A design method of cooling structure of an ultrahigh-temperature wind tunnel nozzle

Abstract

The application discloses a kind of hypersonic wind tunnel nozzle cooling structure design method, belongs to aerodynamics wind tunnel design technical field.The application solves the problem that the temperature limit of currently commonly used material is lower than the temperature of wind tunnel operation during the operation of hypersonic equipment, and it is difficult to simultaneously consider support-thermal protection performance.The application determines the inner wall surface pressure according to the design Mach number of nozzle by designing the thickness of nozzle inner shell, calculates the thickness of nozzle inner shell according to the national standard of pressure vessel, determines the position and size range of nozzle cooling structure, carries out CFD simulation calculation on nozzle cooling structure, carries out multi-objective optimization on nozzle cooling structure, selects materials and processing technology.The application solves the problem that hypersonic wind tunnel can normally operate under existing material system by reasonable cooling structure design when the operating temperature of hypersonic wind tunnel exceeds the temperature limit of existing materials.

Description

Technical Field

[0001] This invention belongs to the field of aerodynamic wind tunnel design technology, specifically relating to a design method for a cooling structure of an ultra-high temperature wind tunnel nozzle. Background Technology

[0002] Flying higher and faster has always been a central theme of human development, and hypersonic flight inevitably brings aerodynamic and thermal problems. As the only experimental equipment capable of simulating the flight conditions of aircraft, the need for hypersonic ultra-high temperature wind tunnels is urgent. However, the operating temperature of ultra-high temperature wind tunnels is generally around 2000K. When hypersonic equipment is running, the heated, high-temperature, and high-pressure gas flowing through the tunnel inevitably transfers heat to the tunnel structure. The nozzle throat of the wind tunnel will undergo severe thermal stress. If effective measures are not taken, the structure will be damaged under the action of high-temperature and high-pressure airflow, leading to serious safety hazards. Currently, the operating temperature limit of commonly used materials is lower than the wind tunnel operating temperature, making it difficult to simultaneously ensure support and thermal protection performance.

[0003] Therefore, this application proposes a design method for an ultra-high temperature wind tunnel nozzle cooling structure to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to address the problem that, during the operation of hypersonic equipment, the operating temperature limit of commonly used materials is lower than the wind tunnel operating temperature, making it difficult to simultaneously ensure support and thermal protection performance. A brief overview of the invention is provided below to offer 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.

[0005] The technical solution of the present invention: A design method for a cooling structure of an ultra-high temperature wind tunnel nozzle includes the following steps: Step 1: Design the nozzle inner shell thickness, determine the inner wall pressure according to the wind tunnel design similarity criteria, and calculate the nozzle inner shell thickness according to the national standard for pressure vessels. Step 2: Determine the location and size range of the nozzle cooling structure based on Step 1, and establish three-dimensional models of different cooling structures; Step 3: CFD simulation calculation of nozzle cooling structure; Step 31: Construct different computational domain models from the different cooling structure assumptions in Step 2; Step 32: Use Pointwise 18.6 to mesh the computational domain model into multiple mesh blocks; Step 33: Set boundary conditions for the gas flow domain based on the actual Mach number of the nozzle, set the water flow rate of the cooling water flow domain as a variable, and perform flow numerical solution to obtain the temperature distribution inside the nozzle. Step 34: Calculate the average cooling efficiency of the inner wall surface by measuring the heat conduction at the interface between the fluid boundary layer and the solid wall surface, evaluate the actual temperature of the inner wall surface, complete the simulation, and generate training and test sets for machine learning. Step 4: Multi-objective optimization of nozzle cooling structure; Step 41: Design the variables, constraints, and target parameters of the nozzle cooling structure; Step 42: Accuracy analysis of multi-objective optimization computational model, test the computational accuracy of multi-objective genetic algorithm, and select algorithm model; Step 43: Multi-objective optimization to obtain the optimal solution; Step 5: Select materials and processing techniques.

[0006] Furthermore, step 2 specifically involves: assuming that the cooling channels have different shapes when the volume ratio and number of cooling channels are the same; assuming that the cooling channels have different cooling volume ratios when the shape and number of cooling channels are the same; and assuming that the cooling channels have different numbers when the shape and volume ratio of cooling channels are the same.

[0007] Furthermore, step 41 specifically involves: using the size, shape, number, and cooling water volume of the cooling channels in the test set generated in step 2 as design variables, setting constraints according to actual working conditions, and the target parameters including the highest temperature of the nozzle inner wall and the nozzle cooling efficiency. With channel water flow Q The area of ​​the cooling channel at the throat cross-section is a percentage of the total area. A Cooling channel diameter L and number of cooling channels n To design variables, use x =( x 1, x 2, x 3, x 4) = ( Q , A , L , n (This indicates the highest temperature on the inner wall of the nozzle.) T max Minimum, nozzle cooling efficiency η To maximize the optimization objective, two objective functions were established. η = f 1( x ), T max = f 2( x ): (1); Based on the size limitations of the nozzle cooling structure, set the constraints for the design variables in step 3.

[0008] Furthermore, step 42 specifically involves: using different multi-objective genetic algorithms MOGA, NSGA-II, multi-objective parallel Pareto search gradient method-MGE, and MGP to perform multi-objective optimization on the test set, comparing and analyzing the accuracy of different optimization models, and selecting an algorithm model.

[0009] Furthermore, step 43 specifically involves: calculating the optimization results for the two optimal response parameters, comparing the optimization results with the results verified by simulation, selecting the optimal solution set for the two response parameters, and obtaining the corresponding optimal variables.

[0010] Furthermore, step 5 specifically involves: selecting the corresponding operating temperature material based on the optimal solution set, providing design error, and selecting the processing technology based on the material and the optimal cooling structure, including machining, additive manufacturing, and laser surface polishing.

[0011] The present invention has the following beneficial effects: The present invention discloses a design method for a cooling structure of an ultra-high temperature wind tunnel nozzle. First, the thickness of the nozzle inner shell and the size of the cooling channel are designed. Then, simulation calculations are performed using computational fluid dynamics software. Finally, the cooling structure is optimized for multiple objectives to find the optimal cooling structure and water flow rate. Ultimately, suitable materials and processing technology are designed to solve the problem of enabling ultra-high temperature wind tunnels to operate normally under existing material systems when the operating temperature exceeds the temperature limit of existing materials. Attached Figure Description

[0012] Figure 1 This is a flowchart of a design method for a cooling structure of an ultra-high temperature wind tunnel nozzle. Figure 2 This is a schematic diagram of the water-cooled structure of the nozzle in an ultra-high temperature wind tunnel, where (a) is a wave-shaped cooling channel, (b) is a circular cooling channel, (c) is a rectangular cooling channel, and (d) is a left view of the nozzle. Figure 3 This is a schematic diagram of a grid model of an ultra-high temperature wind tunnel nozzle; Figure 4 This is a schematic diagram of the computational fluid dynamics calculation results for an ultra-high temperature wind tunnel nozzle. Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0014] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0015] Example 1, combined with Figures 1-4 This embodiment describes a design method for an ultra-high temperature wind tunnel nozzle cooling structure. Before designing the wind tunnel cooling structure, design input conditions are provided, mainly experimental requirements and aerodynamic profiles, to determine the main design parameters of the wind tunnel cooling structure.

[0016] The test requirements mainly include the test velocity range, pressure range, temperature range, test model shape parameters, and test type. In this embodiment, the velocity range of the high-temperature supersonic wind tunnel is Ma=1~7, and the total pressure range is... P 0 = 0.2 bar ~ 5 bar, total temperature range T 0 = 2800K~1000K, model span within 1.8m, model length within 2m, average aerodynamic chord length 0.2m~0.3m, reference area 0.2m² 2 ~0.4m 2。

[0017] Aerodynamic profile, mainly including aerodynamic curves at the corresponding Mach number and nozzle diameter, length and profile.

[0018] Step 1: Design the nozzle inner shell thickness. Determine the inner wall pressure according to the wind tunnel design similarity criteria, and calculate the inner shell thickness according to GB150-1998 "Steel Pressure Vessels". The specific formula is as follows: (1); In the formula: P c To calculate pressure, D i The inner diameter of the cylinder, [ σ ] t Material requires stress, ϕ The welding coefficient; P c and D i Derived from the design input conditions, [ σ ] t Select from Table 1. ϕ =1.0 (all non-destructive testing) or 0.85 (partial non-destructive testing).

