scholarly journals Evaluation of mean velocity and mean speed for test ventilated room from RANS and LES CFD modeling

2019 ◽  
Vol 85 ◽  
pp. 02004 ◽  
Author(s):  
Nikolay Ivanov ◽  
Marina Zasimova ◽  
Evgueni Smirnov ◽  
Detelin Markov
Keyword(s):  
Kinetic Energy ◽  
Cfd Modeling ◽  
Navier Stokes ◽  
Velocity Data ◽  
Mean Velocity ◽  
Energy Field ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
The Difference

The paper presents and discusses data for the ventilation airflow in an isothermal room corresponding to the Nielsen et al. (1978) test computed with Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) approaches. As LES computations provide directly both the speed and velocity components data, the difference between the mean speed and mean velocity values is computed and discussed. For the RANS computations that give the mean velocity data only, application of the velocity-to-speed conversion procedure based on the turbulence kinetic energy field provided by a turbulence model resulted in accurate mean speed evaluation.

Kinetic-energy-flux-constrained model using an artificial neural network for large-eddy simulation of compressible wall-bounded turbulence

2021 ◽  
Vol 932 ◽  
Author(s):  
Changping Yu ◽  
Zelong Yuan ◽  
Han Qi ◽  
Jianchun Wang ◽  
Xinliang Li ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Energy Flux ◽  
Mean Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Bounded Turbulence

Kinetic energy flux (KEF) is an important physical quantity that characterizes cascades of kinetic energy in turbulent flows. In large-eddy simulation (LES), it is crucial for the subgrid-scale (SGS) model to accurately predict the KEF in turbulence. In this paper, we propose a new eddy-viscosity SGS model constrained by the properly modelled KEF for LES of compressible wall-bounded turbulence. The new methodology has the advantages of both accurate prediction of the KEF and strong numerical stability in LES. We can obtain an approximate KEF by the tensor-diffusivity model, which has a high correlation with the real value. Then, using the artificial neural network method, the local ratios between the real KEF and the approximate KEF are accurately modelled. Consequently, the SGS model can be improved by the product of that ratio and the approximate KEF. In LES of compressible turbulent channel flow, the new model can accurately predict mean velocity profile, turbulence intensities, Reynolds stress, temperature–velocity correlation, etc. Additionally, for the case of a compressible flat-plate boundary layer, the new model can accurately predict some key quantities, including the onset of transitions and transition peaks, the skin-friction coefficient, the mean velocity in the turbulence region, etc., and it can also predict the energy backscatters in turbulence. Furthermore, the proposed model also shows more advantages for coarser grids.

scholarly journals Prediction of flow and dispersion in cross–ventilated buildings

2019 ◽  
Vol 128 ◽  
pp. 05002
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Ali Nahavandi
Keyword(s):  
Computational Analysis ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Turbulence Structure ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Grid Independence

The present paper presents a detailed computational analysis of flow and dispersion in a generic isolated single–zone buildings. First, a grid generation strategy is discussed, that is inspired by a previous computational analysis and a grid independence study. Different turbulence models are appliedincluding two-equation turbulence models, the differential Reynolds Stress Model, Detached Eddy Simulation and Zonal Large Eddy Simulation. The mean velocity and concentration fields are calculated and compared with the measurements. A satisfactory agreement with the experiments is not observed by any of the modelling approaches, indicating the highly demanding flow and turbulence structure of the problem.

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

2011 ◽  
Vol 383-390 ◽  
pp. 5344-5349
Author(s):  
Zhen Bu
Keyword(s):  
Natural Ventilation ◽  
Ventilation Rate ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Ventilation ◽  
The Mean ◽  
Ventilation Rates ◽  
Les Model ◽  
Good Agreement

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

Effect of Impeller Speed Perturbation in a Rushton Impeller Stirred Tank

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Somnath Roy ◽  
Sumanta Acharya
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Rotational Speed ◽  
Stirred Tank ◽  
Azimuthal Direction ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Rushton Impeller

Flow inside an unbaffled Rushton-impeller stirred tank reactor (STR) is perturbed using a time dependent impeller rotational speed. Large eddy simulation (LES) revealed that the perturbation increased the width of impeller jet compared to the constant rotational speed cases. The turbulent fluctuations were also observed to be enhanced in the perturbed flow and showed higher values of production and convection of turbulent kinetic energy. Changes in the mean flow-field during the perturbation cycle are investigated. The trailing edge vortices were observed to propagate farther both in the radial and azimuthal direction in the perturbed case. Production of turbulent kinetic energy is observed to be related to the breakup of the impeller jet in the perturbed case. Dissipation of turbulent kinetic energy is augmented due to the perturbation ensuring a better mixing at the molecular scale.

