a schematic diagram of the structural layout for a diaphragm burst test.

[0042] Figure 4 This is a schematic diagram of the pressure change curve of a thick diaphragm during a diaphragm burst test.

[0043] Reference numerals: 1. Inlet; 2. Inlet outlet; 3. Diaphragm; 4. High-pressure chamber. Detailed Implementation

[0044] To make the technical solutions and advantages of the embodiments of the present invention clearer, the exemplary embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0045] refer to Figures 1-4 This embodiment details the calculation method for intake duct hammer wave based on high-pressure cavity diaphragm rupture, specifically including the following steps:

[0046] S1. Perform steady numerical simulation of the flow field inside and outside the intake duct to obtain the calculation results of the steady flow field, and use the calculation results as the initial field;

[0047] S2. Based on the pressure-bearing characteristics of the diaphragm used in the experiment, and combined with the pressure data at the diaphragm before and after the burst test, determine the pressure change function of the high-pressure cavity diaphragm at the moment of burst with time, and design the calculation code to simulate the burst of the diaphragm based on the change function.

[0048] S3. Add the calculation code for simulating diaphragm bursting to the high-pressure cavity calculation module, and use it as the boundary condition for the directional release of high-pressure gas in the high-pressure cavity;

[0049] S4. Solidify the high-pressure cavity calculation module and add it to the downstream flow field of the inner flow channel of the air intake in the steady flow field inside and outside the air intake in step S1. Given the high-pressure cavity volume, the pressure before the explosion, etc., input conditions and start using the high-pressure cavity calculation module.

[0050] S5. The process of high-pressure gas propagating forward against the airflow to form a hammer wave and propagating in the intake duct was simulated by an unsteady numerical simulation method. The influence of the hammer wave on the internal and external flow fields of the intake duct and the load on the intake duct wall was obtained.

[0051] S6. Change the high-pressure cavity volume, pre-explosion pressure, etc. (i.e., input conditions) and repeat step S5 to obtain the effects of different intensities of intake hammer waves on the intake internal and external flow and wall load.

[0052] S7. Change the intake duct type, reconstruct the intake duct internal and external flow digital model, repeat steps S1 to S6 to obtain the influence of intake duct hammer waves of different types and intensities on the intake duct internal and external flow and avoidance load, and complete the intake duct hammer wave calculation.

[0053] Specifically, in steady numerical simulations, according to the convergence criteria of internal flow numerical simulation calculations, it is usually required that the residuals of each physical quantity (such as velocity, pressure, energy, etc.) reach the preset convergence standard (such as 10⁻⁵ to 10⁻¹⁰) and continue to decrease steadily without large fluctuations. At the same time, the mass flow rate difference between the inlet and outlet of the air intake 1 is less than 1% to ensure the physical rationality of the flow and obtain a reasonable and reliable steady flow field as the initial field.

[0054] The high-pressure cavity calculation module can be a software tool for simulating and analyzing closed or semi-closed containers filled with high-pressure fluid (gas or liquid);

[0055] The steady flow field calculation results of the internal and external flow of the intake duct 1 mentioned in this invention must be convergent.

[0056] The high-pressure cavity calculation module mentioned in this invention needs to be added downstream of the internal flow channel of the intake duct 1. When performing steady numerical simulation of the internal and external flow of the intake duct 1, a certain space needs to be reserved for the high-pressure cavity 4. The high-pressure cavity 4 is generally a cylinder and its diameter cannot exceed the diameter of the intake duct outlet 2. The grid of the flow field inside the high-pressure cavity 4 is added to the steady flow field of the intake duct 1 through overlapping grids.

[0057] The pressure change function of the diaphragm 3 at the moment of bursting in the high-pressure cavity 4 mentioned in this invention needs to be given by fitting the pressure-bearing characteristics of the high-pressure cavity 4 and the diaphragm 3 used in the experiment and combined with the experimental data.

[0058] The pressure before the high-pressure cavity 4 mentioned in this invention must ensure that when the pressure wave formed by the high pressure is transmitted to the intake outlet, the pressure ratio before and after the wave at the intake outlet 2 usually reaches about 3, and the flow reverses, exhibiting the characteristics of a typical hammer wave in the intake 1.

[0059] In step S6 of the present invention, a non-steady numerical simulation method can be used to simulate the process of high-pressure gas propagating forward against the airflow to form a hammer wave and propagating in the intake duct 1. The time step of the non-steady numerical simulation method of the hammer wave in the intake duct 1 is 1e-6 seconds, and the number of internal iteration steps ensures that the residual decreases by at least two orders of magnitude.

[0060] Furthermore, in S2, reference Figure 3 A diaphragm of a certain thickness was selected for the experiment, which could withstand a pressure difference of 4.2 atmospheres. It was planned to burst the diaphragm when the pressure in front of the diaphragm was 220,000 Pa. Based on the pressure change curve measured at the diaphragm, the instantaneous pressure of the high-pressure cavity diaphragm bursting was obtained. Over time The variation function is given in the form of a piecewise function fitted with the highest term being cubic, and the coefficients and expressions of each term are as follows;

[0061] The change function is expressed in piecewise form as follows:

[0062] (0≤) ≤600)

[0063] (600< ≤1300)

[0064] (1300< ≤2000)

[0065] Among them, time The unit is ms. The change function only represents the propagation process of the first high-pressure wave generated when the high-pressure gas in the high-pressure cavity 4 is released upstream in a directional manner when the diaphragm 3 bursts. After 2000ms, the pressure value of the gas in the high-pressure cavity 4 released in a directional manner is far from the peak value of the high-pressure wave. Therefore, the calculation of the intake hammer wave can be ignored and can be given according to the pressure at 2000ms.

