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1.
Direct measurements of eddy diffusivities for momentum K m and heat K h by Doppler radar and by a radio acoustic sounding system in the upper troposphere and lower stratosphere were used to examine the applicability of three Reynolds-averaged Navier-Stokes (RANS) schemes of stratified turbulence in the environment: the E — ? turbulence scheme modified for stratified flows, the algebraic two-parameter E — ? Reynolds-stress scheme, and the three-parameter \(E - \varepsilon - \overline {\theta ^2 } \) turbulence scheme. All turbulence parameters-the turbulent kinetic energy (E), the dissipation rate (?), and vertical profiles of potential temperature (atmospheric stability) and mean wind velocity-were derived from direct measurements for all three turbulence schemes. It is shown that the profile of the vertical diffusivity of momentum (K m ) obtained from the three-parameter RANS turbulence scheme agrees well with its directly measured analog. The profile of K m calculated by the two-parameter turbulence schemes fits measurements rather qualitatively. 相似文献
2.
O. F. Vasil’ev O. F. Voropaeva A. F. Kurbatskii 《Izvestiya Atmospheric and Oceanic Physics》2011,47(3):265-280
Specific features of the turbulent transfer of the momentum and heat in stably stratified geophysical flows, as well as possibilities for including them into RANS turbulence models, are analyzed. The momentum (but not heat) transfer by internal gravity waves under conditions of strong stability is, for example, one such feature. Laboratory data and measurements in the atmosphere fix a clear dropping trend of the inverse turbulent Prandtl number with an increasing gradient Richardson number, which must be reproduced by turbulence models. Ignoring this feature can cause a false diffusion of heat under conditions of strong stability and lead, in particular, to noticeable errors in calculations of the temperature in the atmospheric boundary layer. Therefore, models of turbulent transfer must include the effect of the action of buoyancy and internal gravity waves on turbulent flows of the momentum. Such a strategy of modeling the stratified turbulence is presented in the review by a concrete RANS model and original results obtained during the modeling of stratified flows in the environment. Semiempirical turbulence models used for calculations of complex turbulent flows in deep stratified bodies of water are also analyzed. This part of the review is based on the data of investigations within the framework of the large international scientific Comparative Analysis and Rationalization of Second-Moment Turbulence Models (CARTUM) project and other publications of leading specialists. The most economical and effective approach associated with modified two-parameter turbulence models is a real alternative to classical variants of these models. A class of test problems and laboratory and full-scale experiments used by the participants of the CARTUM project for the approbation of numerical models are considered. 相似文献
3.
The results obtained from both atmospheric and laboratory measurements and from LES data show that, in the stably stratified
flows of the atmospheric boundary layer, turbulent mixing occurs at gradient Richardson numbers Ri
g
that significantly exceed one: the inverse turbulent Prandtl number Pr
t
−1 decreases with an increase in the thermal flow stability. The decreasing trend of the inverse turbulent Ptandtl number is
reproduced in a stably stratified atmospheric boundary layer in agreement with measurement data with the aid of an improved
three-parameter turbulence model. In this model, a modified model that takes into account the effect of stratification in
the expression for the time scale of the scalar field is used for the pressure-scalar correlation. 相似文献
4.
A. V. Glazunov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(3):282-299
The neutrally stratified boundary layer over a smooth rough surface is consider. The turbulent flow is simulated using a finite-difference eddy-resolving model of the atmospheric boundary layer (ABL). The model includes different turbulence closure schemes and numerical approximations for advection components of the momentum balance equation. We investigate the quality of reproduction of spectral characteristics of the turbulent flow and the model’s capabilities to reproduce the observed profile of mean wind velocity near the rough surface. It is shown that the best result is obtained by coupling a numerical scheme of higher order of accuracy with a mixed closure scheme based on an adaptive estimation of the mixing length for subgrid-scale fluctuations. Here, we are able to reproduce the asymptotics of the fluctuation spectrum of the longitudinal component of wind velocity near the surface and within the boundary layer as well as the logarithmic profile of mean velocity near the surface. 相似文献
5.