Large eddy simulation of a stratified boundary layer under an oscillatory current

2009 ◽  
Vol 643 ◽  
pp. 233-266 ◽  
Author(s):  
BISHAKHDATTA GAYEN ◽  
SUTANU SARKAR ◽  
JOHN R. TAYLOR
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Numerical Study ◽  
Bottom Boundary Layer ◽  
Mean Velocity ◽  
Bottom Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean

A numerical study based on large eddy simulation is performed to investigate a bottom boundary layer under an oscillating tidal current. The focus is on the boundary layer response to an external stratification. The thermal field shows a mixed layer that is separated from the external stratified fluid by a thermocline. The mixed layer grows slowly in time with an oscillatory modulation by the tidal flow. Stratification strongly affects the mean velocity profiles, boundary layer thickness and turbulence levels in the outer region although the effect on the near-bottom unstratified fluid is relatively mild. The turbulence is asymmetric between the accelerating and decelerating stages. The asymmetry is more pronounced with increasing stratification. There is an overshoot of the mean velocity in the outer layer; this jet is linked to the phase asymmetry of the Reynolds shear stress gradient by using the simulation data to examine the mean momentum equation. Depending on the height above the bottom, there is a lag of the maximum turbulent kinetic energy, dissipation and production with respect to the peak external velocity and the value of the lag is found to be influenced by the stratification. Flow instabilities and turbulence in the bottom boundary layer excite internal gravity waves that propagate away into the ambient. Unlike the steady case, the phase lines of the internal waves change direction during the tidal cycle and also from near to far field. The frequency spectrum of the propagating wave field is analysed and found to span a narrow band of frequencies clustered around 45°.

scholarly journals Large-eddy simulation of large-scale structures in long channel flow

2010 ◽  
Vol 661 ◽  
pp. 341-364 ◽  
Author(s):  
D. CHUNG ◽  
B. J. McKEON
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Filter Width ◽  
Half Height ◽  
Large Eddy ◽  
The Mean ◽  
Scale Structures

We investigate statistics of large-scale structures from large-eddy simulation (LES) of turbulent channel flow at friction Reynolds numbers Reτ = 2K and 200K (where K denotes 1000). In order to capture the behaviour of large-scale structures properly, the channel length is chosen to be 96 times the channel half-height. In agreement with experiments, these large-scale structures are found to give rise to an apparent amplitude modulation of the underlying small-scale fluctuations. This effect is explained in terms of the phase relationship between the large- and small-scale activity. The shape of the dominant large-scale structure is investigated by conditional averages based on the large-scale velocity, determined using a filter width equal to the channel half-height. The conditioned field demonstrates coherence on a scale of several times the filter width, and the small-scale–large-scale relative phase difference increases away from the wall, passing through π/2 in the overlap region of the mean velocity before approaching π further from the wall. We also found that, near the wall, the convection velocity of the large scales departs slightly, but unequivocally, from the mean velocity.

Steady/Unsteady Reynolds Averaged Navier-Stokes and Large Eddy Simulations of a Turbine Blade at High Subsonic Outlet Mach Number

2010 ◽  
Author(s):  
Thomas Le´onard ◽  
Florent Duchaine ◽  
Nicolas Gourdain ◽  
Laurent Y. M. Gicquel
Keyword(s):  
Mach Number ◽  
Turbine Blade ◽  
Suction Side ◽  
Navier Stokes ◽  
Sound Waves ◽  
Trailing Edge ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Reynolds Averaged Navier Stokes

