Unsteady Wake Effect on Film Effectiveness and Heat Transfer Coefficient From a Turbine Blade With One Row of Air and CO₂ Film Injection

The effect of unsteady wake and film injection on heat transfer coefficients and film effectiveness from a gas turbine blade was found experimentally. A spoked wheel type wake generator produced the unsteady flow. Experiments were done with a five airfoil linear cascades in a low-speed wind tunnel at a chord Reynolds number of 3 × 10⁵, two wake Strouhal numbers of 0.1 and 0.3, and a no-wake case. A model turbine blade injected air or CO₂ through one row of film holes each on the pressure and suction surfaces. The results show that the large-density injectant (CO₂) causes higher heat transfer coefficients on the suction surface and lower heat transfer coefficients on the pressure surface. At the higher blowing ratios of 1.0 and 1.5, the film effectiveness increases with increasing injectant-to-mainstream density ratio at a given Strouhal number. However, the density ratio effect on film effectiveness is reversed at the lowest blowing ratio of 0.5. Higher wake Strouhal numbers enhance the heat transfer coefficients but reduce film effectiveness for both density ratio injectants at all three blowing ratios. The effect of the wake Strouhal number on the heat transfer coefficients on the suction surface is greater than that on the pressure surface.