Aerodynamic character of partial squealer tip arrangements in an axial flow turbine. Part I: Detailed aerodynamic field modifications via three dimensional viscous flow simulations around baseline tip

This paper deals with the viscous flow simulations of the complex tip leakage flow in Axial Flow Turbine Research Facility (AFTRF). Special attention is paid to the 3D structure of the tip leakage flow mechanisms in a baseline tip configuration with no desensitisation. Although past experimental studies provide much insight into the physical understanding of the tip region aerodynamics, there are still many areas of the flow-field in which experiments are extremely difficult to perform. Fine details of the entrance flow near the pressure side where the tip leakage jet starts to form, the leakage jet formation between the tip surface and outer casing, the re-circulatory flow zone very near the pressure side corner, the interaction area of the tip vortex with the conventional passage flow, the influence of the relative motion of the outer casing and leakage flow reversal can be visualised with excellent resolution. After the presentation of the measured inlet boundary conditions and a grid independency study, the baseline tip flow simulations are discussed in detail.