Uncertainty Estimation for Numerical Solutions of Wall Bounded Turbulent Flows

2006 ◽  
Author(s):  
Francisco Elizalde-Blancas ◽  
Ismail Celik ◽  
Suryanarayana Pakalapati
Keyword(s):  
Laminar Flow ◽  
Turbulent Flows ◽  
Numerical Solutions ◽  
Turbulence Models ◽  
Grid Size ◽  
Gradient Term ◽  
True Error ◽  
Flow Solver ◽  
Solution Convergence ◽  
Manufactured Solution

In this study numerical solutions are presented for a steady state, incompressible, 2-D turbulent flow near a wall. For this specific problem a manufactured (exact) solution was provided by the organizers of the 2006 Lisbon Workshop [6]. With the help of manufactured solution, assessment of the true error and other relevant uncertainty measures are possible. The calculations were performed using the commercial flow solver FLUENT along with some user defined functions to define source terms and velocity profiles at boundaries. Though the flow regime is turbulent; the numerical solution is carried out for pseudo-laminar flow. This was done in order to avoid the errors implicit in turbulence models. The transformation from turbulent to laminar flow was done by defining a momentum source term which precludes the pressure gradient term. A detailed grid convergence analysis was performed. Using three-grid triplets the limiting values of the variables solved as the grid size tends to zero were calculated using different extrapolations. The L2 norms of the true error obtained from various extrapolations are assessed. These results exhibit solution convergence as the grid size decreases. It was also shown that cubic spline extrapolation perform the best among the methods considered.

A Geometric Preprocessor for Immersed Boundary Method Calculations

2015 ◽  
Author(s):  
Inanc Senocak ◽  
Micah Sandusky ◽  
Rey DeLeon ◽  
Derek Wade
Keyword(s):  
Turbulent Flows ◽  
Complex Geometry ◽  
Turbulence Models ◽  
Urban Environments ◽  
Immersed Boundary ◽  
Flow Solver ◽  
Distance Field ◽  
Fast Sweeping ◽  
Sweeping Method ◽  
Ib Method

Computer implementation of an immersed boundary (IB) module inside a flow solver can be accomplished non-intrusively. However a versatile preprocessor is needed at the first place to extract the geometric information pertinent to the immersion of an arbitrarily complex geometry inside a Cartesian mesh. Geometric errors can negatively impact the correct implementation of the IB method as part of the solution algorithm. Additionally, the distance field from the geometry is needed to implement various turbulence models or flow initialization. Geometric processing stage for complex geometry have received less attention despite the popularity of the IB method. Our experience has shown that some of the procedures described in the literature have difficulties processing highly complex geometry or can be inflexible to implement reconstruction schemes for turbulent flows. To address these issues, we present a geometric preprocessor with a distance field solver. We constructed our procedure from computational geometry algorithms such as point-in-triangle and point-in-edge. The distance field solver uses the initial distance field at the immersed boundaries and propagates it to the rest of the domain by solving the Eikonal equation with the fast sweeping method. We demonstrate the versatility of our preprocessor for challenging test geometries from the computer graphics field, complex terrain and urban environments.

Assessment of RANS, LES, and Hybrid RANS/LES Models for the Prediction of Low-Pr Turbulent Flows

2018 ◽  
Author(s):  
S. Bhushan ◽  
O. ElFajri ◽  
W. D. Jock ◽  
D. K. Walters ◽  
J. K. Lai ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Plane Channel ◽  
Turbulence Models ◽  
Spectral Element ◽  
Flow Conditions ◽  
Predictive Capability ◽  
Flow Solver ◽  
Flow Simulations ◽  
Point Velocity ◽  
Plane Channel Flow

The predictive capability of RANS, hybrid RANS/LES and LES turbulence models for momentum and thermal energy transfer in wall bounded low-Pr turbulent flows is investigated. Plane channel flow simulations are performed for Reτ = 150 and 640 for Pr = 0.025 and 0.71 with and without buoyancy effects, including both forced and mixed force/natural convection conditions, using the open source spectral element flow solver Nek5000. The prediction of one-point velocity and temperature statistics from the simulations are compared against available DNS results. Results are analyzed to understand the effect of flow conditions on turbulent thermal transport, and assess the relative strengths and weaknesses of the different modeling methods.

A Methodology for Simulations of Complex Turbulent Flows

2002 ◽  
Vol 124 (4) ◽  
pp. 933-942 ◽  
Author(s):  
H. F. Fasel ◽  
J. Seidel ◽  
S. Wernz
Keyword(s):  
Turbulent Flows ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Grid Size ◽  
Coarse Grid ◽  
Navier Stokes ◽  
Turbulent Shear ◽  
Fine Grid ◽  
Subgrid Scales ◽  
Grid Points

A new flow simulation methodology (FSM) for computing turbulent shear flows is presented. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The centerpiece of FSM is a strategy to provide the proper amount of modeling of the subgrid scales. The strategy is implemented by use of a “contribution function” which is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is obtained during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that the computation approaches a direct numerical simulation in the fine grid limit, or provides modeling of all scales in the coarse grid limit and thus approaches an unsteady RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in traditional large-eddy simulations (LES). However, a LES that is based on the present strategy is distinctly different from traditional LES in that the required amount of modeling is determined by physical considerations, and that state-of-the-art turbulence models (as developed for Reynolds-averaged Navier-Stokes) can be employed for modeling of the unresolved scales. Thus, in contrast to traditional LES based on the Smagorinsky model, with FSM a consistent approach (in the local sense) to the coarse grid and fine grid limits is possible. As a consequence of this, FSM should require much fewer grid points for a given calculation than traditional LES or, for a given grid size, should allow computations for larger Reynolds numbers. In the present paper, the fundamental aspects of FSM are presented and discussed. Several examples are provided. The examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating complex wall bounded flows, and on the other hand demonstrate the potential of the FSM approach.

A numerical study on combined baffles quick-separation device

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ehsan Dehdarinejad ◽  
Morteza Bayareh ◽  
Mahmud Ashrafizaadeh
Keyword(s):  
Turbulent Flows ◽  
Separation Efficiency ◽  
Numerical Study ