Measurements for Turbulent Channel Flow Containing Microbubbles Using PIV/LIF Technique

2002 ◽  
Author(s):  
Shigeki Nagaya ◽  
Koichi Hishida ◽  
Yoshiaki Kodama ◽  
Akira Kakugawa
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Experimental Approach ◽  
Turbulent Channel Flow ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Local Skin ◽  
Local Skin Friction ◽  
Turbulent Flow Field ◽  
Skin Friction Reduction

It is known that local skin friction can be reduced by injecting microbubbles into a trubulent boundary layer. However, so far the mechanism of the reduction has never been understood. In the present study, the objective is to understand the characteristics of a turbulent flow field containing microbubbles with an experimental approach in order that the mechanism for the skin friction reduction is clearly elucidated. In order to measure the flow with the microbubbles, a combination of PIV and LIF methods is developed. Measurements are carried out for a horizontal channel flow with microbubbles by which the skin friction is reduced. Modifications of the wall turbulence due to the injection of the microbubbles are discussed.

Influence of Heel on Bubble Layer at the Plate Bottom

2013 ◽  
Vol 753-755 ◽  
pp. 2683-2688
Author(s):  
Xiao Shuai Sun ◽  
Wen Cai Dong
Keyword(s):  
Skin Friction ◽  
Void Ratio ◽  
Reduction Rate ◽  
Longitudinal Direction ◽  
Friction Reduction ◽  
Local Skin ◽  
Local Skin Friction ◽  
Bubble Layer ◽  
The Difference ◽  
Skin Friction Reduction

In order to study the influence of heel on bubble layer shape and stability, based on Fluent and Mixture model, a numerical model was established to calculate bubble layer shape at the plate bottom at different main flow velocity, air flow rate and heel degree. The influence on bubble layer shape and skin friction reduction rate caused by heel was investigated. The results show that: bubble layer at the plate bottom spreads with the inflow transversely and longitudinally. When there is heel degree, bubble layer drifts to the smaller draft side. As heel degree increases, the drift of bubble layer becomes larger and the skin friction reduction rate decreases greatly. The local skin friction even increases greatly at the plate bottom apart from the air injection board. Both local void ratio and local friction reduction rate decreases in the longitudinal direction along the plate. Local void ratio is bigger than local friction reduction rate and the difference increases in the longitudinal direction along the plate.

Flat-Plate Skin Friction Under The Conditions Of Air Blowing Through A Wall With Intermittent In Length Permeability

2015 ◽  
Vol 10 (3) ◽  
pp. 48-62
Author(s):  
Vladimir Kornilov ◽  
Andrey Boiko ◽  
Ivan Kavun
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Unit Area ◽  
Friction Reduction ◽  
Local Skin ◽  
Air Blowing ◽  
Local Skin Friction ◽  
Incompressible Boundary ◽  
Skin Friction Reduction

Possibility of turbulent skin-friction reduction in an incompressible boundary layer of a flat plate with air blowing through a microperforated surface consisting of alternating permeable and impermeable sections was studied experimentally and computationally. The mass flow rate of the air per unit area was varied in the range from 0 to 0.0709 kg/s/m2 , which corresponds to the maximum blowing coefficient equal to 0.00344. A consistent reduction of the local skin-friction values along the chord of the microperforated insert was found, the reduction achieving nearly 70 % at the end of the last active blowing sections, except the impermeable surface sections demonstrating, on the contrary, the skin friction increase: the longer section, the higher skin friction.

Linear proportional–integral control for skin-friction reduction in a turbulent channel flow

2017 ◽  
Vol 814 ◽  
pp. 430-451 ◽  
Author(s):  
Euiyoung Kim ◽  
Haecheon Choi
Keyword(s):  
Skin Friction ◽  
Channel Flow ◽  
Flow Model ◽  
Turbulent Channel Flow ◽  
Friction Reduction ◽  
Normal Velocity ◽  
Integral Control ◽  
Velocity Fluctuations ◽  
Proportional Integral ◽  
Skin Friction Reduction

In the present study, we apply a proportional (P)–integral (I) feedback control to a turbulent channel flow for skin-friction reduction. The instantaneous wall-normal velocity at a sensing plane above the wall is measured as a sensing parameter, and blowing/suction is provided at the wall based on the PI control. The performance of PI controls is estimated by the change in the skin friction while varying the sensing plane location $y_{s}$ and the proportional and integral feedback gains ($\unicode[STIX]{x1D6FC}$ and $\unicode[STIX]{x1D6FD}$ respectively). The opposition control proposed by Choi et al. (J. Fluid Mech., vol. 262, 1994, pp. 75–110) corresponds to a P control with $\unicode[STIX]{x1D6FC}=1$. When the sensing plane is located close to the wall ($y_{s}^{+}\lesssim 10$), PI controls result in greater skin-friction reductions than corresponding P controls. The root-mean-square (r.m.s.) sensing velocity fluctuations, considered as the control error, approach zero with successful PI controls, but do not with P controls. Successful PI controls reduce the strength of near-wall coherent structures and the r.m.s. velocity fluctuations above the wall apart from those near the wall due to the control input. The frequency spectra of the sensing velocity show that the I component of PI controls significantly reduces the energy at low frequencies, much more than P controls do. Proportional–integral controls are also applied to a linearized flow model having transient growth of disturbances. The performance of PI controls for a linearized flow model is very similar to that for a turbulent channel flow, i.e. the low-frequency components of disturbances are significantly reduced by the I component of PI controls, and the transient energy growth is suppressed more than by P controls.

