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    Publication
    DNS of an Oscillating Shear Layer Between Two Parallel Couette Flows
    (01-01-2021)
    Manohar Teja, Kalluri
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    A non-planar mixing layer observed between parallel Couette flows by Narasimhamurthy et al. (Phys Rev E 85:036,302, 2012) is considered. Direct numerical simulation is chosen, and simulations are run in order to determine the critical Reynolds number at which the interface between the co-flowing laminar and non-laminar flow becomes unstable exhibiting a meandering motion. The necessary conditions required to trigger the shear-layer instability were also discussed. Different combinations of Reynolds numbers are chosen keeping the Reynolds number ratio between the laminar and non-laminar flows as constant. Preliminary results indicate that the onset of instability occurs, and a meandering motion is observed at the interface when Reynolds number for the non-laminar flow corresponds to 650.
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    Publication
    DNS of wake from perforated plates: Aspect ratio effects
    (01-01-2021)
    Singh, Abhinav
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    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.