UNSTEADY WAKE OVER A LINEAR TURBINE BLADE CASCADE WITH AIR AND CO2 FILM INJECTION .1. EFFECT ON HEAT-TRANSFER COEFFICIENTS

The effect of unsteady wake flow and air (D.R. = 1.0) or CO2 (D.R. = 1 .52) film injection on blade heal transfer coefficients was experiment ally determined. A spoked wheel-type wake generator produced the unste ady wake. Experiments were performed on a five-airfoil linear cascade in a low-speed wind tunnel at the chord Reynolds number of 3 x 10(5) f or the no-wake case and at the wake Strouhal numbers of 0.1 and 0.3. R esults from a blade with three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces show tha t the Nusselt numbers are much higher than those for the blade without film holes. On a large portion of the blade, the Nusselt numbers ''wi thout wake but with film injection'' are much higher than for ''with w ake but no film holes.'' An increase in wake Strouhal number causes an increase in pressure surface Nusselt numbers; but the increases are r educed at higher blowing ratios. AS blowing ratio increases, the Nusse lt numbers for both density ratio injectants (air and CO2) increase ov er the entire blade except for the transition region where the effect is reversed. Higher density injectant (CO2) produces lower Nusselt num bers on the pressure surface, but the numbers for air and CO2 injectio ns are very close on the suction surface except for the transition reg ion where the numbers for CO2 injection are higher. From this study, o ne may conclude that the additional increases in Nusselt numbers due t o unsteady wake, blowing ratio, and density ratio are only secondary w hen compared to the dramatic increases in Nusselt numbers only due to film injection over the no film holes case.