Investigation of the Flopping Regime of Two-, Three-, and Four-Plate Arrays

The variation of the base pressure coefficient (Cp) and the characteristics of the power spectra of the velocity for arrays of two-, three- and four-plates aligned normal to the flow are presented. The wakes downstream of the plates in the array are shown to exhibit behavior that varies between stable modes, flopping and quasi-stable behavior depending on the $s/t$ distance (where s is the spacing between the top and bottom surfaces of adjacent plates and t is the thickness of the plate). For the two and three-plate arrays with $s/t=0.25,$ peaks in the power spectra of about 48.2 and 98.1 Hz which correspond to Strouhal numbers of 0.06 and 0.11 are observed. For the four-plate array with $s/t=0.192,$ no clear peaks are visible. Probability density functions of uncalibrated hot-wire signals show that the peaks in the power do not correspond to continuously periodic fluctuations. [S0098-2202(00)00604-0]