Unsteady wake effect on film effectiveness and heat transfer coefficient from a turbine blade with one row of air and CO2film injection
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The effect of unsteady wake and film injection on heat transfer coefficients and film effectiveness from a gas turbine blade was experimentally found. A spoked wheel type wake generator produced the unsteady flow. Experiments were done with a five airfoil linear cascade in a low speed wind tunnel at a chord Reynolds number of 3105and at wake Strouhal numbers of 0 (no wake), 0.1, and 0.3. A model turbine blade injected air or CO2through one row of film holes each on the pressure and suction surfaces. The results show that the heavy density injectant (CO2) causes a higher heat transfer coefficient on the suction surface and a lower heat transfer coefficient 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 the film effectiveness is reversed at the lowest blowing ratio of 0.5. Higher wake Strouhal numbers enhance the heat transfer coefficients but reduce the 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 on the pressure surface despite the density ratio or blowing ratio.
