ORCID Profile
0000-0001-6947-3605
Current Organisation
Johns Hopkins University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Turbulent Flows | Interdisciplinary Engineering |
ANZSRC Socio-Economic Objective (SEO)
Management of Greenhouse Gas Emissions from Transport Activities | Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering
Related Links
Publications
Scaling of second- and higher-order structure functions in turbulent boundary layers
Publisher: Cambridge University Press (CUP)
Date: 30-03-2015
DOI: 10.1017/JFM.2015.122
Abstract: The statistical properties of wall turbulence in the logarithmic region are investigated using structure functions of the streamwise velocity. To this end, datasets that span several orders of magnitude of Reynolds numbers are used, up to $Re_{{\\it\\tau}}=O(10^{6})$ , providing uniquely large scale separations for scrutinising previously proposed scaling laws. For the second-order structure functions strong support is found simultaneously for power-law scalings in the Kolmogorov inertial subrange and for logarithmic scaling at larger scales within the inertial range ( $z r\\ll {\\it\\delta}$ , where $z$ is the distance from the wall, $r$ the scale, and ${\\it\\delta}$ the boundary layer thickness). The observed scalings are shown to agree between the datasets, which include both temporal and spatial velocity signals and span from laboratory to atmospheric flows, showing a degree of universality in the results presented. An examination of higher even-order structure functions also shows support for logarithmic scaling behaviour for $z r\\ll {\\it\\delta}$ , provided that the Reynolds number is sufficiently high. These findings are interpreted by generalising the work of Meneveau & Marusic ( J. Fluid Mech. , vol. 719, 2013) and introducing bridging relations between higher-order moments of velocity fluctuations and structure functions. Further, a physical model based on the attached-eddy hypothesis is utilised to derive various properties of the structure functions for the energy-containing scales of the logarithmic region. The descriptions derived from the model are shown to be supported by the experimental data.
Large eddy simulation study of scalar transport in fully developed wind-turbine array boundary layers
Publisher: AIP Publishing
Date: 12-2011
DOI: 10.1063/1.3663376
Abstract: Wind harvesting is fast becoming an important alternative source of energy. As wind farms become larger, they begin to attain scales at which two-way interactions with the atmospheric boundary layer (ABL) must be taken into account. Several studies have shown that there is a quantifiable effect of wind farms on the local meteorology, mainly through changes in the land-atmosphere fluxes of heat and moisture. In particular, the observed trends suggest that wind farms increase fluxes at the surface and this could be due to increased turbulence in the wakes. Conversely, simulations and laboratory experiments show that underneath wind farms, the friction velocity is decreased due to extraction of momentum by the wind turbines, a factor that could decrease scalar fluxes at the surface. In order to study this issue in more detail, a suite of large eddy simulations of an infinite (fully developed) wind turbine array boundary layer, including scalar transport from the ground surface without stratification, is performed. Results show an overall increase in the scalar fluxes of about 10%–15% when wind turbines are present in the ABL, and that the increase does not strongly depend upon wind farm loading as described by the turbines’ thrust coefficient and the wind turbines spacings. A single-column analysis including scalar transport shows that the presence of wind farms can be expected to increase slightly the scalar transport from the bottom surface and that this slight increase is due to a delicate balance between two strong opposing trends.
Atmospheric stability effect on subgrid-scale physics for large-eddy simulation
Publisher: Elsevier BV
Date: 11-2001
A Hybrid Spectral/Finite-Volume Algorithm for Large-Eddy Simulation of Scalars in the Atmospheric Boundary Layer
Publisher: Springer Science and Business Media LLC
Date: 05-08-2008
A comparative quadrant analysis of turbulence in a plant canopy
Publisher: American Geophysical Union (AGU)
Date: 05-2007
DOI: 10.1029/2006WR005583
A scale-dependent Lagrangian dynamic model for large eddy simulation of complex turbulent flows
Publisher: AIP Publishing
Date: 19-01-2005
DOI: 10.1063/1.1839152
Abstract: A scale-dependent dynamic subgrid model based on Lagrangian time averaging is proposed and tested in large eddy simulations (LES) of high-Reynolds number boundary layer flows over homogeneous and heterogeneous rough surfaces. The model is based on the Lagrangian dynamic Smagorinsky model in which required averages are accumulated in time, following fluid trajectories of the resolved velocity field. The model allows for scale dependence of the coefficient by including a second test-filtering operation to determine how the coefficient changes as a function of scale. The model also uses the empirical observation that when scale dependence occurs (such as when the filter scale approaches the limits of the inertial range), the classic dynamic model yields the coefficient value appropriate for the test-filter scale. Validation tests in LES of high Reynolds number, rough wall, boundary layer flow are performed at various resolutions. Results are compared with other eddy-viscosity subgrid-scale models. Unlike the Smagorinsky–Lilly model with wall-d ing (which is overdissipative) or the scale-invariant dynamic model (which is underdissipative), the scale-dependent Lagrangian dynamic model is shown to have good dissipation characteristics. The model is also tested against detailed atmospheric boundary layer data that include measurements of the response of the flow to abrupt transitions in wall roughness. For such flows over variable surfaces, the plane-averaged version of the dynamic model is not appropriate and the Lagrangian averaging is desirable. The simulated wall stress overshoot and relaxation after a jump in surface roughness and the velocity profiles at several downstream distances from the jump are compared to the experimental data. Results show that the dynamic Smagorinsky coefficient close to the wall is very sensitive to the underlying local surface roughness, thus justifying the use of the Lagrangian formulation. In addition, the Lagrangian formulation reproduces experimental data more accurately than the planar-averaged formulation in simulations over heterogeneous rough walls.
