scholarly journals Time Resolved PIV Investigation on the Skin Friction Reduction Mechanism of Outer-Layer Vertical Blades Array

2014 ◽  
Vol 7 (2) ◽  
pp. 901421
Author(s):  
Seong Hyeon Park ◽  
Nam Hyun An ◽  
Hyun Sik Yoon ◽  
Hyun Park ◽  
Ho Hwan Chun ◽  
...  
Keyword(s):  
Skin Friction ◽  
Outer Layer ◽  
Friction Reduction ◽  
Reduction Mechanism ◽  
Time Resolved ◽  
Skin Friction Reduction

scholarly journals PIV Investigation on the Skin Friction Reduction Mechanism of Outer-layer Vertical Blades

2011 ◽  
Vol 9 (1) ◽  
pp. 20-28 ◽  
Author(s):  
Hyun Park ◽  
Nam-Hyun An ◽  
Seong-Hyoen Park ◽  
Ho-Hwan Chun ◽  
In-Won Lee
Keyword(s):  
Skin Friction ◽  
Outer Layer ◽  
Friction Reduction ◽  
Reduction Mechanism ◽  
Skin Friction Reduction

Towards a Greater Understanding of Turbulent Skin-Friction Reduction

2002 ◽  
Author(s):  
Nick Hutchins ◽  
Kwing-So Choi
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Outer Layer ◽  
Large Scale ◽  
Convection Velocity ◽  
Friction Reduction ◽  
Horseshoe Vortices ◽  
Layer Region ◽  
Skin Friction Reduction ◽  
Near Wall

Measurements have been made in a turbulent boundary layer modified by flow aligned vertical (sub-boundary layer) elements. Comparisons between the coherent structure (near-wall and outer-layer region) for both modified and canonical cases have been conducted in order to better understand the mechanism of skin friction reduction. Thus far we can report a modified near-wall convection velocity obeying inner scaling and a reduced spread of correlated events away from the wall. The outer-layer appears to be characterised by large-scale arch-like structures which produce a velocity field consistent with the heads of lifted near-wall horseshoe vortices. The modified case shows reduced convection velocity, increased frequency of occurrence and increased entrainment for this type of outer-layer event.

Application of Air Microblowing Through a Porous Wall for Skin Friction Reduction on a Flat Plate

2010 ◽  
Vol 5 (3) ◽  
pp. 38-46
Author(s):  
Vladimir I. Kornilov ◽  
Andrey V. Boiko
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Porous Wall ◽  
Friction Reduction ◽  
Local Skin ◽  
Skin Friction Reduction

The effect of air microblowing through a porous wall on the properties of a turbulent boundary layer formed on a flat plate in an incompressible flow is studied experimentally. The Reynolds number based on the momentum thickness of the boundary layer in front of the porous insert is 3 900. The mass flow rate of the blowing air per unit area was varied within Q = 0−0.0488 кg/s/m2 . A consistent decrease in local skin friction, reaching up to 45−47 %, is observed to occur at the maximal blowing air mass flow rate studied.

Multiple slot skin friction reduction

1975 ◽  
Vol 12 (9) ◽  
pp. 753-754 ◽  
Author(s):  
F. G. Howard ◽  
J. N. Hefner ◽  
A. J. Srokowski
Keyword(s):  
Skin Friction ◽  
Friction Reduction ◽  
Skin Friction Reduction

Skin friction reduction by large air bubbles in a horizontal channel flow

2007 ◽  
Vol 33 (2) ◽  
pp. 147-163 ◽  
Author(s):  
Yuichi Murai ◽  
Hiroshi Fukuda ◽  
Yoshihiko Oishi ◽  
Yoshiaki Kodama ◽  
Fujio Yamamoto
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Friction Reduction ◽  
Horizontal Channel ◽  
Air Bubbles ◽  
Skin Friction Reduction

Proposal of control laws for turbulent skin friction reduction based on resolvent analysis

2019 ◽  
Vol 866 ◽  
pp. 810-840 ◽  
Author(s):  
Aika Kawagoe ◽  
Satoshi Nakashima ◽  
Mitul Luhar ◽  
Koji Fukagata
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Reduction ◽  
Suboptimal Control ◽  
Spectral Space ◽  
Control Laws ◽  
Wall Shear ◽  
Skin Friction Reduction

This paper evaluates and modifies the so-called suboptimal control technique for turbulent skin friction reduction through a combination of low-order modelling and direct numerical simulation (DNS). In a previous study, Nakashima et al. (J. Fluid Mech., vol. 828, 2017, pp. 496–526) employed resolvent analysis to show that the efficacy of suboptimal control was mixed across spectral space when the streamwise wall shear stress (case ST) was used as a sensor signal, i.e. specific regions of spectral space showed drag increment. This observation suggests that drag reduction may be attained if control is applied selectively in spectral space. DNS results presented in the present study, however, do not show a significant effect on the flow with selective control. A posteriori analyses attribute this lack of efficacy to a much lower actuation amplitude in the simulations compared to model assumptions. Building on these observations, resolvent analysis is used to design and provide a preliminary assessment of modified control laws that also rely on sensing the streamwise wall shear stress. Control performance is then assessed by means of DNS. The proposed control laws generate as much as $10\,\%$ drag reduction, and these results are broadly consistent with resolvent-based predictions. The physical mechanisms leading to drag reduction are assessed via conditional sampling. It is shown that the new control laws effectively suppress the near-wall quasi-streamwise vortices. A physically intuitive explanation is proposed based on a separate evaluation of clockwise and anticlockwise vortices.

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