Numerical investigation on effect of heat transfer on tip clearance flow in micro centrifugal impellers

Three-dimensional numerical simulations were carried out on a centrifugal micro impeller under adiabatic and isothermal wall temperature boundary conditions in order to compare the impeller performance and the detailed flow features affected by heat transfer. The comparison was especially focused on the heat transfer effect on tip clearance flow in micro centrifugal impeller. It is found out that the performance of impeller is mainly attributed to the influence of heat transfer on tip clearance flow. The trajectory of tip clearance flow develops along the suction side of the blade towards impeller outlet under adiabatic condition, while the tip clearance flow is driven away from the suction side of the blade towards the pressure side of the adjacent blade when heat transfer is involved. Meanwhile, heat transfer also lead to the increase of mixing between tip clearance flow and the main flow resulted in greater loss. Although heat transfer can reduce the pressure gradient within blade passage to certain extent as compared with adiabatic condition, it eventually causes more tip blockage in impeller passage as the initial tip clearance blockage was enlarged due to heat addition.