扇形喷孔气膜冷却流场的大涡模拟

Large Eddy Simulation on Field of Film Cooling with a Cone-shaped Hole

对锥形角γ=30°扇形喷孔横向紊动射流进行了大涡模拟，在吹风比M=1．0工况下模拟了不同截面上涡量随时间变化的过程，并对各种涡的流动机理进行了分析．结果表明：对称面的正、反向旋转涡、垂直截面的马蹄形涡的两翼周期性地交替脱落成新的涡，对称面涡的周期为0．024S，马蹄形涡的周期为0．032S；反向旋涡对气膜冷却流场有重要影响，沿主气流流动方向的无量纲长度X／D在1～2时，反向旋涡的涡量值逐渐衰减；当X／D〉4时，反向旋涡开始逐渐消失，导致壁面附近的能量交换快，对底面的冷却效果好；由于在射流上游和下游的压力梯度不等，造成射流两侧的脉动速度变化不一致，导致了反向旋涡的不对称分布．

Large eddy simulation （LES） was performed on turbulent motion caused by the injections through a cone-shaped hole with γ= 30° into cross-flow. The development process of vorticity on different sections under the condition of blowing rate M= 1. 0 was simulated. The flow mechanism of various vortices was analyzed. The results show that the positive and negative vortices in the centreplane and the two wings of the horseshoe vortices in the vertical profiles are alternately shed off to form new vortices periodically with period of 0. 024s and 0. 032 s separately. The counter-rotating vortex plays an important effect on the fields of film cooling. The vorticity of counter-rotating vortex decays gradually with the dimensionless length of X/D along the main steam＇s flow direction within the range of 1～2. When X/D〉 4, counter-rotating vortex is vanishing. This causes quick exchanging of energy near the wall and further makes good cooling effectiveness on bottom surface. Because of unequal pressure gradients between the upstream and downstream of the injections, the variation of fluctuating velocity on either sides is not the same, and the counter-rotation vortex is not symmetry distributed.