Both wind turning with height and ageostrophic flow in a stably stratified atmospheric boundary layer are analyzed using a three-parameter turbulence model. For a quasi-steady state of the boundary layer, the cross-isobaric flow is determined only by turbulent stress at the surface in the direction of geostrophic wind. The “operative” prediction models, in which the first-order turbulence closure schemes are used, tend to overestimate the boundary-layer depth and underestimate the angle between the surface and geostrophic winds when compared to “research” models (schemes of high-level turbulence closure). The true value of the angle between the surface and geostrophic winds is significant for the presentation of a large-scale flow. A nocturnal low-level jet is a mesoscale phenomenon reflected in data obtained from measurements in a stably stratified atmospheric boundary layer. It is found that such jets are of great importance in transporting humidity, momentum, and air pollution. In this study, the difference between jet flows over a homogeneous underlying surface and over a spatially localized large-scale aerodynamic roughness is shown. 相似文献
6.
A recently developed fully explicit algebraic model of Reynolds stress and turbulent heat flux in a thermally stratified planetary atmospheric boundary layer without stratification has been used for a numerical study of the Ekman turbulent boundary layer over a homogeneous rough surface for different dimensionless surface Rossby numbers. A comparative analysis has been conducted for a closure model of the transport term in the prognostic equation of turbulent kinetic energy dissipation including third-order moments. Dependences of the total wind rotation angle on the Rossby number have been obtained. The calculated vertical profiles of mean velocity, turbulent stress, turbulent kinetic energy, surface-friction velocity, and boundary-layer height agree satisfactorily with observational and earlier obtained LES data. 相似文献
7.
The features of the structure of a stable boundary layer over an urbanized surface are studied using a nonlocal model for the turbulent momentum and heat fluxes, which physically adequately takes into account the effect of buoyancy on turbulent transfer. The transformation of the structure of the boundary layer during transition from a state of convective mixing to a stable state is described by unified expressions for the turbulent momentum and heat fluxes. In some known schemes, different models are used for unstable and stable states. The model reproduces a stable dependence of the Prandtl number on the Richardson number and countergradient heat transfer in a strongly stable boundary layer. The results of numerical simulation are compared to the data of a laboratory experiment and the data obtained using the large-eddy simulation (LES) method. 相似文献
8.
Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes and were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and cγ were found to decrease and increase respectively as Ri increases. 相似文献
9.
10.
Both horizontal and vertical heat exchanges and feedbacks between air temperature and anthropogenic heat fluxes significantly affect the characteristics of the urban heat island (UHI). The UHI intensity depends, in particular, on the ratio between the scales LA (area of anthropogenic forcing) and Lγ (distance passed by an air particle of the oncoming stably stratified flow before its temperature approaches air temperature within the UHI). Both advection and feedback effects may be estimated based on the equation for the local heat balance of the underlying surface. In this case, heat advection is taken into account by calculating temperatures individually for the atmospheric boundary layer and the surface of the urban canopy layer. The estimates show that the asymptotics of strong advection is more characteristic of a typical city. However, under weak winds, with consideration for the feedback between air temperature and anthropogenic heat flux, some deviations from this asymptotics are probable. 相似文献
11.
《Coastal Engineering》2004,51(10):1021-1049
A numerical process-based model to forecast beach profile morphodynamics has been developed. In the present paper, an analysis of various modelling approaches and key parametrizations involved in the estimation of the wave-driven current and the suspended sediment concentration is carried out.Several resolution techniques for the 1DV horizontal (i.e., in the x-direction perpendicular to coastline) momentum equation governing the Mean Horizontal Velocity (MHV) are analysed. In the first kind of techniques, the mean horizontal velocity is computed from the momentum equation, whereas the Mean Water Level (MWL) is computed using a parametrization of the depth-averaged momentum equation. Two boundary or integral conditions are thus needed. In the second kind, both mean horizontal velocity and mean water level gradient in the x-direction are the unknowns of the momentum equation, thus, three boundary or integral conditions are needed. Various additional conditions are discussed. We show that using a technique of the first kind is equivalent to imposing the difference between the surface and the bottom shear stresses in the 1D vertical equation. Both techniques lead to results that are in good agreement with the Delta Flume experimental data, provided the Stokes drift flow discharge is imposed as an additional condition. The influence of the breaking roller model and of the turbulent viscosity parametrization are also analysed.Suspended sediment transport by the mean current and wave-induced bedload transport are taken into account in the sediment flux. Three turbulent diffusivity parametrizations are compared for suspended sediment concentration estimations. A linear profile for the turbulent diffusivity taking into account the wave bottom shear stress and the surface wave breaking turbulence production is shown to give the best results. Using experimental data, we put forward the poor estimation of the bottom sediment concentration given by the three implemented parametrizations. We thus propose a new parametrization relying on a Shields parameter based on the breaking roller induced surface shear stress. Using this new parametrization, the bottom profile used in the tests keeps its two bars which disappear otherwise. However, the morphodynamical model still overestimates the bars offshore motion, a bias already observed in other models. 相似文献
12.