Large-eddy simulation of plant canopy flows using plant-scale representation
Publisher: Springer Science and Business Media LLC
Date: 30-03-2007
The Local Structure of Atmospheric Turbulence and Its Effect on the Smagorinsky Model for Large Eddy Simulation
Publisher: American Meteorological Society
Date: 06-2007
DOI: 10.1175/JAS3930.1
Abstract: Phenomena such as large-scale shear, buoyancy, and the proximity to the ground surface significantly affect interactions among scales in atmospheric boundary layer turbulent flows. Hence, these phenomena impact parameters that enter subgrid-scale (SGS) parameterizations used in large eddy simulations (LES) of the atmospheric boundary layer. The effects of these phenomena upon SGS parameters have, to date, been studied mostly as functions of the global state of the flow. For instance, the Smagorinsky coefficient has been measured as a function of the mean shear and stability condition of the atmosphere as determined from the average surface heat and momentum fluxes. However, in LES the global average field values are often difficult to determine a priori and the SGS parameters ideally must be expressed as a function of local flow variables that characterize the instantaneous flow phenomena. With the goal of improving the Smagorinsky closure, in this study several dimensionless parameters characterizing the local structure and important dynamical characteristics of the flow are defined. These local parameters include enstrophy, vortex stretching, self- lification of strain rate, and normalized temperature gradient and all are defined in such a way that they remain bounded under all circumstances. The dependence of the Smagorinsky coefficient on these local parameters is studied a priori from field data measured in the atmospheric surface layer and, as a reference point, from direct numerical simulation of neutrally buoyant, isotropic turbulence. To capture the local effects in a statistically meaningful fashion, conditional averaging is used. Results show various important and interrelated trends, such as significant increases of the coefficient in regions of large strain-rate self- lification and vortex stretching. Results also show that the joint dependence on the parameters is rather complicated and cannot be described by products of functions that depend on single parameters. Dependence on locally defined parameters is expected to improve the SGS model by sensitizing it to local flow conditions and by enabling possible generalizations of the dynamic model based on conditional averaging.
Numerical study of dynamic Smagorinsky models in large‐eddy simulation of the atmospheric boundary layer: Validation in stable and unstable conditions
Publisher: American Geophysical Union (AGU)
Date: 06-2006
DOI: 10.1029/2005WR004685
Multiscale Geometry and Scaling of the Turbulent-Nonturbulent Interface in High Reynolds Number Boundary Layers
Publisher: American Physical Society (APS)
Date: 24-07-2013
Large‐eddy simulation of a diurnal cycle of the atmospheric boundary layer: Atmospheric stability and scaling issues
Publisher: American Geophysical Union (AGU)
Date: 06-2006
DOI: 10.1029/2005WR004651
Concentration profiles of particles settling in the neutral and stratified atmospheric boundary layer
Publisher: Springer Science and Business Media LLC
Date: 11-05-2007
Scale dependence of subgrid-scale model coefficients: An a priori study
Publisher: AIP Publishing
Date: 11-2008
DOI: 10.1063/1.2992192
Abstract: Dynamic subgrid-scale models require an a priori assumption about the variation in the model coefficients with filter scale. The standard dynamic model assumes independence of scale while the scale dependent model assumes power-law dependence. In this paper, we use field experimental data to investigate the dependence of model coefficients on filter scale for the Smagorinsky and the nonlinear models. The results indicate that the assumption of a power-law dependence, which is often used in scale dependent dynamic models, holds very well for the Smagorinsky model. For the nonlinear model, the power-law assumption seems less robust but still adequate.
