瞬态热冲击缝槽气膜冷却传热实验及仿真研究

Experimental Investigation and CFD Simulation of

关键词:  瞬态热冲击  缝槽气膜冷却  实验研究  DES仿真分析

Key words:  Transient thermal shock  Slot film cooling  Experimental investigation  DES approach

摘要:

为了分析瞬态热冲击过程中气膜冷却传热规律，采用实验研究和CFD仿真分析方法，研究了瞬态热冲击工况下的平板缝槽气膜冷却传热特性。实验中，主流燃气以约60℃/s～100℃/s的增温速率来模拟瞬态热冲击工况，CFD仿真中，采用DES方法模拟瞬态混合层剪切涡结构对气膜冷却传热影响。结果表明:(1)实验结果显示，当吹风比处于临界值以下时，瞬态热冲击过程中，气膜绝热有效温比逐渐下降直至稳态值，对流换热系数存在同样的规律。(2)DES模拟结果显示，混合层摆动位置及剪切涡发展到壁面的位置随着吹风比的增大而向下游移动，使得壁面传热特性主要由剪切涡流决定逐渐转变为由冷却气流决定。(3)DES结果显示由于混合层剪切涡的不稳定性使得气膜绝热有效温比存在较大幅度的波动；相比RANS方法，DES方法预测的平均绝热有效温比与实验结果吻合更好。

Abstract:

In order to identify the heat transfer of film cooling under thermal shock conditions，the performance of a slot film cooling scheme over a flat plat was analyzed using experimental technique and CFD approach. It was assumed that the slot film cooling scheme was tested under the transient thermal shock conditions performed by the mainstream temperature gradient ranging from 60℃/s to 100℃/s，and calculated using DES(Detached eddy simulation) model to estimate the effects of coherent shear vortex created by the mixing layer on the heat transfer. It is found that: (1)When the blowing ratio is under the critical one，the adiabatic effectiveness and convective heat transfer coefficient of the slot film cooling scheme decreases during the thermal shock course. (2)The results of DES show that the locations of shear vortex begins to swing and attach the wall move along while the blowing ratio increases，and which，gradually makes the cooling air performance instead of the shear vortex performance as the dominant factor that influence the heat transfer. (3)The adiabatic effectiveness is found to be highly oscillatory，which is mainly caused by the fluctuation of the unsteady vortex structures in the mixing layer. Compared with RANS method，DES approach performs more efficiently in predicting the adiabatic effectiveness.