An intercomparison and validation of a range of turbulence closure schemes used in three dimensional tidal models

1995 ◽  
pp. 71-95 ◽  
Author(s):  
Alan M. Davies ◽  
Jiuxing Xing
Keyword(s):  
Three Dimensional ◽  
Turbulence Closure

Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part I: Simulation of the Vortex Rope

2014 ◽  
Vol 81 (6) ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Experimental Data ◽  
Axial Velocity ◽  
Draft Tube ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Turbulence Closure ◽  
Francis Turbine ◽  
Outer Flow ◽  
Vortex Rope ◽  
Partial Load

Numerical simulations and analysis of the vortex rope formation in a simplified draft tube of a model Francis turbine are carried out in this paper, which is the first part of a two-paper series. The emphasis of this part is on the simulation and investigation of flow using different turbulence closure models. Two part-load operating conditions with same head and different flow rates (91% and 70% of the best efficiency point (BEP) flow rate) are considered. Steady and unsteady simulations are carried out for axisymmetric and three-dimensional grid in a simplified axisymmetric geometry, and results are compared with experimental data. It is seen that steady simulations with Reynolds-averaged Navier–Stokes (RANS) models cannot resolve the vortex rope and give identical symmetric results for both the axisymmetric and three-dimensional flow geometries. These RANS simulations underpredict the axial velocity (by at least 14%) and turbulent kinetic energy (by at least 40%) near the center of the draft tube, even quite close to the design condition. Moving farther from the design point, models fail in predicting the correct levels of the axial velocity in the draft tube. Unsteady simulations are performed using unsteady RANS (URANS) and detached eddy simulation (DES) turbulence closure approaches. URANS models cannot capture the self-induced unsteadiness of the vortex rope and give steady solutions while DES model gives sufficient unsteady results. Using the proper unsteady model, i.e., DES, the overall shape of the vortex rope is correctly predicted and the calculated vortex rope frequency differs only 6% from experimental data. It is confirmed that the vortex rope is formed due to the roll-up of the shear layer at the interface between the low-velocity inner region created by the wake of the crown cone and highly swirling outer flow.

scholarly journals INFLUENCE OF TURBULENCE CLOSURE ON ESTUARINE SEDIMENT DYNAMICS AND MORPHODYNAMICS

2011 ◽  
Vol 1 (32) ◽  
pp. 78
Author(s):  
Laurent Amoudry ◽  
Alejandro Souza
Keyword(s):  
River Flow ◽  
Tidal Flow ◽  
Three Dimensional ◽  
Sediment Dynamics ◽  
Ocean Modeling ◽  
Turbulence Closure ◽  
Three Dimensional Model ◽  
Ocean Turbulence ◽  
Rectangular Basin ◽  
The Impact

Turbulence significantly impacts hydrodynamics, mixing and sediment dynamics in coastal environments. We employ a three-dimensional model, the Proudman Oceanographic Laboratory Coastal Ocean Modeling System (POLCOMS), to investigate the effects of implementing various turbulence closure schemes on sediment dynamics and morphodynamics. This model is applied to an idealized estuary, which is represented by a straight rectangular basin. A simple tidal flow is forced at one end and a constant river flow is imposed at the other. Most of the turbulence closure schemes employed are implemented via coupling to the General Ocean Turbulence Model (GOTM). Their effects are also compared to the impact of different erosion parameterizations on the numerical results and observed for different sediment properties.

The Numerical Simulation of Airflow and Dispersion in Three-Dimensional Atmospheric Recirculation Zones

1991 ◽  
Vol 30 (7) ◽  
pp. 1005-1024 ◽  
Author(s):  
Paul Dawson ◽  
David E. Stock ◽  
Brian Lamb
Keyword(s):  
Surface Layer ◽  
Atmospheric Transport ◽  
Three Dimensional ◽  
Field Measurements ◽  
Ground Level ◽  
Turbulence Closure ◽  
Numerical Code ◽  
Recirculation Zones ◽  
Transport And Diffusion ◽  
And Diffusion

