An Experimental Investigation of the Structure of a Turbulent Wind Over Water Waves PDF Download
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Author: Susumu Karaki
Publisher:
ISBN:
Category : Ocean waves
Languages : en
Pages : 126
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Book Description
This investigation presents experimental results from a study of the structure of a turbulent boundary layer developed by air flow over water waves in a lab wind-wave channel. It was demonstrated that the sheared flow region is two-layered, similar to rough wall boundary layers. The inner layer, adjacent to the wall, is describable by the 'law of the wall' and the outer flow by the 'defect law.' The data were taken in two-dimensional flow with small favorable pressure gradients. The first part of the two-part investigation involved air flow over an initially still water surface on which waves developed in response to wind excitation. In the second part, air was passed over water waves of a single frequency and varied amplitude. The results indicated that within the range of this study the water surface can be classed as aerodynamically rough at wind speeds greater than 12 fps and the flow structure of the boundary layer corresponds to that over a rough wall. The velocity decrement due to surface roughness is shown to be a function of the local root-mean-square wave height. The effect of wave-induced fluctuations in the air is limited to a very close neighborhood of the wavy surface. For the specific combination of wind and wave speeds of this study it was found that while the amplitudes of the horizontal components of the fluctuation decreased with increasing elevation, the vertical component increased. (Author).
Author: Susumu Karaki
Publisher:
ISBN:
Category : Ocean waves
Languages : en
Pages : 126
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Book Description
This investigation presents experimental results from a study of the structure of a turbulent boundary layer developed by air flow over water waves in a lab wind-wave channel. It was demonstrated that the sheared flow region is two-layered, similar to rough wall boundary layers. The inner layer, adjacent to the wall, is describable by the 'law of the wall' and the outer flow by the 'defect law.' The data were taken in two-dimensional flow with small favorable pressure gradients. The first part of the two-part investigation involved air flow over an initially still water surface on which waves developed in response to wind excitation. In the second part, air was passed over water waves of a single frequency and varied amplitude. The results indicated that within the range of this study the water surface can be classed as aerodynamically rough at wind speeds greater than 12 fps and the flow structure of the boundary layer corresponds to that over a rough wall. The velocity decrement due to surface roughness is shown to be a function of the local root-mean-square wave height. The effect of wave-induced fluctuations in the air is limited to a very close neighborhood of the wavy surface. For the specific combination of wind and wave speeds of this study it was found that while the amplitudes of the horizontal components of the fluctuation decreased with increasing elevation, the vertical component increased. (Author).
Author: Susumu Karaki
Publisher:
ISBN:
Category :
Languages : en
Pages : 100
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Author: Nasiruddin Shaikh
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The study of airside flow structure and its interaction with water at the air-water interface is important in order to understand the exchange of momentum, heat and mass fluxes between the two mediums. The present dissertation deals with the quantitative investigation of the near-surface flow above wind-sheared water surface through a series of laboratory experiments conducted over a wind speed range of 1.5 m s -1 to 4.4 m s-1 and at a fetch of 2.1 m. The two-dimensional velocity fields were measured using particle image velocimetry (PIV). To compare the airflow structure over the water surface with that over solid wall, the measurements were also made over the smooth and wavy walls at the same location, under identical conditions. The results show a reduction in the mean velocity magnitudes and the tangential stresses when gravity waves appear on the water surface. An enhanced vorticity layer was observed immediately above the water surface that extended to a height of approximately two times of the significant wave height. A novel approach is used to separate the wave-induced component from the instantaneous velocity fields. The flow structure was analyzed as a function of wave phase. The phase-averaged profiles of wave-induced velocity, vorticity and Reynolds stress showed different behaviour on the windward and leeward sides of the wave in the near-surface region. The results also show that the turbulent Reynolds stress mainly supports downward momentum transfer whereas the wave-induced Reynolds stress is responsible for the upward momentum transfer from wave to wind. This dissertation also provides first quantitative comparison of the mean, wave-induced and turbulent properties for the separated and non-separated flows over wind generated water waves. The maximum difference between the flow characteristics of the separated and non-separated flows is observed on the leeward side, within core of the separation region, where, higher magnitudes of the vorticity and turbulent properties were observed, indicating that the turbulence is significantly enhanced within the separation region. The comparison of the flow over smooth and wavy water and solid surfaces showed that although the trends in profiles over water and solid surfaces are mostly similar, the relative magnitudes of turbulent properties and their level of enhancement towards the surface are different over water and solid surfaces. Thus, the models for the flow over solid surfaces may not accurately predict the flow properties over the water surface especially in the near-surface region.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 836
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Author: A. John Chambers
Publisher:
ISBN:
Category : Energy transfer
Languages : en
Pages : 178
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Author: Richard Ives Hires
Publisher:
ISBN:
Category : Ocean-atmosphere interaction
Languages : en
Pages : 192
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Book Description
An experimental investigation was made to determine the ratio of the wave-supported shear stress, phi sub w; to the total shear stress on the water surface, phi sub o. The experimental conditions were designed to correspond to those required for the application of the viscous shear flow theory of wave generation proposed by Brooke Benjamin (1959) and Miles (1962b). The experiments were performed in a wind-wave tunnel, 48 x 3-1/2 x 2 feet, with a mean water depth of 1-1/2 feet. The wind in the 6 in. air space above the water was fully-developed turbulent channel flow. The mean center-line wind speed, U sub xi, was kept constant at 1.20 m/s during all measurements made with the wind blowing over the water. An artificially generated, single-component, wave train of small amplitude provided a known, initial perturbation of the water surface with which the wind could interact. The range of wave frequencies investigated was from 4.0 to 5.2 cps. Wave measurements were made with capacitance wave probes, wind measurements with hot-wire anemometers. (Author).
Author: S. G. Sajjadi
Publisher: OUP Oxford
ISBN: 9780198501923
Category : Mathematics
Languages : en
Pages : 388
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Book Description
One of the most familiar phenomena on the planet, water waves remain an elusive question for science. The way in which wind blows over water and causes waves is a very active area of research for applied mathematicians, as well as for oceanographers and engineers. The basic mechanisms are still a matter of controversy, although the use of modern techniques of asymptotic and non-linear analysis and large-scale computation, as well as experimental structures, are beginning to reveal the underlying mechanics. These studies are resulting in increasingly powerful methods of forecasting waves and of gauging and controlling their effects on such things as sediment, pollution, and offshore structures. This volume covers the wide range of current research on the relationship between wind and waves and includes contributions from many of the leading authorities in the field.
Author: Donald J. Portman
Publisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 28
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Book Description
Wind velocity components and air temperature fluctuations were measured within a few meters above lake and ocean waves to study the influence of waves on the three-dimensional structure of turbulence and the vertical fluxes of momentum and sensible heat. Analyses were made primarily in terms of variances, covariances, spectrum and cross-spectrum functions and joint probability distribution functions of the measured variables. The report summarizes the methods of measurement and data processing used and gives fourteen abstracts of reports, theses and papers resulting from the investigation. It lists, also, twenty periods of measurement, made during BOMEX, data from which are to be placed in the BOMEX Permanent Archive. (Author).
Author: Jung-Tai Lin
Publisher:
ISBN:
Category : Oil pollution of the sea
Languages : en
Pages : 212
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Author: Joe William Johnson
Publisher:
ISBN:
Category : Wind waves
Languages : en
Pages : 44
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