Turbulent flow over a very rough, random surface

Mulhearn, P. J.; Finnigan, John

doi:10.1007/bf00165509

Cited by 96 publications

(42 citation statements)

References 21 publications

(15 reference statements)

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“…In the 2-D case, shear stress is transported outward and is associated with streamwise deceleration while in the 3-D case the shear stress is transported wallward and is associated with a streamwise acceleration. Behavior similar to the 3-D case was also seen in the cases of sandgrain (Andreapoulos and Bradshaw, 1981) and gravel (Mulhearn and Finnigan, 1978). Bandyopadhyay and Watson (1988) also found the Townsend structural parameter ( 2 1 q uv A − = ) to be a constant between δ y of 0.1 and 0.8 thereby implying that the turbulence structure is independent of wall condition.…”

Section: Turbulence Structurementioning

confidence: 52%

Structure of 2-D and 3-D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements

George¹

2005

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The present study deals with the effects of sparsely distributed three-dimensional elements on two-dimensional (2-D) and three-dimensional (3-D) turbulent boundary layers (TBL) such as those that occur on submarines, ship hulls, etc. This study was achieved in three parts: Part 1 dealt with the cylinders when placed individually in the turbulent boundary layers, thereby considering the effect of a single perturbation on the TBL; Part 2 considered the effects when the same individual elements were placed in a sparse and regular distribution, thus studying the response of the flow to a sequence of perturbations; and in Part 3, the distributions were subjected to 3-D turbulent boundary layers, thus examining the effects of streamwise and spanwise pressure gradients on the same perturbed flows as considered in Part 2. The 3-D turbulent boundary layers were generated by an idealized wing-body junction flow.Detailed 3-velocity-component Laser-Doppler Velocimetry (LDV) and other measurements were carried out to understand and describe the rough-wall flow structure. The measurements include mean velocities, turbulence quantities (Reynolds stresses and triple products), skin friction, surface pressure and oil flow visualizations in 2-D and 3-D rough-wall flows for Reynolds numbers, based on momentum thickness, greater than 7000. Very uniform circular cylindrical roughness elements of 0.38mm, 0.76mm and 1.52mm height (k) were used in square and diagonal patterns, yielding six different roughness geometries of rough-wall surface. For the 2-D rough-wall flows, the roughness Reynolds numbers, + k , based on the element height (k) and the friction velocity ( τ U ), range from 26 to 131. Results for the 2-D rough-wall flows reveal that the velocity-defect law is similar for both smooth and rough surfaces, and the semi-logarithmic velocity-distribution curve is shifted by an amountdepending on the height of the roughness element, showing thatis a function of + k and the wall geometry. For the 3-D flows, the data show that the surface pressure gradient is not strongly influenced by the roughness elements. Higher roughness elements cause greater turbulence intensities near the wall, which cause the pressure-driven mean flow three-dimensionality to propagate or diffuse more rapidly from the wall region. In general, for both 2-D and 3-D rough-wall TBL, the differences between the two roughness patterns (straight and diagonal), as regards the mean velocities and the Reynolds stresses, are limited to about 3 roughness element heights from the wall.For the single elements, the values of + k range from 23 to 92. The study on single elements revealed that the separated shear layers emanating from the top of the elements form a pair of counter rotating vortices that dominate the downstream flow structure. These vortices, termed as the roughness top vortex structure (RTVS), in conjunction with the mean flow, forced over and around the elements, are responsible for the production of large Reynolds stresses in the neighborhood of th...

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Section: Turbulence Structurementioning

confidence: 52%

Structure of 2-D and 3-D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements

George¹

2005

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“…Finnigan [10], relying on wind tunnel experiments over random rough gravel surface, suggested that ! z r = 2D where !…”

Section: Introductionmentioning

confidence: 99%

Flow over cube arrays of different packing densities

Cheng

Hayden

Robins

et al. 2007

Journal of Wind Engineering and Industrial Aerodynamics

150

153

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“…Such exchanges are governed by a turbulent mixing process that appears to exhibit a number of universal characteristics (Amiro 1990;Amiro and Davis 1988;Raupach et al 1989;Gao et al 1992; Meyers 1988, 1989;Paw U et al 1992). Early attempts to predict these universal characteristics made use of rough-wall boundary layer analogies but limited success was reported (for review, see, e.g., Raupach et al 1996;Raupach et al 1991;Raupach 1979;Wilson 1989;Raupach and Thom 1981;Thompson 1979;Mulhearn and Finnigan 1978). A basic distinction between canopy and rough-wall boundary layer turbulence is that the ''for- VOLUME …”

Section: Introductionmentioning

confidence: 99%

Active Turbulence and Scalar Transport near the Forest–Atmosphere Interface

Katul¹,

Geron²,

Hsieh³

et al. 1998

J. Appl. Meteor.

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Turbulent velocity, temperature, water vapor concentration, and other scalars were measured at the canopyatmosphere interface of a 13-14-m-tall uniform pine forest and a 33-m-tall nonuniform hardwood forest. These measurements were used to investigate whether the mixing layer (ML) analogy of Raupach et al. predicts eddy sizes and flow characteristics responsible for much of the turbulent stresses and vertical scalar fluxes. For this purpose, wavelet spectra and cospectra were derived and analyzed. It was found that the ML analogy predicts well vertical velocity variances and integral timescales. However, at low wavenumbers, inactive eddy motion signatures were present in horizontal velocity wavelet spectra, suggesting that ML may not be suitable for scaling horizontal velocity perturbations. Momentum and scalar wavelet cospectra of turbulent stresses and scalar fluxes demonstrated that active eddy motion, which was shown by Raupach et al. to be the main energy contributor to vertical velocity (w) spectral energy (E w ), is also the main scalar flux-transporting eddy motion. Predictions using ML of the peak E w frequency are in excellent agreement with measured wavelet cospectral peaks of vertical fluxes (Kh ϭ 1.5, where K is wavenumber and h is canopy height). Using Lorentz wavelet thresholding of vertical velocity time series, wavelet coefficients associated with active turbulence were identified. It was demonstrated that detection frequency of organized structures, as predicted from Lorentz wavelet filtering, relate to the arrival frequency ͗U͘/h and integral timescale, where ͗U ͘ is the mean horizontal velocity at height z ϭ h. The newly proposed wavelet thresholding approach, which relies on a ''global'' wavelet threshold formulation for the energy in w, provides simultaneous energy-covariance-preserving characterization of ''active'' turbulence at the canopy-atmosphere interface.

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Turbulent flow over a very rough, random surface

Cited by 96 publications

References 21 publications

Structure of 2-D and 3-D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements

Structure of 2-D and 3-D Turbulent Boundary Layers with Sparsely Distributed Roughness Elements

Flow over cube arrays of different packing densities

Active Turbulence and Scalar Transport near the Forest–Atmosphere Interface

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