[0019] Step 2, assumptions about the dimensions and shape of the water-cooled structure; Step 21: Determine the location and size range of the cooling structure according to Step 1. Its location is on the outside of the inner shell, and its height should be less than the outer shell size, and the throat should be supported. Step 22: Based on the determined location and shape, and considering the ease of processing, assume that the cooling channel shape is square, circular, or wavy, assuming the same cooling volume ratio. Step 23: Based on the determined location and shape, under a given cooling channel shape, assuming that the cooling channels have different cooling volume ratios, the area ratios of the cooling channels at the throat cross-section are 40%, 50%, 60%, and 70%, respectively; Step 23: Based on the determined location and shape, and under a determined cooling channel shape and volume ratio, assume that the cooling channels have different numbers, namely 10, 12, and 14.

[0020] Step 3: CFD simulation calculation of the cooling structure; Step 31: Construct different computational domain models from the different cooling structure assumption models in Step 2; Step 32: The computational domain model is meshed using commercial software, divided into multiple meshes. The volume structure is divided into a structured mesh, and the fluid domain is divided into an unstructured mesh. The unstructured mesh has more than 15 boundary layers. The side lengths of the mesh are: horizontally Lx=13x, vertically Ly=13y, and vertically Lz=13z, where x, y, and z are the minimum mesh intervals in the horizontal, vertical, and vertical directions, respectively. Step 33: Set boundary conditions for the gas flow domain based on the actual Mach number of the nozzle, set the cooling water flow rate as a variable, and perform flow numerical solutions to obtain the temperature distribution inside the nozzle. The nozzle cooling effect was assessed using a three-dimensional model and numerical methods. The flow field inside the nozzle was calculated to obtain the thermal environment of the nozzle wall. The conservation form of the three-dimensional Navier-Stokes equations can be simplified as follows: (2); In the formula: Q is the conserved variable; F i For viscosity-free flux, i =1,2,3;F vi It is a viscous flux.

[0021] Discretization of the Navier-Stokes equations: The inviscid terms are discretized using a second-order upwind scheme; the turbulent kinetic energy and dissipation terms are first discretized using a first-order upwind scheme, and then the wall thermal environment is calculated in detail using a second-order upwind scheme after the flow field has initially converged. The nozzle exit is a supersonic boundary condition; the nozzle wall temperature is an isothermal boundary condition considering high-pressure water cooling.

[0022] Cooling effectiveness requires calculation of cooling water flow rate and velocity. The entire heater, nozzle throat section, and part of the expansion section are cooled by high-pressure water. The cooling water flow rate within the cooling channel and the total water flow rate from the high-pressure water pump should meet the following requirements: (3); In the formula: This represents the total water flow rate. Water flow rate for each cooling channel; The density of water; The flow rate of water within the cooling channel; A 1 represents the cross-sectional area of ​​the cooling channel; A 2 represents the sum of the cross-sectional areas of the heater and the nozzle.

[0023] Step 34: Calculate the average cooling efficiency of the inner wall surface by measuring the heat conduction at the interface between the fluid boundary layer and the solid wall surface, evaluate the actual temperature of the inner wall surface, complete the simulation, and generate training and testing sets for machine learning. The heat transfer within the nozzle cooling channel is calculated using the forced convection heat transfer method within the tube. The Mikhaiev formula is used for forced convection heat transfer within the tube. (4); (5); The fluid's characteristic temperature is the average temperature of the pipe's inlet and outlet sections; the pipe length and diameter satisfy... For non-circular pipes, use the equivalent diameter. , The cross-sectional area of ​​the cooling channel. This is the wetted perimeter length; The convective heat transfer coefficient; The value is the thermal conductivity of the cooling water.

[0024] Step 4: Multi-objective optimization of the cooling structure; Step 41: Design variables, constraints, and objective function; With channel water flow Q The area of ​​the cooling channel at the throat cross-section is a percentage of the total area. A Cooling channel diameter L and number of cooling channels n To design variables, use Indicates the highest temperature on the inner wall of the nozzle. Tmax Minimum, nozzle cooling efficiency To maximize the optimization objective, two objective functions were established. , : (6); Based on the size limitations of the nozzle cooling structure and to ensure its economy, the constraints in step 3 are set for the design variables.

[0025] Step 42, Accuracy analysis of the multi-objective optimization calculation model; Different multi-objective genetic algorithms, such as MOGA, NSGA-II, multi-objective parallel Pareto gradient search method-MGE, and MGP, were used to optimize the test set. The accuracy of different optimization models was compared and analyzed, and the algorithm model with higher accuracy was selected. Step 43: Multi-objective optimization to obtain the optimal solution; Calculate the optimal results for the two response parameters and compare them with the results verified by simulation. Find the optimal solution set for the two response parameters and obtain the corresponding optimal variables.

