Influence of Unsteady Wake With Trailing Edge Coolant Ejection on Turbine Blade Film Cooling

Abstract

Detailed film cooling effectiveness distributions along a modeled turbine rotor blade under the combined effects of an upstream trailing edge unsteady wake with coolant ejection are presented using the pressure sensitive paint (PSP) mass transfer analogy method. The experiment is conducted in a low speed wind tunnel facility with a five blade linear cascade. The exit Reynolds number based on the axial chord is 370,000. Unsteady wakes and trailing edge coolant jets are produced by a spoked wheel-type wake generator with hollow rods equipped with several coolant ejections from holes. The coolant-to-mainstream density ratios for both the blade and trailing edge coolant ejection range from 1.5 to 2.0 for simulating realistic engine conditions. Blade blowing ratio studies are 0.5 and 1.0 on the suction surface and 1.0 and 2.0 on the pressure surface. The trailing edge jet blowing ratio and Strouhal numbers are 1.0 and 0.12, respectively. The results show that the unsteady wake reduces the overall film cooling effectiveness. However, the unsteady wake with trailing edge coolant ejection enhances the overall effectiveness. The results also show that the overall filming cooling effectiveness increases by using heavier coolant for trailing edge ejection and for blade surface film cooling.

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

“…Therefore, the density ratio effect can be studied with mass transfer techniques using heavier foreign gases injection, as can be seen in work by Goldstein et al [11] and Pedersen et al [28]. Previous research concerning the density ratio effect combined with the unsteady flow effect on film cooling from the leading edge to the blade surface using a pressure-sensitive paint mass transfer technique can be seen in [29][30][31][32]. The general conclusion is that a higherdensity ratio gives higher film-cooling effectiveness at a given blowing ratio.…”

Effects of Flow Oscillations in the Mainstream on Film Cooling

“…The passing wake increases the turbulence intensity in the main flow resulting in more mixing between the main flow and the injected coolant. Thus, the adiabatic temperature on the blade surface increases and the film cooling effectiveness decreases [12]. Additionally, the Nusselt number increases because of the generation of more disturbances in the main flow.…”

“…Additionally, the Nusselt number increases because of the generation of more disturbances in the main flow. The Strouhal number (Sr), non-dimensional frequency, of unsteady flow is proportional to the rotation speed of the blades (RPM) [12]. If the Strouhal number is increased, the film cooling effectiveness is further decreased and the Nusselt number increases [11][12][13][14].…”

“…The Strouhal number (Sr), non-dimensional frequency, of unsteady flow is proportional to the rotation speed of the blades (RPM) [12]. If the Strouhal number is increased, the film cooling effectiveness is further decreased and the Nusselt number increases [11][12][13][14]. The freestream turbulence can also affect the film cooling performance and it has a full frequency spectrum [15].…”