低压透平叶片表面合成射流非定常流动控制机理研究

Unsteady Flow Control Mechanism of Synthetic Jet on a Low Pressure Turbine Blade

基于Langtry-Menter转捩模型的SST湍流模型,通过求解三维非定常雷诺时均Navier-Stokes方程,数值研究了低雷诺数下合成射流涡发生器对Pak-B低压透平叶片吸力面流动分离的影响,揭示了低压透平叶片表面合成射流非定常流动的控制机理.结果表明,引入合成射流涡发生器能够抑制甚至消除低雷诺数下叶片吸力面上的流动分离.在雷诺数为25 000、自由流湍流强度为0.08%下,提高射流控制频率有助于增强合成射流涡发生器对低压透平叶片表面流动分离的控制效果,减少流动损失.当控制频率为10Hz时,叶栅出口的相对总压损失系数为0.42;当控制频率增加到20Hz时,相对总压损失系数仅下降到0.41.这表明,当合成射流控制频率大于10Hz时,继续增加控制频率来减少叶片表面流动损失的效果是不明显的.

The three-dimensional viscous unsteady Reynolds-averaged Navier-Stokes equations were solved to simulate the flow on a low pressure turbine blade.The effects of synthetic jet on the flow separation in the suction side of the Pak-B low pressure turbine blade were numerically investigated by the SST（shear stress transport） turbulence model coupled with the Langtry-Menter transition model for turbulent flow.The unsteady flow control mechanism of synthetic jet and the flow structure were also presented.The numerical results show that the flow separation in the blade suction side can be effectively suppressed even eliminated by introducing the synthetic jet with the proper control frequency.At the Reynolds number of 25 000 and the free stream turbulence intensity of 0.08%,the increase in synthetic jet frequency can improve the control effectiveness of the flow separation on the low pressure turbine blade and reduce the flow loss.When the synthetic jet frequency is 10 Hz,the flow loss coefficient relative to the total pressure at the turbine blade exit is 0.42.However,the relative loss coefficient decreases to only 0.41 when the synthetic jet frequency increases to 20 Hz.These results imply that the flow loss does not drop clearly for the low pressure turbine blade at low Reynolds number when the synthetic jet frequency is greater than 10 Hz.