Numerical study for optimizing heat transfer in high speed rotating components

Abstract

Cooling of high speed rotating components is a typical situation found in turbomachinery as well as in automobile engines. Accurate knowledge of discharge coefficients and heat transfer of related components is essential for the high performance of the whole engine. This can be achieved by minimized cooling air flows and avoidance of hot spots. In high speed rotating clutches for example aerodynamic investigations improving heat transfer have not been considered in the past. Advanced concepts of modern plate design try to reduce thermal loads by convective cooling methods. Therefore, secondary cooling air flows have to be enhanced by an appropriate design of the rotor stator system with orifices. CFD modelling is used to improve the basic understanding of the flow field in typical geometries used in these systems. The computational results are obtained by a 3-D-finite-volume-code based on body fitted structured grids. The Navier Stokes equations are solved by a pressure-correction method combined with the standard k-ε-turbulence model. Considering the rotation of orifices in disks or shafts, the frame of reference has to be changed to the rotating system. The flow through orifices in high speed rotating disks can be calculated with a high level of accuracy in comparison with experiments as shown in Wittig et al. [1994]. Numerical results of the flow in a high speed rotating system are presented with emphasis on geometrical variations. Calculations are carried out in order to find an optimum design in terms of position and size of the orifices in the housing. These variations induce different physical phenomena. Special consideration is directed towards the basic problems of the flow through orifices in high speed rotating disks and shafts and the flow inside rotor-stator systems. As expected, the very complex flow fields are dominated by rotational effects. In addition it is shown that differences occur between the configuration of optimized mass flow rate and the geometry with a maximum of total heat transfer. Obviously, optimization procedures are dependent on the knowledge of the local flow field and cannot be performed without advanced CFD-methods. It is demonstrated that the approach presented here is suitable for these tasks. © 1998 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.