3D CFD Investigation of Air Flow Behind a Porous Fence Using Different Turbulence Models

2014 ◽  
Author(s):  
Yizhong Xu ◽  
Mohamad Y. Mustafa ◽  
Geanette Polanco
Keyword(s):  
Velocity Profile ◽  
Turbulence Model ◽  
Air Flow ◽  
Turbulence Models ◽  
Experimental Results ◽  
Turbulence Structure ◽  
Cfd Modelling ◽  
Lack Of Information ◽  
Vertical Velocity Profile ◽  
Flow Through

Even after many years of the application of numerical CFD techniques to flow through porous fences, still there is disagreement between researchers regarding the best turbulence model to be implemented in this field. Moreover, different sources claim to have achieved good agreement between numerical results and experimental data; however, it is not always possible to compare numerical and experimental results due to the lack of information or variations in test conditions. In this paper, five different turbulence models namely; K-ε models (standard, RNG and Realizable) and K-ω models (Standard and SST), have been applied through a 3D CFD model to investigate air flow behind a porous panel, under the same conditions (boundary conditions and numerical schemes). Results are compared with wind tunnel experiments. Comparison is based on the vertical velocity profile at a location 925 mm downstream of the fence along its center line. All models were capable of reproducing the velocity profile, however, some turbulence models over-predicted the reduction of velocity while it was under-predicted by other models, however, discrepancy between CFD modelling and experimental results was kept around 20%. Comprehensive description of the turbulence structure and the streamlines highlight the fact that the criterion for selecting the best turbulence model cannot rely only on the velocity comparison at one location, it must also include other variables.

scholarly journals A Numerical Simulation of Turbulent Flow through a Curved Duct

2012 ◽  
Vol 11 (3) ◽  
pp. 169-178
Author(s):  
A K Biswas ◽  
Ashoke K Raman ◽  
A N Mullick
Keyword(s):  
Numerical Simulation ◽  
Turbulence Model ◽  
Experimental Work ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Experimental Results ◽  
Pressure Probe ◽  
Mean Velocity ◽  
Numerical Work ◽  
Flow Through

This paper presents the comparison the results of an experimental work with a numerical work keeping the geometry of the test duct and inlet boundary conditions unaltered. The numerical simulation is validated with the experimental results based on the wall y+ approach for different turbulence models suited for this type of geometry. The experimental work is carried out at mass averaged mean velocity of 40m/s with the measurement of total pressure by a pre-calibrated multi-hole pressure probe and the results presented in the form of a pressure contours in 2-D. For validation of the numerical results Standard k-ε, k-ω and Reynolds Stress Model (RSM) are used to solve the closure problem. The turbulence models are investigated in the commercial CFD code of Fluent using y+ value as guidance in selecting the appropriate grid configuration and turbulence model. Based on the wall y+ values for different turbulence models, it is concluded in the present study that the mesh resolving the fully turbulent region is sufficiently accurate in terms of qualitative features and RSM turbulence model predicts the best results while comparing with the experimental results.

A New Unsteady-Based Turbulence Model to Predict Shear Layer Rollup and Breakdown

2004 ◽  
Author(s):  
D. Scott Holloway ◽  
James H. Leylek
Keyword(s):  
Shear Layer ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Separated Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Aircraft Carrier ◽  
Flow Through

