scholarly journals Unsteady RANS Modeling of Flow around Two-Dimensional Rectangular Cylinders with Different Side Ratios at Reynolds Number 6.85 × 105

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Shubiao Wang ◽  
Wenming Cheng ◽  
Run Du ◽  
Yupu Wang
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Practical Engineering ◽  
Unsteady Rans ◽  
Rectangular Cylinders

In practical engineering, the Reynolds number (Re) of box girder structure is usually very high (Re ≥ 105), while most investigations of the flow around bluff bodies are concentrated on relatively lower Reynolds numbers (i.e., Re = 103–104). This paper presented a numerical study of the unsteady flow around two-dimensional rectangular cylinders under a Reynolds number of 6.85 × 105 with different side ratios (R = b/h, width to height) ranging from 0.1 to 4.0. Three unsteady Reynolds-averaged Navier-Stokes (RANS) two-equation k-ε turbulence models (standard, RNG, and realizable) were adopted in the study. The realizable k-ε model was chosen because it was found to perform the best among three models in the main aerodynamic integral parameters. According to the distinctions of aerodynamic characteristics with different side ratios, three regimes were divided and discussed in detail. The distribution of surface pressure over cylinders, the wake parameters, and vorticity contours of the rectangular cylinders with different side ratios were discussed.

Validation of Numerical Analysis to Estimate Airfoil Aerodynamic Characteristics at Low Reynolds Number Region

2015 ◽  
Author(s):  
Donghwi Lee ◽  
Taku Nonomura ◽  
Akira Oyama ◽  
Kozo Fujii
Keyword(s):  
Reynolds Number ◽  
Numerical Method ◽  
Low Reynolds Number ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Eddy Simulation ◽  
Low Reynolds

In this study, two-dimensional laminar simulation (2-D Lam), two-dimensional Reynolds Averaged Navier-Stokes simulation with the Spalart-Allmaras turbulence model (2-D RANS(SA)), and implicit three-dimensional large-eddy simulation (3-D LES) are performed for NACA0012, NACA0006, and Ishii airfoils at Rec = 3.0 × 104. The relation between a predictability of airfoil aerodynamic characteristics and a dependence of airfoil geometry shape of each numerical method is evaluated at the low Reynolds number. Although little discrepancy is observed for the lift coefficient predictability, significant differences are presented in terms of the separation and reattachment points predictability depending on the numerical methods. The 2-D Lam simulation can predict the lift coefficients as well as the separation and reattachment points qualitatively as similar to the 3-D LES results except for the high angle of attack which is accompanied by the massive separation. The 2-D RANS(SA), the weak nonlinearity and stall phenomena for the lift coefficients are observed. A good predictability of the separation point are shown, however, it cannot be estimated the reattachment points due to the trend to predict widely for the separation region. The predictabilities of each numerical method appear regardless of the airfoil shapes.

Large-Eddy simulation of rim seal ingestion

2011 ◽  
Vol 225 (12) ◽  
pp. 2881-2891 ◽  
Author(s):  
T S D O'Mahoney ◽  
N J Hills ◽  
J W Chew ◽  
T Scanlon
Keyword(s):  
Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Turbulence Models ◽  
Unsteady Rans ◽  
Rans Simulations ◽  
Secondary Air ◽  
The One

Unsteady flow dynamics in turbine rim seals are known to be complex and attempts accurately to predict the interaction of the mainstream flow with the secondary air system cooling flows using computational fluid dynamics (CFD) with Reynolds-averaged Navier–Stokes (RANS) turbulence models have proved difficult. In particular, published results from RANS models have over-predicted the sealing effectiveness of the rim seal, although their use in this context continues to be common. Previous studies have ascribed this discrepancy to the failure to model flow structures with a scale greater than the one which can be captured in the small-sector models typically used. This article presents results from a series of Large-Eddy Simulations (LES) of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first time. The simulations were run at a rotational Reynolds number Reθ = 2.2 × 106 and a main annulus axial Reynolds number Rex = 1.3 × 106 and with varying levels of coolant mass flow. Comparison is made with previously published experimental data and with unsteady RANS simulations. The LES models are shown to be in closer agreement with the experimental sealing effectiveness than the unsteady RANS simulations. The result indicates that the previous failure to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal flow. Consideration is given to the flow structure in this region.

