scholarly journals Effect of the Inlet Boundary Conditions on the Flow over Complex Terrain Using Large Eddy Simulation

Designs ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 34
Author(s):  
Yi Wang ◽  
Giulio Vita ◽  
Bruño Fraga ◽  
Jianchun Wang ◽  
Hassan Hemida
Keyword(s):  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Flow Separation ◽  
Bubble Size ◽  
Flow Region ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Simulation Results ◽  
Case Based

For large eddy simulation, it is critical to choose the suitable turbulent inlet boundary condition as it significantly affects the calculated flow field. In this paper, the effect of different inlet boundary conditions, including random method (RAND), Lund method, and divergence-free synthetic eddies method (DFSEM), on the flow in a channel with a hump are investigated through large-eddy simulation. The simulation results are further compared with experimental data. It has been found that turbulence is nearly fully developed in the case based on the Lund method, not fully developed in the case based on DFSEM, and not developed in the case based on the RAND method. In the flow region before the hump, mean velocity profiles in the case applying the Lund method gradually fit the law of the wall as the main flow moves towards the hump, but the simulation results based on the RAND and DFSEM methods cannot fit the wall function. In the flow region after the hump, cases applying Lund and DFSEM methods could relative precisely predict the size of turbulent bubble and turbulent statistics profiles. Meanwhile, the case based on the RAND method cannot capture the positions of flow separation and re-attachment point and overestimates the turbulent bubble size. From this research, it could be found that different turbulent inflow generation methods have a manifested impact on the flow separation and re-attachment after the hump. If the coherent turbulence is maintained in the approach flow, even though turbulent intensity is not large enough, the simulation can still predict the flow separation and turbulent bubble size relative precisely.

Large eddy simulation of forest canopy flow for wildland fire modeling

2014 ◽  
Vol 44 (12) ◽  
pp. 1534-1544 ◽  
Author(s):  
Eric Mueller ◽  
William Mell ◽  
Albert Simeoni
Keyword(s):  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Periodic Boundary ◽  
Forest Canopy ◽  
Wildland Fire ◽  
Periodic Boundary Conditions ◽  
Static Case ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy

Large eddy simulation (LES) based computational fluid dynamics (CFD) simulators have obtained increasing attention in the wildland fire research community, as these tools allow the inclusion of important driving physics. However, due to the complexity of the models, individual aspects must be isolated and tested rigorously to ensure meaningful results. As wind is a driving force that can significantly dictate the behavior of a wildfire, the simulation of wind is studied in the context of a particular LES CFD model, the Wildland–urban interface Fire Dynamics Simulator (WFDS). As WFDS has yet to be tested extensively with regard to wind flow within and above forest canopies, a study of its ability to do so is carried out. First, three simulations are conducted using periodic boundary conditions. Two of these assume a spatially heterogeneous forest and one models wind downstream of a canopy edge. Second, two simulations are conducted with specified “inflow” conditions using two inflow profiles: one static and one dynamic (driven by a precursor simulation). Using periodic boundary conditions, the model is found to generate profiles of mean velocity and turbulent statistics that are representative of experimental measurements. The dynamic inflow scenario is found to perform better than the static case.

A Method of Measuring Turbulent Flow Structures With Particle Image Velocimetry and Incorporating Into Boundary Conditions of Large Eddy Simulations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Puxuan Li ◽  
Steve J. Eckels ◽  
Garrett W. Mann ◽  
Ning Zhang
Keyword(s):  
Particle Image Velocimetry ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Particle Image ◽  
Advantages And Disadvantages ◽  
Eddy Simulation ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Inlet Conditions

The setup of inlet conditions for a large eddy simulation (LES) is a complex and important problem. Normally, there are two methods to generate the inlet conditions for LES, i.e., synthesized turbulence methods and precursor simulation methods. This study presents a new method for determining inlet boundary conditions of LES using particle image velocimetry (PIV). LES shows sensitivity to inlet boundary conditions in the developing region, and this effect can even extend into the fully developed region of the flow. Two kinds of boundary conditions generated from PIV data, i.e., steady spatial distributed inlet (SSDI) and unsteady spatial distributed inlet (USDI), are studied. PIV provides valuable field measurement, but special care is needed to estimate turbulent kinetic energy and turbulent dissipation rate for SSDI. Correlation coefficients are used to analyze the autocorrelation of the PIV data. Different boundary conditions have different influences on LES, and their advantages and disadvantages for turbulence prediction and static pressure prediction are discussed in the paper. Two kinds of LES with different subgrid turbulence models are evaluated: namely dynamic Smagorinsky–Lilly model (Lilly model) and wall modeled large eddy simulation (WMLES model). The performances of these models for flow prediction in a square duct are presented. Furthermore, the LES results are compared with PIV measurement results and Reynolds-stress model (RSM) results at a downstream location for validation.

