Momentum-Preserving Shaped Holes for Film Cooling

Abstract

Shaped holes increase film-cooling effectiveness by using the Coanda effect to make the cooling jet stay attached to the surface and an expanding flow cross-sectional area about the hole exit to make the cooling jet spread out laterally so that more surface can be cooled. Though shaped holes increase lateral spreading, downstream penetration of the coolant is reduced because the expanding cross-sectional area decreased the momentum of the cooling flow. This paper presents a new shaped-hole design concept to enable increased lateral spreading as well as greater downstream penetration. The new shaped-hole design concept involves a W-shaped cross-sectional area in which the middle part of the W-shape protrudes and widens as the W-shaped hole widens. The goal is to keep the film-cooling flow cross-sectional area nearly constant as the shaped hole widens so that momentum can be preserved to increase both lateral and streamwise coverage of the film-cooling jet. To examine the usefulness of this design concept, CFD analyses were performed for two W-shaped holes. In one design, the W-shaped hole is similar to traditional shaped holes except that the middle part of the shaped hole is protruded to form the W shape. In the other design, the W-shaped hole continues as a shallow trench that is aligned with the main flow direction to minimize the entrainment of hot gases and to reduce pressure drag and aerodynamic interference. Computed results show the W-shaped-hole design concept to be promising in enhancing surface adiabatic effectiveness.