scholarly journals Sampling Error in Aircraft Flux Measurements Based on a High-Resolution Large Eddy Simulation of the Marine Boundary Layer

2020 ◽  
Author(s):  
Grant Petty
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Sampling Error ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flux Measurements ◽  
Aircraft Flux Measurements

scholarly journals Sampling Error in Aircraft Flux Measurements Based on a High-Resolution Large Eddy Simulation of the Marine Boundary Layer

2020 ◽  
Author(s):  
Grant W. Petty
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Random Error ◽  
Marine Boundary Layer ◽  
Sampling Error ◽  
Track Length ◽  
Length Scales ◽  
Eddy Simulation ◽  
Flux Measurements ◽  
Aircraft Flux Measurements

Abstract. A high-resolution (1.25 m) LES simulation of the nocturnal cloud-topped marine boundary layer is used to evaluate random error as a function of continuous track length L for virtual aircraft measurements of turbulent fluxes of sensible heat, latent heat, and horizontal momentum. Results are compared with the theoretically derived formula of Lenschow and Stankov (1986). In support of these comparisons, we also evaluate and document the relevant integral length scales and correlations and show that for heights up to approximately 100 m (z / zi = 0.12), the length scales are accurately predicted by empirical expressions of the form If = Azb. The Lenschow and Stankov expression is found to be remarkably accurate at predicting the random error for shorter flight tracks, but our empirically determined errors decay more rapidly with L than the L−1/2 relationship predicted from theory. Consistent with earlier findings, required track lengths to obtain useful precision increase sharply with altitude.

scholarly journals Sampling error in aircraft flux measurements based on a high-resolution large eddy simulation of the marine boundary layer

2021 ◽  
Vol 14 (3) ◽  
pp. 1959-1976
Author(s):  
Grant W. Petty
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Random Error ◽  
Marine Boundary Layer ◽  
Sampling Error ◽  
Track Length ◽  
Length Scales ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. A high-resolution (1.25 m) large eddy simulation (LES) of the nocturnal cloud-topped marine boundary layer is used to evaluate random error as a function of continuous track length L for virtual aircraft measurements of turbulent fluxes of sensible heat, latent heat, and horizontal momentum. Results are compared with the widely used formula of Lenschow and Stankov (1986). In support of these comparisons, the relevant integral length scales and correlations are evaluated and documented. It is shown that for heights up to approximately 100 m (z/zi=0.12), the length scales are accurately predicted by empirical expressions of the form If=Azb. The Lenschow and Stankov expression is found to be remarkably accurate at predicting the random error for shorter (7–10 km) flight tracks, but the empirically determined errors decay more rapidly with L than the L-1/2 relationship predicted from theory. Consistent with earlier findings, required track lengths to obtain useful precision increase sharply with altitude. In addition, an examination is undertaken of the role of uncertainties in empirically determined integral length scales and correlations in flux uncertainties as well as of the flux errors associated with crosswind and along-wind flight tracks. It is found that for 7.2 km flight tracks, flux errors are improved by factor of approximately 1.5 to 2 for most variables by making measurements in the crosswind direction.

scholarly journals Vertically nested LES for high-resolution simulation of the surface layer in PALM (version 5.0)

2019 ◽  
Vol 12 (6) ◽  
pp. 2523-2538 ◽  
Author(s):  
Sadiq Huq ◽  
Frederik De Roo ◽  
Siegfried Raasch ◽  
Matthias Mauder
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Grid Resolution ◽  
Computational Power ◽  
Fine Grid ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Nesting Algorithm

Abstract. Large-eddy simulation (LES) has become a well-established tool in the atmospheric boundary layer research community to study turbulence. It allows three-dimensional realizations of the turbulent fields, which large-scale models and most experimental studies cannot yield. To resolve the largest eddies in the mixed layer, a moderate grid resolution in the range of 10 to 100 m is often sufficient, and these simulations can be run on a computing cluster with a few hundred processors or even on a workstation for simple configurations. The desired resolution is usually limited by the computational resources. However, to compare with tower measurements of turbulence and exchange fluxes in the surface layer, a much higher resolution is required. In spite of the growth in computational power, a high-resolution LES of the surface layer is often not feasible: to fully resolve the energy-containing eddies near the surface, a grid spacing of O(1 m) is required. One way to tackle this problem is to employ a vertical grid nesting technique, in which the surface is simulated at the necessary fine grid resolution, and it is coupled with a standard, coarse, LES that resolves the turbulence in the whole boundary layer. We modified the LES model PALM (Parallelized Large-eddy simulation Model) and implemented a two-way nesting technique, with coupling in both directions between the coarse and the fine grid. The coupling algorithm has to ensure correct boundary conditions for the fine grid. Our nesting algorithm is realized by modifying the standard third-order Runge–Kutta time stepping to allow communication of data between the two grids. The two grids are concurrently advanced in time while ensuring that the sum of resolved and sub-grid-scale kinetic energy is conserved. We design a validation test and show that the temporally averaged profiles from the fine grid agree well compared to the reference simulation with high resolution in the entire domain. The overall performance and scalability of the nesting algorithm is found to be satisfactory. Our nesting results in more than 80 % savings in computational power for 5 times higher resolution in each direction in the surface layer.

