凹坑-树状分叉微细通道换热特性的数值研究

Numerical investigation on heat transfer characteristics of the tree-like branching microchannel with dimples

通过求解三维雷诺时均N-S方程和SSG雷诺应力模型,数值研究了透平叶片内部树状分叉微细通道中的流动和换热特性,着重分析了壁面凹坑结构对通道强化换热特性的影响。研究表明:在本文研究结构下,通道分叉引起的纵向涡二次流和凹坑引起的分离涡二次流是通道换热得到强化的主要原因。蒸汽和空气在通道中的二次流涡旋流动特性相似,但热物性的差异使得蒸汽的平均努塞尔数比空气的高约48%～67%。在不同的凹坑流向间距下,蒸汽冷却的摩擦系数比均随着雷诺数的增加先减小后增大,努塞尔数比和强化换热因子则均随着雷诺数的增加而减小。当凹坑流向间距为3时,通道中蒸汽冷却的强化换热性能最佳。

The flow and heat transfer characteristics in the tree-like branching microchannel of gas turbine blades have been studied by adopting three dimensional Reynolds averaged Navier-Stokers equations coupled with the SSG turbulence model,with the effects of dimples on the thermal augmentation analyzed.The results reveal that in the studied structures,the longitudinal vortex flow induced by branches and the disperse vortex flow caused by dimples are the major factors of heat transfer enhancement in the dimpled branching microchannel.The secondary vortex flow fields of steam and air in the microchannel are very similar;however,the averaged Nu number of steam is about 48%~67%higher than that of air due to the differences of thermophysical properties.At the ratio of different streamwise spacing to diameter,the friction factor ratios of steam flow in all microchannels first decrease and then increase with the increase of Re number,and the Nu number ratios and thermal enhancement factors reduce as Re number rises.When the streamwise spacing to diameter ratio is 3,the steam cooling displays the best overall thermal performance.