Some Basic Properties of the Surrogate Subgrid-Scale Heat Flux in the Atmospheric Boundary Layer
Publisher: Springer Science and Business Media LLC
Date: 09-1998
Modeling Flow around Bluff Bodies and Predicting Urban Dispersion Using Large Eddy Simulation
Publisher: American Chemical Society (ACS)
Date: 18-03-2006
DOI: 10.1021/ES051708M
Abstract: Modeling air pollutant transport and dispersion in urban environments is especially challenging due to complex ground topography. In this study, we describe a large eddy simulation (LES) tool including a new dynamic subgrid closure and boundary treatment to model urban dispersion problems. The numerical model is developed, validated, and extended to a realistic urban layout. In such applications fairly coarse grids must be used in which each building can be represented using relatively few grid-points only. By carrying out LES of flow around a square cylinder and of flow over surface-mounted cubes, the coarsest resolution required to resolve the bluff body's cross section while still producing meaningful results is established. Specifically, we perform grid refinement studies showing that at least 6-8 grid points across the bluff body are required for reasonable results. The performance of several subgrid models is also compared. Although effects of the subgrid models on the mean flow are found to be small, dynamic Lagrangian models give a physically more realistic subgrid-scale (SGS) viscosity field. When scale-dependence is taken into consideration, these models lead to more realistic resolved fluctuating velocities and spectra. These results set the minimum grid resolution and subgrid model requirements needed to apply LES in simulations of neutral atmospheric boundary layer flow and scalar transport over a realistic urban geometry. The results also illustrate the advantages of LES over traditional modeling approaches, particularly its ability to take into account the complex boundary details and the unsteady nature of atmospheric boundary layer flow. Thus LES can be used to evaluate probabilities of extreme events (such as probabilities of exceeding threshold pollutant concentrations). Some comments about computer resources required for LES are also included.
Multiscale analysis of fluxes at the turbulent/non-turbulent interface in high Reynolds number boundary layers
Publisher: AIP Publishing
Date: 2014
DOI: 10.1063/1.4861066
Abstract: Analysis of fluxes across the turbulent/non-turbulent interface (TNTI) of turbulent boundary layers is performed using data from two-dimensional particle image velocimetry (PIV) obtained at high Reynolds numbers. The interface is identified with an iso-surface of kinetic energy, and the rate of change of total kinetic energy (K) inside a control volume with the TNTI as a bounding surface is investigated. Features of the growth of the turbulent region into the non-turbulent region by molecular diffusion of K, viscous nibbling, are examined in detail, focussing on correlations between interface orientation, viscous stress tensor elements, and local fluid velocity. At the level of the ensemble (Reynolds) averaged Navier-Stokes equations (RANS), the total kinetic energy K is shown to evolve predominantly due to the turbulent advective fluxes occurring through an average surface which differs considerably from the local, corrugated, sharp interface. The analysis is generalized to a hierarchy of length-scales by spatial filtering of the data as used commonly in Large-Eddy-Simulation (LES) analysis. For the same overall entrainment rate of total kinetic energy, the theoretical analysis shows that the sum of resolved viscous and subgrid-scale advective flux must be independent of scale. Within the experimental limitations of the PIV data, the results agree with these trends, namely that as the filter scale increases, the viscous resolved fluxes decrease while the subgrid-scale advective fluxes increase and tend towards the RANS values at large filter sizes. However, a definitive conclusion can only be made with fully resolved three-dimensional data, over and beyond the large dynamic spatial range presented here. The qualitative trends from the measurement results provide evidence that large-scale transport due to the energy-containing eddies determines the overall rate of entrainment, while viscous effects at the smallest scales provide the physical mechanism ultimately responsible for entrainment. Data spanning over a decade in Reynolds number suggest that the fluxes (or the entrainment velocity) scale with the friction velocity (or equivalently the local turbulent fluctuating velocity), whereas Taylor microscale and boundary-layer thickness are the appropriate length scales at small and large filter sizes, respectively.
