Optimized Shroud Design for Axial Turbine Aerodynamic Performance Available to Purchase

This paper presents a comprehensive study of the effect of shroud design in axial turbine aerodynamics. Experimental measurements and numerical simulations has been conducted on three different test cases with identical blade geometry and tip clearances but different shroud designs. The first and the second test cases are representative of a full shroud and a non-axisymmetric partial shroud geometry while the third test case however uses an optimized partial shroud. Partial shrouds are sometimes used in industrial application in order to benefit from the advantage of shrouded configuration as well as reducing mechanical stress on the blades. However, the optimal compromise between mechanical considerations and aerodynamic performances is still an open issue due to the resulting highly 3-dimensional unsteady flow field. Aerodynamic performance is measured in a low-speed axial turbine facility and shows that there are clear differences between the test cases. In addition, steady and time resolved measurements are performed together with computational analysis in order to improve understanding of the effect of the shroud geometry on the flow field and to quantify the sources of the resultant additional losses. The flow field analysis shows that the effect of the shroud geometry is significant from 60% blade height span to the tip. Tip leakage vortex in the first rotor is originated in the partial shroud test cases while the full shroud case present only a weak indigenous tip passage vortex. This results in a significant difference in the secondary flow development in the following second stator with associated losses that varies of about 1% in this row. The analysis shows that the modified partial shroud design has improved considerably the aerodynamic efficiency of about 0.6% by keeping almost unchanged the overall weight of this component and thus blade root stresses. The work therefore presents a comprehensive flow field analysis and the shows the impact of the shroud geometry in the aerodynamic performance.