Interfaces and internal layers in a turbulent boundary layer

Jerke Eisma; Jerry Westerweel; Gijs Ooms; Gerrit E. Elsinga

doi:10.1063/1.4919909

Turbulent Boundary Layer Subjected to a Sudden Change in Surface Roughness and Temperature

10.1115/imece1999-0977 ◽

1999 ◽

Author(s):

João Henrique D. Guimarães ◽

Sergio J. F. dos Santos ◽

Jian Su ◽

Atila P. Silva Freire

Keyword(s):

Boundary Layer ◽

Surface Roughness ◽

Turbulent Boundary Layer ◽

Skin Friction ◽

Sudden Change ◽

Stanton Number ◽

Temperature Profiles ◽

Internal Layers ◽

Mean Velocity ◽

Wall Boundary Conditions

Abstract In present work, the dynamic and thermal behaviour of flows that develop over surfaces that simultaneously present a sudden change in surface roughness and temperature are discussed. In particular, the work is concerned with the physical validation of a newly proposed formulation for the near wall temperature profile. The theory uses the concept of the displacement in origin, together with some asymptotic arguments, to propose a new expression for the logarithmic region of the turbulent boundary layer. The new expressions are, therefore, of universal applicability, being independent of the type of rough surface considered. The present formulation may be used to give wall boundary conditions for two-equation differential models. The theoretical results are validated with experimental data obtained for flows that develop over flat surfaces with sudden changes in surface roughness and in temperature conditions. Measurements of mean velocity and of mean temperature are presented. A reduction of the data provides an estimate of the skin-friction coefficient, the Stanton number, the displacement in origin for both the velocity and the temperature profiles, and the thickness of the internal layers for the velocity and temperature profiles. The skin-friction co-efficient was calculated based on the chart method of Perry and Joubert (J.F.M., 17, 193–211, 1963) and on a balance of the integral momentum equation. The same chart method was used for the evaluation of the Stanton number and the displacement in origin.

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New perspectives on the impulsive roughness-perturbation of a turbulent boundary layer

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.75 ◽

2011 ◽

Vol 677 ◽

pp. 179-203 ◽

Cited By ~ 31

Author(s):

I. JACOBI ◽

B. J. McKEON

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Flow Field ◽

Spectral Energy ◽

Internal Layers ◽

Hot Wire ◽

Mean Velocity ◽

Composite Maps ◽

Downstream Flow ◽

Near Wall

The zero-pressure-gradient turbulent boundary layer over a flat plate was perturbed by a short strip of two-dimensional roughness elements, and the downstream response of the flow field was interrogated by hot-wire anemometry and particle image velocimetry. Two internal layers, marking the two transitions between rough and smooth boundary conditions, are shown to represent the edges of a ‘stress bore’ in the flow field. New scalings, based on the mean velocity gradient and the third moment of the streamwise fluctuating velocity component, are used to identify this ‘stress bore’ as the region of influence of the roughness impulse. Spectral composite maps reveal the redistribution of spectral energy by the impulsive perturbation – in particular, the region of the near-wall peak was reached by use of a single hot wire in order to identify the significant changes to the near-wall cycle. In addition, analysis of the distribution of vortex cores shows a distinct structural change in the flow associated with the perturbation. A short spatially impulsive patch of roughness is shown to provide a vehicle for modifying a large portion of the downstream flow field in a controlled and persistent way.

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Numerical investigation of the turbulent boundary layer over a bump

Journal of Fluid Mechanics ◽

10.1017/s0022112098008982 ◽

1998 ◽

Vol 362 ◽

pp. 229-271 ◽

Cited By ~ 38

Author(s):

XIAOHUA WU ◽

KYLE D. SQUIRES

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Pressure Gradient ◽

Eddy Viscosity ◽

Subgrid Scale ◽

Internal Layers ◽

Mean Flow ◽

Eddy Viscosity Model ◽

The Mean ◽

Shear Production

Large-eddy simulation (LES) has been used to calculate the flow of a statistically two-dimensional turbulent boundary layer over a bump. Subgrid-scale stresses in the filtered Navier–Stokes equations were closed using the dynamic eddy viscosity model. LES predictions for a range of grid resolutions were compared to the experimental measurements of Webster et al. (1996). Predictions of the mean flow and turbulence intensities are in good agreement with measurements. The resolved turbulent shear stress is in reasonable agreement with data, though the peak is over-predicted near the trailing edge of the bump. Analysis of the flow confirms the existence of internal layers over the bump surface upstream of the summit and along the downstream trailing at plate, and demonstrates that the quasi-step increases in skin friction due to perturbations in pressure gradient and surface curvature selectively enhance near-wall shear production of turbulent stresses and are responsible for the formation of the internal layers. Though the flow experiences a strong adverse pressure gradient along the rear surface, the boundary layer is unique in that intermittent detachment occurring near the wall is not followed by mean-flow separation. Certain turbulence characteristics in this region are similar to those previously reported in instantaneously separating boundary layers. The present investigation also explains the driving mechanism for the surprisingly rapid return to equilibrium over the trailing flat plate found in the measurements of Webster et al. (1996), i.e. the simultaneous uninterrupted development of an inner energy-equilibrium region and the monotonic decay of elevated turbulence shear production away from the wall. LES results were also used to examine response of the dynamic eddy viscosity model. While subgrid-scale dissipation decreases/increases as the turbulence is attenuated/enhanced, the ratio of the (averaged) forward to reverse energy transfers predicted by the model is roughly constant over a significant part of the layer. Model predictions of backscatter, calculated as the percentage of points where the model coefficient is negative, show a rapid recovery downstream similar to the mean-flow and turbulence quantities.

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Measurements of higher-order turbulent statistics in a turbulent boundary layer subjected to a short roughness strip

Thermal Science ◽

10.2298/tsci0704041o ◽

2007 ◽

Vol 11 (4) ◽

pp. 41-48

Author(s):

Olanrewaju Oyewola

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Outer Region ◽

Higher Order ◽

Turbulence Structure ◽

Internal Layers ◽

Smooth Wall ◽

Third Order ◽

Turbulent Statistics ◽

Roughness Strip

Hot-wire measurements have been undertaken in a turbulent boundary layer which is subjected to an impulse in form of a short roughness strip with the aim of determining its effect on turbulence structure. The quantifications were made through the measurements of higher-order turbulent statistics. The changes observed in the distributions of correlation coefficient, third-order moments, skew ness and flatness factor relative to the smooth wall suggests that the turbulence structure is modified downstream of the short roughness strip. Relative to the undisturbed smooth wall, the third-order moments were increased in the region between the two internal layers. This increased extends to significant portion of the outer region of the boundary layer. While a gain in turbulent kinetic energy by diffusion occurs throughout the boundary layer for a flow over the short roughness strip, those of the smooth wall occur near the wall.

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