摘要
In gas turbines,there are strong flow interactions between the last stage turbine and the exhaust diffuser which have a significant influence on the aerodynamic performance of the turbine and diffuser.The supporting strut in the diffuser plays a major role in the coupled flow between the turbine and the diffuser.But the influence mechanism imposed by strut on the coupled flow is not fully understood.In this paper,the effects of the strut on the flow pattern evolution and aerodynamic performance of the coupled system are numerically investigated.A full-scale last stage turbine and exhaust diffuser are included in the calculation domains to obtain the full velocity coupling flow field.Annular diffusers with or without struts were designed and compared under different operational conditions.Qualitative and quantitative coupling relationships between the turbine and the exhaust diffuser in terms of flow and performance were concluded and validated in this paper.Under the different operational conditions,the sum of the static pressure coefficient and the total pressure loss coefficient tends to be a constant which is related to the inflow Mach number,the area ratio,and flow uniformity at inlet and outlet of the diffuser no matter with or without strut.There is an exponential relationship between the efficiency of the turbine and the static pressure recovery coefficient of the diffuser.The struts cause the circumferential non-uniformity flow field in the turbine passages,but impose slight influences on the radial distributions of the averaged flow parameters at the turbine exit.The struts help to suppress the vortices near the diffuser case and induce flow separation under the conditions of strut’s attack angle larger than±20°,which results in the performances of the diffuser and turbine fluctuate within a wider range due to the changes of the operational conditions.
基金
supported by the National Science and Technology Major Project (J2019-Ⅱ-0017-0038).
