Simultaneous kHz-rate temperature and velocity field measurements in the flow emanating from angled and trenched film cooling holes
Simultaneous kHz-rate temperature and velocity field measurements in the flow emanating from angled and trenched film cooling holes
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DOI：
10.1016/j.ijheatmasstransfer.2016.06.092
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发表时间：
2016-12-01
影响因子：
5.2
通讯作者：
Pfitzner, M.
中科院分区：
文献类型：
--
作者：
Schreivogel, P.;Abram, C.;Pfitzner, M.
为了设计更高效的燃气轮机气膜冷却几何形状，需要在定义明确的通用流动配置中对流动温度、速度和湍流热通量等导出量进行非侵入式测量。有了这个目的，我们已经应用热粒子图像测速（热像层）调查的流动产生的角度和沟槽冷却孔在一个闭环的光学可访问的风洞设施。BAM：Eu 2+热成像磷光体颗粒作为示踪剂被接种到流中。一个脉冲高速紫外激光被用来激发粒子和发光检测使用两个高速摄像机，以确定温度场的双色比率法。采用普通高速PIV测量了流场。同时测量的字段采样率为6 kHz的垂直平面通过对称的单排冷却孔的中心线。选择冷却空气和加热主流的流量和温度，以分别实现1.6和8的密度和动量通量比。在这些条件下，平均温度场和RMS温度场表明，对于普通的倾斜孔，射流与表面分离。相比之下，沟槽几何形状导致冷却膜附接到表面。然而，时间分辨图像序列显示热空气突破冷却膜并几乎到达表面的情况。倾斜孔的类似图像序列显示，分离的冷却剂射流在下游变得不稳定，并且冷空气袋被喷射到主流中。这种不稳定性可以部分解释观测结果，即测得的湍流热通量朝向冷核，但偏离平均温度梯度的方向，从而与RANS模拟中常用的简单梯度扩散假设相矛盾。(C)2016年6月，作者。爱思唯尔有限公司出版
To design more efficient film cooling geometries for gas turbines, non-intrusive measurements of the flow temperature, velocity and derived quantities like the turbulent heat flux are needed in well-defined, generic flow configurations. With this aim we have applied thermographic particle image velocimetry (thermographic Ply) to investigate the flow emanating from angled and trenched cooling holes in a closed-loop optically-accessible wind tunnel facility. BAM:Eu2+ thermographic phosphor particles were seeded into the flow as a tracer. A pulsed high-speed UV laser was used to excite the particles and the luminescence was detected using two high-speed cameras to determine the temperature field by a two-colour ratiometric approach. The velocity field was measured using ordinary high-speed PIV. The simultaneously measured fields were sampled at a rate of 6 kHz in a vertical plane through the centreline of the symmetrical single; row cooling holes. The flowrate and temperature of the cooling air and heated main flow were chosen to achieve density and momentum flux ratios of 1.6 and 8 respectively. For these conditions the average and RMS temperature fields show that for ordinary angled holes the jet is detached from the surface. In contrast, the trenched geometry leads to a cooling film attached to the surface. However, time-resolved image sequences show instances where hot air breaks through the cooling film and almost reaches the surface. Similar image sequences for the angled holes show that the detached coolant jet becomes unstable downstream and pockets of cold air are ejected into the main flow. This intermittency may in part explain the observation that the measured turbulent heat flux is oriented towards the cold core, but deviates from the direction of the mean temperature gradient, thereby contradicting the simple gradient diffusion hypothesis commonly used in RANS simulations. (C) 2016 The Authors. Published by Elsevier Ltd.