Turbulent Boundary Layer Distorted by a Longitudinal Ridge : Mean Flow Quantities and Skin-Friction Coefficient

2002 ◽  
Vol 2002 (0) ◽  
pp. 61-62
Author(s):  
Shinsuke Mochizuki ◽  
Daisuke Kohama ◽  
Hideo Osaka
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Skin Friction Coefficient ◽  
Mean Flow ◽  
Longitudinal Ridge

The skin-friction coefficient of a turbulent boundary layer modified by a large-eddy break-up device

2021 ◽  
Vol 33 (3) ◽  
pp. 035153
Author(s):  
I. C. Chan ◽  
R. Örlü ◽  
P. Schlatter ◽  
R. C. Chin
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Skin Friction Coefficient ◽  
Large Eddy ◽  
Break Up

PIV Study of Shallow Open Channel Flow Over d- and k-Type Transverse Ribs

2007 ◽  
Vol 129 (8) ◽  
pp. 1058-1072 ◽  
Author(s):  
M. F. Tachie ◽  
K. K. Adane
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Cross Section ◽  
Open Channel ◽  
Skin Friction Coefficient ◽  
Mixing Length ◽  
Mean Flow ◽  
Turbulent Statistics ◽  
The Mean

A particle image velocimetry was used to study shallow open channel turbulent flow over d-type and k-type transverse ribs of square, circular, and semi-circular cross sections. The ratio of boundary layer thickness to depth of flow varied from 50% to 90%. The mean velocities and turbulent quantities were evaluated at the top plane of the ribs to characterize interaction between the cavities and overlying boundary layer. It was found that the overlying boundary layer interacts more strongly with k-type cavities than observed for d-type cavities. The profiles of the mean velocities and turbulent statistics were then spatially averaged over a pitch, and these profiles were used to study the effects of rib type and cross section on the flow field. The mean velocity gradients were found to be non-negligible across the boundary layer, and the implications of this observation for momentum transport, eddy viscosity, and mixing length distributions are discussed. The results show that the skin friction coefficient, Reynolds stresses and mixing length distributions are independent of rib cross section for d-type. For the k-type ribs, significant variations in skin friction coefficient values, mean flow, and turbulence fields are observed between square ribs and circular/semi-circular ribs.

Measurement and Calculation of Fluid Dynamic Characteristics of Rough-Wall Turbulent Boundary-Layer Flows

1993 ◽  
Vol 115 (3) ◽  
pp. 383-388 ◽  
Author(s):  
M. H. Hosni ◽  
H. W. Coleman ◽  
R. P. Taylor
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Rough Surface ◽  
Skin Friction Coefficient ◽  
Rough Wall ◽  
Momentum Thickness ◽  
Boundary Layer Flows ◽  
Mean Velocity

Experimental measurements of profiles of mean velocity and distributions of boundary-layer thickness and skin friction coefficient from aerodynamically smooth, transitionally rough, and fully rough turbulent boundary-layer flows are presented for four surfaces—three rough and one smooth. The rough surfaces are composed of 1.27 mm diameter hemispheres spaced in staggered arrays 2, 4, and 10 base diameters apart, respectively, on otherwise smooth walls. The current incompressible turbulent boundary-layer rough-wall air flow data are compared with previously published results on another, similar rough surface. It is shown that fully rough mean velocity profiles collapse together when scaled as a function of momentum thickness, as was reported previously. However, this similarity cannot be used to distinguish roughness flow regimes, since a similar degree of collapse is observed in the transitionally rough data. Observation of the new data shows that scaling on the momentum thickness alone is not sufficient to produce similar velocity profiles for flows over surfaces of different roughness character. The skin friction coefficient data versus the ratio of the momentum thickness to roughness height collapse within the data uncertainty, irrespective of roughness flow regime, with the data for each rough surface collapsing to a different curve. Calculations made using the previously published discrete element prediction method are compared with data from the rough surfaces with well-defined roughness elements, and it is shown that the calculations are in good agreement with the data.

