An efficient physics-based preconditioner for the fully implicit solution of small-scale thermally driven atmospheric flows

Winds associated with mountainous terrain are generally of two types. Terrain-forced flows are produced when large-scale winds are modified or channeled by the underlying complex terrain. Diurnal mountain winds are produced by temperature contrasts that form within the mountains or between the mountains and the surrounding plains and are therefore also called thermally driven circulations. Terrain-forced flows and diurnal mountain winds are nearly always combined to some extent. Both can occur in conjunction with small-scale winds, such as thunderstorm inflows and outflows, or with large-scale winds that are not influenced by the underlying mountainous terrain. Terrain forcing can cause an air flow approaching a mountain barrier to be carried over or around the barrier, to be forced through gaps in the barrier, or to be blocked by the barrier. Three factors determine the behavior of an approaching flow in response to a mountain barrier: •the stability of the air approaching the mountains, •the speed of the air flow approaching the mountains, and •the topographic characteristics of the underlying terrain. Unstable or neutrally stable air (section 4.3) is easily carried over a mountain barrier. The behavior of stable air approaching a mountain barrier depends on the degree of stability, the speed of the approaching flow, and the terrain characteristics. The more stable the air, the more resistant it is to lifting and the greater the likelihood that it will flow around, be forced through gaps in the barrier, or be blocked by the barrier. A layer of stable air can split, with air above the dividing streamline height flowing over the mountain barrier and air below the dividing streamline height splitting upwind of the mountains, flowing around the barrier (figure 10.1), and reconverging on the leeward side (section 10.3.2). A very stable approaching flow may be blocked on the windward side of the barrier (section 10.5.1). Moderate to strong cross-barrier winds are necessary to produce terrain-forced flows, which therefore occur most frequently in areas of cyclogenesis (section 5.1) or where low pressure systems (figure 1.3) or jet streams (section 5.2.1.3) are commonly found. Whereas unstable and neutral flows are easily lifted over a mountain barrier, even by moderate winds, strong cross-barrier winds are needed to carry stable air over a mountain barrier.

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Observational analysis of thermally-driven topographic flows and their turbulence-waves interaction

10.5194/egusphere-egu2020-19735 ◽

2020 ◽

Author(s):

Carlos Yagüe ◽

Carlos Román-Cascón ◽

Marie Lothon ◽

Fabienne Lohou ◽

Jon Ander Arrillaga ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Gravity Waves ◽

Sonic Anemometer ◽

Extended Period ◽

Chem Phys ◽

Small Scale ◽

Mixing Ratios ◽

Synoptic Conditions ◽

Thermally Driven

Thermally-driven flows (TDFs) are mesoscale circulations driven by horizontal thermal contrasts in scales ranging from 1 and 100-200 km. The presence of mountains can generate a kind of these TDFs called thermally-driven topographic flows, with a typical daily cycle which is observed when weak synoptic conditions are present. These flows impact the turbulence features in the Atmospheric Boundary Layer (ABL), as well as different scalars (temperature, CO2, water vapor, pollutants, etc.). Moreover, these circulations, which can be of different scales (from small-scale shallow drainage flows to for example the larger Mountain &#8211; Plain flows) can generate gravity waves (GWs) along the transition to the stable boundary layer (SBL) and during the night. In this work, 88 days belonging to an extended period of the BLLAST field campaign[1] have been analysed. The corresponding nocturnal TDFs have been detected through a systematic and objective algorithm which considers both synoptic and local meteorological conditions. The main objectives of the study are: to characterize the TDFs at CRA (which is placed on a plateau near the Pyrenees in France); to evaluate the performance of the objective algorithm[2] in obtaining the events of interest; to establish different categories of TDFs and search for driving mechanisms (local, synoptic,..); and finally to explore the connections between TDFs and the generation of Gravity Waves (GWs), often observed in the nocturnal SBL[3]. Their interaction with turbulence is also analysed using different multiscale techniques, such as wavelets applied to pressure measurements obtained from high accurate microbarometers, and MultiResolution Flux Decomposition &#8211;MRFD- applied to sonic anemometer data. The contribution of different scales to turbulent parameters will be deeply evaluated and related to the arrival of TDFs and to the presence of GWs.&#160;[1] Lothon, M., Lohou, F. et al (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence. Atmos. Chem. Phys., 14, 10931-10960.&#160;[2] Rom&#225;n-Casc&#243;n, C., Yag&#252;e, C., Arrillaga, J.A., Lothon, M., Pardyjak, E,R., Lohou, F., Incl&#225;n, R.M., Sastre, M., Maqueda, G., Derrien, S., Meyerfeld, Y., Hang, C., Campargue-Rodr&#237;guez, P. & Turki, I. (2019): Comparing mountain breezes and their impacts on CO2 mixing ratios at three contrasting areas. Atmos. Res., 221, 111-126.[3] Sun, J., Nappo, C.J., Mahrt, L., Belusic, D., Grisogono, B., Stauffer, D.R., Pulido, M., Staquet, C., Jiang, Q., Pouquet, A., Yag&#252;e, C. Galperin, B., Smith, R.B., Finnigan, J.J., Mayor, S.D., Svensson, G., Grachev, A.A. & Neff., W.D.: (2015): Review of wave-turbulence interactions in the stable atmospheric boundary layer, Rev. Geophys., 53, 956&#8211;993.

