An engineering calculation method for predicting wall heat flux for different ejector fluids

Abstract

The present invention discloses an engineering calculation method for predicting wall heat flux for different ejector media, relating to the field of aerospace. The method calculates the mass ejection coefficient to derive the wall heat flux under different ablative gas ejection media. Based on the existing mass ejection coefficient formula, the method introduces the ratio of the average molecular weight (MW) of the incoming gas to the average molecular weight (MW) of the ejected gas, as well as the ratio of the unit mass enthalpy of the incoming gas to the unit mass enthalpy of the ejected gas. Furthermore, the method considers both the MW and MW conditions, achieving rapid and accurate prediction of wall heat flux under different gas ejection media. The accuracy of the method is significantly higher than that of the existing mass ejection coefficient formula.

Description

Technical Field

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

[0002] During hypersonic flight, the heat flux on the vehicle's surface increases rapidly with approximately the cube of the flight speed, while aerodynamic drag increases approximately proportional to the square of the flight speed. This leads to an increasingly severe aerodynamic heating environment for hypersonic vehicles. To protect hypersonic vehicles from the severe aerodynamic heating during high-speed flight, ablative heat protection systems are often added to the vehicle's surface. In high-temperature environments, ablative heat protection systems not only absorb heat through complex aerodynamic-chemical processes such as pyrolysis, melting, vaporization, sublimation, and radiation of the ablative material, but also absorb significant amounts of heat through the ejection of ablative gases generated by the ablative material. This reduces frictional resistance and heat flux on the vehicle's surface, achieving a "heat and drag reduction" effect. Different gas ejection media (referring to the different pyrolysis gases generated by different ablative protection materials during the ablation process) have varying heat and drag reduction effects. However, in the design of ablative thermal protection systems, the thickness of the ablative material layer is particularly important. Too thick a thickness will increase the overall weight of the aircraft, raising manufacturing and flight costs; too thin a thickness will not provide adequate thermal protection, and in severe cases, it will cause the aircraft to burn. This requires predicting the material's ablation mass loss rate when designing the ablative material layer thickness. The ablation mass loss rate is related to the wall heat flux density. In other words, accurately predicting the wall heat flux is key to designing ablative thermal protection systems.

[0003] Currently, the commonly used methods for predicting wall heat flux include wind tunnel tests, CFD numerical calculations, and theoretical formula calculations. Among them, wind tunnel tests are limited by experimental conditions and often have difficulty simulating the actual flight environment, and the experimental cost is high; CFD numerical calculation methods can simulate the actual flight environment and can more accurately predict wall heat flux, but this method requires too much computing resources and takes too long to calculate, making it unsuitable for engineering calculations; in terms of theoretical formula calculations, predecessors have derived a formula for calculating the mass ejection coefficient (based on a large number of CFD numerical calculations and experimental results) , , the original formula). This mass ejection coefficient calculation formula is often used in engineering to quickly calculate wall heat flux. However, this formula only considers the relationship between the gas ejection mass flow rate and heat flux, ignoring the impact of different gas ejection media on the wall heat flux. Therefore, there is an urgent need for an engineering calculation method that can quickly and accurately predict wall heat flux under different gas ejection media. 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:

[0006] An engineering calculation method for predicting wall heat flux for different ejector fluids is provided, which includes the following steps:

[0007] S1. Construct an improved formula for mass ejection coefficient, which is expressed as follows:

[0008]

[0009] in is the mass ejection coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux when there is gas mass ejection; 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;

[0010] 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.

[0011] Furthermore, and The values ​​of are 0.3 and 3 respectively.

[0012] Furthermore, 、 、 and The values ​​of are 0.3, 12, 0.3 and 6 respectively.

[0013] Furthermore, and The values ​​of are 0.07 and 0.15 respectively.

[0014] Furthermore, the unit mass enthalpy of gas s is The calculation expression is:

[0015]

[0016] in is the gas constant of gas s; 、 、 、 、 and is a constant; T is the wall temperature.

[0017] Furthermore, the recovery enthalpy The calculation expression is:

[0018]

[0019] in is the static enthalpy at the outer edge of the boundary layer; is the coefficient of restitution; is the velocity at the outer edge of the boundary layer.

[0020] Furthermore, the wall enthalpy The calculation expression is:

[0021]

[0022] Where T is the wall temperature; K represents degrees Kelvin; exp represents the exponential with the natural constant e as the base; a is the intermediate parameter; P is the wall pressure; ln represents the natural logarithm.

