Experimental Investigation of Flow Structures Around an Oscillating Airfoil in Steady Current PDF Download

Author: İdil Fenercioğlu
Publisher:
ISBN:
Category :
Languages : en
Pages : 183

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Author: Panayiote Gerontakos
Publisher:
ISBN:
Category :
Languages : en
Pages : 218

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"The detailed behaviour of the unsteady boundary layer and stall events occurred on a sinusoidally oscillating NACA 0012 airfoil at Re = 1.35 x 105 was investigated experimentally by using closely-spaced multiple hot-film sensor arrays. The hot-film measurements were supplemented by surface pressure measurements, hot-wire wake velocity surveys and smoke-flow visualizations. Three typical oscillation parameters: attached flow, light stall, and deep stall were tested. Special attention was focused on the non-intrusive identification of the spatial-temporal progression of the locations of the boundary-layer transition and separation and reattachment points for a range of oscillation frequencies and amplitudes both prior to, during, and post the stall. The results show that for an unsteady airfoil, the reduced frequency of the oscillation was found to be highly significant and only small values of reduced frequency were required to delay the onset of the various boundary-layer events, and to produce significant variations and hysteresis in the peak values of lift and drag forces and the pitching moments, which are fundamentally different from their static counterparts. Lift stall was observed to occur when the leading-edge vortex reached 90% of the chord, while moment stall occurred at the end of the upward spread of the trailing-edge flow reversal. The convection speed of the leading-edge and the secondary vortices were also reported. Dynamic stall was found to be caused by an abrupt turbulent separation near the leading-edge region and not with the bursting of the laminar separation bubble, as is commonly observed for a static NACA 0012 airfoil; the result being the initiation, growth and convection of an energetic leading-edge vortex. Moreover, the detection of the sudden turbulent breakdown could serve as an indicator for dynamic stall detection and control. The results reported on here provide a deepened insight into the detailed nature of" --

Author: Douglas Carl Heinrich
Publisher:
ISBN:
Category :
Languages : en
Pages : 230

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Author: Lakshmendra Shanker Saxena
Publisher:
ISBN:
Category :
Languages : en
Pages : 213

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Author: George J. Mullaney
Publisher:
ISBN:
Category :
Languages : en
Pages : 35

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Author: Robert L. Halfman
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 92

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Experimental measurements of the aerodynamic reactions on a symmetrical airfoil oscillating harmonically in a two-dimensional flow are presented and analyzed in this paper. Harmonic motions include pure pitch and pure translation, for several amplitudes and superimposed on an initial angle of attack, as well as combined pitch and translation. Considerable consistent data for pure pitch were obtained from a search of available reference material, and several definite Reynolds number effects are evident.

Author: Jiannwoei Yue
Publisher:
ISBN: 9781423574583
Category :
Languages : en
Pages : 94

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Flapping airfoils generate thrust-producing jet-like wakes. It therefore is the objective of this investigation to explore whether this feature can be used for effective flow control. To this end, the flow characteristics of flapping airfoils are first explored in a water tunnel experiment, using dye flow visualization and laser-doppler velocimeter. The effect of airfoil flapping frequency and amplitude of oscillation and of flow velocity on the wake flow characteristics are determined. This is followed by a second water tunnel experiment, where a small flapping airfoil is mounted in and near the separated flow region caused by the flow over a backward-facing step. The effect of airfoil size, location, frequency, and amplitude of oscillation on the separated flow region is again determined by means of laser-doppler velocimeter. It is found that the reattachment length of the separated flow region can be reduced by as much as 70%.

Author: J. M. Simmons
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 10

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Author: Osama M. Mahmoud
Publisher:
ISBN: 9781423522966
Category : Aerofoils
Languages : en
Pages : 200

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A wind tunnel investigation of low speed flow over flapping airfoils and airfoil combinations was performed using flow visualization and laser Doppler velocimetry. Specifically, three cases were studied: A NACA0014 airfoil oscillating in a sinusoidal plunge mode, A NACA0014 airfoil oscillating in a sinusoidal plunge mode near a ground plane, and two NACA0014 airfoils arranged in a biplane configuration and oscillating in counterphase in a sinusoidal plunge mode. The plunge amplitude-to-airfoil chord ratio was 0.4, the reduced frequency of oscillation was 1.0 and the Reynolds number based on airfoil chord was set at 8760. Conditionally sampled measurements of the axial flow velocity were taken at numerous flow field points providing detail information about the flow features generated by this type of flapping motion. These measurements were complemented by time-averaged flow field data and by visualization of the instantaneous flow field at various points during the flapping cycle. Furthermore, the thrust generated by the sinusoidal plunge motion was measured with a laser range finder. The results shows that vortex shedding occurs both from the airfoil leading and trailing edge.

Author: Kenneth W. McAlister
Publisher:
ISBN:
Category : Aerofoils
Languages : en
Pages : 86

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