Enhancing the Performance of Turbine Rows under Nonuniform Inlet Boundary Conditions

Abstract

Some rows of steam and gas turbines, with the exception of the first vanes, operate at the inlet flow conditions created by the upstream turbine stages. In particular, the conditions of the flow at the inlet of a low-pressure turbine vanes (LPT vanes) depend on the upstream high-pressure turbine (HPT). The first stages of the gas turbines are, as a rule, cooled and transonic stages with high power losses; therefore, the nonuniformity of the radial distribution of the angles of flow, the total pressure, and the total temperature may be extremely substantial at the LPT inlet. This leads to increased levels of profile and, especially, secondary losses in the LPT rows. Normally, the LPT vanes have a meridional opening along the inner and outer outlines of the flow path that causes the intensification of the secondary flows and, accordingly, an increase in the secondary losses. To minimize adverse effects on the operation of LPT vanes, such as a nonuniform distribution of the flow parameters at the vane inlet, the meridional opening, and the unfavorable aspect ratio, the width of the blade was increased to decrease the meridional angle of the opening and the three-dimensional design of the vanes was applied to reduce the secondary losses. In particular, variants of the LPT vanes of different spatial configurations were investigated, viz., “reversed bow” vanes, bowed vanes, and leaned vanes in a circumferential direction. The radical change in the vane shape was restricted by the design of the cooling system of the blades that comprises a deflector in the inner hollow of the blade designed to enhance the efficiency of the cooling. As a result, a compromise between the aerodynamic characteristics and the restrictions imposed by the cooling system was found.