A cooling technique for small-scale radial turbines: experimental and numerical investigation

Efficient cooling of turbines has been in continuous development to enhance the performance of micro gas turbines by enabling higher turbine inlet temperatures. Yet, cooling small-scale radial turbines (SSRTs) is very challenging due to their compact and thin structures. This paper proposes and examines an impingement cooling technique tailored for SSRTs. This technique is a novel groove-based cooling scheme that imparts cooling air easily through an inclined continuous slot in the turbine heat shield. It delivers a uniform, axisymmetric coolant distribution, which reduces localized thermal peaks and hence, in turn, stress. Moreover, it has a lower effect on the main stream than hole-based injection. This cooling technique is investigated numerically on a turbocharger turbine using the CFD-CHT model, which is validated experimentally on the same radial turbine by mounting it on an experimental test bench and inspecting its temperature distribution with an infrared camera. Various geometric configurations and coolant mass flow rates were investigated to evaluate their impact on temperature reduction and turbine efficiency. The findings reveal that a groove with a width of 1 mm and an inclination of 33°, combined with a coolant mass flow rate of 1.5% of the turbine mass flow, provided effective and uniform cooling of the disc and blades. This configuration led to a temperature reduction of 47 K at the blade leading edge and 65 K on the disc, with a power reduction less than 4.5%.