[0066] Using the user-defined function udf (udf) in computational fluid dynamics (CFD) simulation software, the pressure at the instant of diaphragm rupture in the high-pressure cavity was analyzed. Over time The code for calculating the set of change functions s, i.e., pressure Change is represented by time The function;

[0067] The calculation code is represented as follows:

[0068] face_t f;

[0069] Declare a face identifier variable, which will be used in subsequent loops to iterate over each mesh face f on the boundary;

[0070] real t;

[0071] t = CURRENT_TIME;

[0072] Declare a real number variable time t, and use the CURRENT_TIME macro to get the current physical time of the calculation, and assign it to time t;

[0073] if (t <= 600)

[0074] ;

[0075] When time t is greater than or equal to 600, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function;

[0076] if ((t>600)&&(t<=1300))

[0077] ;

[0078] When time t is greater than 600 and less than or equal to 1300, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function;

[0079] if((t>1300)&&(t<=2000))

[0080] ;

[0081] When time t is greater than 1300 and less than or equal to 2000, the result of the mathematical expression calculated on the right side of the equals sign is assigned to the currently looping mesh surface f by the F_PROFILE assignment function.

[0082] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

Claims

1. A method for calculating the hammer wave in an air intake based on the high-pressure cavity diaphragm explosion, characterized in that, Includes the following steps: S1. Perform steady numerical simulation of the flow field inside and outside the intake duct to obtain the calculation results of the steady flow field, and use the calculation results as the initial field; S2. Based on the pressure-bearing characteristics of the diaphragm used in the experiment, and combined with the pressure data at the diaphragm before and after the burst test, determine the pressure change function of the high-pressure cavity diaphragm at the moment of burst with time, and design the calculation code to simulate the burst of the diaphragm based on the change function. S3. Add the calculation code for simulating diaphragm bursting to the high-pressure cavity calculation module, and use it as the boundary condition for the directional release of high-pressure gas in the high-pressure cavity; S4. Solidify the high-pressure cavity calculation module and add it to the downstream flow field of the inner flow channel of the air intake in the steady flow field inside and outside the air intake in step S1. Given the high-pressure cavity volume and the pressure before the explosion, i.e., input conditions, and start using the high-pressure cavity calculation module. S5. The process of high-pressure gas propagating forward against the airflow to form a hammer wave and propagating in the intake duct was simulated by an unsteady numerical simulation method. The influence of the hammer wave on the internal and external flow fields of the intake duct and the load on the intake duct wall was obtained. S6. Change the high-pressure cavity volume and the pre-explosion pressure (i.e., input conditions) and repeat step S5 to obtain the effects of different intensities of intake hammer waves on the intake internal and external flow and wall load. S7. Change the intake duct type, reconstruct the intake duct internal and external flow digital model, repeat steps S1 to S6 to obtain the influence of intake duct hammer waves of different types and intensities on the intake duct internal and external flow and avoidance load, and complete the intake duct hammer wave calculation.

2. The method for calculating the intake duct hammer wave based on the high-pressure cavity diaphragm explosion method according to claim 1, characterized in that, In step S2, a diaphragm of a certain thickness is selected from the experiment, which can withstand a pressure difference of 4.2 atmospheres. It is planned to burst the diaphragm when the pressure in front of the diaphragm is 220,000 Pa. Based on the pressure change curve measured at the diaphragm, the instantaneous pressure of the high-pressure cavity diaphragm bursting is obtained. Over time The function of change; The change function is expressed in piecewise form as follows: （0≤ ≤600）； （600< ≤1300）； （1300< ≤2000）； Among them, time The unit is ms; Using the user-defined function (udf) in computational fluid dynamics simulation software, the instantaneous pressure of the high-pressure cavity diaphragm rupture was determined. Over time The code for calculating the set of change functions s, i.e., pressure Change is represented by time The function; The calculation code is represented as follows: face_t f; Declare a face identifier variable, which will be used in subsequent loops to iterate over each mesh face f on the boundary; real t; t = CURRENT_TIME; Declare a real number variable time t, and use the CURRENT_TIME macro to get the current physical time of the calculation, and assign it to time t; if (t <= 600) ； When time t is greater than or equal to 600, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function; if ((t>600)&&(t<=1300)) ； When time t is greater than 600 and less than or equal to 1300, the result of the mathematical expression calculated on the right side of the equal sign is assigned to the mesh surface f currently being processed in the loop using the F_PROFILE assignment function; if((t>1300)&&(t<=2000)) ； When time t is greater than 1300 and less than or equal to 2000, the result of the mathematical expression calculated on the right side of the equals sign is assigned to the currently looping mesh surface f by the F_PROFILE assignment function.

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