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.

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

Measurement of the Wall Shear Stress With Sublayer Thin Plate of Thermochromic Liquid Crystal

2015 ◽  
Author(s):  
Takashi Kodama ◽  
Shinsuke Mochizuki
Keyword(s):  
Shear Stress ◽  
Liquid Crystal ◽  
Friction Coefficient ◽  
Wall Shear Stress ◽  
Skin Friction ◽  
Channel Flow ◽  
Skin Friction Coefficient ◽  
Local Skin ◽  
Local Skin Friction ◽  
Wall Shear

New optical method for measurement of the local wall shear stress has been developed by using thermo-chromic liquid crystal temperature measurement based on hue [1], [2] of the camera view. The flow field is the fully developed turbulent channel flow. Thin film made of thermo-chromic liquid crystal is placed on the wall. A rectangular shaped obstacle is glued on the film. The obstacle is within a region of buffer layer with height from the wall. Temperature of the film and the obstacle are slightly raised by a heater below the wall. The air flow makes non-uniform temperature distribution and non-uniform color distribution appears on the surface of the film. Relations between hue and local skin friction coefficient were examined in a turbulent air channel flow. It is indicated that a certain hue of a point is varying linearly against the corresponding local skin friction coefficient.

Turbulent Skin Friction Reduction through the Application of Superhydrophobic Coatings to a Towed Submerged SUBOFF Body

2020 ◽  
pp. 1-9
Author(s):  
James W. Gose ◽  
Kevin Golovin ◽  
Mathew Boban ◽  
Brian Tobelmann ◽  
Elizabeth Callison ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Channel Flow ◽  
Friction Reduction ◽  
Doppler Velocity ◽  
Reynolds Stresses ◽  
Average Decrease ◽  
Skin Friction Reduction ◽  
Overall Resistance ◽  
Near Wall

In the present study, the drag-reducing effect of sprayed superhydrophobic surfaces (SHSs) is determined for two external turbulent boundary layer (TBL) flows. We infer the modification of skin friction created beneath TBLs using near-wall laser Doppler velocity measurements for a series of tailored SHSs. Measurements of the near-wall Reynolds stresses were used to infer reduction in skin friction between 8% and 36% in the channel flow. The best candidate SHS was then selected for application on a towed submersible body with a SUBOFF profile. The SHS was applied to roughly 60% of the model surface over the parallel midbody of the model. The measurements of the towed resistance showed an average decrease in the overall resistance from 2% to 12% depending on the speed and depth of the towed model, which suggests a SHS friction drag reduction of 4-24% with the application of the SHS on the model. The towed model results are consistent with the expected drag reduction inferred from the measurements of a near-zero pressure gradient TBL channel flow.

scholarly journals Turbulent drag reduction through oscillating discs

2014 ◽  
Vol 746 ◽  
pp. 536-564 ◽  
Author(s):  
Daniel J. Wise ◽  
Pierre Ricco
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Oscillation Period ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Reynolds Stresses ◽  
Disc Diameter ◽  
Tip Velocity

AbstractThe changes in a turbulent channel flow subjected to sinusoidal oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations (DNS). The Reynolds number is ${Re}_{\tau }=180$, based on the friction velocity of the stationary-wall case and the half-channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20 %. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim of identifying the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, the latter computed by taking into account the power spent to actuate the discs. This may be positive and reaches 6 %. The Rosenblat viscous pump flow, namely the laminar flow induced by sinusoidal in-plane oscillations of an infinite disc beneath a quiescent fluid, is used to predict accurately the power spent for disc motion in the fully developed turbulent channel flow case and to estimate localized and transient regions over the disc surface subjected to the turbulent regenerative braking effect, for which the wall turbulence exerts work on the discs. The Fukagata–Iwamoto–Kasagi identity is employed effectively to show that the wall-friction reduction is due to two distinguished effects. One effect is linked to the direct shearing action of the near-wall oscillating-disc boundary layer on the wall turbulence, which causes the attenuation of the turbulent Reynolds stresses. The other effect is due to the additional disc-flow Reynolds stresses produced by the streamwise-elongated structures which form between discs and modulate slowly in time. The contribution to drag reduction due to turbulent Reynolds stress attenuation depends on the penetration thickness of the disc-flow boundary layer, while the contribution due to the elongated structures scales linearly with a simple function of the maximum tip velocity and oscillation period for the largest disc diameter tested, a result suggested by the Rosenblat flow solution. A brief discussion on the future applicability of the oscillating-disc technique is also presented.

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