Drag reduction by active control for flow past cylinders

2000 ◽  
pp. 287-363 ◽  
Author(s):  
J.-W. He ◽  
M. Chevalier ◽  
R. Glowinski ◽  
R. Metcalfe ◽  
A. Nordlander ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Active Control ◽  
Flow Past

Influence of active control on STG-based generation of streamwise vortices in near-wall turbulence

2012 ◽  
Vol 710 ◽  
pp. 234-259 ◽  
Author(s):  
B.-Q. Deng ◽  
C.-X. Xu
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Active Control ◽  
Phase Control ◽  
Transient Growth ◽  
Vortex Generation ◽  
Streamwise Vortices ◽  
Detection Plane ◽  
Near Wall ◽  
Opposition Control

AbstractNear-wall streamwise vortices are closely related to the generation of high skin friction in wall-bounded turbulent flows. A common feature of controlled, friction-reduced turbulent flows is weakened near-wall streamwise vortices. In the present study, the streak transient growth (STG) mechanism for generating near-wall streamwise vortices by Schoppa & Hussain (J. Fluid Mech., vol. 453, 2002, pp. 57–108) is employed, and the opposition control proposed by Choi, Moin & Kim (J. Fluid Mech., vol. 262, 1994, pp. 75–110) is imposed during the transient growth process of perturbations to determine how active control affects the generation of quasi-streamwise vortices. In the transient growth stage, when the detection plane is located near the wall (${ y}_{d}^{+ } = 15$), the control can suppress the production of streamwise vorticity by weakening the near-wall vertical velocity; when the detection plane moves away from the wall (${ y}_{d}^{+ } = 28$), the control has the opposite effect. In the vortex generation stage, the control cannot change the dominance of the stretching effect. Controls imposed at different stages reveal the importance of the STG stage in vortex generation. Strengthened out-of-phase control and lessened in-phase control are proposed as an extension of the original opposition-control scheme. Application in a fully developed turbulent channel flow shows that strengthened ${ y}_{d}^{+ } = 10$ control can yield an even higher drag reduction rate than the original ${ y}_{d}^{+ } = 15$ control. Moreover, lessened ${ y}_{d}^{+ } = 28$ control can also achieve drag reduction and turbulence suppression.

Experimental study of the active control applied to the flow past a backward facing ramp

2018 ◽  
Vol 59 (3) ◽  
Author(s):  
Dan Hlevca ◽  
Patrick Gilliéron ◽  
Francesco Grasso
Keyword(s):  
Experimental Study ◽  
Active Control ◽  
Flow Past

Active control of turbulent flow over a model vehicle for drag reduction

2004 ◽  
Vol 5 ◽  
Author(s):  
Jeonglae Kim ◽  
Seonghyeon Hahn ◽  
Jinsung Kim ◽  
Dong-kon Lee ◽  
Jin Choi ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Active Control

Active Control Methods for Drag Reduction in Flow Over Bluff Bodies (Keynote)

2002 ◽  
Author(s):  
Haecheon Choi
Keyword(s):  
Circular Cylinder ◽  
Drag Reduction ◽  
Active Control ◽  
High Frequency ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Control Methods ◽  
Periodic Forcing ◽  
Time Periodic

In this paper, we present two successful results from active controls of flows over a circular cylinder and a sphere for drag reduction. The Reynolds number range considered for the flow over a circular cylinder is 40∼3900 based on the free-stream velocity and cylinder diameter, whereas for the flow over a sphere it is 105 based on the free-stream velocity and sphere diameter. The successful active control methods are a distributed (spatially periodic) forcing and a high-frequency (time periodic) forcing. With these control methods, the mean drag and lift fluctuations decrease and vortical structures are significantly modified. For example, the time-periodic forcing with a high frequency (larger than 20 times the vortex shedding frequency) produces 50% drag reduction for the flow over a sphere at Re = 105. The distributed forcing applied to the flow over a circular cylinder results in a significant drag reduction at all the Reynolds numbers investigated.

Experimental investigation of wall-bounded turbulence drag reduction by active control of double piezoelectric vibrator

2020 ◽  
Vol 32 (4) ◽  
pp. 747-757
Author(s):  
Jian-xia Bai ◽  
Yong-xiang Huang ◽  
Nan Jiang ◽  
Xing-yu Ma ◽  
Zhan-qi Tang
Keyword(s):  
Experimental Investigation ◽  
Drag Reduction ◽  
Active Control ◽  
Piezoelectric Vibrator ◽  
Wall Bounded Turbulence

Numerical Simulation of Fluid Slip at a Hydrophobic Surface

Volume 4 ◽  
2004 ◽  
Author(s):  
Takao Fujita ◽  
Keizo Watanabe
Keyword(s):  
Boundary Condition ◽  
Laminar Flow ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Hydrophobic Surface ◽  
Friction Reduction ◽  
Water Repellent ◽  
Two Dimensional ◽  
Hydrophobic Property ◽  
Flow Past

Laminar drag reduction is achieved by using a hydrophobic surface. In this method, fluid slip is applied at the hydrophobic surface. An initial experiment to clarify for a laminar skin friction reduction was conducted using ducts with a highly water-repellent surface. The surface has a fractal-type structure with many fine grooves. Fluid slip at a hydrophobic surface has been analyzed by applying a new wet boundary condition. In this simulation, an internal flow is assumed to be a two-dimensional laminar flow in a rectangular duct and an external flow is assumed to be a two-dimensional laminar flow past a circular cylinder. The VOF technique has been used as the method for tracking gas-liquid interfaces, and the CSF model has been used as the method for modeling surface tension effects. The wet boundary condition for the hydrophobic property on the surface has been determined from the volume ratio in contact with water near the surface. The model with a stable gas-liquid interface and the experimental results of flow past a circular cylinder at Re = 250 without growing the Karman vortex street are made, and these results show that laminar drag reduction occurring due to fluid slip can be explained in this model.

scholarly journals High-Reynolds-number weakly stratified flow past an obstacle

1996 ◽  
Vol 317 ◽  
pp. 155-178 ◽  
Author(s):  
S. I. Chernyshenko ◽  
Ian P. Castro
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Turbulent Flows ◽  
High Reynolds Number ◽  
Bluff Body ◽  
Physical Mechanisms ◽  
Flow Past ◽  
Large Channel ◽  
Weak Stratification ◽  
High Reynolds

Stably stratified steady flow past a bluff body in a channel is considered for cases in which the stratification is not sufficiently strong to give solutions containing wave motions. The physical mechanisms by which stratification influences the flow are revealed. In particular, the drag reduction under weak stratification, observed in experiments, is explained. This is achieved by constructing an asymptotic laminar solution for high Reynolds number (Re) and large channel width, which explicitly gives the mechanisms, and using comparisons with numerical results for medium Re and experiments for turbulent flows to argue that these mechanisms are expected to be common in all cases. The results demonstrate the possibility, subject to certain restrictions, of using steady high-Re theory as a tool for studying qualitative features of real flows.

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