The heat flux and the temperature gradient in the lower atmosphere
Publisher: American Geophysical Union (AGU)
Date: 11-2004
DOI: 10.1029/2004GL020053
Modeling turbulent flow over fractal trees with renormalized numerical simulation
Publisher: Elsevier BV
Date: 07-2007
On the Parameterization of Surface Roughness at Regional Scales
Publisher: American Meteorological Society
Date: 2007
DOI: 10.1175/JAS3826.1
Abstract: A parameterization for surface roughness and blending height at regional scales, under neutral atmospheric stability, is studied and tested. The analysis is based on a suite of large-eddy simulations (LES) over surfaces with varying roughness height and multiple variability scales. The LES are based on the scale-dependent Lagrangian dynamic subgrid-scale model, and the surface roughnesses at the ground are imposed using the rough-wall logarithmic law. Several patterns of roughness distribution are considered, including random tiling of patches with a wide distribution of length scales. An integral length scale, based on the one-dimensional structure function of the spatially variable roughness height, is used to define the characteristic surface variability scale, which is a critical input in many regional parameterization schemes. Properties of the simulated flow are discussed with special emphasis on the turbulence properties over patches of unequal roughness. The simulations are then used to assess a generalized form of the parameterization for the blending height and the equivalent surface roughness at regional scales that has been developed earlier for regular patterns of surface roughness (regular stripes). The results are also compared with other parameterizations proposed in the literature. Good agreement is found between the simulations and the regional-scale parameterization for the surface roughness and the blending height when this parameterization is combined with the characteristic surface variability scale proposed in this paper.
Subgrid-Scale Dynamics of Water Vapour, Heat, and Momentum over a Lake
Publisher: Springer Science and Business Media LLC
Date: 05-07-2008
Generalized logarithmic law for high-order moments in turbulent boundary layers
Publisher: Cambridge University Press (CUP)
Date: 19-02-2013
DOI: 10.1017/JFM.2013.61
Abstract: High-Reynolds-number data in turbulent boundary layers are analysed to examine statistical moments of streamwise velocity fluctuations ${u}^{\\prime } $ . Prior work has shown that the variance of ${u}^{\\prime } $ exhibits logarithmic behaviour with distance to the surface, within an inertial sublayer. Here we extend these observations to even-order moments. We show that the $2p$ -order moments, raised to the power $1/ p, $ also follow logarithmic behaviour according to $\\langle \\mathop{({u}^{\\prime + } ){}^{2p} \\rangle }\\nolimits ^{1/ p} = {B}_{p} - {A}_{p} \\ln (z/ \\delta )$ , where ${u}^{\\prime + } $ is the velocity fluctuation normalized by the friction velocity, $\\delta $ is an outer length scale and ${B}_{p} $ are non-universal constants. The slopes ${A}_{p} $ in the logarithmic region appear quite insensitive to Reynolds number, consistent with universal behaviour for wall-bounded flows. The slopes differ from predictions that assume Gaussian statistics, and instead are consistent with sub-Gaussian behaviour.
The Effect of Filter Dimension on the Subgrid-Scale Stress, Heat Flux, and Tensor Alignments in the Atmospheric Surface Layer
Publisher: American Meteorological Society
Date: 03-2007
DOI: 10.1175/JTECH1991.1
Abstract: In field experiments designed to study subgrid-scale parameterizations for large eddy simulation, the flow field is often measured and then filtered in two-dimensional planes. This two-dimensional filtering serves as a surrogate for three-dimensional filtering. The question of whether this will yield accurate results in subgrid-scale (SGS) models is addressed by analyzing data from a field experiment in which 16 sonic anemometers were deployed in a four by four grid. The experiment was held in July 2002 at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility in the Utah West Desert. The full SGS stress tensor and its parameterizations using both two- and three-dimensional filterings are obtained. Comparisons are given between two- and three-dimensional filterings of the field measurements based on probability density functions (PDFs) and energy spectra of the SGS stress elements. The PDFs reveal that quantities calculated with two-dimensional filtering exhibit greater intermittency than those computed with three-dimensional filtering at the same scale. From the spectra it is observed that the different filtering methods result in similar behavior, but that spectra of SGS stress components computed with a three-dimensional filter roll off at a slightly lower wavenumber than those computed with a two-dimensional filter. The PDFs and spectra of the stresses calculated with two- and three-dimensional filters can be made to collapse by reducing the three-dimensional filter scale according to Δ3−D = 0.84Δ2−D. Geometric alignment analyses are performed for the SGS heat flux, SGS stress, and filtered strain rate for the cases of stable, near-neutral, and unstable atmospheric stabilities. Under unstable and near-neutral atmospheric stability, two-dimensional filtering yields acceptable results however, under stable atmospheric stability, a new approach is recommended and delineated.
Turbulent kinetic energy budgets in a model canopy: comparisons between LES and wind-tunnel experiments
Publisher: Springer Science and Business Media LLC
Date: 02-2008
Alignment Trends of Velocity Gradients and Subgrid-Scale Fluxes in the Turbulent Atmospheric Boundary Layer
Publisher: Springer Science and Business Media LLC
Date: 10-2003
Related Organisations
Related Funding Activities
Discovery Projects - Grant ID: DP210102172
Start Date: 04-2021
End Date: 12-2024
Amount: $465,000.00
Funder: Australian Research Council
View Funded Activity