A numerical study of the effects of superhydrophobic surface on skin-friction drag in turbulent channel flow

2013 ◽  
Vol 25 (11) ◽  
pp. 110815 ◽  
Author(s):  
Hyunwook Park ◽  
Hyungmin Park ◽  
John Kim
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Superhydrophobic Surface ◽  
Numerical Study ◽  
Turbulent Channel Flow ◽  
Friction Drag

Effects of the air layer of an idealized superhydrophobic surface on the slip length and skin-friction drag

2016 ◽  
Vol 790 ◽  
Author(s):  
Taeyong Jung ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Superhydrophobic Surface ◽  
Slip Length ◽  
Joint Probability ◽  
Turbulent Channel Flow ◽  
Water Interface ◽  
Friction Drag ◽  
Recirculating Flow ◽  
Air Water Interface

The anisotropy of the slip length and its effect on the skin-friction drag are numerically investigated for a turbulent channel flow with an idealized superhydrophobic surface having an air layer, where the idealized air–water interface is flat and does not contain the surface-tension effect. Inside the air layer, both the shear-driven flow and recirculating flow with zero net mass flow rate are considered. With increasing air-layer thickness, the slip length, slip velocity and percentage of drag reduction increase. It is shown that the slip length is independent of the water flow and depends only on the air-layer geometry. The amount of drag reduction obtained is in between those by the empirical formulae from the streamwise slip only and isotropic slip, indicating that the present air–water interface generates an anisotropic slip, and the streamwise slip length ($b_{x}$) is larger than the spanwise one ($b_{z}$). From the joint probability density function of the slip velocities and velocity gradients at the interface, we confirm the anisotropy of the slip lengths and obtain their relative magnitude ($b_{x}/b_{z}=4$) for the present idealized superhydrophobic surface. It is also shown that the Navier slip model is valid only in the mean sense, and it is generally not applicable to fluctuating quantities.

Deposition of Small Particles From Turbulent Flows

2003 ◽  
Author(s):  
Z. Wu ◽  
J. B. Young
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Channel Flow ◽  
Gas Turbines ◽  
Particle Deposition ◽  
Numerical Study ◽  
Turbulent Channel Flow ◽  
Brownian Diffusion ◽  
Small Particles ◽  
Two Fluid

This paper deals with particle deposition onto solid walls from turbulent flows. The aim of the study is to model particle deposition in industrial flows, such as the one in gas turbines. The numerical study has been carried out with a two fluid approach. The possible contribution to the deposition from Brownian diffusion, turbulent diffusion and shear-induced lift force are considered in the study. Three types of turbulent two-phase flows have been studied: turbulent channel flow, turbulent flow in a bent duct and turbulent flow in a turbine blade cascade. In the turbulent channel flow case, the numerical results from a two-dimensional code show good agreement with numerical and experimental results from other resources. Deposition problem in a bent duct flow is introduced to study the effect of curvature. Finally, the deposition of small particles on a cascade of turbine blades is simulated. The results show that the current two fluid models are capable of predicting particle deposition rates in complex industrial flows.

Numerical study of high-order Lagrangian structure functions in a turbulent channel flow with low Reynolds number

2010 ◽  
Vol 22 (S1) ◽  
pp. 215-218 ◽  
Author(s):  
Jian-ping Luo ◽  
Zhi-ming Lu ◽  
TatsLo Ushijima ◽  
Osami Kitoh ◽  
Xiang Qiu ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Turbulent Channel Flow ◽  
Structure Functions ◽  
High Order ◽  
Low Reynolds

Suboptimal control of turbulent channel flow for drag reduction

1998 ◽  
Vol 358 ◽  
pp. 245-258 ◽  
Author(s):  
CHANGHOON LEE ◽  
JOHN KIM ◽  
HAECHEON CHOI
Keyword(s):  
Shear Stress ◽  
Feedback Control ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Suboptimal Control ◽  
Local Distribution ◽  
Friction Drag ◽  
Control Laws ◽  
Simple Feedback

Two simple feedback control laws for drag reduction are derived by applying a suboptimal control theory to a turbulent channel flow. These new feedback control laws require pressure or shear-stress information only at the wall, and when applied to a turbulent channel flow at Reτ=110, they result in 16–22% reduction in the skin-friction drag. More practical control laws requiring only the local distribution of the wall pressure or one component of the wall shear stress are also derived and are shown to work equally well.

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