Boundary Layer Separation Control With Fluidic Oscillators

Abstract

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.

Data-driven selection of actuators for optimal control of airfoil separation

“…Open-loop flow control strategies based on various actuator technologies [3]-such as plasma actuators [4][5][6], fluidic oscillators [7][8][9][10][11], and synthetic jets [12][13][14][15][16]-have been shown to effectively alter separated flows, and in some cases to even yield complete reattachment. In [17], oscillatory forcing was found to improve control authority for separation control.…”

Active Boundary Layer Control on a Highly Loaded Turbine Exit Case Profile

“…Since the profile is supposed to be applicable over a wide Reynolds number range, an active flow control method was favoured. Comparing different active methods, several authors like Bons et al [6] and Cerretelli and Kirtley [7] reported that unsteady excitation of the boundary layer flow is much more efficient than, for example, steady blowing. Cerretelli and Kirtley [7] achieved with fluidic oscillators a 60% reduction of injection momentum combined with a 30% reduction in blowing power compared to optimal steady blowing in a diffuser test rig.…”

“…Comparing different active methods, several authors like Bons et al [6] and Cerretelli and Kirtley [7] reported that unsteady excitation of the boundary layer flow is much more efficient than, for example, steady blowing. Cerretelli and Kirtley [7] achieved with fluidic oscillators a 60% reduction of injection momentum combined with a 30% reduction in blowing power compared to optimal steady blowing in a diffuser test rig. Different dimensionless frequencies were investigated by Cerretelli and Kirtley [7] following the work by Glezer et al [8] who investigated high frequency actuation with synthetic jet actuators.…”

“…Cerretelli and Kirtley [7] achieved with fluidic oscillators a 60% reduction of injection momentum combined with a 30% reduction in blowing power compared to optimal steady blowing in a diffuser test rig. Different dimensionless frequencies were investigated by Cerretelli and Kirtley [7] following the work by Glezer et al [8] who investigated high frequency actuation with synthetic jet actuators. Cerretelli and Kirtley [7] used dimensionless blowing frequencies which were about 5 to 10 times higher than the frequencies for the shear layer vortices actuation.…”

“…Different dimensionless frequencies were investigated by Cerretelli and Kirtley [7] following the work by Glezer et al [8] who investigated high frequency actuation with synthetic jet actuators. Cerretelli and Kirtley [7] used dimensionless blowing frequencies which were about 5 to 10 times higher than the frequencies for the shear layer vortices actuation. These frequencies showed less reduction of the losses than the frequencies for the shear layer vortices.…”