涡轮叶片对流换热对周期性波动气流状态的瞬时响应特性与机理研究

Convective heat transfer processes on turbine blades are inherently unsteady due to the periodically unsteady aero-thermal conditions around the turbine blades. In the current proposal, time-resolved characteristics of heat transfer on a turbine blade under time-periodic aero-thermal situations, including periodic variations in flow temperature, in flow velocity and in both, will be investigated. Time-resolved heat transfer measurement technique will be employed to obtain the time-resolved response characteristics of the heat transfer parameters, including heat transfer coefficient and heat flux, to the periodically pulsating aero-thermal behaviors in frequency, amplitude and phase. The flow characteristics around the turbine blade are complex and different in space-distribution under unsteady aero-thermal conditions. The differences in the time-resolved response characteristics of the heat transfer parameters on different regions of the turbine blade model will be analyzed to find out the regular patterns and reasons for the influences of the complex flow features. Time-resolved numerical simulations, including LES and URANS, will be performed to study the instantaneous distribution features of the flow and temperature field in the unsteady convective heat transfer process. These numerical studies can help to obtain deep insight into the mechanism for the time-resolved response characteristics of the unsteady heat transfer parameters on the turbine blade to the instantaneous flow state under periodic aero-thermal conditions.This research proposal is of much academic significance in the research on turbine blade's unsteady heat transfer characteristics under complex unsteady aero-thermal conditions, and can help to obtain deeper insight into the instantaneous correlation rules and mechanism between the unsteady heat transfer behavior on the turbine blade and the unsteady flow conditions.

在叶栅风洞中研究周期性波动气流温度和周期性波动气流速度在各自单独作用、以及共同作用条件下的涡轮叶片外表面非定常对流换热的瞬时特性与机理。通过可获得时间分辨结果的测量方法，突破常规时均测量方法的局限，揭示周期性气动-热条件下的涡轮叶片对流换热特性参数（对流换热系数与热流）在频率、振幅和相位上对周期性波动气流状态的瞬时响应特性；针对非定常条件下涡轮叶片上的流动特性复杂且空间分布差别大的特点，分析涡轮叶片不同区域的对流换热特性参数在瞬时响应特性上的差别，揭示复杂流动特性影响非定常对流换热瞬时特性的规律和原因；应用大涡模拟等非定常数值模拟方法，分析周期性气动-热条件下涡轮叶栅中流场/温度场的瞬时分布特性，揭示非定常对流换热过程中涡轮叶片外表面对流换热特性对气流状态的瞬时响应机理。本项目有助于深入认识非定常气动-热条件下涡轮叶片对流换热的瞬时特性及其与非定常气流状态之间的瞬时关联机制。

本项目以新一代高性能航空发动机涡轮叶片的精细化传热分析为背景，通过研究分析非定常气动-热环境下涡轮叶片前缘、压力面和吸力面三个典型区域内的非定常对流换热系数，揭示了气流温度单独波动、气流速度单独波动与气流温度-速度共同波动条件下的涡轮叶片非定常对流换热系数的瞬时行为特性与发生机理、以及主要影响因素的影响机理。研究发现：基于SST k-ω湍流模型的非定常RANS方法可以准确计算平板、涡轮叶片前缘、压力面与吸力面非定常对流换热系数在周期性波动气流温度下的非定常波动行为，是非定常对流换热数值计算的合适方法；非定常气动-热条件下的涡轮叶片对流换热系数有着与传统认识完全不同的瞬时行为特性，以主流温度定义的对流换热系数受非定常气流温度的影响非常显著，在气流速度恒定的条件下仍表现出强烈的非定常波动特性，尤其是在湍流条件下，这个新发现与湍流对流换热系数对气流温度波动不敏感的传统观点完全不同；涡轮叶片前缘、压力面与吸力面的非定常对流换热系数随着壁面热边界条件的改变而表现出不同的波动强度，但总体而言，非定常对流换热强度随着气流温度-速度波动频率的增加，而且气流温度波动的影响随着波动频率的增加而逐渐增强；基于本项目发展建立的温度瞬态项空间分布分析法，我们研究发现非定常气动-热条件下的涡轮叶片对流换热系数瞬时行为特性主要决定于对流换热系数参考温度的选取与壁面热流的时变特性，当以绝热壁温为参考温度定义对流换热系数时，壁面热流的时变特性是决定对流换热系数瞬时行为特性的关键因素，当壁面热流随时间变化时，即便是在恒定的气流速度-温度条件下，非定常壁面热流仍会诱发非定常的对流换热系数。以上研究成果揭示了传统准稳态假设在非定常对流换热分析中的不足及其内在原因，获得了非定常气动-热条件下涡轮叶片对流换热系数的非定常行为与主流/边界层内气流状态参数及壁面热边界条件的关联机制，对提高我国航空发动机高温部件传热分析的准确度有重要参考价值。