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Numerical Computation of Instabilities and Internal Waves from In Situ Measurements via the Viscous Taylor–Goldstein Problem

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-19-0155.1 ◽

2020 ◽

Vol 37 (5) ◽

pp. 759-776 ◽

Cited By ~ 1

Author(s):

Qiang Lian ◽

William D. Smyth ◽

Zhiyu Liu

Keyword(s):

Numerical Methods ◽

Internal Gravity Waves ◽

Small Scale ◽

Atmospheric Flows ◽

Convective Instabilities ◽

Parallel Shear Flows ◽

Scale Turbulence ◽

The Stability ◽

Speed And Accuracy

AbstractWe explore numerical methods for the stability analysis of stratified, parallel shear flows considering the effects of small-scale turbulence represented by eddy viscosity and diffusivity. The result is an extension of the classical Taylor–Goldstein problem applicable to oceanic and atmospheric flows. Solutions with imaginary frequency describe shear and convective instabilities, whereas those with real frequency represent internal gravity waves. Application to large observational datasets can involve considerable computation and therefore requires a compromise between speed and accuracy. We compare several numerical methods to identify optimal approaches to various problems.

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Instabilities and small-scale waves within the Stewartson layers of a thermally driven rotating annulus

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.10 ◽

2018 ◽

Vol 841 ◽

pp. 380-407 ◽

Cited By ~ 6

Author(s):

Thomas von Larcher ◽

Stéphane Viazzo ◽

Uwe Harlander ◽

Miklos Vincze ◽

Anthony Randriamampianina

Keyword(s):

Finite Difference ◽

Direct Numerical Simulations ◽

Flow Structures ◽

Small Scale ◽

Flow Solver ◽

Physical Mechanisms ◽

Short Period ◽

Thermally Driven ◽

Scale Structures ◽

Small Scale Structures

We report on small-scale instabilities in a thermally driven rotating annulus filled with a liquid with moderate Prandtl number. The study is based on direct numerical simulations and an accompanying laboratory experiment. The computations are performed independently with two different flow solvers, that is, first, the non-oscillatory forward-in-time differencing flow solver EULAG and, second, a higher-order finite-difference compact scheme (HOC). Both branches consistently show the occurrence of small-scale patterns at both vertical sidewalls in the Stewartson layers of the annulus. Small-scale flow structures are known to exist at the inner sidewall. In contrast, short-period waves at the outer sidewall have not yet been reported. The physical mechanisms that possibly trigger these patterns are discussed. We also debate whether these small-scale structures are a gravity wave signal.

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A Scalable Fully Implicit Compressible Euler Solver for Mesoscale Nonhydrostatic Simulation of Atmospheric Flows

SIAM Journal on Scientific Computing ◽

10.1137/130919167 ◽

2014 ◽

Vol 36 (5) ◽

pp. S23-S47 ◽

Cited By ~ 24

Author(s):

Chao Yang ◽

Xiao-Chuan Cai

Keyword(s):

Atmospheric Flows ◽

Fully Implicit ◽

Compressible Euler ◽

Euler Solver

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Effects of 3-D Local Unsteadiness on Heat Transfer Prediction in Turbulated Passages

Heat Transfer, Volume 1 ◽

10.1115/imece2003-42268 ◽

2003 ◽

Cited By ~ 1

Author(s):

Pamela A. McDowell ◽

William D. York ◽

D. Keith Walters ◽

James H. Leylek

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Turbulence Model ◽

Three Dimensional ◽

Reynolds Numbers ◽

Navier Stokes ◽

Successful Outcome ◽

Small Scale ◽

Cross Sectional ◽

Fully Implicit

A newly developed unsteady turbulence model was used to predict heat transfer in a turbulated passage typical of turbine airfoil cooling applications. Comparison of fullyconverged computational solutions to experimental measurements reveal that accurate prediction of heat transfer coefficient requires the effects of local small-scale unsteadiness to be captured. Validation was accomplished through comparison of the time- and area-averaged Nusselt number on the passage wall between adjacent ribs with experimental data from the open literature. The straight channel had a square cross-sectional area with multiple rows of staggered and rounded-edge ribs on opposite walls that were orthogonal to the flow. Simulations were run for Reynolds numbers of 5500, 16500, and 25000. Computational solutions were obtained on a multi-block, multi-topology, unstructured, and adaptive grid, using a pressure-correction based, fully-implicit Navier-Stokes solver. The computational results include two-dimensional (2-D) and three-dimensional (3-D) steady and unsteady simulations with viscous sublayers resolved (y+ ≤ 1) on all the walls in every case. Turbulence closure was obtained using a new turbulence model developed in-house for the unsteady simulations, and a realizable k-ε turbulence model was used for the steady simulations. The results obtained from the unsteady simulations show greatly improved agreement with the experimental data, especially at realistically high Reynolds numbers. The key 3-D physics mechanisms responsible for the successful outcome include: (1) shear layer roll-up over the turbulators; (2) recirculation zones both upstream and downstream of the rib faces; and (3) reattachment regions between each rib pair. Results from the unsteady case are superior to those of the steady because they capture the aforementioned mechanisms, and therefore more accurately predict the heat transfer.

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