An approximate theory for incompressible viscous flow past two-dimensional bluff bodies in the intermediate Reynolds number regime O(1) < Re < O(102)

1976 ◽  
Vol 77 (1) ◽  
pp. 129-152 ◽  
Author(s):  
Sheldon Weinbaum ◽  
Michael S. Kolansky ◽  
Michael J. Gluckman ◽  
Robert Pfeffer
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layer Theory ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Approximate Theory ◽  
Two Dimensional ◽  
First Order ◽  
Flow Past

A new approximate theory is proposed for treating the flow past smoothly contoured two-dimensional bluff bodies in the intermediate Reynolds number rangeO(1) <Re< 0(102), where the displacement effect of the thick viscous layer near the surface of the body is large and a steady laminar wake is present. The theory is based on a new pressure hypothesis which enables one to take account of the displacement interaction and centrifugal effects in thick viscous layers using conventional first-order boundary-layer equations. The basic question asked is how the wall pressure gradient in ordinary boundary -layer theory must be modified if the pressure gradient along the displacement surface using the Prandtl pressure hypothesis is to be equal to the pressure gradient along this surface using a higher-order approximation to the Navier-Stokes equation in which centrifugal forces are considered. The inclusion of the normal pressure field with displacement interaction is shown to be equivalent to stretching the streamwise body co-ordinate in first-order boundary-layer theory such that the streamwise pressure gradient as a function of distance along the original and displacement body surfaces are equal.While the new theory is of a non-rigorous nature, it yields results for the location of separation and detailed surface pressure and vorticity distribution which are in remarkably good agreement with the large body of available numerical Navier-Stokes solutions. A novel feature of the new boundary-value problem is the development of a simple but accurate approximate method for determining the inviscid flow past an arbitrary two-dimensional displacement body with its wake.

Unsteady RANS Computations of the Flow Past an Airfoil in the Wake of a Rod

2002 ◽  
Author(s):  
Je´roˆme Boudet ◽  
Damiano Casalino ◽  
Marc C. Jacob ◽  
Pascal Ferrand
Keyword(s):  
Vortex Shedding ◽  
Turbulence Models ◽  
Leading Edge ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Vorticity Field ◽  
Unsteady Rans ◽  
Variable Configuration ◽  
Naca 0012 ◽  
Insight Into

Two-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved in order to simulate the interaction between a Ka´rma´n vortex street shed from a rod and a NACA-0012 airfoil in the wake of the rod. Two closure turbulence models are tested, a linear and a nonlinear k-ω model, for a chord based Reynolds number Rec ∼ 4.8105. These models provide consistent results in terms of both mean and fluctuating flow quantities. Insight into the instantaneous vorticity field shows that the vortex shedding pattern near the wall is quite well predicted, despite an over-estimated frequency. Downstream, computations always exhibit head-on interactions of the vortices with the airfoil leading edge whereas the experiments show a more variable configuration.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Numerical Study on Heat Transfer Characteristics From Parallel Plates With Cavities Swept by a Visco-Elastic Fluid

2010 ◽  
Author(s):  
Hiroshi Suzuki ◽  
Shinpei Maeda ◽  
Yoshiyuki Komoda
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Field ◽  
Numerical Study ◽  
Geometric Parameters ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Heat Transfer Characteristics ◽  
Elastic Fluid ◽  
Heat Transfer Augmentation

Two-dimensional numerical computations have been performed in order to investigate the development characteristics of flow and thermal field in a flow between parallel plates swept by a visco-elastic fluid. In the present study, the effect of the cavity number in the domain and of Reynolds number was focused on when the geometric parameters were set constant. From the results, it is found that the flow penetration into the cavities effectively causes the heat transfer augmentation in the cavities in any cavity region compared with that of water case. It is also found that the development of thermal field in cases of the present visco-elastic fluid is quicker compared with that of water cases. The present heat transfer augmentation technique using Barus effect of a visco-elastic fluid is effective in the range of low Reynolds number.

Two-dimensional global low-frequency oscillations in a separating boundary-layer flow

2008 ◽  
Vol 614 ◽  
pp. 315-327 ◽  
Author(s):  
UWE EHRENSTEIN ◽  
FRANÇOIS GALLAIRE
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Perturbation Analysis ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Low Frequency ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Optimal Perturbation ◽  
Layer Flow

