Investigation On The Flow And Heat Transfer Characteristics Of Mass Injection Pre-cooling In An Aero-turbine Engine

The propulsion power of turbine-based ramjet combined cycle engine can satisfy the wide flight range of aircraft from subsonic to hypersonic,so as to realize “horizontal take-off and landing” and “repeated use”.Due to the effect of stagnation high temperature caused by highspeed airflow at high altitude and high Mach number flight,the turbine engine provides insufficient initial power to the ramjet,which restricts their mode conversion.However,the mass injection pre-cooling technology is an effective way and an important development direction to expand the working range of turboengine.It can reduce the stagnation high temperature air to the normal intake temperature of normal engine,so that the turboengine is not limited to higher flight altitude and Mach number.Since the mass injection pre-cooling engine is based on the existing turbine engine,which has the potential advantages of low cost and fast forming,this will greatly support the research and development of the subsequent highspeed or hypersonic vehicle power technology.Therefore,it is of great engineering significance and scientific value to study the mass injection precooling technology in order to meet the working requirements of turboengine at high Mach number.Aiming at the high-temperature intake problem of an aero-turbine engine,this paper focuses on the effect of mass injection cooling on heat flow and heat transfer characteristics of engine inlet air.A calculation model for the multi-fluid coupling process of inlet air mass injection cooling is established under high-altitude and high-temperature similar flow field.Based on the Eulerian-Lagrangian particle tracking method,the numerical simulation is carried out for heat and mass transfer of air-liquid.Then,the accuracy of the calculation model is verified by the existing test data.Moreover,the mechanism of high-temperature inlet air precooling effect caused by non-equilibrium phase change cooling of low-temperature droplets is revealed.Firstly,the flow and heat transfer characteristics of phase change cooling are conducted thorough research in the pre-cooling section coupled with a compressor.The effect of incompletely evaporated droplets in the pre-cooling section on the flow and stability in the compressor of the downstream engine is analyzed.Then,mass injection conditions on the improvement of inlet temperature and compressor performance are compared at different highaltitude and high Mach flight conditions.The phenomenon of droplet vaporization will induce the non-equilibrium pulsation of flow field in time and space,the flow field based on time evolution is conducive to the analysis of the sensitivity effect of vapor-liquid phase change evaporative cooling on the non-equilibrium flow field.Therefore,an analysis of aerodynamic fluctuation in the time domain can be directly transformed into the fluctuation degree of power spectral density based on the fast Fourier transform(FFT)method.Then,the transient flow features and flow field characteristics of air-liquid two-phase are discussed by the FFT analysis.Moreover,the relationship between mist parameters and fluctuation sensitivity of the flow field is revealed due to the air-liquid coupling cooling,as well as a comparative influence caused by with/without film formation or dry/wet air conditions.Some of the results show that the sensitivity of the mist flow rate to the time-domain fluctuation of the flow field in wet compression is greater than that of the mist diameter.Secondly,in view of the important role of inlet air cooling in improving engine performance,a numerical study is carried out on the pre-cooling section of an actual highaltitude simulation test.Simultaneously,the variation law of the uniform distribution of the velocity,temperature and pressure of the flow field in the pre-cooling section is analyzed.Furthermore,the temperature drop and pressure drop characteristics of the flow field before and after mass injection cooling are compared under different high Mach number intake conditions.Through the analysis of the relationship between the entropy production caused by the flow and heat transfer,it is found that the flow loss in the pre-cooling section with consideration of mass injection device is mainly from the dissipative entropy production caused by the viscous dissipation,while the heating entropy production caused by the temperature gradient change of the flow field from the gas-liquid heat transfer temperature difference is not significant.By optimizing the structure of the mass injection device,the flow loss in the pre-cooling section can be reduced by about 60%.Finally,based on the quadratic regression orthogonal test method,the potential correlation between the multi-factors of mist parameters and the flow field characteristics is established.Then,the effect of cooling parameters on the flow and heat transfer characteristics of the precooled engine is evaluated and predicted.The results show that the relationship between mass injection cooling parameters and both total-temperature drop and total-pressure drop is linear and non-linear,respectively.The droplet size and mist flow rate are the most important sensitive factors for the cooling degree of the flow field,where their contribution shares are 46.57% and43.94%,respectively.However,the droplet size is the most important sensitive factor for flow loss,accounting for 68.63%.Given different mass injection cooling parameters,the mass flow rate of intake air can be increased by 1.54% ? 28.7%.And,within 27 ms,the total-temperature drop coefficient is in the range of 1.57% ? 29.13%(i.e.7.3 ? 135.5 K)after mass injection cooling,and the total-pressure drop coefficient is in the range of 0.461% ? 1.683%,so as to achieve a greater cooling degree and smaller flow loss.