scholarly journals Experimental study of wall boundary conditions for large-eddy simulation

2001 ◽  
Vol 446 ◽  
pp. 309-320 ◽  
Author(s):  
IVAN MARUSIC ◽  
GARY J. KUNKEL ◽  
FERNANDO PORTÉ-AGEL
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Streamwise Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy

An experimental investigation was conducted to study the wall boundary condition for large-eddy simulation (LES) of a turbulent boundary layer at Rθ = 3500. Most boundary condition formulations for LES require the specification of the instantaneous filtered wall shear stress field based upon the filtered velocity field at the closest grid point above the wall. Three conventional boundary conditions are tested using simultaneously obtained filtered wall shear stress and streamwise and wall-normal velocities, at locations nominally within the log region of the flow. This was done using arrays of hot-film sensors and X-wire probes. The results indicate that models based on streamwise velocity perform better than those using the wall-normal velocity, but overall significant discrepancies were found for all three models. A new model is proposed which gives better agreement with the shear stress measured at the wall. The new model is also based on the streamwise velocity but is formulated so as to be consistent with ‘outer-flow’ scaling similarity of the streamwise velocity spectra. It is therefore expected to be more generally applicable over a larger range of Reynolds numbers at any first-grid position within the log region of the boundary layer.

scholarly journals Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

2019 ◽  
Vol 11 (12) ◽  
pp. 168781401989783
Author(s):  
Yun Ren ◽  
Zuchao Zhu ◽  
Denghao Wu ◽  
Xiaojun Li ◽  
Lanfang Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Separation ◽  
Hybrid Algorithm ◽  
Internal Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Vorticity Flux

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

Application of Near Wall Model to Large Eddy Simulation Based on Boundary Layer Approximation

2006 ◽  
Author(s):  
Takashi Takata ◽  
Akira Yamaguchi ◽  
Masaaki Tanaka ◽  
Hiroyuki Ohshima
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Frequency Characteristic ◽  
Large Scale ◽  
Plane Channel ◽  
Boundary Layer Approximation ◽  
Eddy Simulation ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Near Wall

Turbulent statistics near a structural surface, such as a magnitude of temperature fluctuation and its frequency characteristic, play an important role in damage progression due to thermal stress. A Large Eddy Simulation (LES) has an advantage to obtain the turbulent statistics especially in terms of the frequency characteristic. However, it still needs a great number of computational cells near a wall. In the present paper, a two-layer approach based on boundary layer approximation is extended to an energy equation so that a low computational cost is achieved even in a large-scale LES analysis to obtain the near wall turbulent statistics. The numerical examinations are carried out based on a plane channel flow with constant heat generation. The friction Reynolds numbers (Reτ) of 395 and 10,000 are investigated, while the Prandtl number (Pr) is set to 0.71 in each analysis. It is demonstrated that the present method is cost-effective for a large-scale LES analysis.

scholarly journals Optimization of the Turbulence Model on Numerical Simulations of Flow Field within a Hydrocyclone

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Yan Xu ◽  
Zunce Wang ◽  
Lin Ke ◽  
Sen Li ◽  
Jinglong Zhang
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Cross Sections ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Computational Grids ◽  
Test Results ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

Reynolds Stress Model and Large Eddy Simulation are used to respectively perform numerical simulation for the flow field of a hydrocyclone. The three-dimensional hexahedral computational grids were generated. Turbulence intensity, vorticity, and the velocity distribution of different cross sections were gained. The velocity simulation results were compared with the LDV test results, and the results indicated that Large Eddy Simulation was more close to LDV experimental data. Large Eddy Simulation was a relatively appropriate method for simulation of flow field within a hydrocyclone.

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