Engineering calculation method for predicting wall surface heat flow for different injection working media

Abstract

The invention discloses an engineering calculation method for predicting wall surface heat flow for different injection working media, and relates to the field of aerospace. According to the method, the wall surface heat flow under different ablation gas injection working media is obtained by calculating the mass injection coefficient, and the ratio of the average molecular weight (# imgabs0 #) of incoming flow gas to the average molecular weight (# imgabs1 #) of injection gas and the ratio of the unit mass enthalpy value of the incoming flow gas to the unit mass enthalpy value of the injection gas are introduced on the basis of an existing mass injection coefficient formula. Two conditions of # imgabs2 and # imgabs3 are considered at the same time, the wall surface heat flow can be quickly and accurately predicted under the action of different gas injection working media, and the precision of the method is remarkably higher than the calculation precision of an existing mass injection coefficient formula.

Description

Technical Field

[0001] The present invention relates to the field of aerospace, and specifically relates to an engineering calculation method for predicting wall heat flux for different injection working fluids. Background Art

[0002] During the hypersonic flight of a hypersonic vehicle, the heat flux on the vehicle surface approximately increases rapidly with the cube of the flight speed, while the aerodynamic drag is approximately proportional to the square of the flight speed. This results in a more severe aerodynamic heating environment for hypersonic vehicles. To protect hypersonic vehicles from severe aerodynamic heating under high-speed flight conditions, an ablation heat protection system is often added to the surface of hypersonic vehicles. The ablation heat protection system can not only absorb heat through complex aerodynamic-chemical-physical processes such as pyrolysis, melting, vaporization, sublimation, and radiation of the ablating material in a high-temperature heat environment, but also absorb a large amount of heat through the injection of ablation gases generated by the ablating material, thereby reducing the frictional drag and heat flux density on the vehicle wall, playing the role of "reducing heat and drag". Moreover, different gas injection working fluids (referring to different pyrolysis gases generated by different ablation protection materials during ablation) have different effects on reducing heat and drag. However, in the design process of the ablation heat protection system, the thickness design of the ablating material layer is particularly important. An overly thick thickness will lead to an increase in the overall weight of the vehicle, as well as an increase in manufacturing and flight costs; an overly thin thickness will not achieve the heat protection effect, and in severe cases, it will cause the vehicle to burn out. This requires predicting the ablation mass loss rate of the material in advance when designing the thickness of the ablating material layer, and the ablation mass loss rate is related to the wall heat flux density, that is: accurate prediction of the wall heat flux is the key to designing the ablation heat protection system.

[0003] Currently, the commonly used methods for predicting wall heat flux are: wind tunnel tests, CFD numerical calculations, and theoretical formula calculations. Among them, wind tunnel experiments are limited by experimental conditions, often difficult to simulate the real flight environment and with high experimental costs; the CFD numerical calculation method can simulate the real flight environment and can predict the wall heat flux more accurately, but this method has excessive requirements for computing resources and a long calculation time, and is not suitable for engineering calculations; in terms of theoretical formula calculations, based on a large number of CFD numerical calculations and experimental results, predecessors obtained a mass injection coefficient calculation formula ( , , that is, the original formula). This mass injection coefficient calculation formula is often used for engineering rapid calculation of wall heat flux. However, this mass injection coefficient calculation formula only considers the relationship between the gas injection mass flow rate and the heat flux, ignoring the influence of different gas injection working fluids on the wall heat flux. Therefore, there is an urgent need for an engineering calculation method that can quickly and accurately predict the wall heat flux under the action of different gas injection working fluids. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present invention provides an engineering calculation method for predicting wall heat flux for different ejector fluids, which solves the problem that the existing mass ejection coefficient formula ignores the influence of different gas ejector fluids on the wall heat flux, resulting in large errors in the wall heat flux prediction results.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: An engineering calculation method for predicting wall heat flux for different ejector fluids is provided, which includes the following steps: S1. Construct an improved formula for mass ejection coefficient, which is expressed as follows:

[0006] in is the mass ejection coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux when there is gas mass injection; is the wall heat flux when there is no gas mass ejection; Indicates the unit mass enthalpy of the incoming gas; is the unit mass enthalpy of gas s; is the component ratio of gas s; is the average molecular weight of the ejected gas; is the average molecular weight of the incoming gas; is the gas injection mass flow rate; is the recovery enthalpy; is the wall enthalpy; 、 、 、 、 、 、 and are all constants; S2. Calculate the wall heat flux when gas mass is ejected using the improved mass ejection coefficient formula, and complete the engineering calculation for predicting the wall heat flux for different ejection working fluids.

