| With the rapid development of hypersonic flight technology,the flight speed of aerospace vehicle continues to increase,and the external aerodynamic thermal environment faced by the vehicles has become more and more severe.As a result,thermal protection system has gradually become a technical bottleneck restricting the development of hypersonic flight technology.The transpiration cooling has extremely high cooling efficiency and supports active control.It is very suitable as a thermal protection solution for key high-temperature parts of hypersonic vehicle.Therefore,it has received extensive attention from scientific researchers.At present,the application maturity of transpiration cooling engineering is not high,and there are still some problems to be solved in the coolant injection and control system.For example,common pumps generally work in cyclic reciprocating mode,and there are periodic fluctuations when the coolant is injected.How does the injection method affect the cooling effect of transpiration cooling?In order to adapt to the complex and changing aerodynamic thermal environment,how to control the injection volume of the coolant so as to ensure that the thermal protection structure does not ablate with the minimum consumption of the cooling medium?An accurate control system is inseparable from the effective mathematical model of the controlled object,but the mathematical model used to calculate the transpiration cooling transient process is difficult to solve and takes a long time to solve.How to achieve rapid and effective prediction of the transpiration cooling process under real working conditions?This paper adopts the methods of experiment,theoretical derivation and numerical simulation to study the key issues in the application of transpiration cooling:(1)The influence of periodic injection of coolant on the effect of transpiration cooling.The high-precision screw-type injection pump is selected and the host computer program for controlling various actions of the injection pump is self-compiled,so that the injection flow rate and injection time of the liquid coolant can be accurately online controllable in real time.Then the transpiration cooling experiments on a porous flat-plate with periodic coolant injection are carried out in the subsonic high-temperature wind tunnel.The results show that the periodic injection of coolant would arouse the surface temperature fluctuation of the structure.Finally,measures to reduce the negative impact of surface temperature fluctuation are proposed,which provides a reference for the selection of pumps in the engineering applications of transpiration cooling.(2)Effective simplified model of transient transpiration cooling process.By analyzing the experimental data of the phase change transpiration cooling with periodic coolant injection,a linear simplified transient model for describing the temperature change of the hot surface of the transpiration cooling system and the injection pressure of coolant is proposed,the validity of the model is verified by experiments and the influencing factors of important parameters in the model are analyzed.In addition,by quantifying the relationship between injection mass flow rate and injection pressure of coolant,a linear correlation model between these two variables is obtained and then verified by experiments.These two models support fast and effective calculations of transient transpiration cooling process and can be used as predictive models for transpiration cooling optimal control systems.(3)The design of the optimal control system for gaseous transpiration cooling.The gaseous transpiration cooling process is theoretically analyzed and deduced,and the transient response expression of the surface temperature to the coolant mass flow rate is obtained.The form of this theoretical expression is consistent with the linear empirical model fitted with the experimental data.Based on this model,considering the various interferences in actual applications,the model predictive control scheme with rolling optimization characteristics is selected,and the optimal control system for gaseous transpiration cooling is established,and the given performance is achieved.Optimal control system under optimal indicators and constraints is realized.(4)Optimal control system for transpiration cooling with liquid phase change.Considering that the transient model transpiration cooling with liquid phase change is composed of a large number of coupled nonlinear equations,on one hand it is difficult to obtain an accurate simplified model through theoretical derivation,and on the other hand direct numerical calculation takes a long time and does not have the timeliness of real time control.Therefore,the linear simplified model obtained from the experiment is selected as the predictive model,a parameter estimation scheme is designed to estimate the relevant parameters in the model in real time,the optimal control system based on the model predictive control method is established,and finally a multi-region transpiration cooling scheme is proposed for solving the uneven cooling problem of the traditional transpiration cooling.The multi-region cooling structure and optimal control system provide a reference for the design of the control system for transpiration cooling with liquid phase change in the future. |
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