Computational Study of the Effects of Shroud Geometric Variation on Turbine Performance in a 1.5-Stage High-Loaded Turbine

Generally speaking, main flow path of gas turbine is assumed to be perfect for standard 3D computation. But in real engine, the turbine annulus geometry is not completely smooth for the presence of the shroud and associated cavity near the end wall. Besides, shroud leakage flow is one of the dominant sources of secondary flow in turbomachinery, which not only causes a deterioration of useful work but also a penalty on turbine efficiency. It has been found that neglect shroud leakage flow makes the computed velocity profiles and loss distribution significantly different to those measured. Even so, the influence of shroud leakage flow is seldom taken into consideration during the routine of turbine design due to insufficient understanding of its impact on end wall flows and turbine performance. In order to evaluate the impact of tip shroud geometry on turbine performance, a 3D computational investigation for 1.5-stage turbine with shrouded blades was performed in this paper. The following geometry parameters were varied respectively: -Inlet cavity length and exit cavity length, -Shroud overhang upstream of the rotor leading edge and downstream of the trailing edge, -Shroud radial tip clearance, The aim of this paper is to isolate the influence of shroud and cavity geometry modifications on turbine aerodynamic performance and to obtain clear trends of efficiency changes caused by different tip shroud geometry. Moreover, interaction between leakage flow and mainstream for different shroud configuration is also highlighted in order to penetrate into the physical mechanisms producing them. Due to the limitations of the model selected in this paper, the aim of research is not to put forward the design rules of turbine shroud. However, the results obtained from this work will be useful to the integrated design and optimization of turbine with shrouded blades.