An Experimental Study on Flow Control with Longitudinal Vortices and Enhancement of Target Plate Heat Transfer

提高燃气涡轮机的工作温度是提高能量转换效率的最基本原则之一。为了实现高温燃气涡轮机，开发有效的涡轮机叶片冷却系统是必不可少的。利用纵向涡强化涡轮机叶片内表面的局部换热是一个值得关注的问题。本文对斜向喷入横流的射流进行了速度测量和换热实验。射流的方向由以下两个角度表征;一个是从安装有射流的板的表面升高的俯仰角，另一个是在横流和投射到安装有射流的板上的冲击射流的方向之间测量的偏斜角。用二维光纤激光多普勒测速仪测量了二元流动，用热致变色液晶进行了传热实验。采用分层神经网络系统将液晶的彩色图像转换为温度分布。速度数据表明，倾斜射流能有效地在横流中产生一对反向旋转的纵向涡。换热强化区与时均速度矢量及其湍流脉动分布有较好的对应关系。结果表明，纵向涡对强化靶板射流冲击换热是有效的。因此，它有望作为一种有效冷却高温燃气涡轮机叶片内表面的手段。

One of the most fundamental principles to improve the energy conversion efficiency is to raise the working temperature of a gas turbine. in order to realize high temperature gas turbine, development of effective cooling system of turbine blades and vanes is indispensable. The attention was paid to the utilization of longitudinal vortices to enhance the local heat transfer from the inner surfaces of turbine vanes, In this study, flow velocity measurements and heat transfer experiments were carried out for a jet obliquely discharged into a crossflow in a duct. The direction of the jet is characterized by the following two angles ; one is a pitch angle raised from the surface of the jet-installed plate, and the other a skew angle measured between the directions of the crossflow and the impinging jet projected onto the jet-installed plate. Two-component flow measurements were made with two-dimensinal optical fiber laser Doppler velocimetry, and the heat transfer experiments were made by making use of a thermochromic liquid crystal. A hierarchy neural network system was applied to convert color images of the liquid crystal into temperature distributions. The obtained velocity data reveal that the inclined jet is effective in generating a pair of counter-rotating longitudinal vortices in the crossflow. The heat transfer enhancement areas correspond well to the distributions of the time-averaged velocity vectors and their turbulent fluctuations. It is demonstrated that the longitudinal vortices are effective in enhancing target plate jet impingement heat transfer. It is, therefore, promising as a means to effectively cool inner surfaces of high temperature gas turbine vanes.