Abstract A three-dimensional, nonhydrostatic numerical code using the two-equation turbulence closure was developed to model the atmospheric transport and diffusion of pollutants over buildings and a three-dimensional hill. The standard engineering two-equation, first-order turbulence closure was modified to account for surface layer effects and the reduced production of dissipation in the region above the surface layer found in an atmospheric boundary layer. The computations for the dispersion of a building rooftop release showed good agreement with wind tunnel measurements, except when very close to the ground. The transport and dispersion of a plume over a 300-m conical hill, Steptoe Butte, was also simulated. The computations are compared with near ground-level field measurements.

scholarly journals Estimation of three-dimensional aerodynamic damping using CFD

2019 ◽  
Vol 124 (1271) ◽  
pp. 24-43 ◽  
Author(s):  
R.J. Higgins ◽  
G.N. Barakos ◽  
E. Jinks
Keyword(s):  
Three Dimensional ◽  
Separated Flow ◽  
Turbulence Closure ◽  
Flow Structures ◽  
Test Cases ◽  
Aerodynamic Damping ◽  
Initial Investigation ◽  
Time Marching ◽  
Negative Damping ◽  
Naca 0012

AbstractAeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.

Computation of unsteady three-dimensional transonic nozzle flows using k-epsilon turbulence closure

AIAA Journal ◽  
1996 ◽  
Vol 34 (7) ◽  
pp. 1331-1340 ◽  
Author(s):  
G. A. Gerolymos ◽  
I. Vallet ◽  
A. Bolcs ◽  
P. Ott
Keyword(s):  
Three Dimensional ◽  
Turbulence Closure ◽  
Nozzle Flows

scholarly journals Application of a 3D numerical model to a river with vegetated floodplains

2003 ◽  
Vol 5 (2) ◽  
pp. 99-112 ◽  
Author(s):  
T. Stoesser ◽  
C. A. M. E. Wilson ◽  
P. D. Bates ◽  
A. Dittrich
Keyword(s):  
Drag Force ◽  
Large Scale ◽  
Three Dimensional ◽  
West Germany ◽  
Plant Distribution ◽  
Turbulence Closure ◽  
River Rhine ◽  
Plant Populations ◽  
Vegetated Floodplain ◽  
Water Elevation

This paper describes the application of a three-dimensional computational fluid dynamics code to a large-scale river scheme. One of the primary aims of this paper is to provide a tool, which utilises a roughness closure derived from physical processes, requiring minimal calibration. Accordingly, a roughness closure based on the traditional drag-force approach is implemented. Unlike other implementations of this approach, the drag force is only introduced in the momentum equations and not into the turbulence closure. This ensures that the coefficients of the turbulence closure model (in this case the k−ε scheme) do not require recalibration for each application. An existing vegetated floodplain is used as a reference site and parameters characterising the dimensions of riparian vegetation and its distribution are quantified. A 100 year flood event on a considerable reach length (3500 m) of the lower River Rhine in South-West Germany is then simulated. Mean floodplain velocities are measured using dilution gauging techniques and these are compared with the computed values. Given information such as plant distribution and geometric properties of the various plant populations, the proposed tool can predict floodplain velocities, water elevation and hydrodynamic features indicative of vegetated compound channel flow.

Numerical Analysis of Turbulent Wakes of Turbomachinery Rotor Blades

1980 ◽  
Vol 102 (4) ◽  
pp. 462-472 ◽  
Author(s):  
C. Hah ◽  
B. Lakshminarayana
Keyword(s):  
Numerical Analysis ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Rotor Blades ◽  
Turbulence Closure ◽  
Turbulence Structure ◽  
Closure Model ◽  
Mean Velocity ◽  
Turbulence Closure Model ◽  
The Mean

The wakes of turbomachinery rotor blades are turbulent, three-dimensional, and are subjected to curvature and rotation effects. The objective of this study is to predict the development of such wakes and compare the predictions with the existing data. A finite difference procedure is employed in the numerical analysis of the wake utilizing the continuity, momentum, and turbulence closure equations in the rotating curvilinear and non-orthogonal coordinate system. The turbulence closure is affected by the modified Reynolds stress model. The effects of curvature and rotation on the turbulence structure are accounted for with this turbulence closure model. The pedictions from the present turbulence model agree well with the mean velocity and the turbulence wake data.

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