Effects of pressure side film cooling hole placement and condition on surface heat transfer coefficients along a transonic turbine blade tip

Abstract

Considered is thermal performance for the squealer blade tip of four film cooling configurations, B1, B2, B3 and B4, with hole exits for each arrangement positioned along a different portion of the upper pressure side of a transonic turbine blade. Each upper pressure side configuration includes five film cooling holes, such that each hole has a compound angle of 45$°$ with respect to the circumferential/axial plane, also with an angle orientation of 40$°$ relative to the plane tangent to the exit cross sectional area of each hole. Results are given for blowing ratios ranging from 0.42 to 3.20 in the form of spatially-resolved and spatially-averaged surface distributions of heat transfer coefficients and heat transfer coefficient ratios. In regard to tip surface variations, surface heat transfer coefficient ratios distributions are a consequence of the manner in which the film coolant collects in a substantial manner along the pressure side rim and then advects above and across the squealer recess with little to no coolant collecting within the cavity, or along the recess surface, to then collect in a substantial manner further downstream along the suction side rim. Such flow characteristics affect heat transfer coefficient ratio variations for all four film cooling configurations, but are especially influential for the B3 arrangement. Considering local heat transfer coefficient ratio distributions along the upper pressure side surface, the most significant local variations in the vicinity of a film cooling hole exit locations. Here, heat transfer coefficient ratio distributions for the B1 and the B4 configurations, in particular, show evidence of a horseshoe-shaped vortex which forms around each emerging coolant concentration. The two downstream legs of each vortex are associated with a pair of locally augmented heat transfer coefficient streaks, often with a streak of locally-lower coefficient ratios positioned between. Local and line-averaged heat transfer coefficient ratios along the upper pressure side also vary significantly with blowing ratio, with additional periodic variations as the normalized circumferential/axial coordinate varies. Within the resulting distributions, local heat transfer coefficient ratio increases are associated with locally augmented mixing and turbulent transport, which are especially present near the exits of different film cooling hole locations.