旋转状态下孔排构型气膜冷却特性实验研究

Experimental Study of Film Cooling on a Rotating Model with a Single Row of Holes

通过对旋转状态下带有孔排构型平板叶片模型表面的气膜冷却换热特性进行实验研究,得到了不同吹风比、旋转数、主流雷诺数和密度比情况下气膜孔下游流向位置上绝热效率的变化规律,同时提出了一个新的用于评价气膜冷却效果优劣的无量纲参数——有效覆盖率(EAR)。实验采用空气和二氧化碳作为冷却工质,利用热色液晶测温(TLC)技术对测试表面的二维温度场进行测量,并通过旋转拍照系统对液晶图片进行即时采集。研究结果表明,吹风比对旋转状态下二次流的流动形态起着决定性作用。随着吹风比的增大,二次流经历了附壁流动、分离流动和分离再附壁流动3种形态。当旋转数增大时,吸力面和压力面上的绝热效率呈现先上升后下降趋势,且压力面上整体绝热效率要高于吸力面对应值。主流雷诺数的增大导致壁面绝热效率出现降低趋势,但整体冷却效果变化不大;冷气对主流密度比的增大则有助于壁面冷却效果的改善。此外,EAR可以对不同工况下的壁面气膜冷却效果进行量化比较和评判,因而极具工程推广价值。

Distributions of adiabatic film cooling effectiveness for different blowing ratios,rotation numbers,mainstream Reynolds numbers and density ratio are experimentally investigated on a rotating flat blade model with a single row of four injection holes,and a new dimensionless parameter,namely effective area ratio（EAR）,is proposed to evaluate the integrated cooling performance of film cooling.Both the air and carbon dioxide are used as coolant,and the steady-state thermochromic liquid crystal（TLC） technique is employed to measure the temperature profiles on the test surface while the TLC images are recorded instantaneously by means of a rotating shooting system.The results show that the average blowing ratio plays a decisive role in the flow patterns.With the increase of the blowing ratio the coolant flows first appressedly,then separately and then again attaching after separation.With the augmentation of the rotation number,the laterally averaged adiabatic effectiveness on the pressure and suction surfaces increases first but declines again,and overall effectiveness on the pressure surface is superior to that on the suction side.Increase of the Reynolds numbers tends to diminish the adiabatic effectiveness slightly,and coolant with high values of density ratio is prone to improve the final cooling performance.Furthermore,the EAR can provide reasonable evaluation and comparison to cooling performance under different operating conditions.Therefore,it may find wide application in film cooling studies.