Computational investigation of effect of axial spacing on blade row interaction in a 1½ stage axial flow turbine

This paper presents computational investigation of the flow in a 1½ stage axial turbine using finite volume based commercial CFD package namely CFX 5.7.1. The blade row interaction effect is studied in unsteady computations. The effect of axial spacing on the flow field of the turbine is studied for four different axial spacings between the nozzle-rotor and rotor-stator, viz. XS =15%, 25%, 35% and 50%. The computational results are utilized to suggest the optimum axial spacing between nozzle-rotor and rotor-stator blade rows. The results of static pressure coefficient distribution, spanwise variation of lift coefficient in nozzle, rotor and stator, variation of lift coefficient at midspan with axial spacing, contours of total loss coefficient at 5% down stream of nozzle, rotor and stator, distribution of mass averaged total pressure loss coefficient with axial distance, and variation of mass averaged total pressure loss coefficient with axial spacing are presented. The total pressure loss coefficient contours show the clear structure of the vortices and loss cores.