Evaluation of SA-DES and SST-DES models using OpenFOAM for calculating the flow around a train subjected to crosswinds

2019 ◽  
Vol 234 (10) ◽  
pp. 1346-1357 ◽  
Author(s):  
Tian Li ◽  
Hassan Hemida ◽  
Jiye Zhang
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Flow Field ◽  
Lift Force ◽  
Pressure Coefficient ◽  
Mean Flow ◽  
Side Force ◽  
Force Coefficients ◽  
Rans Model ◽  
Eddy Simulation

Detached eddy simulation (DES) has been widely applied in crosswind stability simulations of trains in recent years. As DES is a hybrid Reynolds Averaged Navier–Stokes (RANS)/large eddy simulation approach, the choice of the RANS model associated with DES is a key factor for an accurate numerical simulation. However, the influence of the RANS model on the flow around trains was not fully investigated in previous researches. In this study, DES with the Spalart–Allmaras (SA) model (SA-DES) and shear stress transport (SST) k−ω model (SST-DES) have been investigated owing to their ability to predict the surface pressure, aerodynamic forces, and the flow field around a 1/25th scale Class 390 train subjected to crosswinds. Numerical simulation results were validated with experimental data. Results show that both SA-DES and SST-DES predict similar trends of the mean flow field around the train. However, there were considerable differences observed in the position of separation points and consequently the separation and attachment lines on the roof and bottom of the train body. The SST-DES results correlated more closely to the experimental data than SA-DES for pressure coefficient on the roof and leeward surface at almost all loops. A slight difference in the side force and roll moment coefficients and a considerable difference in the lift force coefficient were observed for SA-DES and SST-DES. The side force coefficients calculated using SST-DES remain within the experimental uncertainty, whereas the lift force coefficients deviated greatly due to the omission of some underbody geometrical features. Compared to the experimental data, the SST-DES performs better than SA-DES. Therefore, the SST k−ω model is recommended for the RANS model associated with DES.

Comparisons of Shear Stress Transport and Detached Eddy Simulations of the Flow Around Trains

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Tian Li ◽  
Hassan Hemida ◽  
Jiye Zhang ◽  
Mohammad Rashidi ◽  
Dominic Flynn
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Flow Field ◽  
Surface Pressure ◽  
Experimental Uncertainty ◽  
Detached Eddy Simulation ◽  
Aerodynamic Forces ◽  
Force Coefficients ◽  
Eddy Simulation ◽  
Shear Stress Transport

Shear stress transport (SST) k–ω model and detached eddy simulation (DES) have been widely applied in crosswind stability simulations for trains in the literature. In the previous research, the influence of the SST and DES approaches on the flow field around trains, which affects the surface pressure and consequently the aerodynamic forces of the train, was not properly investigated in terms of their influence flow field. The SST and improved delayed detached eddy simulation (IDDES) turbulence models have been tested in this study for their ability to predict the flow field around, surface pressure, and aerodynamic forces on a 1/25th scale Class 390 train subjected to crosswinds. Numerical simulation results were validated with experimental data. Results show that both SST and IDDES predict similar trends in the mean flow field around the train. However, there were some slight differences observed in the size of vortices, the position of separation points, and consequently, the separation and attachment lines. The SST results compared more closely to the experimental data than IDDES for pressure coefficient on the leeward surface and roof at certain loops. Slight differences were observed in force coefficients for SST and DES. The side force coefficients calculated using computational fluid dynamics (CFD) sit within the experimental uncertainty, whereas the lift force coefficients deviated greatly due to the omission of some underbody geometrical features. Both SST and IDDES approaches used the linear-upwind stabilized transport (LUST) scheme and were able to predict accurately the time-averaged surface pressure within the margin of the experimental uncertainty.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

scholarly journals Investigation of the velocity field downstream of a benchmark vent using numerical simulation and hot-wire anemometry

2019 ◽  
Vol 213 ◽  
pp. 02076
Author(s):  
Jan Sip ◽  
Frantisek Lizal ◽  
Jakub Elcner ◽  
Jan Pokorny ◽  
Miroslav Jicha
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulation ◽  
Velocity Field ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Turbulence Models ◽  
Hot Wire ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Precise Prediction

