Free-Stream Turbulence Effects on Film Cooling With Shaped Holes

Abstract

A comprehensive set of generic experiments has been conducted to investigate the effect of elevated free-stream turbulence on film cooling performance of shaped holes. A row of three cylindrical holes as a reference case, and two rows of holes with expanded exits, a fanshaped (expanded in lateral direction), and a laidback fanshaped hole (expanded in lateral and streamwise direction) have been employed. With an external (hot gas) Mach number of Mam=0.3 operating conditions are varied in terms of free-stream turbulence intensity (up to 11%), integral length scale at constant turbulence intensity (up to 3.5 hole inlet diameters), and blowing ratio. The temperature ratio is fixed at 0.59 leading to an enginelike density ratio of 1.7. The results indicate that shaped and cylindrical holes exhibit very different reactions to elevated free-stream turbulence levels. For cylindrical holes film cooling effectiveness is reduced with increased turbulence level at low blowing ratios whereas a small gain in effectiveness can be observed at high blowing ratios. For shaped holes, increased turbulence intensity is detrimental even for the largest blowing ratio M=2.5. In comparison to the impact of turbulence intensity the effect of varying the integral length scale is found to be of minor importance. Finally, the effect of elevated free-stream turbulence in terms of heat transfer coefficients was found to be much more pronounced for the shaped holes.

CFD Simulations of Film Cooling Effectiveness and Heat Transfer for Annular Film Hole

“…Shaped holes have proven to provide the highest adiabatic effectiveness among film cooling configurations as investigated in Saumweber and Schulz [2], Goldstein et al [3], Sen et al [4], Thole et al. [5], Laveau and Abhari [6], and Gao and Han [7].…”

Film cooling effectiveness and flow structures for novel upstream steps

“…Shaped holes have been proven to provide the highest adiabatic effectiveness among film cooling configurations as investigated in Saumweber and Schulz [2], Goldstein et al [3], Sen et al [4], Thole et al. [5], Laveau and Abhari [6] and Gao and Han [7].…”

Film Cooling for Cylindrical and Fan-Shaped Holes Using Pressure-Sensitive Paint Measurement Technique

“…(3) to (5) are 0.31 < t∕P < 0.75, 0.2 < M < 4, 4 < P∕D < 8, 2.5 < AR < 4.7, and 1 < DR < 2. According to Saumweber et al [23], the mainstream turbulence intensity up to 11% only had a marginal effect on the film-cooling effectiveness for shaped holes. Therefore, the parameter of mainstream turbulence intensity Tu was not included in the current correlation and the range for this parameter was 0.2% < Tu < 4%.…”

“…Consequently, the first-stage stator vane usually experiences higher turbulence. The turbulence intensity varies at different locations of the vane and the blade, typically ranging from 8 to 12%, as indicated in Saumweber et al [23]. They concluded that increasing the turbulence intensity results in a lower effectiveness at lower blowing ratios, whereas the effectiveness slightly increases at higher blowing ratios for cylindrical holes.…”