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Research Papers

# Boundary Layer Separation Control With Fluidic Oscillators

[+] Author and Article Information
Ciro Cerretelli

Kiepe Electric S.p.A., Cernusco S.N. (MI), 20063, Italycirissimo@yahoo.com

Kevin Kirtley

GE Energy, Greenville, SC 29515kevin.kirtley@ge.com

J. Turbomach 131(4), 041001 (Jun 30, 2009) (9 pages) doi:10.1115/1.3066242 History: Received October 27, 2006; Revised July 22, 2008; Published June 30, 2009

## 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 is therefore 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 nondimensional blowing frequencies $(F+)$ in the range of $0.6. 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 with optimal steady blowing. Particle image velocimetry velocity and vorticity measurements have been performed, which show no large-scale unsteadiness in the controlled boundary layer flow.

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## Figures

Figure 1

GE GRC diffuser test rig, aft looking forward

Figure 2

Hump diffuser cross section

Figure 3

Layout of wall static pressure taps on (a) lower and (b) upper model walls

Figure 4

Schematic of data acquisition system

Figure 5

(a) Schematic of PIV setup. (b) Example of a full-resolution PIV velocity field.

Figure 8

Centerline pressure for 1.905 mm discrete injection at different recovery levels as per Fig. 6. Flow control insert is located between 0.5≤s/c≤0.62.

Figure 15

U velocity and U¯rms profiles for steady blowing and fluidic oscillators

Figure 16

Diffuser pressure recovery curves for steady and unsteady blowing as a function of Cμ for α=0 deg

Figure 9

Feedback fluidic oscillator: switching mechanism. PS indicates the supply plenum pressure.

Figure 10

Feedback fluidic oscillator in insert A, F+≈0.7. (a) Velocity waveform. (b) Frequency response as a function of supply pressure.

Figure 11

Feedback fluidic oscillator in insert B, 3≤F+≤6. (a) Velocity waveform. (b) Frequency response as a function of supply pressure.

Figure 12

Frictionless nozzle velocity and oscillator maximum and minimum velocities as functions of the supply pressure

Figure 7

Diffuser pressure recovery for discrete injection insert as a function of Cμ for α=0 deg

Figure 13

Diffuser pressure recovery curves for steady and unsteady blowing as a function of Cμ for α=0 deg

Figure 14

U velocity fields and streamlines for unsteady flow control applied by insert A over the hump diffuser

Figure 6

(a) Baseline local pressure recovery curves along the lower surface for α=0 deg and −5 deg. Flow control insert is located between 0.5≤s/c≤0.62. (b) Spanwise lower wall pressure distribution at s/c=0.12, 0.64, and 0.81 (α=−5 deg).

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