Mountain waves produced by a stratified shear flow with a boundary layer: transition from downstream sheltering to upstream blocking

2020 ◽  
Author(s):  
Francois Lott ◽  
Bruno Deremble ◽  
Clément Soufflet
Keyword(s):  
Boundary Layer ◽  
Reynolds Stress ◽  
Internal Waves ◽  
Large Scale ◽  
Wave Drag ◽  
Mountain Waves ◽  
Reflected Waves ◽  
Stable Case ◽  
Large Scale Flow ◽  
Neutral Case

<p>A non-hydrostatic theory for mountain flow with a boundary layer of constant eddy viscosity is presented. The theory predicts that dissipation impacts the dynamics over a an inner layer which depth δ is predicted by viscous critical level theory. In the near neutral case, the surface pressure decreases when the flow crosses the mountain to balance an increase in surface friction along the ground. This produces a form drag which can be predicted quantitatively. With stratification, internal waves start to control the dynamics and produce a wave drag that can also be predicted. For weak stratification, upward propagating mountain waves and reflected waves interact destructively and low drag states occur, whereas for moderate stability they interact constructively and high drag states are reached. In very stable cases the reflected waves do not affect the drag much.</p><p>The sign and vertical profiles of the Reynolds stress are profoundly affected by stability. In the neutral case and up to the point where internal waves interact constructively, the Reynolds stress in the flow is positive, with maximum around the top of the inner layer, decelerating the large scale flow in the inner layer and accelerating it above. In the stable case, the opposite occurs, and the large scale flow above the inner layer is decelerated as expected for dissipated mountain waves. These opposed behaviors challenge how mountain form drag and mountain wave drag should be parameterized in large-scale models.</p><p>The structure of the flow around the mountain is also strongly affected by stability: it is characterized by non separated sheltering in the neutral case, by upstream blocking in the very stable case, and at intermediate stability by the presence of a strong but isolated wave crest immediately downstream of the ridge.</p>

scholarly journals Mountain waves produced by a stratified shear flow with a boundary layer. Part II: Form drag, wave drag, and transition from downstream sheltering to upstream blocking

2020 ◽  
Author(s):  
François Lott ◽  
Bruno Deremble ◽  
Clément Soufflet
Keyword(s):  
Reynolds Stress ◽  
Large Scale ◽  
Wave Drag ◽  
Wave Crest ◽  
Form Drag ◽  
Mountain Waves ◽  
Reflected Waves ◽  
Stable Case ◽  
Large Scale Flow ◽  
Neutral Case

AbstractThe non-hydrostatic version of the mountain flow theory presented in Part I is detailed. In the near neutral case, the surface pressure decreases when the flow crosses the mountain to balance an increase in surface friction along the ground. This produces a form drag which can be predicted qualitatively. When stratification increases, internal waves start to control the dynamics and the drag is due to upward propagating mountain waves as in part I. The reflected waves nevertheless add complexity to the transition. First, when stability increases, upward propagating waves and reflected waves interact destructively and low drag states occur. When stability increases further, the interaction becomes constructive and high drag state are reached. In very stable cases the reflected waves do not affect the drag much. Although the drag gives a reasonable estimate of the Reynolds stress, its sign and vertical profile are profoundly affected by stability. In the near neutral case the Reynolds stress in the flow is positive, with maximum around the top of the inner layer, decelerating the large-scale flow in the inner layer and accelerating it above. In the more stable cases, on the contrary, the large-scale flow above the inner layer is decelerated as expected for dissipated mountain waves. The structure of the flow around the mountain is also strongly affected by stability: it is characterized by non separated sheltering in the near neutral cases, by upstream blocking in the very stable case, and at intermediate stability by the presence of a strong but isolated wave crest immediately downstream of the ridge.

Transient Mountain Waves and Their Interaction with Large Scales

2007 ◽  
Vol 64 (7) ◽  
pp. 2378-2400 ◽  
Author(s):  
Chih-Chieh Chen ◽  
Gregory J. Hakim ◽  
Dale R. Durran
Keyword(s):  
Potential Vorticity ◽  
Large Scale ◽  
Wave Drag ◽  
Mountain Waves ◽  
Flow Acceleration ◽  
Spatial Response ◽  
Flow Deceleration ◽  
Large Scale Flow ◽  
The Impact ◽  
Zonal Momentum

