Stably stratified air-flow over a waved water surface. Part 2: Wave-induced pre-turbulent motions

2015 ◽  
Vol 142 (695) ◽  
pp. 773-780 ◽  
Author(s):  
O. A. Druzhinin ◽  
Y. I. Troitskaya ◽  
S. S. Zilitinkevich
Keyword(s):  
Water Surface ◽  
Air Flow ◽  
Surface Part ◽  
Wave Induced

scholarly journals Numerical Evidence of Turbulence Generated by Nonbreaking Surface Waves

2015 ◽  
Vol 45 (1) ◽  
pp. 174-180 ◽  
Author(s):  
Wu-ting Tsai ◽  
Shi-ming Chen ◽  
Guan-hung Lu
Keyword(s):  
Surface Waves ◽  
Water Surface ◽  
Nonlinear Boundary Conditions ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Langmuir Turbulence ◽  
Near Surface ◽  
Order Of Magnitude ◽  
Turbulence Production ◽  
Wave Induced

AbstractNumerical simulation of monochromatic surface waves propagating over a turbulent field is conducted to reveal the mechanism of turbulence production by nonbreaking waves. The numerical model solves the primitive equations subject to the fully nonlinear boundary conditions on the exact water surface. The result predicts growth rates of turbulent kinetic energy consistent with previous measurements and modeling. It also validates the observed horizontal anisotropy of the near-surface turbulence that the spanwise turbulent intensity exceeds the streamwise component. Such a flow structure is found to be attributed to the formation of streamwise vortices near the water surface, which also induces elongated surface streaks. The averaged spacing between the streaks and the depth of the vortical cells approximates that of Langmuir turbulence. The strength of the vortices arising from the wave–turbulence interaction, however, is one order of magnitude less than that of Langmuir cells, which arises from the interaction between the surface waves and the turbulent shear flow. In contrast to Langmuir turbulence, production from the Stokes shear does not dominate the energetics budget in wave-induced turbulence. The dominant production is the advection of turbulence by the velocity straining of waves.

Wave-Induced Effect on the Airside Velocity Field Above the Wind-Generated Water Waves

2008 ◽  
Author(s):  
Nasiruddin Shaikh ◽  
Kamran Siddiqui
Keyword(s):  
Velocity Field ◽  
Water Waves ◽  
Water Surface ◽  
Flow Behavior ◽  
Wave Crest ◽  
Reynolds Stresses ◽  
Momentum Exchange ◽  
Significant Wave ◽  
Wind Speeds ◽  
Wave Induced

An experimental study was conducted to investigate the influence of surface waves on the airside flow behavior over the water surface. Two-dimensional velocity field in a plane perpendicular to the surface was measured using particle image velocimetry (PIV) at wind speeds of 3.7 and 4.4 m s−1. The results show that the wave induced velocities are significant immediately adjacent to the water surface and their magnitudes decreases with height and become negligible at a height three times the significant wave height. The structure of the wave induced vorticity indicates two different type of flow pattern on the windward and leeward sides of the wave crest. Positive and negative magnitudes of the turbulent and wave induced Reynolds stress respectively, indicates upward and down transfer of momentum flux across air water interface. The results also indicate that the flow dynamics in the region two to three times significant wave heights are significantly different than that at greater heights. Higher magnitudes of the turbulent and wave induced Reynolds stresses were observed in this region which could not be predicted from the measurements at greater heights. Thus, it is concluded the understanding of the wave effects to the airflow field especially within the crest-trough region is vital to improve our knowledge about the air-water heat, mass and momentum exchange.

An analytic model of the generation of surface gravity waves by turbulent air flow

1992 ◽  
Vol 236 ◽  
pp. 197-215 ◽  
Author(s):  
Cornelis A. Van Duin ◽  
Peter A. E. M. Janssen
Keyword(s):  
Growth Rate ◽  
Air Flow ◽  
Phase Speed ◽  
Surface Gravity ◽  
Mixing Length ◽  
Surface Gravity Wave ◽  
Eddy Viscosity Model ◽  
Induced Field ◽  
Turbulent Air Flow ◽  
Wave Induced

Turbulent air flow over a surface gravity wave of small amplitude is studied on the basis of a family of first-order closure models, of which the eddy viscosity model and Prandtl's mixing-length model are members. Results are obtained by the method of matched asymptotic expansions in three layers. The problem is modelled by taking into account the combined effects of turbulence and molecular viscosity, which accommodates a proper imposition of the boundary conditions at the wave surface. The detailed structure of the various wave-induced field variables throughout the flow is then investigated. In addition, it is found that the growth rate of the waves by wind depends on the turbulence model. In particular, the more sensitively the mixing length depends on the shear in the mean air flow, the higher the growth rate. The validity of the results we obtain is restricted to small drag coefficient and small phase speed. Comparisons are made with other theoretical studies and with recent laboratory and field observations.

scholarly journals Statistical Parameters of the Air Turbulent Boundary Layer over Steep Water Waves Measured by the PIV Technique