[0023] Furthermore, in step S2, the specific method for calculating the wall heat flux when gas mass is ejected using the improved mass ejection coefficient formula is:

[0024] Calculate the recovery enthalpy separately , wall enthalpy , average molecular weight of incoming gas , average molecular weight of ejected gas and unit mass enthalpy; CFD calculation software is used to obtain the wall heat flux when there is no gas mass injection , put the improved mass ejection coefficient formula into it, and get the wall heat flux when there is gas mass ejection , complete the engineering calculation of wall heat flux prediction for different ejector working fluids.

[0025] A computer device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes an engineering calculation method for predicting wall heat flux for different ejected working fluids.

[0026] A computer-readable storage medium is provided, which stores a computer program. When the computer program is executed by a processor, the processor executes an engineering calculation method for predicting wall heat flux for different ejected working fluids.

[0027] The beneficial effects of the present invention are:

[0028] 1. This method introduces the average molecular weight of the incoming gas based on the existing mass ejection coefficient formula ( ) and the average molecular weight of the ejected gas ( ) and the ratio of the unit mass enthalpy of the incoming gas to the unit mass enthalpy of the ejected gas, and at the same time taking into account and The two cases are analyzed, which realizes the rapid and accurate prediction of wall heat flux under different gas ejection working fluids, and the accuracy of this method is significantly higher than the calculation accuracy of the existing mass ejection coefficient formula.

[0029] 2. This method fully considers the influence of different ejector fluids on the wall heat flux of hypersonic vehicles and can accurately predict the wall heat flux when the molecular weight of the ejector gas is greater than, less than, or equal to the molecular weight of the incoming flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the process of this method;

[0031] Figure 2 It is a schematic diagram of the blunt wedge calculation model;

[0032] Figure 3 This is a comparison chart of the calculation results under different working conditions when the ejection medium is pyrolysis gas 1, and the calculation results of the original mass ejection coefficient formula (i.e., the original formula) and the improved mass ejection coefficient formula (i.e., the improved formula);

[0033] Figure 4 This is a comparison chart of the calculation results under different working conditions when the ejection medium is pyrolysis gas 2, and the calculation results of the original mass ejection coefficient formula (i.e., the original formula) and the improved mass ejection coefficient formula (i.e., the improved formula);

[0034] Figure 5 This is a comparison chart of the calculation results under different working conditions when the ejection medium is air, and the calculation results of the original mass ejection coefficient formula (i.e., the original formula) and the improved mass ejection coefficient formula (i.e., the improved formula). DETAILED DESCRIPTION

[0035] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0036] like Figure 1 As shown, the engineering calculation method for predicting wall heat flux for different ejected working fluids includes the following steps:

[0037] S1. Add the ratio of the average molecular weight of the incoming gas to the average molecular weight of the ejected gas to the original mass ejection coefficient formula ( ), while increasing the ratio of the unit mass enthalpy of the incoming gas to the unit mass enthalpy of the ejected gas ( ), considering the influence of different gas ejection components on the wall heat flux, an improved mass ejection coefficient formula is constructed, which is expressed as follows:

[0038]

[0039] in is the mass ejection coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux when there is gas mass ejection; 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;

[0040] 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.

[0041] In this embodiment, 、 、 、 、 、 、 and The values ​​are 0.3, 3, 0.3, 12, 0.3, 6, 0.07 and 0.15 respectively.

[0042] Enthalpy per unit mass of gas s The calculation expression is:

[0043]

[0044] in is the gas constant of gas s; 、 、 、 、 and is a constant (these values ​​are from Zhao Yipu. Numerical study of sweating-type heat reduction and drag reduction in bluff body flow with chemical non-equilibrium effect. Beijing Jiaotong University, 2022. DOI: 10.26944 / d.cnki.gbfju.2022.000278); T is the wall temperature.

[0045] Gas s is the component of the incoming gas or the ejected gas. For example, if the incoming gas contains oxygen and nitrogen, then gas s represents oxygen and nitrogen. The gas constant of oxygen needs to be calculated separately. and the gas constant of nitrogen .

[0046] The average molecular weight is obtained by multiplying the molecular weight of the corresponding component by the proportion of the gas component content. For example, if the incoming gas is air, the gas composition is 0.77 N2 and 0.23 O2, the molecular weight of N2 is 28, and the molecular weight of O2 is 32, then the average molecular weight of the incoming gas is M air =0.77×28+0.23×32=29.

[0047] Recovery enthalpy The calculation expression is:

[0048]

[0049] in is the static enthalpy at the outer edge of the boundary layer; is the coefficient of recovery, which is a function of the Prandtl number Pr, laminar flow: ( r )=Pr 1 / 2 , turbulence:( r )=Pr 1 / 3 ; is the velocity at the outer edge of the boundary layer.

