进口不重合和轴对称造型对跨声速涡轮叶栅端壁传热特性的影响

为有效评估实际燃气涡轮叶栅进口端壁不重合和轴对称收敛端壁造型对叶栅端壁传热特性的影响,以某工业燃气涡轮第一级跨声速导向叶栅为研究对象,基于商用CFD软件ANSYS Fluent 15.0,研究了3种端壁结构:简化平板端壁、具有子午面轴对称收敛造型的实际涡轮叶栅外端壁(叶顶)和内端壁(叶根)在设计工况(进口湍流强度为16%,出口马赫数为0.85)下的流动和传热特性。计算分析了2种进口端壁不重合度(进口后向台阶高度为0、 6.78 mm)下,3种叶栅端壁结构的端壁热负荷分布、近端壁二次流结构和后台阶涡系发展。结果表明:轴对称收敛端壁造型和进口端壁不重合均会显著改变叶栅端壁二次流结构和热负荷分布规律;轴对称收敛端壁造型可在一定程度上减小端壁热负荷,尤其是叶片前缘肩部和喉部下游等易发生热腐蚀的冷却气膜难以覆盖区域;燃气涡轮实际运行中产生的进口端壁不重合导致叶栅前缘上游典型高传热区面积和强度(增大约140%)显著增大并向叶栅通道内迁移,使叶栅端壁承受着极高热负荷;实际燃气涡轮第一级导向叶栅端壁冷却方案设计必须充分考虑实际端壁造型结构和燃烧室-涡轮交界面端壁不重合对端壁热负荷分布的影响。 

Effects of inlet misalignment and axisymmetric contouring on endwall heat transfer characteristics in transonic turbine cascade

To evaluate the effects of endwall misalignment and axisymmetric endwall contouring on the endwall heat transfer characteristics in the realistic transonic gas turbine cascade, the guide cascade in the first stage of an industry gas turbine was taken as the research object. The commercial CFD software ANSYS Fluent 15.0 was adopted to numerically investigate the endwall flow and heat transfer characteristics for three types of endwall configurations, including: the simplified flat endwall, the realistic cascade outer endwall (vane shroud) and inner endwall (vane hub) with axisymmetric convergent endwall contouring in axial direction, at the gas turbine design condition (inlet turbulence intensity of 16%, exit Mach number of 0.85). The endwall thermal load distribution, secondary flow field near endwall and backward step vortices development were illustrated and compared for three endwall configurations with two combustor-turbine platform misalignment structures (inlet endwall step height of 0, 6.78 mm). Results showed that compared with the flat endwall configuration, the axisymmetric convergent endwall contouring and upstream endwall misalignment can result in dramatical changes in the endwall secondary flow pattern and thermal load distribution. In general, the axisymmetric convergent endwall contouring can result in a relative reduction in the endwall thermal load, especially for regions of endwall juction around the vane leading edge and downstream the vane throat, where thermal corrosions were more likely caused due to the poor cooling film coverage. In real gas turbine engines, the combustor-turbine endwall misalignment can dramatically enlarge the high thermal load region (upstream the cascade leading edge) which was migrating to the downstream cascade passage, and result in a significant increase (up to 140%) in the heat transfer level. Therefore, the important influences of the endwall contouring and endwall misalignment should be carefully taken into account for the endwall cooling scheme design of the first stage guide cascade in the real gas turbine engines.