基于时间推进法的涡轮通流设计

Turbine through flow design based on time-marching method

为建立合理的涡轮设计参数计算方法,保证设计准确性,基于Euler方程时间推进通流设计方法,提出了一种基于二次函数的叶排通道S2流面周向角和堵塞系数近似计算方法。通流设计方法利用有限体积法求解正交曲线坐标系下的二维非守恒型Euler方程,使用Riemann精确解确定网格单位界面参数,采用具有TVD性质的3阶精度Godunov格式,时间方向采用半隐式格式。利用经验损失模型计算叶型损失、二次流损失和叶尖间隙泄漏流损失,并将二次流损失和叶尖间隙泄漏流损失沿径向进行重新分布,而激波损失被认为是可以准确计算。对某型单级涡轮进行了通流设计研究,并根据通流设计结果进行了三维叶片造型,利用三维黏性CFD软件对涡轮进行数值模拟,校验了通流设计方法的有效性。当涡轮进出口条件一定时,相比于三维CFD结果,通流流量结果高约1.46%,膨胀比低0.005,绝热效率高0.007 7。最后可以得到如下结论:通流设计方法所需网格量少,计算效率高,收敛性好;叶排通道S2流面周向角和堵塞系数计算方法合理;涡轮总体性能参数,以及流量系数、载荷系数和反力度等无量纲参数计算准确度较高。

To establish reasonable turbine design parameter calculation method and guarantee the accuracy of design work on the basis of quadratic function,an approximate computation method of S2stream surface circumferential angle and blockage coefficient inside blade row passage was proposed for Euler equation time-marching through design method.The through-flow design method utilized finite volume method to solve 2D unconservative Euler equation in orthogonal curvilinear coordinate.Exact Riemann solution was used to calculate interface parameters of grid element.And third order Godunov scheme with TVD property was implemented.While semi-implicit scheme was employed in temporal discretization.The blade profile loss,secondary loss,and blade tip clearance leakage loss were computed by empirical loss model.Then secondary loss and tip clearance leakage loss could be redistributed radially.On the other hand,shock wave loss was regarded as accurate after solution.A single stage turbine was then designed with the through flow design method.After that,3D blade shapes were profiled according to through flow result.Next,3D viscous CFD software was used to simulate turbine and verify the effectiveness of through flow design method.Given the same inlet and outlet conditions,compared with3D result,through flow mass flow result was about 1.46% higher,expansion ratio was 0.005 lower,and isentropic efficiency was 0.007 7 higher.Finally,it can be concluded that through flow design method required fewer grid points,featuring higher computation efficiency with favorable convergence.Besides,the calculation method of blade row passage S2 stream surface circumferential angle and blockage coefficient was rational.And also,accurate results of turbine overall performance,as well as dimensionless parameters like flow coefficient,loading coefficient and reaction could be obtained.