Abstract The impact of transient mountain waves on a large-scale flow is examined through idealized numerical simulations of the passage of a time-evolving synoptic-scale jet over an isolated 3D mountain. Both the global momentum budget and the spatial flow response are examined to illustrate the impact of transient mountain waves on the large-scale flow. Additionally, aspects of the spatial response are quantified by potential vorticity inversion. Nearly linear cases exhibit a weak loss of domain-averaged absolute momentum despite the absence of wave breaking. This transient effect occurs because, over the time period of the large-scale flow, the momentum flux through the top boundary does not balance the surface pressure drag. Moreover, an adiabatic spatial redistribution of momentum is observed in these cases, which results in an increase (decrease) of zonally averaged zonal momentum south (north) of the mountain. For highly nonlinear cases, the zonally averaged momentum field shows a region of flow deceleration downstream of the mountain, flanked by broader regions of weak flow acceleration. Cancellation between the accelerating and decelerating regions results in weak fluctuations in the volume-averaged zonal momentum, suggesting that the mountain-induced circulations are primarily redistributing momentum. Potential vorticity anomalies develop in a region of wave breaking near the mountain, and induce local regions of flow acceleration and deceleration that alter the large-scale flow. A “perfect” conventional gravity wave–drag parameterization is implemented on a coarser domain not having a mountain, forced by the momentum flux distribution from the fully nonlinear simulation. This parameterization scheme produces a much weaker spatial response in the momentum field and it fails to produce enough flow deceleration near the 20 m s−1 jet. These results suggest that the potential vorticity sources attributable to the gravity wave–drag parameterization have a controlling effect on the longtime downstream influence of the mountain.

Identification of Bypass Transition Onset Markers Using Direct Numerical Simulation

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Shanti Bhushan ◽  
D. Keith Walters ◽  
S. Muthu ◽  
Crystal L. Pasiliao
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
General Purpose ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Flow Parameters ◽  
Rans Models ◽  
Large Scale Flow

Efficacy of several large-scale flow parameters as transition onset markers are evaluated using direct numerical simulation (DNS) of boundary layer bypass transition. Preliminary results identify parameters (k2D/ν) and u′/U∞ to be a potentially reliable transition onset marker, and their critical values show less than 15% variation in the range of Re and turbulence intensity (TI). These parameters can be implemented into general-purpose physics-based Reynolds-averaged Navier–Stokes (RANS) models for engineering applications.

Turbulent mixing in a sloping benthic boundary layer energized by internal waves

2000 ◽  
Vol 418 ◽  
pp. 59-76 ◽  
Author(s):  
G. N. IVEY ◽  
K. B. WINTERS ◽  
I. P. D. DE SILVA
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Buoyancy Frequency ◽  
Benthic Boundary Layer ◽  
Incoming Wave ◽  
Velocity Fluctuations ◽  
Reflected Waves ◽  
Wave Forcing ◽  
Orthogonal Components ◽  
Vertical Density

A laboratory study was carried out to directly measure the turbulence properties in a benthic boundary layer (BBL) above a uniformly sloping bottom where the BBL is energized by internal waves. The ambient fluid was continuously stratified and the steadily forced incoming wave field consisted of a confined beam, restricting the turbulent activity to a finite region along the bottom slope. Measurements of dissipation showed some variation over the wave phase, but cycle-averaged values indicated that the dissipation was nearly constant with height within the BBL. Dissipation levels were up to three orders of magnitude larger than background laminar values and the thickness of the BBL could be defined in terms of the observed dissipation variation with height. Assuming that most of the incoming wave energy was dissipated within the BBL, predicted levels of dissipation were in good agreement with the observations.Measurements were also made of density and two orthogonal components of the velocity fluctuations at discrete heights above the bottom. Cospectral estimates of density and velocity fluctuations showed that the major contributions to both the vertical density flux and the momentum flux resulted from frequencies near the wave forcing frequency, rather than super-buoyancy frequencies, suggesting a strong nonlinear interaction between the incident and reflected waves close to the bottom. Within the turbulent BBL, time-averaged density fluxes were significant and negative near the wave frequencies but negligible at frequencies greater than the buoyancy frequency N. While dissipation rates were high compared to background laminar values, they were low compared to the value of εtr ≈ 15vN2, the transition value often used to assess the capacity of a stratified flow to produce mixing. Existing models relating mixing to dissipation rate rely on the existence of a positive-definite density flux at frequencies greater than N as a signature of fluid mixing and therefore cannot apply to these experiments. We therefore introduce a simple model, based on the concept of diascalar fluxes, to interpret the mixing in the stratified fluid in the BBL and suggest that this may have wider application than to the particular configuration studied here.

Simulating the emission and transport of gases on 100-meter resolution in a 100-kilometer domain.

2021 ◽  
Author(s):  
Marco de Bruine ◽  
Fredrik Jansson ◽  
Bart van Stratum ◽  
Pieter Rijsdijk ◽  
Sander Houweling
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
The Netherlands ◽  
Large Scale ◽  
Satellite Monitoring ◽  
Free Atmosphere ◽  
Activity Data ◽  
Eddy Simulation ◽  
Large Scale Flow ◽  
Insight Into