This paper documents the computational investigation of the unsteady rollup and breakdown of a turbulent separated shear layer. This complex phenomenon plays a key role in many applications, such as separated flow at the leading edge of an airfoil at off-design conditions; flow through the tip clearance of a rotor in a gas turbine; flow over the front of an automobile or aircraft carrier; and flow through turbulated passages that are used to cool turbine blades. Computationally, this problem poses a significant challenge in the use of traditional RANS-based turbulence models for the prediction of unsteady flows. To demonstrate this point, a series of 2-D and 3-D unsteady simulations have been performed using a variety of well-known turbulence models, including the “realizable” k-ε model, a differential Reynolds stress model, and a new model developed by the present authors that contains physics that account for the effects of local unsteadiness on turbulence. All simulations are fully converged and grid independent in the unsteady framework. A proven computational methodology is used that takes care of several important aspects, including high-quality meshes (2.5 million finite volumes for 3-D simulations) and a discretization scheme that will minimize the effects of numerical diffusion. To isolate the shear layer breakdown phenomenon, the well-studied flow over a blunt leading edge (Reynolds number based on plate half-thickness of 26,000) is used for validation. Surprisingly, none of the traditional eddy-viscosity or Reynolds stress models are able to predict an unsteady behavior even with modifications in the near-wall treatment, repeated adaption of the mesh, or by adding small random perturbations to the flow field. The newly developed unsteady-based turbulence model is shown to predict some important features of the shear layer rollup and breakdown.

Effects of Different Turbulence Models on Three-Dimensional Unsteady Cavitating Flows in the Centrifugal Pump and Performance Prediction

2019 ◽  
Vol 20 (3-4) ◽  
pp. 487-509 ◽  
Author(s):  
Ahmed Ramadhan Al-Obaidi
Keyword(s):  
Centrifugal Pump ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Experimental Results ◽  
Centrifugal Pumps ◽  
Operation Condition ◽  
Sst Model ◽  
And Performance ◽  
Turbulent Models

AbstractIn centrifugal pumps, it is important to select appropriate turbulence model for the numerical simulation in order to obtain reliable and accurate results. In this work, ten turbulence models in 3-D transient simulation for the centrifugal pump are chosen and compared. The pump performance is validated with experimental results. The numerical results reveal that the SST turbulence model was closer to the experimental results in predicting head. In addition, the pressure variation trend for the ten models is very similar which increases and then decreases from the inlet to outlet of the pump along the streamline. The SST k-ω model predicts the performance of the pump was more accurately than other turbulent models. Furthermore, the results also found that the error is the least at design operation condition 300(l/min), which is around 1.98 % for the SST model and 2.14 % and 2.38 % for the LES and transition omega model. Within 7.61 %, the errors at higher flow rate 350(l/min) for SST. The error for SST model is smaller as compared to different turbulent models. For the Realizable k-ɛ model, the errors fluctuate were more high than other models.

Some experiments on the secondary flow in pipe bends

1956 ◽  
Vol 234 (1198) ◽  
pp. 335-346 ◽  
Keyword(s):  
Differential Equation ◽  
Secondary Flow ◽  
Air Flow ◽  
Experimental Results ◽  
Radius Of Curvature ◽  
General Behaviour ◽  
Sine Curve ◽  
Uniform Velocity ◽  
Non Linear ◽  
Flow Through

Secondary vorticity in the direction of flow is developed after fluid with a non-uniform velocity passes through a bend. The secondary flow may be increased or decreased by reversal of the radius of curvature of the bend, depending on the location of the reversal. The general behaviour of the secondary flow in a bend in which the radius of curvature is repeatedly reversed is analyzed by assuming the centre line of the bend is a sine curve. The resulting differential equation describing the flow is non-linear, and a variety of solutions are obtained for different entry conditions. These solutions are compared with experimental results obtained from observations of the air flow through various configurations of pipe.

2-D CFD Model for Free Surface River Flow with Tilt Rigid Leave of Submerged Vegetation

2012 ◽  
Vol 212-213 ◽  
pp. 332-335 ◽  
Author(s):  
Yan Hong Li ◽  
Li Quan Xie
Keyword(s):  
Free Surface ◽  
Velocity Profile ◽  
River Flow ◽  
Longitudinal Velocity ◽  
Submerged Vegetation ◽  
Two Dimensional ◽  
Cfd Model ◽  
Cross Sectional ◽  
Vertical Velocity Profile ◽  
Flow Through

