Investigation On The Effects Of Wake Rod To Film Cooling Hole Diameter Ratio In Unsteady Wake Studies

In recent decades, greater interest in the effect of rotational wakes on gas turbine film cooling applications has produced increasing numbers of studies on these unsteady phenomena. Wakes are primarily shed from upstream components such as transition duct walls, stator vanes, and rotors. Studies have shown that in areas of unsteady flow, the best performing parameters in conventional steady investigations may not be the best for unsteady applications. One common method of modeling the rotor-stator interaction in subsonic flows is the use of spoke wheel type wake generators using cylindrical rods to produce the velocity detriment and local increase in turbulence intensity. Among the results published to date, no mention on the potential effect of the wake rod to film cooling hole diameter ratio has been addressed. Disagreement among investigators concerning the trailing edge thickness and the effect of boundary layer growth has led to diameter ratios from 0.5 to 5.6 in open literature. This investigation measures the effect of the diameter ratio on the adiabatic film cooling effectiveness over three diameter ratios of 2.375, 4.75, and 9.5 in order to determine any dependence on this typically unidentified parameter. Blowing ratios of 0.25, 0.5, and 0.75 will be tested at wake Strouhal numbers of 0 and 0.3 in order to determine the effects for weak and strong injection rates. Measurements are taken in a low speed induced flow annular duct with jet Reynolds numbers of 2000 to 8000. Among the cases studied no discernable trend based on the diameter ratio is found, indicating that this effect is negligible in wake impact comparisons. The effect of wakes is consistent for both weak and strong injection with similar magnitude of wake impact for each diameter ratio tested. The existence or lack of dependence on diameter ratio allows for more purposeful comparisons among present and future investigations which use this method of producing unsteady wakes. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved