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Intermittency and Cessation of Vortex Shedding in the Wake of a Thin Flat Plate with a Circular Trailing EdgeThe near and very near wake of thin flat plates with both sharp and circular trailing edges (TEs) are investigated with direct numerical simulations (DNSs). The TE is circular in two of the cases (IN & NS) and sharp in one of them (ST). The separating boundary layers are turbulent in all cases. The objectives of this study are twofold. The first is to explore the effect of significantly reducing Re(sub D) (Reynolds number based on circular TE diameter, D) on the flow in the TE region, and the shedding process (Cases IN and NS). The second is to better understand the reasons underlying the findings of an earlier experimental wake investigation (sharp TE) where (1) the center-line values in normal intensity, and the peak in shear stress profiles in the cross-stream direction, were found to first increase in the streamwise direction (x), from that obtained at the TE, before diminishing further downstream, and (2) a broadband peak was observed in centerline cross-stream velocity (v) spectra (indicating quasi-periodicity, possibly due to vortices or wave-like motions). Case ST from the present study showed a near wake instability resulting in spanwise vortices (with a streamwise component). The instability is intermittent and contributes to both the broadband peak in the v spectrum and the initial increases in normal intensity and shear stress (as in the experiment). Case NS, with the lower value of ReD is an "essentially" non-shedding case where the flow in the TE region continually changes direction (upward/downward) because of turbulence. Case IN, with twice the value of ReD as Case NS, also exhibits a swaying motion in the TE region. In addition, vortex shedding is initiated during periods when the flow direction changes rapidly. Shedding in this case is intermittent. It results in a peak in the v spectrum obtained at the centerline (x/D = 1.0).
Document ID
20180006622
Acquisition Source
Ames Research Center
Document Type
Technical Memorandum (TM)
Authors
Rai, Man Mohan (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
October 24, 2018
Publication Date
August 1, 2018
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
NASA/TM-2018-219976
ARC-E-DAA-TN60310
Funding Number(s)
WBS: WBS 106148.03.01.03
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
direct numerical simulations
Turbulent wakes

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