Turbulence in Wind Turbine Wake: Effect of Atmospheric Forcings

2014 ◽  
Author(s):  
Kiran Bhaganagar ◽  
Mithu Debnath
Keyword(s):  
Mixing Layer ◽  
Average Power ◽  
Flow Characteristics ◽  
Atmospheric Conditions ◽  
Wake Effect ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Vortex Merging ◽  
Horizontal Axis Wind Turbines ◽  
Atmospheric Forcings

Large eddy simulation (LES) is used as a tool to understand the near-wake effects of large 5-MW, 3-blade horizontal-axis wind turbines (WT) in convective atmospheric boundary layer (ABL). The simulations are performed for two inline WT separated by distance of 2.5D (D is diameter of the rotor) in unstable ABL so that the downstream WT is operated under the wake of the upstream WT. The flow characteristics are analyzed in the wake regions behind WT to understand the flow physics. Tip and root vortices undergo vortex merging due to instability. Turbulent mixing layer that develops in the wake region is stronger for the downstream WT. The rate of growth/decay of the mean velocity and turbulence is much higher for WT2 than WT1. The time evolution of the wake of WT1 and WT2 revealed additional wake induced shear that contributes to faster turbulence diffusion which results in shrinking of the shear layer (in height) downstream. The average power output of WT2 is 40% lower than WT1 during unstable stratified atmospheric conditions.

LES and Hybrid RANS/LES of a Fundamental Trailing Edge Slot

2014 ◽  
Author(s):  
Elizaveta Ivanova ◽  
Gregory M. Laskowski
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Numerical Study ◽  
Mixing Layer ◽  
Detached Eddy Simulation ◽  
Trailing Edge ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer, mean velocity, and turbulence in a fundamental trailing edge slot. The geometry represents a landless slot (two-dimensional wall jet) with adjustable slot lip thickness. The reference experimental data taken from the publications of Kacker and Whitelaw [1] [2] [3] [4] contains the adiabatic wall effectiveness together with the velocity and the Reynolds-stress profiles for various blowing ratios and slot lip thicknesses. The simulations were conducted at three different lip thickness and several blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against unsteady RANS. The predictive capability of the tested LES models (dynamic ksgs-equation [5] and WALE [6]) was comparable. The Improved Delayed Detached Eddy Simulation (IDDES) hybrid method [7] also shows satisfactory agreement with the experimental data. In addition to the described baseline investigations, the influence of the inlet turbulence boundary conditions and their implication for the initial mixing layer and heat transfer development were studied for both LES and IDDES.

Assessment of Large-Eddy Simulation (LES) Models for Engine Type Flows: Effect of Model Type and Grid Size

2013 ◽  
Author(s):  
Jun Han ◽  
Satbir Singh ◽  
Eric Pomraning
Keyword(s):  
Eddy Viscosity ◽  
Flow Characteristics ◽  
Computer Code ◽  
Viscosity Model ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Eddy Viscosity Model ◽  
Large Eddy ◽  
Flow Configurations ◽  
Engine Type

In this paper, large-eddy simulations (LES) of engine type flow are performed using commercially available computer code CONVERGE. First, accuracy of the numerical discretization scheme of the code is assessed using well established laminar flow configurations. Then, two different subgrid scale (SGS) models, an eddy-viscosity model of Vreman (Physics of fluids, 16, 2004) and a non eddy-viscosity model of Pomraning and Rutland (AIAA Journal, 40, 2002) are employed to predict turbulent flow characteristics in a piston-valve assembly. A number of grid resolutions are employed to perform the simulations, with and without the SGS models. The mean velocity and the root-mean-squared (RMS) values of the velocity fluctuations are compared with available experimental data. Although satisfactory comparison of model predictions with measured data is obtained, it is found that the predictions are more influenced by the grid resolution than the SGS model contribution.

scholarly journals Effects of roof configuration on natural ventilation for an isolated building

