Film Cooling Effectiveness Downstream of Compound and Fan-Shaped Holes

Abstract

The steady-state wide band liquid crystal technique is used to study the film cooling performance downstream of a variety of geometries in a flat plate. This technique provides a detailed measurement of both cooling effectiveness and heat transfer coefficient. This paper presents the effects of compound and fan–shaped holes, the effect of streamwise angle variation has been presented at previous meetings. The following configurations are investigated: a single hole, a row of holes with a pitch-to-diameter ratio, p/D, of 3, two inline rows with p/D of 3 and two staggered rows with p/D of 6; all with a stream–wise angle of 30°. The spacing between two rows was chosen as 12.4D. Two lateral injection are investigated: 30° and 60° compound angle. The fan shaped hole used comprised of a lateral expansion of 14° from the original simple cylindrical shape with streamwise inclination of 30°; forward expansion was not incorporated. The length-to-diameter ratio, L/D, was maintained at a value of 4 for all the compound cases, the L/D for the fan shaped-hole was 6, larger due to its physical limitation. The tests were performed with a jet-to-freestream density ratio of 1.5; achieved by using a foreign gas (CO2) injection. The range of momentum flux ratios (M) covered was 0.33 to 1.67. The row of 30° compound angle holes gave a lower value of effectiveness when compared to the non-compound case at M<0.67, but greater values and coverage at M>1.0, consistent with previous experiments. The row of 60° compound angle gave greater effectiveness, coverage and uniformity than the row of 30° compound at a given blowing ratio; the jet-to-jet interaction was greater for the 60° row due to the added lateral momentum. The row of 60° compound gave an increase of order 100% relative to the non-compounded row for M>1. Two inline rows of fan-shape holes delivered less effectiveness than the corresponding single row at the same spanwise distance for a given jet fluid mass, or blowing ratio with twice the jet fluid mass. For equal blowing ratios and equal flow rates the fan-shaped hole gave a much higher effectiveness.