Keywords: river flow; two-dimensional CFD model; velocity profile; submerged vegetation leave Abstract. River flow with submerged foliage vegetation in straight and rectangular cross-sectional channel is numerically simulated through a vertical two-dimensional CFD model. Tilt thin strips are assigned in river flow to mimic the configuration of vegetation leave. The free surface line and the vertical profiles of longitudinal velocity are presented. The vertical velocity profile differs from the well acknowledged logarithmic or semi-logarithmic law. The submerged leave canopy resist the flow through it and pilots the flow upward over it, resulting in a decreased velocity within the canopy and an increased velocity above the canopy. The velocity profiles within the leave canopy are impacted by the configurations of the leave.

scholarly journals Modelling Shallow Water Wakes Using a Hybrid Turbulence Model

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Clemente Rodriguez-Cuevas ◽  
Carlos Couder-Castañeda ◽  
Esteban Flores-Mendez ◽  
Israel Enrique Herrera-Díaz ◽  
Rodolfo Cisneros-Almazan
Keyword(s):  
Shallow Water ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Physical Phenomenon ◽  
Computing Time ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Free Surface Flows ◽  
Experimental Results ◽  
Volume Method

A numerical research with different turbulence models for shallow water equations was carried out. This was done in order to investigate which model has the ability to reproduce more accurately the wakes produced by the shock of the water hitting a submerged island inside a canal. The study of this phenomenon is important for the numerical methods application advancement in the simulation of free surface flows since these models involve a number of simplifications and assumptions that can have a significant impact on the numerical solutions quality and thus can not reproduce correctly the physical phenomenon. The numerical experiments were carried out on an experimental case under controlled conditions, consisting of a channel with a submerged conical island. The numerical scheme is based on the Eulerian-Lagrangian finite volume method with four turbulence models, three mixing lengths (ml), and one joiningk-ϵon the horizontal axis with a mixing-length model (ml) on the vertical axis. The experimental results show that ak-ϵwith ml turbulence model makes it possible to approach the experimental results in a more qualitative manner. We found that when using only ak-ϵmodel in the vertical and horizontal direction, the numerical results overestimate the experimental data. Additionally the computing time is reduced by simplifying the turbulence model.

An Assessment of Turbulence Models for S-Duct Diffusers With Flow Control

2013 ◽  
Author(s):  
S. P. Bhat ◽  
R. K. Sullerey
Keyword(s):  
Experimental Data ◽  
Flow Control ◽  
Turbulence Model ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Experimental Results ◽  
Cfd Analysis ◽  
Duct Flow ◽  
Ansys Fluent ◽  
Sst Model

The selection of a turbulence model for a problem is not trivial and has to be done systematically after comparison of various models with experimental data. It is a well known fact that there is no such turbulence model which fits all problems ([3], [13]). The flow in S-duct diffuser is a very complex one where both separation and secondary flow coexist. Previous work by the author on CFD analysis of S-duct diffuser was done using k-ε-Standard model [1], however it has been seen that choosing other turbulence model may result in better capturing of the physics in such a problem. Also flow control, to reduce energy losses, is achieved using a technique called Zero Net Mass Flow (ZNMF), in which suction and vortex generation jets (VGJ) are combined and positioned at optimum location. A proper turbulence model has to be chosen for capturing these phenomena effectively. Extensive experimental data is available on this problem and ZNMF technique from previous work done by one of the authors which is used for validating the CFD results. Here the focus is on choosing the best turbulence model for the S-duct diffuser. Numerical (CFD) analysis is carried out using Ansys Fluent 13.0 with six turbulence models for the geometry with (ZNMF) and without (Bare duct) flow control and then compared with the experimental results. The turbulence models used are Spalart-Allmaras, three variants of k-ε – Standard, RNG and Realizable and two variants of k-ω – Standard and SST model. All the parameters of comparison are non-dimensionalized using the free stream properties, so that the results are applicable to a wider range of problems. This work is limited to incompressible flow analysis, as the experimental data is only available for low Mach number flows. Comparison of all these models clearly shows that results obtained using k-ω-SST model are very comparable to the experimental results for the bare duct (without flow control) and flow controlled duct both in terms of distribution of properties and aggregate results. Compressible flow analysis can be attempted to achieve reliable results in future with ZNMF using the best turbulence model based on this study.

