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 coeffi cients and film effectiveness from a gas turbine blade was found exper imentally. A spoked wheel type wake generator produced the unsteady fl ow. Experiments were done with a five airfoil linear cascades in a low -speed wind tunnel at a chord Reynolds number of 3 X 10(5), two wake S trouhal numbers of 0.1 and 0.3, and a no-wake case. A model turbine bl ade injected air or CO2 through one row of film holes each on the pres sure and suction surfaces. The results show that the large-density inj ectant (CO2) causes higher hear transfer coefficients on the suction s urface and lower heat transfer coefficients on the pressure surface. A t the higher blowing ratios of 1.0 and 1.5, the film effectiveness inc reases with increasing injectant-to-mainstream density ratio at a give n Strouhal number. However, the density ratio effect on film effective ness is reversed at the lowest blowing ratio of 0.5. Higher wake Strou hal numbers enhance the heat transfer coefficients but reduce film eff ectiveness for both density ratio injectants at all three blowing rati os. The effect of the wake Strouhal number on the heat transfer coeffi cients on the suction surface is greater than that on the pressure sur face.