[0007] Furthermore, and The values of are 0.3 and 3 respectively.

[0008] Furthermore, 、 、 and The values of are 0.3, 12, 0.3 and 6 respectively.

[0009] Furthermore, and The values of are 0.07 and 0.15 respectively.

[0010] Furthermore, the specific enthalpy per unit mass of gas s is calculated by the following expression:

[0011] where is the gas constant of gas s; , , , , and are constants; T is the wall temperature.

[0012] Furthermore, the recovery enthalpy is calculated by the following expression:

[0013] where is the static enthalpy at the outer edge of the boundary layer; is the recovery coefficient; is the velocity at the outer edge of the boundary layer.

[0014] Furthermore, the wall enthalpy is calculated by the following expression:

[0015] where T is the wall temperature; K represents Kelvin; exp represents the exponential function with the natural constant e as the base; a is an intermediate parameter; P is the wall pressure; ln represents the natural logarithm.

[0016] Furthermore, the specific method for calculating the wall heat flux with gas mass injection in step S2 using the improved mass injection coefficient formula is as follows: Calculate the recovery enthalpy , the wall enthalpy , the average molecular weight of the incoming gas , the average molecular weight of the injected gas and the specific enthalpy per unit mass respectively; use CFD calculation software to obtain the wall heat flux without gas mass injection, substitute it into the improved mass injection coefficient formula to obtain the wall heat flux with gas mass injection, and complete the engineering calculation for predicting the wall heat flux for different injection working fluids.

[0017] A computer device is provided, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor performs the engineering calculation method for predicting the wall heat flux for different injection working fluids.

[0018] Provided is a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to execute an engineering calculation method for predicting wall heat flux for different ejecting working fluids.

[0019] The beneficial effects of the present invention are as follows: 1. Based on the existing mass entrainment coefficient formula, this method introduces the ratio of the average molecular weight of the incoming flow gas ( ) to the average molecular weight of the entrained gas ( ), as well as the ratio of the specific enthalpy per unit mass of the incoming flow gas to the specific enthalpy per unit mass of the entrained gas. At the same time, it considers both and cases, realizing fast and accurate prediction of wall heat flux under the action of different gas ejecting working fluids. Moreover, the accuracy of this method is significantly higher than that of the existing mass entrainment coefficient formula.

[0020] 2. This method fully considers the influence of different ejecting working fluids on the wall heat flux of hypersonic vehicles and can accurately predict the wall heat flux when the molecular weight of the entrained gas is greater than, less than, or equal to the molecular weight of the incoming flow air. Description of the Drawings

[0021] Figure 1 is a schematic flow diagram of this method; Figure 2 is a schematic diagram of a blunt wedge calculation model; Figure 3 is a comparison diagram of the calculation results under different working conditions with the calculation results of the original mass entrainment coefficient formula (i.e., the original formula) and the improved mass entrainment coefficient formula (i.e., the improved formula) when the ejecting working fluid is pyrolysis gas 1; Figure 4 is a comparison diagram of the calculation results under different working conditions with the calculation results of the original mass entrainment coefficient formula (i.e., the original formula) and the improved mass entrainment coefficient formula (i.e., the improved formula) when the ejecting working fluid is pyrolysis gas 2; Figure 5 is a comparison diagram of the calculation results under different working conditions with the calculation results of the original mass entrainment coefficient formula (i.e., the original formula) and the improved mass entrainment coefficient formula (i.e., the improved formula) when the ejecting working fluid is air. Detailed Embodiments

[0022] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the inventive concept of the present invention are within the scope of protection.