A separated boundary-layer flow at the rear of a bump is considered. Two-dimensional equilibrium stationary states of the Navier–Stokes equations are determined using a nonlinear continuation procedure varying the bump height as well as the Reynolds number. A global instability analysis of the steady states is performed by computing two-dimensional temporal modes. The onset of instability is shown to be characterized by a family of modes with localized structures around the reattachment point becoming almost simultaneously unstable. The optimal perturbation analysis, by projecting the initial disturbance on the set of temporal eigenmodes, reveals that the non-normal modes are able to describe localized initial perturbations associated with the large transient energy growth. At larger time a global low-frequency oscillation is found, accompanied by a periodic regeneration of the flow perturbation inside the bubble, as the consequence of non-normal cancellation of modes. The initial condition provided by the optimal perturbation analysis is applied to Navier–Stokes time integration and is shown to trigger the nonlinear ‘flapping’ typical of separation bubbles. It is possible to follow the stationary equilibrium state on increasing the Reynolds number far beyond instability, ruling out for the present flow case the hypothesis of some authors that topological flow changes are responsible for the ‘flapping’.

Assessment of Different Turbulence Models for Predicting Laminar Separation Bubble Over Thick Airfoils

2015 ◽  
Author(s):  
Saravana Kumar Lakshmanan ◽  
Alok Mishra ◽  
Ashoke De
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Performance Variables ◽  
Rans Models ◽  
High Angles Of Attack ◽  
Aerodynamic Lift

Accurate laminar-turbulent prediction is very much important to understand the complete performance characteristics of any airfoil which operates at low and medium Reynolds number. In this article, a numerical study has been performed over two different thick airfoils operating at low Reynolds number using k-ω SST, k-kl-ω and Spalart-Allmaras (SA) RANS models. The unsteady two dimensional (2D) simulations are performed over NACA 0021 and NACA 65-021 at Re 120,000 for a range of angle of attacks. The performances of these models are assessed through aerodynamic lift, drag and pressure coefficients. To obtain better comparison, the simulated results are compared with the experimental measurements and XFOIL results as well. In this present study, it is found that the k-kl-ω transition model is capable of predicting correct lift, drag coefficient and separation bubble as reported in experiments. At high angles of attack, this model fails to predict performance variables accurately. The SA and SST models are fail to predict laminar separation bubble. However, At high angle of attack, SA model shows better predictions compared to k-kl-ω and k-ω SST models.

Investigation of the Flow Structures in Supersonic Free and Impinging Jet Flows

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
C. Chin ◽  
M. Li ◽  
C. Harkin ◽  
T. Rochwerger ◽  
L. Chan ◽  
...  
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Experimental Studies ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Optical Methods ◽  
Navier Stokes ◽  
Jet Flows ◽  
Shock Cell ◽  
Rans Turbulence Models

A numerical study of compressible jet flows is carried out using Reynolds averaged Navier–Stokes (RANS) turbulence models such as k-ɛ and k-ω-SST. An experimental investigation is performed concurrently using high-speed optical methods such as Schlieren photography and shadowgraphy. Numerical and experimental studies are carried out for the compressible impinging at various impinging angles and nozzle-to-wall distances. The results from both investigations converge remarkably well and agree with experimental data from the open literature. From the flow visualizations of the velocity fields, the RANS simulations accurately model the shock structures within the core jet region. The first shock cell is found to be constraint due to the interaction with the bow-shock structure for nozzle-to-wall distance less than 1.5 nozzle diameter. The results from the current study show that the RANS models utilized are suitable to simulate compressible free jets and impinging jet flows with varying impinging angles.

Numerical Study of the Wave Impact on a Square Column Using Large Eddy Simulation

2007 ◽  
Author(s):  
H. T. C. Pedro ◽  
K.-W. Leung ◽  
M. H. Kobayashi ◽  
H. R. Riggs
Keyword(s):  
Numerical Study ◽  
Turbulence Models ◽  
Simple Algorithm ◽  
Navier Stokes ◽  
Wave Impact ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy ◽  
Volume Approximation ◽  
The Impact

This work concerns the numerical investigation of the impact of a wave on a square column. The wave is generated by a dam break in a wave tank. Two turbulence models were used: Large Eddy Simulations (LES) and Unsteady Reynolds Averaged Navier-Stokes (URANS). The numerical simulations were carried out using a finite volume approximation and the SIMPLE algorithm for the solution of the governing equations. Turbulence was modeled with the standard Smagorinsky-Lilly subgrid-model for the LES and the standard κ-ε model for the URANS. The results are validated against experimental data for the wave impact on a square column facing the flow. The results, especially for LES, show very good agreement between the predictions and experimental results. The overall accuracy of the LES, as expected, is superior to the URANS. However, if computational resources are limited, URANS can still provide satisfactory results for structural design.

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