Fluid dynamics of flapping rigid and spanwise-flexible elliptical flat plates at low Reynolds numbers

Presented here is an experimental investigation of sinusoidal plunging rigid and flexible elliptical flat plates at Reynolds number 5.3 × 10 ³. The sinusoidal plunging motion is characterized by the normalized plunge amplitude 0.175, and the Strouhal number 0.203. The investigation varies flexibility by varying the Π₁-parameter by varying the thickness of the models while maintaining the planform shape, the root chord 79 mm, and the span 241 mm. A range of Π₁ was used from 30 to 90,240. Dye flow visualization was performed using a 7-prongedrake oriented in the plane of the chord. Two camera views are used for dye flow visualization, one is normal to the plane of the chord and the other is perpendicular to the plane's normal. Structural deformations were performed with Laser Doppler vibrometry (LDV). Deformations were sampled at the quarter and three-quarter chord location at 0%, 25%, 50% and 75% span. Particle image velocimetry (PIV) measurements have been performed at 50% and 75% span at 30° phase increments of the motion. Results show that a flexibility effect is only observed at Pi;₁ = 30. The flexibility effect is marked by bending (40% of motion's root amplitude at 75% span) and a phase lag (60° phase at 75% span).