Abstract:

Based on the cooling heat transfer in the air-kerosene heat exchanger for aero-engine applications, numerical studies on the heat transfer of supercritical-pressure RP-3 aviation kerosene in vertical U-turn circular tubes have been carried out. The heat transfer characteristics and heat transfer mechanisms of the inlet vertical section, the bend section, and the outlet vertical section were explored. The influence mechanisms of operating pressure and heat-mass ratio on heat transfer were analyzed. The results show that the inlet vertical section presents the characteristic of uniform heat transfer. The centrifugal force in the bend section leads to the abnormal stratification of fluid temperature, the uneven circumferential density distribution, and the lateral unbalanced kinetic energy, thus induces the strong secondary flow phenomenon. The maximum secondary flow velocity reaches 0.45 m·s^-1. The heat conduction process in the solid region is also affected, and the abnormal stratification of solid temperature is observed. The combined effect results in the circumferential differences in inner-wall temperature and heat flux. The circumferential heat transfer difference in the outlet vertical section still exists, and the secondary flow is weakened. Increasing the operating pressure or reducing the heat-mass ratio, the thermo-physical properties with more moderate variations in tube cross sections, and the difference in circumferential heat transfer is weakened.

Key words: supercritical fluid, aviation kerosene, heat transfer, centrifugal force, secondary flow, numerical analysis

摘要：

基于航空发动机空-油换热器的冷却换热问题，开展了竖直U形圆管内超临界压力RP-3航空煤油换热的数值研究。探究了进口竖直段、弯管段、出口竖直段的换热特征和换热机理，阐述了运行压力和热质比对换热的影响机制。结果表明：进口竖直段呈现均匀换热的特征。弯管段离心力作用致使流体温度出现异常分层，周向密度不均匀，横向不平衡动能诱发强二次流问题，最大二次流速度达到0.45 m·s^-1。固体热传导过程也受到影响，出现固体温度异常分层。两者综合作用下导致管壁温度和热通量的周向差别。出口竖直段的周向换热差别依然存在，二次流被削弱。提高运行压力或降低热质比，管截面热物性变化趋缓，周向换热差别减弱。

关键词: 超临界流体, 航空煤油, 传热, 离心力, 二次流, 数值分析