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Paper Information

Journal:   JOURNAL OF APPLIED FLUID MECHANICS (JAFM)   2016 , Volume 9 , Number 6; Page(s) 2769 To 2779.
 
Paper: 

EFFECT OF SIDE-WALLS ON FLAPPING-WING POWER-GENERATION: AN EXPERIMENTAL STUDY

 
 
Author(s):  KARAKAS F., FENERCIOGLU I.*
 
* ISTANBUL TECHNICAL UNIVERSITY, DEPARTMENT OF ASTRONAUTICAL ENGINEERING, ISTANBUL, 34469, TURKEY
 
Abstract: 

Effect of constrained flow is investigated experimentally for a flapping foil power-generator. The flow structures around and in the near wake of a flat plate placed between two side walls are captured via PIV technique with simultaneous direct force measurements in uniform flow at Re=10 000. The rectangular flat plate oscillates with periodic non-sinusoidal pitching and plunging motions about its 0.44 chord position with stroke reversal times (D TR) of 0.1 (rapid reversal) to 0.5 (sinusoidal reversal), phase angles of f=90o and 110o, plunge amplitude of 1.05 chords and pitch amplitude of 73° at a constant reduced frequency of k=0.8. The non-dimensional distances between the side walls and the oscillating flat plate aredw=0.1, 0.5 and 1.0. Airfoil rotation speed dictates the strength, evolution and timing of shedding of leading and trailing edge vortices; as the stroke reversal time is decreased, earlier shedding of stronger vortices are observed. Increasing the phase angle between the pitching and plunging motions decreases the power generation efficiency for all cases. The highest power extraction coefficient is acquired for the non-sinusoidal case ofD TR=0.4 in free flow. Optimum choice of side-wall distance improves power generation of flapping foils compared to free flow performance, up to 6.52% increase in efficiency is observed for the non-sinusoidal caseD TR=0.4 with dw=0.5, with remarkable enhancements for the sinusoidal case; 27.85% increase is observed with dw=0.5 and 43.50% increase with dw=1.0 where both cases outperform the highest power generation efficiency of the finite flat plate with non-sinusoidal flapping motion.

 
Keyword(s): CONSTRAINED FLOW, OSCILLATING FOIL, FLAPPING WING, POWER GENERATION, PIV
 
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