Reynolds Averaged Navier-Stokes (RANS), Unsteady RANS (URANS) and Large Eddy Simulation (LES) numerical approaches are clear candidates for the understanding of turbine blade flows. For such blades, the flow unsteady nature appears critical in certain situations and URANS or LES should provide more physical understanding as illustrated here for a laboratory high outlet subsonic Mach blade specifically designed to ease numerical validation. Although RANS offers good estimates of the mean isentropic Mach number and boundary layer thickness, LES and URANS are the only approaches that reproduce the trailing edge flow. URANS predicts the mean trailing edge wake but only LES offers a detailed view of the flow. Indeed LES’s identify flow phenomena in agreement with the experiment, with sound waves emitted from the trailing edge separation point that propagate upstream and interact with the lower blade suction side.

Quantitative Visualization of the Flow in a Centrifugal Pump With Diffuser Vanes—II: Addressing Passage-Averaged and Large-Eddy Simulation Modeling Issues in Turbomachinery Flows

1999 ◽  
Vol 122 (1) ◽  
pp. 108-116 ◽  
Author(s):  
Manish Sinha ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Particle Image Velocimetry Data ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Vaned Diffuser ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Quantitative Visualization ◽  
The Difference

The present paper addresses two basic modeling problems of the flow in turbomachines. For simulation of flows within multistage turbomachinery, unsteady Reynolds-averaged Navier–Stokes (RANS) of an entire series of blade rows is typically impractical. On the other hand, when performing RANS of each blade row separately one is faced with major difficulties in matching boundary conditions. A popular remedy is the “passage-averaged” approach. Unsteady effects caused by neighboring rows are averaged out over all blade orientations, but are accounted for through “deterministic” stresses, which must be modeled. To experimentally study modeling issues for deterministic stresses we use particle image velocimetry data of the flow in a centrifugal pump with a vaned diffuser that includes the flow in the impeller, the gap between the impeller and diffuser, between the diffuser vanes and within the volute downstream. The data have been presented in part A of this paper (Sinha and Katz, 1998, “Flow Structure and Turbulence of a Centrifugal Pump with a Vaned Diffuser,” Proceedings of the ASME Fluids Engineering Division, Washington, DC). Deterministic stresses are obtained from the difference between the phase-averaged and passage-averaged data, whereas the Reynolds stresses are determined from the difference between the instantaneous and phase averaged data. In agreement with previous findings, the deterministic stresses are larger than the Reynolds stresses in regions close to the interface between blade rows, and thus must be carefully accounted for in passage-averaged simulations. The Reynolds stresses are larger in regions located far from the transition region. The second series of issues involves modeling for large-eddy simulation. The measured subgrid stresses determined by spatially filtering the data are compared to eddy viscosity models and show significant discrepancies, especially in regions with separating shear layers. Backscatter of energy that persists during phase averaging is also observed. [S0098-2202(00)00901-9]

scholarly journals Wake Statistics of Different-Scale Wind Turbines under Turbulent Boundary Layer Inflow

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 3004
Author(s):  
Xiaolei Yang ◽  
Daniel Foti ◽  
Christopher Kelley ◽  
David Maniaci ◽  
Fotis Sotiropoulos
Keyword(s):  
Kinetic Energy ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Full Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Surface Models ◽  
The Mean ◽  
Velocity Deficits

Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation.

Large-Eddy Simulation of Turbulent Flow in a Curved Pipe

1996 ◽  
Vol 118 (2) ◽  
pp. 248-254 ◽  
Author(s):  
B. J. Boersma ◽  
F. T. M. Nieuwstadt
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Mean Velocity ◽  
Curved Pipe ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Secondary Motion ◽  
Fully Developed Turbulent Flow ◽  
The Mean

In this paper, we use Large-Eddy Simulation (LES) to compute a fully-developed turbulent flow in a curved pipe. The results allow us to study how the curvature influences the mean velocity profile and also various turbulent statistics. We find reasonable agreement with the few experiments that are available. Our simulation also allows a detailed study of secondary motion in the cross section of the pipe which are caused by the centrifugal acceleration due to the pipe curvature. It is known that this secondary motion may consist of one, two, or three circulation cells. In our simulation results we find one circulation cell.

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