Influence of Discrete Pin Shaped Surface Roughness (P-Pins) on Heat Transfer and Aerodynamics of Film Cooled Aerofoil

Abstract

The influence of localized pin-shaped surface roughness (P-Pins) on heat transfer and aerodynamics of a fully film cooled engine aerofoil has been studied in a transonic annular cascade. The “P-Pins”, present on some casting film cooled turbine blades and vanes, are the residues left in the manufacturing process. This paper investigates the effect of the P-Pins on the aerodynamic performance and measures the heat transfer consequences both for the aerofoils and the P-Pins. The effect on performance was determined independently on the pressure and suction surface of the aerofoil. For comparison, the aerofoil without P-Pins was also tested to provide baseline results. The measurements have been made at engine representative Mach and Reynolds numbers. Wide band liquid crystal and direct heat flux gauge technique were employed in the heat transfer tests. A four-hole pyramid probe was used to obtain the aerodynamic data. The aerodynamic and thermodynamic characteristics of the coolant flow have been modelled to represent engine conditions by using a heavy “foreign gas” (30.2% SF6 and 69.8% Ar by weight). The paper concludes that P-Pins as usually placed on the blade do not have detrimental effects to the heat transfer performance of film-cooled aerofoil. P-Pins, located in thick boundary layer regions of the aerofoil, such as the later portion of the suction surface, do not cause any reduction of aerofoil aerodynamic efficiency. For contrast, the P-Pins located in the thin boundary layer regions on the pressure side of the aerofoil cause noticeably more losses.