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Basic Research on Heat Transfer Augmentation in Rotating Boundary Layers

旋转边界层强化传热的基础研究

基本信息

批准号：
11650189
负责人：
MASUDA Shigeaki
金额：
$ 2.18万
依托单位：
Keio University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

In order to obtain fundamental knowledge for heat transfer augmentation in rotating machinery, the influence of system rotation on the heat transfer characteristics of transitional and turbulent zero-pressure gradient boundary layers have been experimentally investigated. A test plate is installed in a wind tunnel, which is rotatable around the axis parallel to the plate leading edge with constant speed of rotation. Local heat transfer coefficient during rotation is determined by employing a temperature sensitive liquid crystal. The thermo-couples were employed for compensation of conductive heat loss to the solid wall. Effects of the Coriolis force and the centrifugal buoyancy force have been examined by comparing the heat transfer coefficient with different freestream velocity, rotational speed and wall temperature.When the Coriolis force acts toward the wall, heat transfer in a laminar boundary layer is dramatically enhanced. This can be explained by generation of streamwise vortices by Coriolis torque and resulting enhancement of transverse convection of energy. The turbulent heat transfer is slightly enhanced by wall-ward Coriolis force, which may be attributed to the elevated turbulent diffusion through the modifications of turbulent eddies by system rotation.For the opposite direction of rotation, Coriolis force stabilization exhibits no systematic effect on a laminar heat transfer, while it causes the slight decrease in heat transfer coefficient in a turbulent boundary layer. The latter is attributed to the attenuation of turbulent diffusion by Coriolis stabilization.The centrifugal buoyancy enhances the turbulent heat transfer both in pressure and suction side boundary layers. It has been suggested that this effect may be due to the modified convection through the buoyancy term in the Reynolds stress equation.

为了获得旋转机械内强化换热的基础知识，实验研究了系统旋转对过渡和湍流零压力梯度边界层换热特性的影响。风洞中安装有试验板，试验板可绕平行于试验板前缘的轴线以恒定的速度旋转。旋转过程中的局部换热系数是通过使用温度敏感液晶来确定的。采用热电偶对固体壁导热损失进行补偿。通过比较不同自由流速度、转速和壁温下的换热系数，考察了科里奥利力和离心浮力对换热的影响。当科里奥利力作用于壁面时，层流边界层内的换热显著增强。这可以用科里奥利力矩产生的流向涡以及由此导致的能量横向对流的增强来解释。向壁方向的科里奥利力对湍流换热有轻微的强化作用，这可能是由于系统旋转对湍流涡旋的修正导致了湍流扩散的加剧，而对于相反的旋转方向，科里奥利力稳定化对层流换热没有系统的影响，而使湍流边界层内的换热系数略有下降。后者归因于科里奥利稳定化对湍流扩散的抑制作用，离心力强化了压力面和吸力面边界层内的湍流换热。这种影响可能是由于雷诺应力方程中浮力项的修正对流所致。