[0026] Step 5: Selection of suitable materials and processing techniques; Step 51: Find the appropriate material for the operating temperature based on the optimal solution set, refer to Table 1, and provide a certain design error; Step 52: Based on the material and optimal cooling structure, find a suitable processing technology, including but not limited to precision machining, additive manufacturing, laser surface polishing, etc.

[0027] Table 1 Material Operating Temperature Reference

[0028] This embodiment is merely an exemplary illustration of the present invention and does not limit its scope of protection. Those skilled in the art can make partial changes to it, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A design method for a cooling structure of an ultra-high temperature wind tunnel nozzle, characterized in that, Includes the following steps: Step 1: Design the nozzle inner shell thickness, determine the inner wall pressure according to the wind tunnel design similarity criteria, and calculate the nozzle inner shell thickness according to the national standard for pressure vessels. Step 2: Determine the location and size range of the nozzle cooling structure based on Step 1, and establish three-dimensional models of different cooling structures; Assuming that the volume ratio and number of cooling channels are the same, the cooling channels are assumed to have different shapes respectively; Assuming that the cooling channels have different cooling volume ratios while maintaining the same shape and number of cooling channels; Assuming that the cooling channels have the same shape and volume ratio, the cooling channels may have different numbers; Step 3: CFD simulation calculation of nozzle cooling structure; Step 31: Construct different computational domain models from the different cooling structure assumptions in Step 2; Step 32: Use Pointwise 18.6 to mesh the computational domain model into multiple mesh blocks; Step 33: Set boundary conditions for the gas flow domain based on the actual Mach number of the nozzle, set the water flow rate of the cooling water flow domain as a variable, and perform flow numerical solution to obtain the temperature distribution inside the nozzle. Step 34: Calculate the average cooling efficiency of the inner wall surface by measuring the heat conduction at the interface between the fluid boundary layer and the solid wall surface, evaluate the actual temperature of the inner wall surface, complete the simulation, and generate training and test sets for machine learning. Step 4: Multi-objective optimization of nozzle cooling structure; Step 41: Design the variables, constraints, and target parameters of the nozzle cooling structure; The size, shape, number, and cooling water volume of the cooling channels in the test set generated in step 2 are used as design variables. Constraints are set according to actual working conditions. Target parameters include the highest temperature of the nozzle inner wall and the nozzle cooling efficiency. The design variables are: channel water flow rate Q, cooling channel area ratio A at the throat cross-section, cooling channel diameter L, and number of cooling channels n, represented by x=(x1, x2, x3, x4)=(Q, A, L, n); and the highest temperature T on the nozzle inner wall is used as the design variable. max With the optimization objectives of minimizing the nozzle cooling efficiency η and maximizing the nozzle cooling efficiency η, two objective functions η=f1(x) and T are established. max =f2(x): （1） Based on the size limitations of the nozzle cooling structure, set the constraints for the design variables in step 3; Step 42: Accuracy analysis of multi-objective optimization computational model, test the computational accuracy of multi-objective genetic algorithm, and select algorithm model; Step 43: Multi-objective optimization to obtain the optimal solution; Step 5: Select materials and processing techniques.

2. The design method for a cooling structure of an ultra-high temperature wind tunnel nozzle according to claim 1, characterized in that, Step 42 specifically involves: using different multi-objective genetic algorithms MOGA, NSGA-II, multi-objective parallel Pareto search gradient method-MGE, and MGP to perform multi-objective optimization on the test set, comparing and analyzing the accuracy of different optimization models, and selecting an algorithm model.

3. The design method for a cooling structure of an ultra-high temperature wind tunnel nozzle according to claim 2, characterized in that, Step 43 specifically involves: calculating the optimization results for the two optimal response parameters, comparing the optimization results with the results verified by simulation, selecting the optimal solution set for the two response parameters, and obtaining the corresponding optimal variables.

4. The design method for a cooling structure of an ultra-high temperature wind tunnel nozzle according to claim 3, characterized in that, Step 5 specifically involves: selecting the corresponding operating temperature material based on the optimal solution set, providing design error, and selecting the processing technology based on the material and the optimal cooling structure, including precision machining, additive manufacturing, and laser surface polishing.

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