DNS of wake from perforated plates: aspect ratio effects Online publication date: Tue, 30-Nov-2021
by Abhinav Singh; Vagesh D. Narasimhamurthy
Progress in Computational Fluid Dynamics, An International Journal (PCFD), Vol. 21, No. 6, 2021
Abstract: Flow over a perforated plate is studied at Reynolds number 250. Effect of the plate aspect-ratio L/d (where, L is length and d is width) is studied by varying L from 1d-12d. Hydrodynamic forces on the plate and the shedding-frequency match for all the cases, though the wake-dynamics is distinct between the lower and upper L/d cases. In the low L/d cases, wake is coherent along the span and has reduced three-dimensionality. Flow here is undergoing wake-transition, where the wavelength of the secondary instability is about 1d. Further, jets from the perforation holes exhibit in-phase oscillation. Another feature is the presence of energetic sub-harmonics, where the wake is experiencing period-doubling bifurcations. In high L/d cases, wake exhibits higher incoherence due to vortex-dislocations and incoherent jet oscillations, which promotes flow three-dimensionality. Present study indicates that an L/d of about six is required for the simulations to be free from numerical effects.
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