The velocity field in the area behind the automotive vent was measured by hot-wire anenemometry in detail and intensity of turbulence was calculated. Numerical simulation of the same flow field was performed using Computational fluid dynamics in commecial software STAR-CCM+. Several turbulence models were tested and compared with Large Eddy Simulation. The influence of turbulence model on the results of air flow from the vent was investigated. The comparison of simulations and experimental results showed that most precise prediction of flow field was provided by Spalart-Allmaras model. Large eddy simulation did not provide results in quality that would compensate for the increased computing cost.

scholarly journals Flow Field Research of the Reciprocating Baffled Flocculation Tank

2020 ◽  
Vol 2 (1) ◽  
pp. 29
Author(s):  
Ying Xu ◽  
Yuebin Wu ◽  
Huan Liang ◽  
Qiang Sun
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Flow Field ◽  
Particle Image ◽  
Field Research ◽  
Hydraulic Characteristics ◽  
Flocculation Efficiency ◽  
Image Velocimetry ◽  
Hydraulic Conditions ◽  
The Standard Model

To research the reasons for the unsatisfactory hydraulic conditions of the reciprocating baffled flocculation tank, this paper investigates its flow field through PIV (Particle Image Velocimetry) laboratory experiment tests and numerical simulation. Three numerical schemes, the standard model, RNG model and realizable model, are calibrated and validated with the experimental data gained in this study. They are adopted for comparative study of their validity and accuracy for modeling the effect of the hydraulic characteristics of the flow field on flocculation. The best validated model is then applied to explain the reasons for the low flocculation efficiency and is applied to improve the structure of the reciprocating baffled flocculation tank.

scholarly journals Numerical Simulation of Rotor in Hover and Forward Flight

2018 ◽  
Vol 179 ◽  
pp. 03011
Author(s):  
Qinghe Zhao
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Flow Field ◽  
Moving Grid ◽  
Steady State Flow ◽  
Forward Flight ◽  
Numerical Simulation Result ◽  
Structured Grid ◽  
Pressure Distributions ◽  
Good Agreement

The flow around rotor is numerical simulated in hover and forward flight based on multi-structured grid. In hover the flow field can be transformed into a steady-state flow field in the rotating coordinate system. The experimental data of Caradonna and Tung rotor is used to verify the numerical simulation result. The numerical results compare well with the experimental data for both non-lifting and lifting cases. Non-lifting forward flight is simulated and the prediction capabilities have been validated through the ONERA two-blade rotor. The pressure distributions of different positions under different azimuth angles are compared, which is in good agreement with the experimental data. There is unsteady shock wave when forward flight. Dual-time method is used to obtain unsteady flow field with rigid moving grid in the inertial system.

Effect of Turbulent Intensity and Axial Gap on Turbine Heat Transfer Using Steady and Harmonic Models

2013 ◽  
Author(s):  
Sridhar Murari ◽  
Sunnam Sathish ◽  
Ramakumar Bommisetty ◽  
Jong S. Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Pressure Coefficient ◽  
Heat Transfer Characteristics ◽  
Complex Flow ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Heat Loads

The knowledge of heat loads on the turbine is of great interest to turbine designers. Turbulence intensity and stator-rotor axial gap plays a key role in affecting the heat loads. Flow field and associated heat transfer characteristics in turbines are complex and unsteady. Computational fluid dynamics (CFD) has emerged as a powerful tool for analyzing these complex flow systems. Honeywell has been exploring the use of CFD tools for analysis of flow and heat transfer characteristics of various gas turbine components. The current study has two objectives. The first objective aims at development of CFD methodology by validation. The commercially available CFD code Fine/Turbo is used to validate the predicted results against the benchmark experimental data. Predicted results of pressure coefficient and Stanton number distributions are compared with available experimental data of Dring et al. [1]. The second objective is to investigate the influence of turbulence (0.5% and 10% Tu) and axial gaps (15% and 65% of axial chord) on flow and heat transfer characteristics. Simulations are carried out using both steady state and harmonic models. Turbulence intensity has shown a strong influence on turbine blade heat transfer near the stagnation region, transition and when the turbulent boundary layer is presented. Results show that a mixing plane is not able to capture the flow unsteady features for a small axial gap. Relatively close agreement is obtained with the harmonic model in these situations. Contours of pressure and temperature on the blade surface are presented to understand the behavior of the flow field across the interface.

