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.

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.

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.

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.

Wind Tunnel Tests of Two Lucy Ashton Reflex Geosims

1970 ◽  
Vol 14 (04) ◽  
pp. 241-276
Author(s):  
P. N. Joubert ◽  
N. Matheson
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Viscous Drag ◽  
Two Dimensional ◽  
Local Skin ◽  
Wind Tunnel Tests ◽  
Local Skin Friction

A 9-ft and a 4½-ft reflex model of the Lucy Ashton were tested in a wind tunnel. Both pins and wires were used as stimulators to promote a turbulent boundary layer. The effects of the stimulators could be taken into account by considering the virtual origin of the turbulent boundary layer. Slightly different viscous drag curves were found for each model, both with a slope much steeper than previously anticipated. The skin friction was determined using two independent methods. Large increases and deficits in local skin friction coefficients were found at the bow and stern of the models respectively as compared with those for a two-dimensional flat plate.

Air Blowing Into Boundary Layer Of A Flat Plate With Length-Dependent Permeability

2016 ◽  
Vol 11 (3) ◽  
pp. 16-26
Author(s):  
Vladimir Kornilov ◽  
Andrey Boiko ◽  
Ivan Kavun ◽  
Anatoliy Popkov
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Skin Friction Coefficient ◽  
Air Blowing ◽  
The Mean

A generalized analysis of the results of numerical and experimental studies of air blowing into a turbulent boundary layer through finely perforated surface consisting of alternating permeable and impermeable sections of varying length providing a sudden change in the flow conditions at the boundaries of these sections is presented. The air blowing coefficient Cb determined by the mass flow rate per unit area of the active perforated sample varied in the range from 0 to 0.008. It is shown that as Cb grows, the maximum reduction in the mean surface skin-friction coefficient CF, which is the value through the permeable area of perforated sample, reaches about 65 %. When keeping the equal mass flow rate Q for all tested combinations, the mean skin-friction coefficient remains constant, independent of geometrical parameters of permeable and impermeable sections. Increasing the length of the last permeable section leads to the growth of relaxation region which is characterized by the reduced skin friction values on the impermeable part of the flat plate.

Experience of the Using of Cascade Method for Turbulent Boundary-Layer Control Through Air Blowing

2014 ◽  
Vol 9 (1) ◽  
pp. 49-61
Author(s):  
Vladimir Kornilov ◽  
Ivan Kavun ◽  
Anatoliy Popkov
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Wind Tunnel Test ◽  
Barometric Pressure ◽  
Local Skin ◽  
Air Blowing ◽  
Ground Conditions ◽  
Local Skin Friction ◽  
The Difference ◽  
Cascade Method

The possibilities of turbulent drag reduction in an incompressible turbulent boundary layer of a flat plate with air blowing through a microperforated surface which consists of sequentially arranged one behind the other self-contained permeable areas were studied. Mass flow rate of air blowing per unit area Q was increased with increasing distance downstream, but in total was not more than 0.0768 kg/s/m2 . A consistent reduction of the local skin friction values along the length of the model, up to 70% at the end of the last active blowing area was shown. The experimental data characterizing the ability to manage a turbulent boundary layer in the ground conditions by passive air overflow generated by the difference between the barometric pressure and the pressure in the wind tunnel test section were obtained

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