The Effect of Biofilms on Turbulent Boundary Layers

1999 ◽  
Vol 121 (1) ◽  
pp. 44-51 ◽  
Author(s):  
M. P. Schultz ◽  
G. W. Swain
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Layer Structure ◽  
Reynolds Shear Stress ◽  
Skin Friction Coefficient ◽  
Laser Doppler Velocimeter ◽  
Reynolds Stresses ◽  
The Mean

Materials exposed in the marine environment, including those protected by antifouling paints, may rapidly become colonized by microfouling. This may affect frictional resistance and turbulent boundary layer structure. This study compares the mean and turbulent boundary layer velocity characteristics of surfaces covered with a marine biofilm with those of a smooth surface. Measurements were made in a nominally zero pressure gradient, boundary layer flow with a two-component laser Doppler velocimeter at momentum thickness Reynolds numbers of 5600 to 19,000 in a recirculating water tunnel. Profiles of the mean and turbulence velocity components, including the Reynolds shear stress, were measured. An average increase in the skin friction coefficient of 33 to 187 percent was measured on the fouled specimens. The skin friction coefficient was found to be dependent on both biofilm thickness and morphology. The biofilms tested showed varying effect on the Reynolds stresses when those quantities were normalized with the friction velocity.

Large-eddy simulation of flow over a cylinder with from to : a skin-friction perspective

2017 ◽  
Vol 820 ◽  
pp. 121-158 ◽  
Author(s):  
W. Cheng ◽  
D. I. Pullin ◽  
R. Samtaney ◽  
W. Zhang ◽  
W. Gao
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Flow Separation ◽  
Skin Friction Coefficient ◽  
Cylinder Surface ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

We present wall-resolved large-eddy simulations (LES) of flow over a smooth-wall circular cylinder up to$Re_{D}=8.5\times 10^{5}$, where$Re_{D}$is Reynolds number based on the cylinder diameter$D$and the free-stream speed$U_{\infty }$. The stretched-vortex subgrid-scale (SGS) model is used in the entire simulation domain. For the sub-critical regime, six cases are implemented with$3.9\times 10^{3}\leqslant Re_{D}\leqslant 10^{5}$. Results are compared with experimental data for both the wall-pressure-coefficient distribution on the cylinder surface, which dominates the drag coefficient, and the skin-friction coefficient, which clearly correlates with the separation behaviour. In the super-critical regime, LES for three values of$Re_{D}$are carried out at different resolutions. The drag-crisis phenomenon is well captured. For lower resolution, numerical discretization fluctuations are sufficient to stimulate transition, while for higher resolution, an applied boundary-layer perturbation is found to be necessary to stimulate transition. Large-eddy simulation results at$Re_{D}=8.5\times 10^{5}$, with a mesh of$8192\times 1024\times 256$, agree well with the classic experimental measurements of Achenbach (J. Fluid Mech., vol. 34, 1968, pp. 625–639) especially for the skin-friction coefficient, where a spike is produced by the laminar–turbulent transition on the top of a prior separation bubble. We document the properties of the attached-flow boundary layer on the cylinder surface as these vary with$Re_{D}$. Within the separated portion of the flow, mean-flow separation–reattachment bubbles are observed at some values of$Re_{D}$, with separation characteristics that are consistent with experimental observations. Time sequences of instantaneous surface portraits of vector skin-friction trajectory fields indicate that the unsteady counterpart of a mean-flow separation–reattachment bubble corresponds to the formation of local flow-reattachment cells, visible as coherent bundles of diverging surface streamlines.

The measurement of skin friction in a turbulent boundary layer at a Mach number of 2.5, including the effect of a shock-wave

1952 ◽  
Vol 215 (1120) ◽  
pp. 84-99 ◽  
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Mach Number ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Static Pressure ◽  
Pressure Rise ◽  
Skin Friction Coefficient

The skin friction of the wall of a wind tunnel has been measured at a Mach number of 2.5 using the surface-tube technique. The Reynolds number (with the distance from the throat as the representative length) was of the order of 2 to 3 millions and the boundary layer was turbulent. The skin friction coefficient was much less than for a very small Mach number (the incompressible case) and the amount of the decrease agreed with calculation. The effect of a shock-wave of strength 2 was also investigated—the strength of a shock-wave is defined as the pressure rise through it divided by the static pressure in front of it. The shock-wave only affected the boundary layer for a few thicknesses upstream of its point of impingement even though it was strong enough to cause local separation. The results show: ( а ) That the surface, or Stanton, tube is a reliable means of measuring skin friction in spite of the large values (over a million with the second as the unit of time) of the velocity gradient at the wall, and that the skin friction coefficient does decrease with Mach number in the manner predicted by calculation. ( b ) That disturbances due to a shock-wave impinging on a turbulent boundary layer are only propagated upstream a few multiples of the boundary layer thicknesses even when the shock-wave is strong enough to cause local separation.

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