[0023] AsFigure 1 As shown in Figure 1 , the engineering calculation method for predicting the wall heat flux for different entrained working fluids includes the following steps: S1. On the basis of the original mass entrainment coefficient formula, add the ratio of the average molecular weight of the incoming gas to the average molecular weight of the entrained gas ( ), and at the same time add the ratio of the specific enthalpy per unit mass of the incoming gas to the specific enthalpy per unit mass of the entrained gas ( ), consider the influence of different gas entrainment components on the wall heat flux, and construct an improved mass entrainment coefficient formula, the expression of which is:

[0024] where is the mass entrainment coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux with gas mass entrainment; is the wall heat flux without gas mass entrainment; represents the specific enthalpy per unit mass of the incoming gas; is the specific enthalpy per unit mass of gas s; is the component ratio of gas s; is the average molecular weight of the entrained gas; is the average molecular weight of the incoming gas; is the gas entrainment mass flow rate; is the recovery enthalpy; is the wall enthalpy; , , , , , , and are all constants; S2. Calculate the wall heat flux with gas mass entrainment through the improved mass entrainment coefficient formula, and complete the engineering calculation for predicting the wall heat flux for different entrained working fluids.

[0025] In this embodiment, , , , , , , and take the values of 0.3, 3, 0.3, 12, 0.3, 6, 0.07 and 0.15 respectively.

[0026] The calculation expression for the specific enthalpy per unit mass of gas s is:

[0027] Among them is the gas constant of gas s; , , , , and are constants (these values are from Yipu Zhao. Numerical study on transpiration heat reduction and drag reduction of bluff body flow with chemical non-equilibrium effects. Beijing Jiaotong University, 2022. DOI: 10.26944 / d.cnki.gbfju.2022.000278); T is the wall temperature.

[0028] Gas s is a component of the oncoming gas or the entrained gas. For example, if the oncoming gas contains oxygen and nitrogen, then gas s represents oxygen and nitrogen, and the gas constants of oxygen and nitrogen .

[0029] The average molecular weight is obtained by multiplying the content ratio of the gas component by the molecular weight of the corresponding component and then summing up. For example: the oncoming gas is air, the gas components are 0.77 of N2 and 0.23 of O2, the molecular weight of N2 is 28, and the molecular weight of O2 is 32, then the average molecular weight of the oncoming gas M air = 0.77×28 + 0.23×32 = 29.

[0030] Recovery enthalpy The calculation expression of is:

[0031] Among them is the static enthalpy at the outer edge of the boundary layer; is the recovery coefficient, which is a function of the Prandtl number Pr, laminar flow: ( r ) = Pr 1 / 2 , turbulent flow: ( r ) = Pr 1 / 3 ; is the velocity at the outer edge of the boundary layer.

[0032] Wall enthalpy The calculation expression of is:

[0033] Among them, T is the wall temperature; K represents Kelvin; exp represents the exponential with the natural constant e as the base; a is an intermediate parameter; P is the wall pressure; ln represents the natural logarithm.

[0034] The specific method for calculating the wall heat flux with gas mass injection in step S2 through the improved mass injection coefficient formula is: Calculate the recovery enthalpy separately , wall enthalpy , average molecular weight of the incoming flow gas , average molecular weight of the entrained gas and enthalpy per unit mass; The wall heat flux without gas mass entrainment is obtained using CFD calculation software , and substituting it into the improved mass entrainment coefficient formula to obtain the wall heat flux with gas mass entrainment , completing the engineering calculation of predicting the wall heat flux for different entrained working fluids

[0035] In an embodiment of the present invention, taking a two-dimensional blunt wedge model as an example, the improved mass entrainment coefficient formula is verified. The schematic diagram of the two-dimensional blunt wedge model is as shown in Figure 2 . The model has a total length of 2m, a nose radius R n =10mm, no mass entrainment on the leeward side, and the mass entrainment range on the windward side is from 0.4m to 2m at the rear end. The total number of grids is 55,000, the height of the first layer of grids is 0.05mm, and the grid Reynolds number , and it is encrypted near the shock wave in the flow field and at x =0.4m (the junction point of the smooth area and the entrainment area). The incoming flow conditions are shown in Table 1, and the entrained working fluids are three entrained gases with different average molecular weights, named pyrolysis gas 1 (average molecular weight less than the incoming air); pyrolysis gas 2 (average molecular weight greater than the incoming air); air (average molecular weight equal to the incoming air), and the component contents of the entrained gases are shown in Table 2

[0036] Table 1: Incoming flow conditions

[0037] Table 2: Component contents of the entrained gases

[0038] In this embodiment, the comparison results of the CFD calculation results, the results calculated by this method (improved formula), and the original mass entrainment coefficient formula are as shown in Figure 3 , Figure 4 and Figure 5 . The figure shows the verification results of 15 calculation conditions in total. The CFD calculation results are in good agreement with the results calculated by this method. The prediction accuracy of this method is much higher than that of the mass entrainment coefficient formula, and the prediction error is within 10%

[0039] In other embodiments of the present invention, a computer device is provided, which includes a memory and a processor. When the computer program stored in the memory is executed by the processor, the processor executes the engineering calculation method for predicting the wall heat flux for different entrained working fluids

[0040] Provided is a computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to execute an engineering calculation method for predicting wall heat flux for different ejecting working fluids.