One-point modelling of rapidly deformed homogeneous turbulence

1995 ◽  
Vol 451 (1941) ◽  
pp. 87-104 ◽  
Keyword(s):  
Turbulence Model ◽  
Turbulence Models ◽  
Turbulence Structure ◽  
Missing Information ◽  
Point Model ◽  
Transport Models ◽  
Special Cases ◽  
New Type ◽  
The Mean ◽  
Mean Strain

One-point turbulence models are important tools for engineering analysis. A good model should have a viscoelastic character, predicting turbulent stresses proportional to the mean strain rate for slow deformations and stresses determined by the amount of strain for rapid distortions. Our goal is to build a one-point turbulence model with this character, and this requires a one-point model for rapid distortions. Here it is shown that the turbulent stresses introduced by Osborne Reynolds do not, by themselves, provide an adequate tensorial base for one-point modelling of rapidly distorted turbulence because they do not carry critical information about the turbulence structure. The deficiency is shown to be most pronounced in flows subjected to strong mean rotation. Additional one-point tensors that do carry the missing information are introduced, and the complexities of a model that would have an adequate tensorial base are assessed. A new type of one-point structure-based turbulence model that overcomes the basic deficiency of Reynolds-stress transport models, but without the excessive complexity of multiple tensor variables, is then described. The ideas behind the rapid distortion version of this new model are presented, along with results for some special cases.

Turbulence Modeling of Forced Convection Heat Transfer in Two-Dimensional Ribbed Channels

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
E. Elsaadawy ◽  
H. Mortazavi ◽  
M. S. Hamed
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Turbulence Model ◽  
Turbulence Modeling ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Experimental Results ◽  
Electronic Systems ◽  
Sst Turbulence Model ◽  
Stress Models

Although the problem of 2D ribbed channels has been studied heavily in the literature as a benchmark or basic case for cooling of electronic packing, there is still a contradiction in the literature about the suitable turbulence model that should be used in such a problem. The accuracy of the computational predictions of heat transfer rates depends mostly on the choice of the proper turbulence model that is capable of capturing the physics of the problem, and on the corresponding wall treatment. The main objective of this work is to identify the proper turbulence model to be used in thermal analysis of electronic systems. A number of available turbulence models, namely, the standard k-ε, the renormalization group k-ε, the shear stress transport (SST), the k-ω, and the Reynolds stress models, have been investigated. The selection of the most appropriate turbulence model has been based upon comparisons with both direct numerical simulations (DNSs) and experimental results of other works. Based on such comparisons, the SST turbulence model has been found to produce results in very good agreement with the DNS and experimental results and hence it is recommended as an appropriate turbulence model for thermal analysis of electronic packaging.

scholarly journals CFD Simulation Of Air-Flow Over A „Quarter-Circular” Object Valided By Experimental Measurement

2015 ◽  
Vol 15 (2) ◽  
Author(s):  
Juraj Králik ◽  
Oľga Hubová ◽  
Lenka Konečná
Keyword(s):  
Turbulence Model ◽  
Experimental Measurement ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Air Flow ◽  
Turbulence Models ◽  
Ansys Fluent ◽  
Circular Object ◽  
University Of Technology ◽  
Polyhedral Mesh

Abstract A Computer-Fluid-Dynamic (CFD) simulation of air-flow around quarter-circular object using commercial software ANSYS Fluent was used to study iteration of building to air-flow. Several, well know transient turbulence models were used and results were compared to experimental measurement of this object in Boundary Layer Wind Tunnel (BLWT) of Slovak University of Technology (SUT) in Bratislava. Main focus of this article is to compare pressure values from CFD in three different elevations, which were obtained from experimental measurement. Polyhedral mesh type was used in the simulation. Best results on the windward face elevations were obtained using LES turbulence model, where the averaged difference was around 7.71 %. On the leeward face elevations it was SAS turbulence model and averaged differences from was 15.91 %. On the circular face it was SAS turbulence model and averaged differences from all elevations was 12.93 %.

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