Behaviour of Secondary Coolant Flow on the Turbine Blade Surface

Abstract

In this paper, the fluid mechanic behaviour of secondary flows, cooling injection from inside the blade, on the turbine blades surfaces has been studied for its aerodynamic influence. A standard T-106A turbine blade profile has been chosen for study. The blades are arranged in a linear cascade with a solidity of 0.5 and aspect ratio of 1.5. It is first intended to find the most effective single blowing location, which has been found at 10% of the blade surface from the leading edge. Then the study has focussed on finding a blowing ratio at which the secondary flow boundary layer sustains itself over most part of the turbine blade surfaces – both the suction and the pressure surfaces. Further, fluid mechanic studies have been conducted at this effective blowing ratio (≈ 0.8) to explore the boundary layer behaviour of the injected cooling flow. The boundary layer development has been studied at various chord-wise locations along the blades surfaces. It is observed that at the effective blowing ratio a single row of cooling injection at approximately 8.25% of axial chord behind the leading edge may be sufficient to create sustained cooling boundary layer over the entire turbine blade surfaces. The present study has been carried out with cold flows at low speeds to accommodate experimental validation in a low speed cascade tunnel in near future. The heat transfer related issues are not part of the present study.