Experimental Investigation of Tandem Arrangement of two Inverted Flags in the Wake of a Cylinder

Abstract

Analysis of different arrangements of the piezoelectric flexible bodies are of keen interest due to their performance variation. Inverted flags (leading free and trailing clamped end) are currently trending because of their greater amplitudes of oscillation and ambient friendly nature (i.e. they can flap at low flow speed also). Varying flexural rigidities and studying their effects have also been of great interest for the researchers. Here we have observed the tandem arrangement of inverted flags and investigated the effects of increasing flexural rigidity “𝛾”, stream wise gap between them “Gx/L” and velocity of the flow “V” in water tunnel. Voltages produced “Vrms”, flapping frequency of the rear flag decreased by increasing the rigidity whereas the amplitude over length of the flag “A/L” was almost unchanged. A/L and frequency were affected by the increase of velocity. Also varying stream wise gap “Gx/L” had significant influence on the performance of the rear flag. Stream wise gap “Gx/L” between 1~2 showed greater performance of the flag as all the three parameters were at their peaks. Below Gx/L=1, rear flag flaps with negligible amplitudes and flapping frequencies which led to the least values of Vrms generated. Parameters of the upstream flag were not observed because of their minute values due to inverted drafting phenomenon. However, amplitudes of both the flags were compared for the observed purpose of that phenomenon which agreed well. Furthermore, the rear got deflected even at very low flow velocities due to which leading flag did not experience much flapping.