预旋对燃气涡轮排气蜗壳气动性能影响的数值研究

Effect of Preswirl on the Aerodynamic Performance of the Gas Turbine Exhaust Volutes

采用数值求解三维RANS和Realizable k-ε湍流模型的方法对排气蜗壳进行计算,探究燃气涡轮末级叶片造成的进气预旋对排气蜗壳气动性能的影响。数值模拟的排气蜗壳静压恢复系数与实验数据吻合良好。文中研究模型的导叶轴向位置固定,通过改变导叶的偏转角获得排气蜗壳测量段不同的进气预旋,进而研究了7种进气预旋和6种进气流量下,支撑板与导叶在两种不同轴向间距下的排气蜗壳气动性能和流场特性。研究结果表明:在进气预旋为0.3549时,排气涡壳的静压恢复系数达到最大值,这是进出口动压差和总压损失随进气预旋变化的综合结果;超过该进气预旋后,静压恢复系数迅速下降,这是由于此时在支撑板附近产生严重流动分离,总压损失急剧增加所导致;增加支撑板与导叶之间的轴向间距,在预旋小于0.3549的工况下能够提高排气蜗壳的静压恢复系数,在预旋大于0.2338的工况下能够减弱尾缘附近涡系结构,从而减小排气蜗壳的总压损失系数,但也会由于支撑板尾缘到出口距离缩短导致流动发展不充分,从而减弱排气蜗壳出口截面的流场均匀性;支撑板与导叶在两种轴向间距下,总压损失系数均随进气流量的增加呈现降低的趋势。研究工作可为燃气涡轮排气蜗壳设计提供参考。

The effect of preswirl caused by the last stage of gas turbine on the aerodynamic performance of the exhaust volute is numerically investigated using three-dimensional Reynolds-averaged Navier-Stokes(RANS)and Realizable k-εturbulence model.The numerical results of static pressure recovery coefficients of the exhaust volute is well agreeable able with the experimental data.The axial position of the inlet vane of the model is fixed,and the inlet preswirl is obtained by means of changing the inlet vane deflection angle.The aerodynamic performance and flow field of the exhaust volute at seven inlet preswirls and six inlet mass flow rates are numerically conducted for two different axial distances between the inlet vane and strut.The obtained results show that the peak performance of the model’s exhaust volute corresponds to the inlet preswirl around 0.3549,which is the result of the change of the inlet and outlet dynamic pressure and the total pressure loss with the preswirl of the intake air.When the inlet preswirl exceeds this value,the static pressure recovery performance drops rapidly due to the severe flow separation near the strut and the sharp increase in total pressure loss,and raising the axial distance between the inlet vane and strut can increase the static pressure recovery coefficient of the exhaust volute when the inlet preswirl is smaller than 0.3549.When the inlet preswirl is larger than 0.2388 raising the axial distance between the inlet vane and strut can attenuate the vortex structure near the trailing edge and reduce the total pressure loss coefficient.Due to the shortening of the distance from trailing edge to exit,the flow development is insufficient and the flow field uniformity in the outlet section of the exhaust volute is weakened.The total pressure loss coefficient of the exhaust volute shows a decreasing tendency when the inlet mass flow rate increases at two different axial distances.The present work can provide a reference for the design of gas turbine exhaust volutes.