[0050] Wall enthalpy The calculation expression is:

[0051]

[0052] Where T is the wall temperature; K represents degrees Kelvin; exp represents the exponential with the natural constant e as the base; a is the intermediate parameter; P is the wall pressure; ln represents the natural logarithm.

[0053] The specific method for calculating the wall heat flux with gas mass ejection using the improved mass ejection coefficient formula in step S2 is:

[0054] Calculate the recovery enthalpy separately , wall enthalpy , average molecular weight of incoming gas , average molecular weight of ejected gas and unit mass enthalpy; CFD calculation software is used to obtain the wall heat flux when there is no gas mass injection , put the improved mass ejection coefficient formula into it, and get the wall heat flux when there is gas mass ejection , complete the engineering calculation of wall heat flux prediction for different ejector working fluids.

[0055] In one embodiment of the present invention, the improved mass ejection coefficient formula is verified by taking a two-dimensional blunt wedge model as an example. Figure 2 As shown, the model has a total length of 2m and a head radius of R n =10mm, no mass ejection on the leeward side, mass ejection range on the windward side is 0.4m~2m from the rear end. The total number of grids is 55,000, the first layer grid height is 0.05mm, and the grid Reynolds number , and near the shock wave of the flow field and x =0.4m (the intersection of the smooth area and the ejection area). The incoming flow conditions are shown in Table 1. The ejection working fluids are three ejection gases with different average molecular weights, namely pyrolysis gas 1 (average molecular weight less than the incoming air); pyrolysis gas 2 (average molecular weight greater than the incoming air); and air (average molecular weight equal to the incoming air). The content of each ejection gas component is shown in Table 2.

[0056] Table 1: Inflow conditions

[0057]

[0058] Table 2: Content of each component of the ejected gas

[0059]

[0060] In this embodiment, the comparison results of CFD calculation results, calculation results of this method (improved formula) and original mass ejection coefficient formula are as follows: Figure 3 、 Figure 4 and Figure 5 As shown in the figure, the verification results of 15 calculation conditions are shown. The CFD calculation results are highly consistent with the calculation results of this method. The prediction accuracy of this method is much higher than that of the mass ejection coefficient formula, and the prediction error is within 10%.

[0061] In other embodiments of the present invention, a computer device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes an engineering calculation method for predicting wall heat flux for different ejector fluids.

[0062] A computer-readable storage medium is provided, which stores a computer program. When the computer program is executed by a processor, the processor executes an engineering calculation method for predicting wall heat flux for different ejected working fluids.

[0063] In conclusion, the present invention introduces the ratio of the average molecular weight of the incoming gas to the average molecular weight of the ejected gas and the ratio of the unit mass enthalpy of the incoming gas to the unit mass enthalpy of the ejected gas on the basis of the existing mass ejection coefficient formula, and at the same time takes into account and The two cases are analyzed, which realizes the rapid and accurate prediction of wall heat flux under different gas ejection working fluids, and the accuracy of this method is significantly higher than the calculation accuracy of the existing mass ejection coefficient formula.

Claims

1. An engineering calculation method for predicting wall heat flux for different ejector fluids, characterized in that: The following steps are involved: S1. Construct an improved formula for mass ejection coefficient, which is expressed as follows: in is the mass ejection coefficient; is the dimensionless ablation mass flow rate; is the wall heat flux when there is gas mass ejection; 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.

2. The engineering calculation method for predicting wall heat flux for different ejected working fluids according to claim 1 is characterized in that: and The values ​​of are 0.3 and 3 respectively.

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

4. The engineering calculation method for predicting wall heat flux for different ejected working fluids according to claim 3 is characterized in that: and The values ​​of are 0.07 and 0.15 respectively.

5. The engineering calculation method for predicting wall heat flux for different ejected working fluids according to claim 1 is characterized in that: Enthalpy per unit mass of gas s The calculation expression is: in is the gas constant of gas s; 、 、 、 、 and is a constant; T is the wall temperature.

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

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

8. The engineering calculation method for predicting wall heat flux for different ejected working fluids according to claim 1, characterized in that: The specific method for calculating the wall heat flux with gas mass ejection using the improved mass ejection coefficient formula in step S2 is: Calculate the recovery enthalpy separately , wall enthalpy , average molecular weight of incoming gas , average molecular weight of ejected gas and unit mass enthalpy; CFD calculation software is used to obtain the wall heat flux when there is no gas mass injection , put the improved mass ejection coefficient formula into it, and get the wall heat flux when there is gas mass ejection , complete the engineering calculation of wall heat flux prediction for different ejector working fluids.

9. A computer device, characterized in that: The invention comprises a memory and a processor, wherein 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 wall heat flux for different ejected working fluids according to any one of claims 1 to 8.

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

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