Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence

Abstract

Slot film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over two cylindrical leading edge test surfaces. Measurements were conducted at four blowing ratios, two Reynolds numbers and six well documented turbulence conditions for each test surface. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds numbers. The film cooling measurements were acquired at a coolant to free-stream density ratio of approximately 1.04. The flows were subjected to a low turbulence condition (Tu = 0.7%), two levels of turbulence for a smaller sized grid (Tu = 3.5%, and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aero-combustor (Tu = 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the aero-combustor turbulence condition are reduced to as low as 20% of low turbulence values by the furthest downstream region. The slot in each case is located close to the stagnation region of the leading edge and the upstream boundary layers are very thin and accelerating. The slot is angled at 30° to the surface. Film cooling data, from the larger cylindrical stagnation region test surface, show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. These data are expected to be very useful in grounding computational predictions of slot film cooling with elevated turbulence levels and acceleration.