Kevin Richard Kirtley

Boundary Layer Separation Control With Fluidic Oscillators

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to repair the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and therefore is more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% RMS of the average operating at non-dimensional blowing frequencies (F+ ) in the range 0.6 < F+ < 6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared to optimal steady blowing. PIV velocity and vorticity measurements have been performed that show no large-scale unsteadiness in the controlled boundary layer flow.Copyright

Characterization of Steady Blowing for Flow Control in a Hump Diffuser

A study has been performed to characterize the effects of steady boundary-layer injection on the separated flow of a hump diffuser. Results of parametrically varying discrete hole blowing characteristics have identified two separate regimes where the injection momentum coefficient and velocity ratio, respectively, are the primary scaling parameters for pressure recovery. Both discrete hole and slot injection have been investigated for varying degrees of adverse pressure gradient in the streamwise direction, indicating optimal discrete hole injection to be more efficient than slot injection in terms of necessary injection momentum coefficient to achieve maximum levels of increased pressure recovery. The effects of discrete injection parameters such as hole diameter, hole spacing, and streamwise injection (yaw) angle have been studied. Angled injection (45-deg yaw) has been shown to be most effective in removing separated flow and increasing the pressure recovery. The angled injection enhances shear layer mixing through large-scale corotating vortical motion induced by the yawed jet-main flow interaction. A computational fluid dynamics/data comparison study has been performed on the results of the discrete injection tests, capturing overall data trends and representing the net effect of streamwise and angled injection on pressure recovery in the hump diffuser.

Design and Test of an Ultra-Low Solidity Flow-Controlled Compressor Stator

A full annulus fluidic flow-controlled compressor stator ring was designed and tested in the third stage of a four-stage low speed research compressor. The solidity of the flow-controlled stator was near unity and significantly below design practice with a commensurately high diffusion factor. The design intent was to reduce the vane count by 30% and load the stator to the point of stall at the design point then employ flow control to restore attached boundary layers and regain design-point stage-matching. The flow control applied that maintained attached flow was 1% of the compressor mass flow and was introduced via discrete steady jets on the suction side of the stator. The design method used steady CFD with the flow control jets simulated to drive stator exit angles, velocities and blockage to match the baseline machine. The experiment verified the pre-test predictions and demonstrated degraded compressor performance without flow control and restoration of the pumping characteristics of the baseline high solidity compressor when flow control was applied. An assessment of the engine cycle impact of the flow-controlled compressor shows the stage efficiency trade for the increased loading was 2.1 points. Extrapolation of the data and analysis to a high-speed compressor shows a more modest 0.5 points stage efficiency trade.Copyright