Application of High-Resolution Large Eddy Simulation to Simplified Turbomachinery Flows

2016 ◽  
Author(s):  
Susumu Teramoto ◽  
Takuya Ouchi ◽  
Hiroki Sanada ◽  
Koji Okamoto
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Reynolds Stress ◽  
Sudden Expansion ◽  
Compressor Cascade ◽  
Rans Model ◽  
Eddy Simulation ◽  
Large Eddy

Fully resolved large eddy simulation (LES) is applied to two simple geometry flowfields with well-defined boundary conditions. The LES results are compared with simulations based on a Reynolds-averaged Navier-Stokes (RANS) model with turbulence, and pros and cons of using high-resolution LES for turbomachinery flows are discussed. One flow is a linear compressor cascade flow composed of the tip section of GE rotor B at Rec = 4 × 105 with a clearance, and the other is a Mach 1.76 supersonic turbulent boundary layer at Reδ = 5000 that laminerizes through a 12-degree expansion corner. The grids are prepared fine enough to resolve the turbulent boundary layer through a grid sensitivity study. The liner cascade result shows that all the turbulent shear layers and boundary layers including those in the small tip clearance are well resolved with 800 million grid points. The Reynolds stress derived from the LES results are compared directly with those predicted from the Spalart-Allmaras one-equation RANS turbulence model. The two results agreed qualitatively well except for the shear layer surrounding the tip leakage vortex, demonstrating that the RANS model performs well at least for flowfields near the design condition. From the simulation of the turbulent boundary layer experiencing sudden expansion, noticeable decreases of both Reynolds stress and local friction coefficient were observed, showing that the turbulent boundary layer has relaminarized through the sudden expansion. The boundary layer downstream of the expansion exhibits a nonequilibrium condition and was different from the laminar boundary layer.

Evaluation of the WRF PBL Parameterizations for Marine Boundary Layer Clouds: Cumulus and Stratocumulus

2013 ◽  
Vol 141 (7) ◽  
pp. 2265-2271 ◽  
Author(s):  
Hsin-Yuan Huang ◽  
Alex Hall ◽  
Joao Teixeira
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Layer Structure ◽  
Model Performance ◽  
Simulation Models ◽  
Eddy Diffusivity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Boundary Layer Cloud

Abstract The performance of five boundary layer parameterizations in the Weather Research and Forecasting Model is examined for marine boundary layer cloud regions running in single-column mode. Most parameterizations show a poor agreement of the vertical boundary layer structure when compared with large-eddy simulation models. These comparisons against large-eddy simulation show that a parameterization based on the eddy-diffusivity/mass-flux approach provides a better performance. The results also illustrate the key role of boundary layer parameterizations in model performance.

scholarly journals Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

2013 ◽  
Vol 13 (1) ◽  
pp. 1489-1526 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Subgrid Scale ◽  
Field Campaign ◽  
Eddy Simulation ◽  
Warm Rain ◽  
Large Eddy ◽  
Double Moment ◽  
The Mean

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) of the 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds were advected from the north-east by the prevailing lower-tropspheric winds, and featured stratocumulus-over-cumulus cloud formations. Almost-solid stratocumulus deck in the upper part of the relatively deep weakly decoupled marine boundary layer overlaid a field of small cumuli with a cloud fraction of ~10%. The two cloud formations featured distinct microphysical characteristics that were in general agreement with numerous past observations of strongly-diluted shallow cumuli on the one hand and solid marine boundary-layer stratocumulus on the other. Macrophysical and microphysical cloud properties were reproduced well by the double-moment warm-rain microphysics large-eddy simulation. A novel feature of the model is its capability to locally predict homogeneity of the subgrid-scale mixing between the cloud and its cloud-free environment. In the double-moment warm-rain microphysics scheme, the homogeneity is controlled by a single parameter α, that ranges from 0 to 1 and limiting values representing the homogeneous and the extremely inhomogeneous mixing scenarios, respectively. Parameter α depends on the characteristic time scales of the droplet evaporation and of the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, the mean cloud droplet radius, and the humidity of the cloud-free air entrained into the cloud. Simulated mixing is on average quite inhomogeneous, with the mean parameter α around 0.7 across the entire depth of the cloud field, but with local variations across almost the entire range, especially near the base and the top of the cloud field.

scholarly journals A Nested Multi-Scale System Implemented in the Large-Eddy Simulation Model PALM model system 6.0

2020 ◽  
Author(s):  
Antti Hellsten ◽  
Klaus Ketelsen ◽  
Matthias Sühring ◽  
Mikko Auvinen ◽  
Björn Maronga ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Large Eddy Simulation ◽  
Model System ◽  
Computational Domain ◽  
Convective Boundary ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Parent Domain

Abstract. Large-eddy simulation provides a physically sound approach to study complex turbulent processes within the atmospheric boundary layer including urban boundary layer flows. However, such flow problems often involve a large separation of turbulent scales, requiring a large computational domain and very high grid resolution near the surface features, leading to prohibitive computational costs. To overcome this problem, an online LES-LES nesting scheme is implemented into the PALM model system 6.0. The hereby documented and evaluated nesting method is capable of supporting multiple child domains which can be nested within their parent domain either in a parallel or recursively cascading configuration. The nesting system is evaluated by simulating first a purely convective boundary layer flow system and then three different neutrally-stratified flow scenarios with increasing order of topographic complexity. The results of the nested runs are compared with corresponding non-nested high- and low-resolution results. The results reveal that the solution accuracy within the high-resolution nest domain is clearly improved as the solutions approach the non-nested high-resolution reference results. In obstacle-resolving LES, the two-way coupling becomes problematic as anterpolation introduces a regional discrepancy within the obstacle canopy of the parent domain. This is remedied by introducing canopy-restricted anterpolation where the operation is only performed above the obstacle canopy. The test simulations make evident that this approach is the most suitable coupling strategy for obstacle-resolving LES. The performed simulations testify that nesting can reduce the CPU time up to 80 % compared to the fine-resolution reference runs while the computational overhead from the nesting operations remained below 16 % for the two-way coupling approach and significantly less for the one-way alternative.

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