2021 ◽  
Vol 15 (3) ◽  
pp. 8379-8389
Author(s):  
Lip Kean Moey ◽  
Man Fai Kong ◽  
Vin Cent Tai ◽  
Tze Fong Go ◽  
Nor Mariah Adam
Keyword(s):  
Kinetic Energy ◽  
Natural Ventilation ◽  
Velocity Ratio ◽  
Mixing Layer ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Gable Roof ◽  
Building Models ◽  
Large Vortex ◽  
Field Information

Numerical analyses based on CFD steady RANS were conducted to investigate the effects of roof configuration on wind-induced natural ventilation for an isolated roofed building. Gable roof and saltbox roof building models were tested with 15˚, 25˚, 35˚ and 45˚ roof pitch in present study. The flow field information and flow characteristics were obtained from the contours and plots generated by CFD. In accordance to the increment of roof pitch, the turbulence kinetic energy and mean velocity ratio show vigorous response. The flow separated at the windward corner do not reattach onto the roof, thus induced higher velocity gradient and form a large vortex at the roof ridge. The vortices behind then building caused by the flow separation at the roof ridge extend along the mixing layer and spread up to the roof. The pressure differences mainly rely on the roof shapes. Greater pressure differences between the upstream, interior and downstream was observed in saltbox roof cases. This is due to the extended roof height which boosted the impinging effect caused by the incoming wind. Generally, the saltbox roof configuration exhibit better performance than gable roof in terms of the measured parameters.

Flow Characteristics of Flapping Motion of a Plane Water Jet Impinging onto Free Surface

2013 ◽  
Vol 5 (06) ◽  
pp. 846-856 ◽  
Author(s):  
Liqing Zhao ◽  
Jianhong Sun
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Flapping Motion ◽  
Eddy Simulation ◽  
Plane Jets ◽  
Velocity Decay ◽  
Turbulent Plane ◽  
Induced Velocity

AbstractA submerged turbulent plane jet in shallow water impinging vertically onto the free surface will produce a large-scale flapping motion when the jet exit velocity is larger than a critical one. The flapping phenomenon is verified in this paper through a large eddy simulation where the free surface is modeled by volume of fluid approach. The quantitative results for flapping jet are found to be in good agreement with available experimental data in terms of mean velocity, flapping-induced velocity and turbulence intensity. Results show that the flapping motion is a new flow pattern with characteristic flapping frequency for submerged turbulent plane jets, the mean centerline velocity decay is considerably faster than that of the stable impinging jet without flapping motion, and the flapping-induced velocities are as important as the turbulent fluctuations.

scholarly journals Unsteady Simulation of Transonic Buffet of a Supercritical Airfoil with Shock Control Bump

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 203
Author(s):  
Yufei Zhang ◽  
Pu Yang ◽  
Runze Li ◽  
Haixin Chen
Keyword(s):  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Control Effect ◽  
Shock Control Bump ◽  
Shock Control ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Unsteady Simulation ◽  
Drag Ratio

The unsteady flow characteristics of a supercritical OAT15A airfoil with a shock control bump were numerically studied by a wall-modeled large eddy simulation. The numerical method was first validated by the buffet and nonbuffet cases of the baseline OAT15A airfoil. Both the pressure coefficient and velocity fluctuation coincided well with the experimental data. Then, four different shock control bumps were numerically tested. A bump of height h/c = 0.008 and location xB/c = 0.55 demonstrated a good buffet control effect. The lift-to-drag ratio of the buffet case was increased by 5.9%, and the root mean square of the lift coefficient fluctuation was decreased by 67.6%. Detailed time-averaged flow quantities and instantaneous flow fields were analyzed to demonstrate the flow phenomenon of the shock control bumps. The results demonstrate that an appropriate “λ” shockwave pattern caused by the bump is important for the flow control effect.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Role of Plaque Morphology in Altering the Flow Characteristics in Diseased Coronary Artery

