Suppression of endwall heat transfer in the junction region with a symmetric airfoil by a vortex generator pair

Abstract

The high endwall heat transfer in the junction of the hub and vane/blade is very crucial in turbomachinery and is of great concern for increasing the gas turbine inlet temperature but avoiding hot spots. The vortices generated in that region are mainly responsible for the high heat transfer. By controlling these vortices, heat transfer in the junction region can be controlled. In this study, a new method is presented to control the vortices and ultimately the heat transfer generated in the junction region. A vortex generator pair was mounted upstream of a symmetric airfoil to interrupt the boundary layer approaching towards the junction region. The heat transfer in terms of Nusselt number was measured experimentally using steady state liquid crystal thermography. The size and position of the vortex generators were varied to control the heat transfer. The insight of the flow features was achieved by numerically solve the three dimensional steady state Reynolds Average Navier Stokes equations (RANS). The experimental results show that the heat transfer is reduced in the junction region and the level of heat reduction is greatly dependent on the size of the vortex generators. Moreover, the lateral gap between the vortex generators has an influence on the peak value of the heat transfer as well as on the local variation of the heat transfer. The flow field demonstrates that the vortices generated upstream of an airfoil are modified and provide an evident of reduction of the high heat transfer in that region.