Unsteady Wake Over a Linear Turbine Blade Cascade With Air and CO2 Film Injection: Part II—Effect on Film Effectiveness and Heat Transfer Distributions

Abstract

The effect of unsteady wake flow and air (D.R. = 0.97) or CO2 (D.R. = 1.48) film injection on blade film effectiveness and heat transfer distributions was experimentally determined. A spoked wheel type wake generator produced the unsteady wake. Experiments were performed on a five-airfoil linear cascade in a low-speed wind tunnel at the chord Reynolds number of 3 × 105 for the no wake case and at the wake Strouhal numbers of 0.1 and 0.3. A model turbine blade with several rows of film holes on its leading edge, and pressure and suction surfaces ( −0.2<X/C< 0.4) was used. Results show that the blowing ratios of 1.2 and 0.8 provide the best film effectiveness over most of the blade surface for CO2 and air injections, respectively. An increase in the wake Strouhal number causes a decrease in film effectiveness over most of the blade surface for both density ratio injectants and at all blowing ratios. On the pressure surface, CO2 injection provides higher film effectiveness than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.8. On the suction surface, CO2 injection provides higher film effectiveness than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.4. Co2 injection provides lower heat loads than air injection at the blowing ratio of 1.2; however, this trend is reversed at the blowing ratio of 0.4. Heat load ratios under unsteady wake conditions are lower than the no wake case. For an actual gas turbine blade, since the blowing ratios can be greater than 1.2 and the density ratios can be up to 2.0, a higher density ratio coolant may provide lower heat load ratios under unsteady wake conditions.

Recent Studies in Turbine Blade Cooling?

“…Ou et al (1994) and Mehendale et al (1994) used the rotating spoked wheel-type wake generators to simulate the effect of unsteady wake on downstream stationary blade film cooling performance. A typical turbine blade was placed in a large-scale low speed linear 2-D turbine cascade facility.…”

Turbine Blade Cooling Studies at Texas A&M University: 1980-2004

“…Ou et al, 108 Mehedale et al, 109 Ou and Han, 110 Mehendale et al, 111 Jiang et al, 112 and Ekkad et al 113 used the rotating spoked wheel-type wake generators, a) Stator-rotor unsteady wake b) Rotating-rod wake simulation Fig. 27 Actual stator rotor interaction and laboratory simulation to study unsteady wake effect, from Mehandale et al 109 as shown in Fig. 27, to simulate the effect of unsteady wake on downstream stationary blade film-cooling performance.…”

Turbine Blade Film Cooling Using PSP Technique

“…A rotating spoke-wheel wake generator installed upstream of a typical high pressure film cooled model turbine blade has been to simulate the effect of an upstream wake by Mehendale et al (1994) and later, Du et al (1997). Film cooling effectiveness on the blade surface (equipped with radial angled holes on the leading edge, two rows of simple angled holes on the suction side, and two rows of compound angled holes on the pressure side) was studied.…”