AERODYNAMIC INVESTIGATION OF A NOZZLE CLEARANCE EFFECT ON RADIAL TURBINE PERFORMANCE

Liebherr Aerospace designs and develops cooling air systems, with notably axial fan and radial turbine or compressor The development of new architectures (especially electrical system) now requires improving the turbine performances on the whole operating range. To reach that industrial request, a variable nozzle area can be used, performed by changing the nozzle blade angle for a given blade height. For the blades to be moveable, tip and hub clearances must be present (and thus modeled) in the nozzle. The impact of that clearance on the turbine performance, and moreover on the flow field, is studied here by 3D numerical way. The clearance mass flow leads to the development of a marginal vortex along the nozzle blade chord that tends to increase the total pressure loss in the nozzle on the one hand, and to modify) the flow angle on the rotor inlet on the other hand. The vortex development in. duces an efficiency loss that must be taken into account during the design.