A. V. Glazunov 《Izvestiya Atmospheric and Oceanic Physics》2010,46(6):727-747
The dependence that the structure and intensity of turbulent and large-scale quasiordered eddies in the atmospheric boundary
layer (ABL) have on the direction of geostrophic wind has been studied on the basis of a series of numerical experiments with
a three-dimensional nonstationary model of high spatial resolution. The presence of the meridional component of the angular
velocity of the Earth’s rotation results in a significant intensification of velocity fluctuations in a neutrally stratified
turbulent flow during the easterly and northeasterly winds and in their decay during the westerly and southwesterly winds.
This, in turn, results in significant variations in the mean velocity profile. It is shown that these variations are associated
with the largest scale fluctuations and are comparable (in scale) to the depth of Ekman’s turbulent layer. It is found that,
in the neutrally stratified ABL bounded in height and under stable stratification inside the ABL, the wind-direction dependence
significantly decreases. The possibilities of parameterizing these effects in locally one-dimensional ABL models are discussed. 相似文献
13.
Nicholas Williamson Atsuki Komiya Shigenao Maruyama Masud Behnia Steve W. Armfield 《Journal of Oceanography》2009,65(3):349-359
The transport of nutrient-rich, deep sea water from an artificial upwelling pipe has been simulated. A numerical model has
been built within a commercial Computational Fluid Dynamics (CFD) package. The model considers the flow of the deep sea water
after it is ejected from the pipe outlet in a negatively buoyant plume (densimetric Froude number = −2.6), within a stably
stratified ocean environment subject to strong ocean current cross flow. Two cross-flow profiles were tested with momentum
flux ratios equal to 0.92 and 3.7. The standard k-ε turbulence model has been employed and a range of turbulent Schmidt and Prandtl numbers tested. In all cases the results
show that the rapid diffusion of heat and salinity at the pipe outlet causes the plume to attain neutral buoyancy very rapidly,
preventing strong fountain-like behavior. At the higher momentum flux ratio fountain-like behavior is more pronounced close
to the pipe outlet. The strong cross-current makes horizontal advection the dominant transport process downstream. The nutrient
plume trajectory remains largely within one relatively thin stratified layer, making any ocean cross-flow profile less important.
Very little unsteady behavior was observed. The results show that the nutrient is reduced to less than 2% of its inlet concentration
10 meters downstream of the inlet and this result is largely independent of turbulent Prandtl or Schmidt number. Initial results
would suggest that if such an artificial upwelling were to be viable for an ocean farming project, a large number of upwelling
pipes would be necessary. Further work will have to determine the minimum nutrient concentration required to sustain a viable
phytoplankton population and the required spacing between upwelling pipes. 相似文献
14.
Some changes in the eddy mixing in the atmospheric boundary layer (ABL) are investigated with the use of the mesoscale RANS turbulence model. It is found that the behavior of parameters of the eddy turbulence mixing is in compliance with the recently obtained data of laboratory and atmospheric measurements. In particular, the flow Richardson number (Ri f ) during the transient flow to a strongly stable state can behave nonmonotonically, growing with the increasing gradient Richardson number (Ri g ) to the state of saturation at a certain gradient Richardson number (Ri g ? 1), which separates two different turbulent regimes: the regimes of strong mixing and weak mixing. An analysis of the energetics based on the balance equations of kinetic and potential turbulence energies shows, in particular, that the weak mixing (Ri g > 1) is quite capable of transferring momentum. This phenomenon can be explained not only by the fact that the flow is sustained by propagating internal waves, which effectively transfer momentum under strong stratification conditions, but also by the fact that turbulence permanently arises in the free atmosphere and in the deep ocean at Ri g ? 1. 相似文献
15.
块体空气动力算法的再计算湍通量与NCEP湍通量的比较 总被引：1，自引：0，他引：1
以NCEP资料提供的水文气象参数作为输入量,利用4种块体空气动力算法重新计算了动量和热量通量,与相应的NCEP自身提供的湍通量进行了比较分析,发现再计算动量、感热和潜热通量的偏差值随风速增加而增大;在中高风速下,再计算动量通量的相对误差较小,其他情况下再计算动量、感热和潜热通量的相对误差最高能达到50%左右;相对误差一般随纬度的增大而增大,表明两者之间存在不协调性。研究还表明,改进后的NCEP2资料与NCEP1资料相比,这种不协调性并没有得到改善。 相似文献
16.