2012 ◽  
Author(s):  
Carlos Moreno ◽  
Kiran Bhaganagar
Keyword(s):  
Coronary Artery ◽  
Nonlinear Response ◽  
Flow Characteristics ◽  
Proximal Region ◽  
Patient Specific ◽  
Plaque Morphology ◽  
Mean Velocity ◽  
Peak Location ◽  
The Mean

Patient specific simulations of a single patient based on an accurate representation of the plaque in a diseased coronary artery with 35% stenosis are performed to understand the effect of inlet forcing frequency and amplitude on the wall shear stress (WSS). Numerical simulations are performed with unsteady flow conditions in a laminar regime. The results have revealed that at low amplitudes, WSS is insensitive to forcing frequency and is it in phase with Q. The maximum WSS is observed at the proximal region of the stenosis, and WSS has highest negative values at the peak location of the stenosis. For higher pulsatile amplitude (a > 1.0), WSS exhibits a strong sensitivity with forcing frequencies. At higher forcing frequency the WSS exhibits nonlinear response to the inlet forcing frequency. Furthermore, significant differences in the mean velocity profile are observed during maximum and minimum volumetric flow rates.

Flow Characteristics of Transitional Boundary Layers on an Airfoil in Wakes

2000 ◽  
Vol 122 (3) ◽  
pp. 522-532 ◽  
Author(s):  
H. Lee ◽  
S.-H. Kang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Skin Friction ◽  
Velocity Fluctuation ◽  
Plate Boundary ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Transitional Region ◽  
Mean Velocity ◽  
Measured Velocity

Transition characteristics of a boundary layer on a NACA0012 airfoil are investigated by measuring unsteady velocity using hot wire anemometry. The airfoil is installed in the incoming wake generated by an airfoil aligned in tandem with zero angle of attack. Reynolds number based on the airfoil chord varies from 2.0×105 to 6.0×105; distance between two airfoils varies from 0.25 to 1.0 of the chord length. To measure skin friction coefficient identifying the transition onset and completion, an extended wall law is devised to accommodate transitional flows with pressure gradient and nonuniform inflows. Variations of the skin friction are quite similar to that of the flat plate boundary layer in the uniform turbulent inflow of high intensity. Measured velocity profiles are coincident with families generated by the modified wall law in the range up to y+=40. Turbulence intensity of the incoming wake shifts the onset location of transition upstream. The transitional region becomes longer as the airfoils approach one another and the Reynolds number increases. The mean velocity profile gradually varies from a laminar to logarithmic one during the transition. The maximum values of rms velocity fluctuations are located near y+=15-20. A strong positive skewness of velocity fluctuation is observed at the onset of transition and the overall rms level of velocity fluctuation reaches 3.0–3.5 in wall units. The database obtained will be useful in developing and evaluating turbulence models and computational schemes for transitional boundary layer. [S0098-2202(00)01603-5]

scholarly journals 3D Numerical Study of the Flow Properties in a Double-Spur Dikes Field during a Flood Process

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1574 ◽  
Author(s):  
Xun Han ◽  
Pengzhi Lin
Keyword(s):  
Water Surface ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Field Measurements ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
River Bed ◽  
Hydrodynamic Evolution ◽  
Spur Dikes ◽  
Potential Damage

A 3D numerical model is developed to study the flow characteristics of a double-spur dikes field on Yangtze River during a flood process, which was presented by the variation of the flow condition. The model is based on Navier–Stokes (NS) equations, the porous medium method (PMM) is employed to treat the solid structures including the river bed surface, the volume of fluid (VOF) method is applied to track the motion of the water surface during the flood process, and large eddy simulation (LES) is adopted to capture the turbulence transport and dissipation. Using this model, the target reach’s flow field before the construction of double-spur dikes is simulated first, while the numerical results are compared to the field measurements on flow velocity and water surface level, and fairly good agreements are shown. Then, the model is applied to reproduce the hydrodynamic evolution during a flood process after double-spur dikes’ constructions, while the detailed 3D flow fields are obtained under some certain states with different submergence rates of the spur dikes; finally, the potential damage positions around these spur dikes are analyzed accordingly.

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