2011 ◽  
Vol 41 (8) ◽  
pp. 1421-1454 ◽  
Author(s):  
Yu. Troitskaya ◽  
D. Sergeev ◽  
O. Ermakova ◽  
G. Balandina
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Interaction Parameter ◽  
Water Waves ◽  
Water Surface ◽  
Wind Wave ◽  
Wave Interaction ◽  
Statistical Parameters ◽  
Piv Technique ◽  
Wave Induced

Abstract A turbulent airflow with a centerline velocity of 4 m s−1 above 2.5-Hz mechanically generated gravity waves of different amplitudes has been studied in experiments using the particle image velocimetry (PIV) technique. Direct measurements of the instantaneous flow velocity fields above a curvilinear interface demonstrating flow separation are presented. Because the airflow above the wavy water surface is turbulent and nonstationary, the individual vector fields are conditionally averaged sampled on the phase of the water elevation. The flow patterns of the phase-averaged fields are relatively smooth. Because the averaged flow does not show any strongly nonlinear effects, the quasi-linear approximation can be used. The parameters obtained by the flow averaging are compared with the theoretical results obtained within the theoretical quasi-linear model of a turbulent boundary layer above the wavy water surface. The wave-induced pressure disturbances in the airflow are calculated using the retrieved statistical ensemble of wind flow velocities. The energy flux from the wind to waves and the wind–wave interaction parameter are estimated using the obtained wave-induced pressure disturbances. The estimated values of the wind–wave interaction parameter are in a good agreement with the theory.

Investigation of droplet-mediated sensible and latent heat fluxes in a turbulent air flow over a waved water surface by direct numerical simulation

2020 ◽  
Author(s):  
Oleg Druzhinin
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Direct Numerical Simulation ◽  
Latent Heat ◽  
Water Surface ◽  
Air Flow ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Coupled Equations ◽  
Turbulent Air Flow

<p>The objective of the present study is to investigate sensible and latent heat transfer mediated by evaporating saline droplets in a turbulent air flow over a waved water surface by performing direct numerical simulation. Equations of the air-flow velocity, temperature and humidity are solved simultaneously with the two-way-coupled equations of individual droplets coordinates and velocities, temperatures and masses. Two different cases of air and water surface temperatures,T<sub>a</sub> = 27 <sup>0</sup>C, T<sub>s</sub> = 28 <sup>0</sup>C,  and T<sub>a</sub> = -10 <sup>0</sup>C, T<sub>s</sub> = 0 <sup>0</sup>C, are considered and conditionally termed as "tropical cyclone" (TC) and "polar low"  (PL) conditions, respectively. Droplets-mediated sensible and latent heat fluxes, Q<sub>S</sub> and Q<sub>L</sub>, are integrated along individual droplets Lagrangian trajectories and evaluated as distributions over droplet diameter at injection, d, and also obtained as Eulerian, ensemble-averaged fields. The results show that under TC-conditions, the sensible heat flux from droplets to air is negative whereas the latent heat flux is positive, and thus droplets cool and moisturize the carrier air. On the other hand, under PL-conditions, Q<sub>S</sub> and Q<sub>L</sub>  are both positive, and Q<sub>L</sub> – contribution is significantly reduced as compared to Q<sub>S</sub> - contribution. Thus in this case, droplets warm up the air. In both cases, the droplet-mediated enthalpy flux, Q<sub>S</sub><sub> </sub>+ Q<sub>L </sub>, is positive, vanishes for sufficiently small droplets (with diameters d ≤ 150 μm) and further increases with d. The results also show that the net fluxes are reduced with increasing wave slope.</p><p>This work is supported by the Ministry of Education and Science of the Russian Federation (Task No. 0030-2019-0020). Numerical algorithms were developed under the support of RFBR (Nos. 18-05-60299, 18-55-50005, 18-05-00265, 20-05-00322). Postprocessing was performed under the support of the Russian Science Foundation (No. 19-17-00209).</p>

scholarly journals A NOTE ON THE DEVELOPMENT OF WIND WAVES IN AN EXPERIMENT

1966 ◽  
Vol 1 (10) ◽  
pp. 5
Author(s):  
Tokuichi Hamada ◽  
Akihiko Shibayama ◽  
Hajime Kato
Keyword(s):  
Boundary Condition ◽  
Tangential Stress ◽  
Water Surface ◽  
Physical Mechanism ◽  
Wind Waves ◽  
Air Flow ◽  
Wave Momentum

This is a note paper of experiment in an air-water experimental waterway. Two cases of the uniform depth of water 50 cm and of the uniform depth of water 15 cm are examined. The boundary condition for air flow is not changed. In a condition of almost the same discharge of air flow on the water surface, the development of wind waves is investigated. The properties of wind waves are slightly different in each case, but the analysis of physical mechanism of the development suggests that almost the same mechanism is active throughout both cases. Stillmore the portion of tangential stress, which is apparently transfered to wave momentum, is numerically obtained, and it is not so different in both cases of depth of water.

Stably stratified airflow over a waved water surface. Part 1: Stationary turbulence regime

2015 ◽  
Vol 142 (695) ◽  
pp. 759-772 ◽  
Author(s):  
O. A. Druzhinin ◽  
Y. I. Troitskaya ◽  
S. S. Zilitinkevich
Keyword(s):  
Water Surface ◽  
Surface Part ◽  
Stationary Turbulence ◽  
Turbulence Regime
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