EFFECT OF VARIABLE TIP CLEARANCE AT THE INLET AND EXIT OF A RADIAL IN-FLOW TURBINE

Radial inflow turbines are widely used in turbochargers, in which they drive the centrifugal compressor, and in auxiliary power units (APUs). Losses in a radial inflow turbine are comprised of profile losses, secondary losses and clearance losses. Therefore, in order to increase the efficiency of the radial inflow turbine, it is necessary to keep the losses due to clearance too as low as possible. There are two clearances in a typical radial turbine - Tip clearance and Hub clearance. The effects of variable tip clearance at the inlet and exit of a radial turbine are investigated, and the relative losses associated with each clearance variation are quantified. Hub clearance is formed due to scalloping. This is carried out to decrease the hub stress and polar moment of inertia, which leads to additional losses. In this paper, the effect of variable tip clearance and scalloping on the performance of a radial turbine is studied through use of numerical simulation.