A new cooling design for rib roughened two-pass channel having positive effects of rotation on heat transfer enhancement on both pressure and suction side internal walls of a gas turbine blade

Abstract

This paper presents a new cooling design for a typical two-pass channel of a high pressure stage turbine blade. Gas turbine blades are subjected to elevated heat loads on the pressure and suction walls. In order to enhance heat transfer from the surfaces to the relatively colder internal air (gas), rib turbulators are installed on the opposite walls of two-pass channel. Combination of Coriolis force and centrifugal buoyancy force result in increase in heat transfer on trailing walls (along the pressure surface, and radially outward coolant flow) and leading walls (along the suction surface, radially inward flow) and vice versa. This leads to non-uniform cooling in both the passes and hence a non-optimum usage of cooling potential. The present study is focused on utilizing the Coriolis force favorably in both the passes by rotating the typical arrangement of two-pass channels by 90°. Detailed heat transfer coefficients were measured by transient liquid crystal thermography under rotating conditions. In order to match the direction of Buoyancy force as it exists in actual engines, colder air was passed during the transient experiment. The heat transfer experiments were carried out at a Reynolds number of 20000 and Rotation numbers of 0 and 0.1. The Nusselt numbers have been reported in two forms, (a) normalized with respect to Dittus-Boelter correlation for developed turbulent flow in circular duct, (b) normalized with corresponding Nusselt number obtained from smooth channel experiments. In order to understand the heat transfer characteristics of both traditional and new design, numerical simulations were also carried out for all configurations and at all experimental conditions to obtain flow and heat transfer predictions. A combined experimental and numerical discussion has been provided to explain the findings of the present study and to support the proposed design. It has been reported that the new design has 11% higher heat transfer enhancement at 8% lower pumping power compared to the traditional two pass rib roughened duct.