Air Driven Water Flow Past Small Scale Roughness

2005 ◽  
Author(s):  
Guoqing Wang ◽  
Alric Rothmayer
Keyword(s):  
Water Flow ◽  
Small Scale ◽  
Flow Past ◽  
Scale Roughness

Water flow drives small scale biogeography of pesticides and bacterial pesticide degraders - A microcosm study using 2,4-D as a model compound

2018 ◽  
Vol 127 ◽  
pp. 137-147 ◽  
Author(s):  
Marc Pinheiro ◽  
Holger Pagel ◽  
Christian Poll ◽  
Franziska Ditterich ◽  
Patricia Garnier ◽  
...  
Keyword(s):  
Water Flow ◽  
Model Compound ◽  
Small Scale ◽  
Microcosm Study

On turbulent separation in the flow past a bluff body

1992 ◽  
Vol 241 ◽  
pp. 443-467 ◽  
Author(s):  
A. Neish ◽  
F. T. Smith
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Separated Flow ◽  
Small Scale ◽  
Supporting Evidence ◽  
Turbulent Regime ◽  
Trailing Edge ◽  
Flow Past ◽  
Starting Point ◽  
Turbulence Factor

The basic model problem of separation as predicted by the time-mean boundary-layer equations is studied, with the Cebeci-Smith model for turbulent stresses. The changes between laminar and turbulent flow are investigated by means of a turbulence ‘factor’ which increases from zero for laminar flow to unity for the fully turbulent regime. With an attached-flow starting point, a small increase in the turbulence factor above zero is found to drive the separation singularity towards the trailing edge or rear stagnation point for flow past a circular cylinder, according to both computations and analysis. A separated-flow starting point is found to produce analogous behaviour for the separation point. These findings lead to the suggestion that large-scale separation need not occur at all in the fully turbulent regime at sufficiently high Reynolds number; instead, separation is of small scale, confined near the trailing edge. Comments on the generality of this suggestion are presented, along with some supporting evidence from other computations. Further, the small scale involved theoretically has values which seem reasonable in practical terms.

Reverberation Intensity Decaying in Range-Dependent Waveguide

2019 ◽  
Vol 27 (03) ◽  
pp. 1950007
Author(s):  
J. R. Wu ◽  
T. F. Gao ◽  
E. C. Shang
Keyword(s):  
Large Scale ◽  
Back Propagation ◽  
Normal Modes ◽  
Small Scale ◽  
Signal Pulse ◽  
First Order ◽  
Orthogonal Property ◽  
Short Signal ◽  
Scale Roughness ◽  
Special Case

In this paper, an analytic range-independent reverberation model based on the first-order perturbation theory is extended to range-dependent waveguide. This model considers the effect of bottom composite roughness: small-scale bottom rough surface provides dominating energy for reverberation, whereas large-scale roughness has the effect of forward and back propagation. For slowly varying bottom and short signal pulse, analytic small-scale roughness backscattering theory is adapted in range-dependent waveguides. A parabolic equation is used to calculate Green functions in range-dependent waveguides, and the orthogonal property of local normal modes is employed to estimate the modal spectrum of PE field. Synthetic tests demonstrate that the proposed reverberation model works well, and it can also predict the reverberation of range-independent waveguide as a special case.

scholarly journals The significant impact of ribs and small-scale roughness on cylinder drag crisis

2020 ◽  
Vol 202 ◽  
pp. 104192 ◽  
Author(s):  
Arne Kilvik Skeide ◽  
Lars Morten Bardal ◽  
Luca Oggiano ◽  
R. Jason Hearst
Keyword(s):  
Small Scale ◽  
Scale Roughness ◽  
Cylinder Drag

scholarly journals Lagrangian and spectral analysis of the forced flow past a circular cylinder using pulsed tangential jets

2012 ◽  
Vol 696 ◽  
pp. 285-300 ◽  
Author(s):  
T. Jardin ◽  
Y. Bury
Keyword(s):  
Circular Cylinder ◽  
Time Series Data ◽  
Excitation Frequency ◽  
Shear Layers ◽  
Forced Flow ◽  
Series Data ◽  
Small Scale ◽  
Characteristic Time Scale ◽  
Momentum Coefficient ◽  
Flow Past

