Numerical Investigation On Temperature Distribution Of Aerodynamic Heating Surface With Liquid Nitrogen Cooling

Suppressing the infrared singles from the aircraft skin has become even more important for the infrared stealthy technology as the development of IR detector system and guided weapons. As the aircraft skin temperature distribution is a key factor affecting the infrared radiation characteristics of aircraft, it is needed to investigate the temperature distribution and control for the aircraft skin. The present paper includes two main aspects:1. By analyzing the heat transfer process governing the aircraft skin temperature, the physical and mathematical model for the transient heat transfer coupling the aerodynamic heating on the skin and radiative heat transfer and internal convective heat transfer was put forward. The aerodynamic heating condition on aircraft skin was transfered as the floating heat flux thermal boundary by introducing a wall heat flux function and the numerical simulations for a simplified two-dimensional flat plate were made to study the transient temperature response under various flight statuses. It is obtained that the thermal response lags were distinct during the acceleration and deceleration of aircraft, and the inner cooling condition affects the thermal response obviously.2. The commercial flow solver FLUENT CFD software was utilized to numerically simulate the heat transfer of liquid nitrogen through a two-dimensional narrow rectangular channel and a three-dimensional narrow channel with a row of 30°angling film-cooling holes, respectively.The mixture multiphase model and expressions of liquid nitrogen properties presented by Lemmon were adopted and the user-defined functions (UDFs) were introduced to simulate the properties of liquid nitrogen and the transfers between gas phase and liquid phase. The heat transfer of liquid nitrogen through a two-dimensional narrow rectangular channel, with one side surface simulating aerodynamic heating flux condition and the other side surface as adiabatic condition was numerically investigated. The results indicat that the liquid nitrogen enhanced heat transfer insides the narrow channel provides an efficient cooling on the surface suffering aerodynamic heating flux. The increase of liquid nitrogen mass-flux leads to heat transfer enhancement and the extending of channel length affects the cooling effectiveness positively with a constant ratio between mass flux and cooling area. The adiabatic film cooling effectiveness and overall cooling effectiveness for the liquid nitrogen cooling narrow channel with a row of film cooling holes were studied. The effects of the film holes arrangement, blowing ratio (or primary to secondary mass flux ratio) and primary flow Mach number on the cooling characteristics were concluded. The results show that the cooling configuration is an efficient cooling mode for the aerodynamic heating skin. The cooling effectiveness would be enhanced with a suitable mass-flux and better film holes arrangement.