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Research Papers: Flows in Complex Systems

Active Flow Control of Dynamic Stall by Means of Continuous Jet Flow at Reynolds Number of 1 × 106

[+] Author and Article Information
Mehran Tadjfar

Mem. ASME
Turbulence Laboratory,
Department of Aerospace Engineering,
Amirkabir University of Technology,
Tehran 15916-34312, Iran
e-mail: mtadjfar@aut.ac.ir

Ehsan Asgari

Turbulence Laboratory,
Department of Aerospace Engineering,
Amirkabir University of Technology,
Tehran 15916-34312, Iran
e-mail: e.asgari@aut.ac.ir

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 30, 2017; final manuscript received August 8, 2017; published online October 4, 2017. Assoc. Editor: Moran Wang.

J. Fluids Eng 140(1), 011107 (Oct 04, 2017) (10 pages) Paper No: FE-17-1258; doi: 10.1115/1.4037841 History: Received April 30, 2017; Revised August 08, 2017

We have studied the influence of a tangential blowing jet in dynamic stall of a NACA0012 airfoil at Reynolds number of 1 × 106, for active flow control (AFC) purposes. The airfoil was oscillating between angles of attack (AOA) of 5 and 25 deg about its quarter-chord with a sinusoidal motion. We have utilized computational fluid dynamics to investigate the impact of jet location and jet velocity ratio on the aerodynamic coefficients. We have placed the jet location upstream of the counter-clockwise (CCW) vortex which was formed during the upstroke motion near the leading-edge; we have also considered several other locations nearby to perform sensitivity analysis. Our results showed that placing the jet slot within a very small range upstream of the CCW vortex had tremendous effects on both lift and drag, such that maximum drag was reduced by 80%. There was another unique observation: placing the jet at separation point led to an inverse behavior of drag hysteresis curve in upstroke and downstroke motions. Drag in downstroke motion was significantly lower than upstroke motion, whereas in uncontrolled case the converse was true. Lift was significantly enhanced during both upstroke and downstroke motions. By investigating the pressure coefficients, it was found that flow control had altered the distribution of pressure over the airfoil upper surface. It caused a reduction in pressure difference between upper and lower surfaces in the rear part, while substantially increased pressure difference in the front part of the airfoil.

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Figures

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Fig. 1

Computational domain

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Fig. 2

Computational mesh in vicinity of leading-edge and trailing-edge with tangential slot

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Fig. 3

Impact of time-step size on the lift coefficient

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Fig. 4

Impact of time-step size on the drag coefficient

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Fig. 5

Impact of grid resolution on the lift coefficient for uncontrolled case

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Fig. 6

Impact of grid resolution on the drag coefficient for uncontrolled case

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Fig. 7

Impact of grid resolution on the lift coefficient for AFC case

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Fig. 8

Impact of grid resolution on the drag coefficient for AFC case

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Fig. 9

Hysteresis curve of the lift coefficient

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Fig. 10

Hysteresis curve of the drag coefficient

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Fig. 16

Vorticity contours of downstroke motion for uncontrolled and controlled cases

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Fig. 11

Flow streamlines demonstrating CCW vortex at AOA of 24 deg during upstroke motion

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Fig. 12

Location of jet slot upstream of the CCW vortex

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Fig. 13

Impact of jet location on lift coefficient

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Fig. 14

Impact of jet location on drag coefficient

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Fig. 15

Vorticity contours of upstroke motion for uncontrolled and controlled cases

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Fig. 17

Effect of jet velocity ratio on lift hysteresis curve

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Fig. 18

Effect of jet velocity ratio on drag hysteresis curve

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Fig. 19

Blowing efficiency during the lift hysteresis for the case of Vj/U∞=3

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Fig. 20

Distribution of pressure coefficient in upstroke motion

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Fig. 21

Distribution of pressure coefficient in downstroke motion

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