The Importance of Shroud Leakage Modelling in Multistage Turbine Flow Calculations

Three-dimensional steady multistage calculations, using the mixing plane approach, are compared with experimental measurement in a low speed 3-stage model turbine. The comparisons are made with two levels of shroud seal clearance, one representative of a real turbine and one with minimal seal clearance and almost no shroud leakage. Three different calculations are compared. The first computes the main blade path with no modelling of shroud leakage. The second includes a simple model of shroud leakage using sources and sinks on the end-walls and the third is a multiblock calculation with all leakage paths and cavities computed. It is found that neglect of shroud leakage makes the computed velocity profiles and loss distributions significantly different to those measured. Simple modelling of shroud leakage gives some improvement but full calculation of the leakage flows and cavities is necessary to obtain good agreement between calculation and measurement.