B. B. Ilyushin 《Izvestiya Atmospheric and Oceanic Physics》2014,50(3):246-255
Results of simulating the diurnal evolution of the atmospheric boundary layer (ABL) with a second-order closure model are presented. The model includes new algebraic expressions for triple correlations to describe their behavior over the entire height of the mixed layer adequately to measurements. The model also takes into account the influence of long-wave radiation on the heat balance, which becomes important in the nocturnal ABL. The modeling results are compared with 24-h ABL evolution simulations by the third-order closure model and available in situ and laboratory measurements. 相似文献
17.
This paper presents a wave-resolving sediment transport model, which is capable of simulating sediment suspension in the field-scale surf zone. The surf zone hydrodynamics is modeled by the non-hydrostatic model NHWAVE (Ma et al., 2012). The turbulent flow and suspended sediment are simulated in a coupled manner. Three effects of suspended sediment on turbulent flow field are considered: (1) baroclinic forcing effect; (2) turbulence damping effect and (3) bottom boundary layer effect. Through the validation with the laboratory measurements of suspended sediment under nonbreaking skewed waves and surfzone breaking waves, we demonstrate that the model can reasonably predict wave-averaged sediment profiles. The model is then utilized to simulate a rip current field experiment (RCEX) and nearshore suspended sediment transport. The offshore sediment transport by rip currents is captured by the model. The effects of suspended sediment on self-suspension are also investigated. The turbulence damping and bottom boundary layer effects are significant on sediment suspension. The suspended sediment creates a stably stratified water column, damping fluid turbulence and reducing turbulent diffusivity. The suspension of sediment also produces a stably stratified bottom boundary layer. Thus, the drag coefficient and bottom shear stress are reduced, causing less sediment pickup from the bottom. The cross-shore suspended sediment flux is analyzed as well. The mean Eulerian suspended sediment flux is shoreward outside the surf zone, while it is seaward in the surf zone. 相似文献
18.
In this paper, a two-fluid model of turbulent two-phase flow is used to simulate turbulent stratified flows. This is a unified multi-fluid model for the motion of each phase in the flow, whose turbulent transport is closed by a two-phase k– model. The exchanges of mass, momentum and energy between the two phases are fully accounted for in the simulation. For illustration, a case of turbulent stratified flow with strong buoyancy effects, for which extensive experimental data are available, is selected for examination. It is shown that the numerical results agree well with the experimental data. 相似文献
19.
Malgorzata Stramska 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):284-296
The diffusive component of the particulate organic carbon (POC) export from the ocean's surface layer has been estimated using a combination of the mixed layer model and SeaWiFS ocean color data. The calculations were carried out for several example sites located in the North Atlantic over a 10-year time period (1998–2007). Satellite estimates of surface POC derived from ocean color were applied as an input to the model driven by local surface heat and momentum fluxes. For each year of the examined period, the diffusive POC flux was estimated at a 200 m depth. The highest flux is generally observed in the spring and fall seasons, when surface waters are weakly stratified. In addition, the model results demonstrate significant interannual and geographical variability of the flux. The highest diffusive POC flux occurs in the northern North Atlantic and the lowest in the subtropical region. The interannual variability of the diffusive POC flux is associated with mixed layer dynamics and underscores the importance of atmospheric forcing for POC export from the surface layer to the ocean's interior. 相似文献
20.
WANG Lixia SUN Yinglan ZHENG Lianyuan Associate Professor Insititute of Environmental Oceanography Ocean University of Qingdao Qingdao China.Professor Insititute of Environmental Oceanography Ocean University of Qingdao Qingdao China. Lecturer Insititute of Environmental Oceanography Ocean University of Qingdao Qingdao China. 《中国海洋工程》1998,(3)
A three-dimensional,first order turbulence closure,thermal diffusion model is described inthis paper.The governing equations consist of an equation of continuity,three components of momentum,conservation equations for salt,temperature and subgridscale energy,and an equation of state.In the mod-el,according to the hypothesis of Kolmogorov and Prandtl,the viscosity coefficient of turbulent flow ofhomogeneous fluid is related to the local turbulent energy,and the horizontal and vertical exchangecoefficients of mass,heat and momentum are computed with the introduction of subgridscale turbulenceenergy.The governing equations are solved by finite difference techniques.This model is applied to theJiaozhou bay to predict thermal pollution by the Huangdao power plant.An instantaneous tidal currentfield is computed,then the distribution of temperature increment is predicted,and finally the effect of windstress on thermal discharge is discussed. 相似文献