<p>Climate regulations and satellite monitoring on increasingly high resolution creates a demand for an insight into emissions on an urban scale. The aim of the Ruisdael Observatory (www.ruisdaelobservatory.nl) is to provide just that: detailed and high-resolution modelling and measurements of weather and air quality in a domain covering the Netherlands.</p><p>The Ruisdael Observatory created a renewed impulse in the developments of the DALES Large-eddy simulation (LES) model (Heus et al., 2010, Ouwersloot et al. 2016) to find and push the limits of atmospheric modelling. Typical simulations with DALES will use a spatial resolution in the order of 100m in domain sizes spanning over 100x100 km. This high resolution justifies the complexity and the multitude of emission sources and resulting transport of pollutants in the atmospheric boundary layer.</p><p>The combination of high resolution and large domain sizes allows us to investigate how emissions disperse in a turbulent environment which is forced by large-scale flow at the same time. Parameterizations are no longer needed to calculate horizontal or vertical transport in the boundary-layer. This way, we can provide new insight into the transport of emissions in the boundary layer and the detrainment of gases out of the boundary layer into the free atmosphere.</p><p>We will discuss the construction of our emission database for the Netherlands with a 100-meter and 1-hourly resolution. For this, we started from the official E-PRTR reported emission inventories (www.emissieregistratie.nl) and enriched with high resolution activity data from mostly open-source datasets. Moreover, large emissions sources (accounting for e.g. >80% of CO2 emissions) are subject to mandatory registration and their locations are known exactly. Emissions from different source categories can be tracked individually and compared to measurements from the Ruisdael Observatory measurement sites. Examples of simulations of fair-weather summer days will be compared to surface measurements and showcase the data richness of our new model and combination to measurements from our network.</p>

scholarly journals Reynolds stress scaling in pipe flow turbulence—first results from CICLoPE

2017 ◽  
Vol 375 (2089) ◽  
pp. 20160187 ◽  
Author(s):  
R. Örlü ◽  
T. Fiorini ◽  
A. Segalini ◽  
G. Bellani ◽  
A. Talamelli ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Reynolds Stress ◽  
Large Scale ◽  
Strong Support ◽  
Wall Turbulence ◽  
Large Reynolds Number ◽  
Normal Distance ◽  
First Results ◽  
Variance Profile

This paper reports the first turbulence measurements performed in the Long Pipe Facility at the Center for International Cooperation in Long Pipe Experiments (CICLoPE). In particular, the Reynolds stress components obtained from a number of straight and boundary-layer-type single-wire and X-wire probes up to a friction Reynolds number of 3.8×10 4 are reported. In agreement with turbulent boundary-layer experiments as well as with results from the Superpipe, the present measurements show a clear logarithmic region in the streamwise variance profile, with a Townsend–Perry constant of A 2 ≈1.26. The wall-normal variance profile exhibits a Reynolds-number-independent plateau, while the spanwise component was found to obey a logarithmic scaling over a much wider wall-normal distance than the other two components, with a slope that is nearly half of that of the Townsend–Perry constant, i.e. A 2, w ≈ A 2 /2. The present results therefore provide strong support for the scaling of the Reynolds stress tensor based on the attached-eddy hypothesis. Intriguingly, the wall-normal and spanwise components exhibit higher amplitudes than in previous studies, and therefore call for follow-up studies in CICLoPE, as well as other large-scale facilities. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

scholarly journals Proper orthogonal decomposition analysis and modelling of large-scale flow reorientations in a cubic Rayleigh–Bénard cell

2019 ◽  
Vol 881 ◽  
pp. 23-50 ◽  
Author(s):  
Laurent Soucasse ◽  
Bérengère Podvin ◽  
Philippe Rivière ◽  
Anouar Soufiani
Keyword(s):  
Boundary Layer ◽  
Proper Orthogonal Decomposition ◽  
Large Scale ◽  
Orthogonal Decomposition ◽  
Mean Flow ◽  
Large Scale Circulation ◽  
Large Scale Flow ◽  
Proper Orthogonal ◽  
Rayleigh Benard ◽  
Reorientation Process

This paper investigates the large-scale flow reorientations of Rayleigh–Bénard convection in a cubic cell using proper orthogonal decomposition (POD) analysis and modelling. A direct numerical simulation is performed for air at a Rayleigh number of $10^{7}$ and shows that the flow is characterized by four quasi-stable states, corresponding to a large-scale circulation lying in one of the two diagonal planes of the cube with a clockwise or anticlockwise motion, with occasional brief reorientations. Proper orthogonal decomposition is applied to the joint velocity and temperature fields of an enriched database which captures the statistical symmetries of the flow. We found that each quasi-stable state consists of a superposition of four spatial modes representing three types of structures: (i) a mean-flow mode consisting of two stacked counter-rotating torus-like structures; (ii) two large-scale two-dimensional rolls (pair of degenerated modes) which form large-scale diagonal rolls when combined together; and (iii) an eight-roll mode that transports fluid from one corner to the other and strengthens the circulation along the diagonal. In addition, we identified three other modes that play a role in the reorientation process: two boundary-layer modes (pair of degenerated modes) that connect the core region with the horizontal boundary layers and one mode associated with corner rolls. The symmetries of the different POD modes are discussed, as well as their temporal dynamics. A description of the reorientation process in terms of POD modes is provided and compared with other modal approaches available in the literature. Finally, Galerkin projection is used to derive a POD-based reduced-order model. Unresolved modes are accounted for in the model by an extra dissipation term and the addition of noise. A seven-mode model is able to reproduce the low-frequency dynamics of the large-scale reorientations as well as the high-frequency dynamics associated with the large-scale circulation rotation. Linear stability analysis and sensitivity analysis confirm the role of the boundary-layer modes and the corner-rolls mode in the reorientation process.

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