DNS of viscoelastic turbulent channel flow with rectangular orifice at low Reynolds number |
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Authors: | Takahiro Tsukahara Tomohiro KawaseYasuo Kawaguchi |
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Institution: | Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan |
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Abstract: | Direct numerical simulations of turbulent viscoelastic-fluid flow in a channel with a rectangular orifice were performed to investigate the influence of viscoelasticity on turbulence statistics and turbulent structures downstream of the orifice. The geometry considered is periodic rectangular orifices with 1:2 expansion. The constitutive equation follows the Giesekus model, valid for polymer (or surfactant) solutions, which are generally capable of reducing the turbulent frictional drag in a smooth channel. The friction Reynolds number and the Weissenberg number were set to 100 and 20-30, respectively. A drag reduction of about 20% was achieved in the viscoelastic flows. The onset Reynolds number for the transition from a symmetric to an asymmetric state was found to be shifted to higher values than that for the Newtonian flow. In the viscoelastic flow, the turbulent kinetic energy was decreased and fewer turbulent eddies were observed, as the Kelvin-Helmholtz vortices were quickly damped. Away from the orifice, quasi-streamwise vortices in the viscoelastic flow were sustained for a longer period, accompanied by energy exchange from elastic energy of the viscoelastic fluid to kinetic energy. |
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Keywords: | Direct numerical simulation Drag reduction Non-Newtonian fluid Orifice Turbulence Viscoelasticity |
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