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

2009 ◽  
Author(s):  
Hayder Schneider ◽  
Dominic von Terzi ◽  
Hans-Jo¨rg Bauer ◽  
Wolfgang Rodi
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

Reynolds-Averaged Navier-Stokes (RANS) calculations and Large-Eddy Simulations (LES) of the flow in two asymmetric three-dimensional diffusers were performed. The numerical setup was chosen to be in compliance with previous experiments. The aim of the present study is to find the least expensive method to compute reliably and accurately the impact of geometric sensitivity on the flow. RANS calculations fail to predict both the extent and location of the three-dimensional separation bubble. In contrast, LES is able to determine the amount of reverse flow and the pressure coefficient within the accuracy of experimental data.

scholarly journals DNS of a turbulent boundary layer using inflow conditions derived from 4D-PTV data

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Jason Appelbaum ◽  
Duncan Ohno ◽  
Ulrich Rist ◽  
Christoph Wenzel
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Nearest Neighbor ◽  
Tracer Particle ◽  
Flow Analysis ◽  
Mean Flow ◽  
Experimental Field ◽  
Inlet Region

AbstractUnsteady, 3D particle tracking velocimetry (PTV) data are applied as an inlet boundary condition in a direct numerical simulation (DNS). The considered flow case is a zero pressure gradient (ZPG) turbulent boundary layer (TBL) flow over a flat plate. The study investigates the agreement between the experimentally measured flow field and its simulated counterpart with a hybrid 3D inlet region. The DNS field inherits a diminishing contribution from the experimental field within the 3D inlet region, after which it is free to spatially evolve. Since the measurement does not necessarily provide a spectrally complete description of the turbulent field, the spectral recovery of the flow field is analyzed as the TBL evolves. The study summarizes the pre-processing methodology used to bring the experimental data into a form usable by the DNS as well as the numerical method used for simulation. Spectral and mean flow analysis of the DNS results show that turbulent structures with a characteristic length on the order of one average tracer particle nearest neighbor radius $${\bar{r}}_{\text {NN}}$$ r ¯ NN or greater are well reproduced and stay correlated to the experimental field downstream of the hybrid inlet. For turbulent scales smaller than $${\bar{r}}_{\text {NN}}$$ r ¯ NN , where experimental data are sparse, a relatively quick redevelopment of previously unresolved turbulent energy is seen. The results of the study indicate applicability of the approach to future DNS studies in which specific upstream or far field boundary conditions (BCs) are required and may provide the utility of decreasing high initialization costs associated with conventional inlet BCs. Graphic abstract

scholarly journals Large Eddy Simulation of Self-Excited Oscillation Pulsed Jet (SEOPJ) Induced by a Helmholtz Oscillator in Underground Mining

Energies ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 2161 ◽  
Author(s):  
Zhenlong Fang ◽  
Qiang Wu ◽  
Mengda Zhang ◽  
Haoyang Liu ◽  
Pan Jiang ◽  
...  
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Coherent Structure ◽  
Underground Mining ◽  
Operating Pressure ◽  
Mean Flow ◽  
The Core ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Field Characteristics

Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation.

scholarly journals Numerical Investigation of Fluid Flow and Performance Prediction in a Fluid Coupling Using Large Eddy Simulation

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Wei Cai ◽  
Yuan Li ◽  
Xingzhong Li ◽  
Chunbao Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Performance Prediction ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Comparison Results ◽  
Large Eddy ◽  
Hydraulic Coupling ◽  
And Performance

Large eddy simulation (LES) with various subgrid-scale (SGS) models was introduced to numerically calculate the transient flow of the hydraulic coupling. By using LES, the study aimed to advance description ability of internal flow and performance prediction. The CFD results were verified by experimental data. For the purpose of the description of the flow field, six subgrid-scale models for LES were employed to depict the flow field; the distribution structure of flow field was legible. Moreover, the flow mechanism was analyzed using 3D vortex structures, and those showed that DSL and KET captured abundant vortex structures and provided a relatively moderate eddy viscosity in the chamber. The predicted values of the braking torque for hydraulic coupling were compared with experimental data. The comparison results were compared with several simulation models, such as SAS and RKE, and SSTKW models. Those comparison results showed that the SGS models, especially DSL and KET, were applicable to obtain the more accurate predicted results than SAS and RKE, and SSTKW models. Clearly, the predicted results of LES with DSL and KET were far more accurate than the previous studies. The performance prediction was significantly improved.

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