振动凸包控制低雷诺数高负荷低压涡轮叶栅层流分离的数值研究

Numerical Study on Laminar Separation Control UsingDynamic Hump in High-Loaded Low Pressure TurbineCascade at Low-Reynolds Number

关键词:  振动凸包  高载荷低压涡轮  低雷诺数  主动流动控制  附着涡团

Key words:  Dynamic hump  High loaded low pressure turbine  Low Reynolds number  Active flow control  Attached vortices

摘要:

为了抑制高载荷低压涡轮PAKB叶栅在低雷诺数2.5×104工况下的层流分离，在叶片吸力面布置振动凸包进行主动流动控制，凸包为半正弦型几何，以最大振幅1mm、频率200Hz垂直于壁面按正弦波形非定常振动，通过非定常数值方法研究了振动凸包位置、几何宽度对叶栅气动性能的影响。结果表明，最佳振动凸包位置位于峰值速度点上游附近，叶栅总压损失系数相较无控叶栅而言降低28.8%，而位于分离点下游以及峰值速度点远上游的振动凸包恶化了叶栅性能；当振动凸包置于吸力面最佳位置时，凸包几何宽度对叶栅损失的影响较小。振动凸包流动控制机理来源于附着于叶片吸力面的连续凸包脱落涡团，涡团通过增加主流与壁面低能流体之间的能量交换，将低能流体限制于壁面附近，有利于抑制大尺度流动分离。

Abstract:

To alleviate the laminar separation on high loaded low pressure turbine cascade of PAKB that operating at low Reynolds number of 2.5×104， a dynamic hump was arranged on the suction surface of the blade for active flow control. The hump， shaped as half sinusoidal， vibrated normal to the blade surface in sine wave， with maximum amplitude of 1 mm and frequency of 200Hz. The effects of hump location and width on cascade performance were studied through unsteady numerical simulation. The cascade with dynamic hump located upstream and close to the peak velocity point has the lowest total pressure loss coefficient， which is reduced by 28.8% compared with uncontrolled cascade. When the hump is placed downstream of separation point or far upstream of peak velocity point， the cascade performance grows worsen. It is also revealed that the effects of hump width on cascade performance are small when putting the hump at the optimum location. The flow control mechanism of laminar separation comes from the continuous small laminar vortices that are detached from the dynamic hump and attached to the suction surface. Continuous vortices confine the low-energy fluid near the suction surface by energy exchange between the free flow and near-wall flow， which suppress the large-scale flow separation.