The effect of shroud design on flow structure at the tip area and stage efficiency

Last blades of heavy-duty gas and steam turbines have shrouds to avoid dangerous resonance frequency. In this paper, a numerical investigation of the flow structure around full and partial shrouds with various geometries and the effect of the various shrouds on the turbine stage efficiency are carried out. Moreover, stage efficiencies for shrouded and unshrouded blades are compared. Taking into account the fact that shrouds run in high temperature conditions, the adiabatic temperature distribution on the shroud surface is analyzed. In particular, effect of the vortex system downstream of the shroud fin and features of the shroud geometry on the non-uniform heating of the shroud surface is demonstrated. Two methods have been used to cool the shroud: cool air injection into a cavity upstream of the shroud and through profiled slot downstream of the fin. In order to validate numerical results, experimental data of a turbine stage with shrouded blade was used.