Effects of axial gap on unsteady secondary flow in one-stage axial turbine

Flow through turbomachinery under stage environment has a very complex structure and is intrinsically unsteady. Especially, recent design trends to the turbomachinery with a short axial gap make the flow extremely complex due to the interaction between stator and rotor. In this paper, effects of axial gap on the unsteady secondary flow and performance in the one-stage turbine are investigated by three-dimensional unsteady flow analysis. The three-dimensional solver is parallelized using domain decomposition and Message Passing Interface(MPI) standard to overcome the limitation of memory and save the CPU time in three-dimensional unsteady calculation. A sliding mesh interface approach has been implemented to exchange flow information between blade rows. It is confirmed in the present study that the upstream flow fields have great effects on the unsteady secondary flow fields and performance at the minimum efficiency instant but have relatively weak effects at the maximum efficiency instant according to the variation of axial gap.