Scalar Subgrid Model with Flow Structure for Large-Eddy Simulations of Scalar Variances

1998 ◽  
pp. 565-566 ◽  
Author(s):  
P. Flohr ◽  
J. C. Vassilicos
Keyword(s):  
Flow Structure ◽  
Large Eddy Simulations ◽  
Subgrid Model ◽  
Large Eddy

scholarly journals Linear-eddy subgrid model for reacting large-eddy simulations - Heat release effects

1997 ◽  
Author(s):  
William Calhoon, Jr. ◽  
Suresh Menon ◽  
William Calhoon, Jr. ◽  
Suresh Menon
Keyword(s):  
Heat Release ◽  
Large Eddy Simulations ◽  
Subgrid Model ◽  
Large Eddy

Stochastic backscatter in large-eddy simulations of boundary layers

1992 ◽  
Vol 242 ◽  
pp. 51-78 ◽  
Author(s):  
P. J. Mason ◽  
D. J. Thomson
Keyword(s):  
Large Scale ◽  
Flow Simulation ◽  
Surface Region ◽  
Large Eddy Simulations ◽  
Flow Profile ◽  
Mean Velocity ◽  
Near Surface ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy

The ability of a large-eddy simulation to represent the large-scale motions in the interior of a turbulent flow is well established. However, concerns remain for the behaviour close to rigid surfaces where, with the exception of low-Reynolds-number flows, the large-eddy description must be matched to some description of the flow in which all except the larger-scale ‘inactive’ motions are averaged. The performance of large-eddy simulations in this near-surface region is investigated and it is pointed out that in previous simulations the mean velocity profile in the matching region has not had a logarithmic form. A number of new simulations are conducted with the Smagorinsky (1963) subgrid model. These also show departures from the logarithmic profile and suggest that it may not be possible to eliminate the error by adjustments of the subgrid lengthscale. An obvious defect of the Smagorinsky model is its failure to represent stochastic subgrid stress variations. It is shown that inclusion of these variations leads to a marked improvement in the near-wall flow simulation. The constant of proportionality between the magnitude of the fluctuations in stress and the Smagorinsky stresses has been empirically determined to give an accurate logarithmic flow profile. This value provides an energy backscatter rate slightly larger than the dissipation rate and equal to idealized theoretical predictions (Chasnov 1991).

A scalar subgrid model with flow structure for large-eddy simulations of scalar variances

2000 ◽  
Vol 407 ◽  
pp. 315-349 ◽  
Author(s):  
P. FLOHR ◽  
J. C. VASSILICOS
Keyword(s):  
Flow Structure ◽  
Kinematic Model ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Inertial Range ◽  
Large Eddy Simulations ◽  
Tracer Particles ◽  
Particle Pairs ◽  
Large Eddy ◽  
Scalar Variance

A new model to simulate passive scalar fields in large-eddy simulations of turbulence is presented. The scalar field is described by clouds of tracer particles and the subgrid contribution of the tracer displacement is modelled by a kinematic model which obeys Kolmogorov's inertial-range scaling, is incompressible and incorporates turbulent-like flow structure of the turbulent small scales. This makes it possible to study the scalar variance field with inertial-range effects explicitly resolved by the kinematic subgrid field while the LES determines the value of the Lagrangian integral time scale TL. In this way, the modelling approach does not rely on unknown Lagrangian input parameters which determine the absolute value of the scalar variance.The mean separation of particle pairs displays a well-defined Richardson scaling in the inertial range, and we find that the Richardson constant GΔ ≈ 0.07 which is small compared to the value obtained from stochastic models with the same TL. The probability density function of the separation of particle pairs is found to be highly non-Gaussian in the inertial range of times and for long times becomes Gaussian. We compute the scalar variance field for an instantaneous line source and find good agreement with experimental data.

Large-eddy simulations of turbulent mixing layers using the stretched-vortex model

2011 ◽  
Vol 671 ◽  
pp. 507-534 ◽  
Author(s):  
T. W. MATTNER
Keyword(s):  
Large Scale ◽  
Large Eddy Simulations ◽  
Mixing Layers ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Subgrid Model ◽  
Large Eddy ◽  
Schmidt Numbers ◽  
Self Similar ◽  
Large Scale Flow

The stretched-vortex subgrid model is used to run large-eddy simulations of temporal mixing layers at various Reynolds and Schmidt numbers, with different initial and boundary conditions. A self-similar flow is obtained, during which the growth rate, mean velocity and Reynolds stresses are in accord with experimental results. However, predictions of the amount of mixed fluid, and of the variation in its composition across the layer, are excessive, especially at high Schmidt number. More favourable comparisons between experiment and simulation are obtained when the large-scale flow is quasi-two-dimensional; however, such states are not self-similar and not sustainable. Present model assumptions lead to predictions of the continued subgrid spectrum with a viscous cutoff that is dependent on grid resolution.

scholarly journals Evaluation of Large-Eddy Simulations via Observations of Nocturnal Marine Stratocumulus

2005 ◽  
Vol 133 (6) ◽  
pp. 1443-1462 ◽  
Author(s):  
Bjorn Stevens ◽  
Chin-Hoh Moeng ◽  
Andrew S. Ackerman ◽  
Christopher S. Bretherton ◽  
Andreas Chlond ◽  
...  
Keyword(s):  
Parameter Space ◽  
Large Eddy Simulations ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Thermodynamic Structure ◽  
Subgrid Model ◽  
Large Eddy ◽  
Cloud Liquid Water Path ◽  
The One ◽  
Vertical Spacing

Abstract Data from the first research flight (RF01) of the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study are used to evaluate the fidelity with which large-eddy simulations (LESs) can represent the turbulent structure of stratocumulus-topped boundary layers. The initial data and forcings for this case placed it in an interesting part of parameter space, near the boundary where cloud-top mixing is thought to render the cloud layer unstable on the one hand, or tending toward a decoupled structure on the other hand. The basis of this evaluation consists of sixteen 4-h simulations from 10 modeling centers over grids whose vertical spacing was 5 m at the cloud-top interface and whose horizontal spacing was 35 m. Extensive sensitivity studies of both the configuration of the case and the numerical setup also enhanced the analysis. Overall it was found that (i) if efforts are made to reduce spurious mixing at cloud top, either by refining the vertical grid or limiting the effects of the subgrid model in this region, then the observed turbulent and thermodynamic structure of the layer can be reproduced with some fidelity; (ii) the base, or native configuration of most simulations greatly overestimated mixing at cloud top, tending toward a decoupled layer in which cloud liquid water path and turbulent intensities were grossly underestimated; (iii) the sensitivity of the simulations to the representation of mixing at cloud top is, to a certain extent, amplified by particulars of this case. Overall the results suggest that the use of LESs to map out the behavior of the stratocumulus-topped boundary layer in this interesting region of parameter space requires a more compelling representation of processes at cloud top. In the absence of significant leaps in the understanding of subgrid-scale (SGS) physics, such a representation can only be achieved by a significant refinement in resolution—a refinement that, while conceivable given existing resources, is probably still beyond the reach of most centers.

scholarly journals High-Resolution Large-Eddy Simulations of Flow in a Steep Alpine Valley. Part II: Flow Structure and Heat Budgets

2006 ◽  
Vol 45 (1) ◽  
pp. 87-107 ◽  
Author(s):  
Andreas P. Weigel ◽  
Fotini K. Chow ◽  
Mathias W. Rotach ◽  
Robert L. Street ◽  
Ming Xue
Keyword(s):  
High Resolution ◽  
Flow Structure ◽  
Mixed Layer ◽  
Heat Budget ◽  
Measurement Data ◽  
Large Eddy Simulations ◽  
Driving Mechanism ◽  
Alpine Valley ◽  
Regional Prediction ◽  
Large Eddy

Abstract This paper analyzes the three-dimensional flow structure and the heat budget in a typical medium-sized and steep Alpine valley—the Riviera Valley in southern Switzerland. Aircraft measurements from the Mesoscale Alpine Programme (MAP)-Riviera field campaign reveal a very pronounced valley-wind system, including a strong curvature-induced secondary circulation in the southern valley entrance region. Accompanying radio soundings show that the growth of a well-mixed layer is suppressed, even under convective conditions. Our analyses are based on the MAP-Riviera measurement data and the output of high-resolution large-eddy simulations using the Advanced Regional Prediction System (ARPS). Three sunny days of the measurement campaign are simulated. Using horizontal grid spacings of 350 and 150 m (with a vertical spacing as fine as 20 m), the model reproduces the observed flow features very well. The ARPS output data are then used to calculate the components of the heat budget of the valley atmosphere, first in profiles over the valley base and then as averages over almost the entire valley volume. The analysis shows that the suppressed growth of the well-mixed layer is due to the combined effect of cold-air advection in the along-valley direction and subsidence of warm air from the free atmosphere aloft. It is further influenced by the local cross-valley circulation. This had already been hypothesized on the basis of measurement data and is now confirmed through a numerical model. Averaged over the entire valley, subsidence turns out to be one of the main heating sources of the valley atmosphere and is of comparable magnitude to turbulent heat flux divergence. On the mornings of two out of the three simulation days, this subsidence is even identified as the only major heating source and thus appears to be an important driving mechanism for the onset of thermally driven upvalley winds.

Sign in / Sign up

Export Citation Format

Share Document