[0041] In summary, based on the existing mass entrainment coefficient formula, the present invention introduces the ratio of the average molecular weight of the incoming gas to the average molecular weight of the ejecting gas and the ratio of the specific enthalpy per unit mass of the incoming gas to the specific enthalpy per unit mass of the ejecting gas, and at the same time considers and two cases, achieving fast and accurate prediction of wall heat flux under the action of different gas ejecting working fluids, and the accuracy of this method is significantly higher than the calculation accuracy of the existing mass entrainment coefficient formula.

Claims

1. An engineering calculation method for predicting wall heat flux for different ejecting working fluids, characterized in that, Including the following steps: S1. Construct an improved formula for the mass entrainment coefficient, and its expression is: wherein is the mass entrainment coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux with gas mass entrainment; is the wall heat flux without gas mass entrainment; represents the specific enthalpy of the incoming flow gas per unit mass; is the specific enthalpy of gas s per unit mass; is the component proportion of gas s; is the average molecular weight of the entrained gas; is the average molecular weight of the incoming flow gas; is the mass flow rate of the entrained gas; is the recovery enthalpy; is the wall enthalpy; , , , , , , and are all constants; S2. Calculate the wall heat flux with gas mass entrainment through the improved formula for the mass entrainment coefficient, and complete the engineering calculation for predicting the wall heat flux for different entrainment working fluids.

2. The engineering calculation method for predicting wall heat flux for different ejecting working fluids according to claim 1, characterized in that, and take values of 0.3 and 3 respectively.

3. The engineering calculation method for predicting wall heat flux for different ejector working fluids according to claim 2, characterized in that , , and take values of 0.3, 12, 0.3, and 6 respectively.

4. The engineering calculation method for predicting the wall heat flux for different ejector working fluids according to claim 3, characterized in that and take the values of 0.07 and 0.15 respectively.

5. The engineering calculation method for predicting wall heat flux for different ejecting working fluids according to claim 1, characterized in that, The specific enthalpy of gas s The calculation expression is as follows: wherein is the gas constant of gas s; , , , , and are constants; T is the wall temperature.

6. The engineering calculation method for predicting wall heat flux for different ejector working fluids according to claim 1, characterized in that, Recovery enthalpy The calculation expression is as follows: wherein is the static enthalpy at the outer edge of the boundary layer; is the recovery coefficient; is the velocity at the outer edge of the boundary layer.

7. The engineering calculation method for predicting wall heat flux for different ejector working fluids according to claim 1, characterized in that, Wall enthalpy The calculation expression is as follows: Where T is the wall temperature; K represents Kelvin; exp represents the exponential with the natural constant e as the base; a is an intermediate parameter; P is the wall pressure; ln represents the natural logarithm.

8. The engineering calculation method for predicting wall heat flux for different ejecting working fluids according to claim 1, characterized in that, The specific method for calculating the wall heat flux with gas mass entrainment through the improved formula for the mass entrainment coefficient in step S2 is: Calculate the recovery enthalpy separately , the wall enthalpy , the average molecular weight of the incoming flow gas , the average molecular weight of the entrained gas and the enthalpy per unit mass; Obtain the wall heat flux without gas mass entrainment using CFD calculation software , substitute it into the improved mass entrainment coefficient formula to obtain the wall heat flux with gas mass entrainment , and complete the engineering calculation of predicting the wall heat flux for different entrained working fluids 9. A computer device, characterized in that, Including a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the engineering calculation method for predicting the wall heat flux for different entrainment working fluids according to any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, Storing a computer program, and when the computer program is executed by the processor, the processor executes the engineering calculation method for predicting the wall heat flux for different entrainment working fluids according to any one of claims 1 to 8.

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