Parametric Study on a Sinusoidal Riblet for Drag Reduction by Direct Numerical Simulation

Flow around a circular cylinder controlled using plasma actuators is investigated by means of direct numerical simulation (DNS). The Reynolds number based on the freestream velocity and the cylinder diameter is set atReD=1000. The plasma actuators are placed at±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.

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0315 Direct Numerical Simulation of Drag Reduction by Uniform Blowing in Turbulent Boundary Layer

The Proceedings of the Fluids engineering conference ◽

10.1299/jsmefed.2009.179 ◽

2009 ◽

Vol 2009 (0) ◽

pp. 179-180

Author(s):

Yukinori KAMETANI ◽

Koji Fukagata

Keyword(s):

Numerical Simulation ◽

Boundary Layer ◽

Turbulent Boundary Layer ◽

Direct Numerical Simulation ◽

Drag Reduction

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Direct numerical simulation of spatially developing turbulent boundary layers with uniform blowing or suction

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.219 ◽

2011 ◽

Vol 681 ◽

pp. 154-172 ◽

Cited By ~ 46

Author(s):

YUKINORI KAMETANI ◽

KOJI FUKAGATA

Keyword(s):

Numerical Simulation ◽

Boundary Layer ◽

Direct Numerical Simulation ◽

Drag Reduction ◽

Skin Friction ◽

Reduction Factor ◽

Stream Velocity ◽

Normal Velocity ◽

Friction Drag ◽

Local Skin

Direct numerical simulation (DNS) of spatially developing turbulent boundary layer with uniform blowing (UB) or uniform suction (US) is performed aiming at skin friction drag reduction. The Reynolds number based on the free stream velocity and the 99% boundary layer thickness at the inlet is set to be 3000. A constant wall-normal velocity is applied on the wall in the range, −0.01U∞ ≤ Vctr ≤ 0.01U∞. The DNS results show that UB reduces the skin friction drag, while US increases it. The turbulent fluctuations exhibit the opposite trend: UB enhances the turbulence, while US suppresses it. Dynamical decomposition of the local skin friction coefficient cf using the identity equation (FIK identity) (Fukagata, Iwamoto & Kasagi, Phys. Fluids, vol. 14, 2002, pp. L73–L76) reveals that the mean convection term in UB case works as a strong drag reduction factor, while that in US case works as a strong drag augmentation factor: in both cases, the contribution of mean convection on the friction drag overwhelms the turbulent contribution. It is also found that the control efficiency of UB is much higher than that of the advanced active control methods proposed for channel flows.

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Direct numerical simulation of viscoelastic turbulent channel flow exhibiting drag reduction: effect of the variation of rheological parameters

Journal of Non-Newtonian Fluid Mechanics ◽

10.1016/s0377-0257(98)00115-3 ◽

1998 ◽

Vol 79 (2-3) ◽

pp. 433-468 ◽

Cited By ~ 171

Author(s):

Costas D. Dimitropoulos ◽

R. Sureshkumar ◽

Antony N. Beris

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Drag Reduction ◽

Channel Flow ◽

Turbulent Channel Flow ◽

Rheological Parameters ◽

Reduction Effect

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A direct numerical simulation of laminar and turbulent flow over riblet-mounted surfaces

Journal of Fluid Mechanics ◽

10.1017/s0022112093001363 ◽

1993 ◽

Vol 250 ◽

pp. 1-42 ◽

Cited By ~ 106

Author(s):

Douglas C. Chu ◽

George Em Karniadakis

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Turbulent Flow ◽

Drag Reduction ◽

Complex Geometry ◽

Fourier Method ◽

Experimental Results ◽

Shear Stresses ◽

Smooth Wall ◽

Turbulent Statistics

The flow in a channel with its lower wall mounted with streamwise riblets is simulated using a highly efficient spectral element-Fourier method. The range of Reynolds numbers investigated is 500 to 3500, which corresponds to laminar, transitional, and turbulent flow states. A complete study is presented for V-groove riblets; the effect of rounded riblets is also investigated. Our results suggest that in the laminar regime there is no drag reduction, while in the transitional and turbulent regimes drag reduction exists (approximately 6 % at Reynolds number 3500) for the riblet-mounted wall in comparison with the smooth wall of the channel. For the first time, we present detailed turbulent statistics (turbulence intensities, Reynolds shear stresses, skewness and flatness) as well as a temporal analysis using a numerical analog of the VITA technique. The flow structure over the riblet-mounted wall is also analysed in some detail and compared with the corresponding flow over the smooth wall in an attempt to identify the physical mechanisms that cause drag reduction. The accuracy of the computation is established by comparing flow quantities corresponding to the smooth wall with previous direct numerical simulation results as well as with experimental results; on the riblet-mounted wall comparison is made with available experimental results. The agreement is very good for both cases. The current computation is the first direct numerical simulation of turbulence in a complex geometry domain.

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