AbstractWe numerically investigate the influence of pulsed tangential jets on the flow past a circular cylinder. To this end a spectral-Lagrangian dual approach is used on the basis of time-series data. The analysis reveals that the flow response to unsteady forcing is driven by strong interactions between shear layers and pulsed jets. The latter preferentially lead to either the lock-on regime or the quasi-steady vortex feeding regime whether the excitation frequency is of the order of, or significantly greater than, the frequency of the natural instability. The intensity of the wake vortices is mainly influenced by the momentum coefficient through the introduction of opposite-sign vorticity in the shear layers. This feature is emphasized using a modal-based time reconstruction, i.e. by reconstructing the flow field upon a specific harmonic spectrum associated with a characteristic time scale. The quasi-steady regime exhibits small-scale counter-rotating vortices that circumscribe the separated region. In the lock-on regime, atypical wake patterns such as 2P or $\mathrm{P} + \mathrm{S} $ can be observed, depending on the forcing frequency and the momentum coefficient, highlighting remarkable analogies with oscillating cylinders.

Inferring Ice/Ocean Surface Roughness from Horizontal Current Measurements

1989 ◽  
Vol 111 (2) ◽  
pp. 155-159 ◽  
Author(s):  
M. G. McPhee
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Local Stress ◽  
Horizontal Stress ◽  
Current Speed ◽  
Small Scale ◽  
Horizontal Current ◽  
Similarity Model ◽  
Scale Roughness ◽  
Shear Production

Turbulence measurements in the underice boundary layer from two Arctic drift stations are used to develop a method for estimating the small-scale roughness, zo, of the ice underside from horizontal current and current variance, sampled at one level. Horizontal variance is shown to be well correlated with turbulent kinetic energy (TKE). Measurements also indicate that at depths where turbulence is fully developed to the surface roughness, shear production of TKE is approximately in balance with viscous dissipation, so that the magnitude of local horizontal stress is proportional to flow variance. A similarity model is used to extrapolate local stress to the interface, and zo is estimated from the logarithmic profile for current speed. The method has application for using remote data buoys, equipped with “smart” current meters, for mapping the underice roughness.

Influence of slip on the flow past superhydrophobic circular cylinders

2011 ◽  
Vol 680 ◽  
pp. 459-476 ◽  
Author(s):  
PRANESH MURALIDHAR ◽  
NANGELIE FERRER ◽  
ROBERT DANIELLO ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Superhydrophobic Surfaces ◽  
Separation Point ◽  
Circular Cylinders ◽  
Recirculation Region ◽  
Small Scale ◽  
Flow Past ◽  
Shedding Frequency

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large- and small-scale channels. In this paper, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from polydimethylsiloxane with well-defined micron-sized patterns of surface roughness. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction, the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. Thus, in this paper we demonstrate that vortex shedding dynamics is very sensitive to changes of feature spacing, size and orientation along superhydrophobic surfaces.

scholarly journals A MODIFIED TWO-SCALE MICROWAVE SCATTERING MODEL FOR A GAUSSIAN-DISTRIBUTED CONDUCTING ROUGH SURFACE

2018 ◽  
Vol XLII-3 ◽  
pp. 2141-2146
Author(s):  
F. Yu ◽  
H. Wang ◽  
Z. Y. Chen
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Large Scale ◽  
Incident Angle ◽  
Wavelet Packet ◽  
Small Scale ◽  
Backscattering Coefficient ◽  
Microwave Scattering ◽  
Scattering Model ◽  
Scale Roughness

A modified two-scale microwave scattering model (MTSM) was presented to describe the scattering coefficient of natural rough surface in this paper. In the model, the surface roughness was assumed to be Gaussian so that the surface height <i>z(x, y)</i> can be split into large-scale and small-scale components relative to the electromagnetic wavelength by the wavelet packet transform. Then, the Kirchhoff Model (KM) and Small Perturbation Method (SPM) were used to estimate the backscattering coefficient of the large-scale and small-scale roughness respectively. Moreover, the ‘tilting effect’ caused by the slope of large-scale roughness should be corrected when we calculated the backscattering contribution of the small-scale roughness. Backscattering coefficient of the MTSM was the sum of backscattering contribution of both scale roughness surface. The MTSM was tested and validated by the advanced integral equation model (AIEM) for dielectric randomly rough surface, the results indicated that, the MTSM accuracy were in good agreement with AIEM when incident angle was less than 30&amp;deg; (<i>&amp;theta;<sub>i</sub></i>&amp;thinsp;&amp;lt;30&amp;deg;) and the surface roughness was small (<i>ks</i>&amp;thinsp;=&amp;thinsp;0.354).

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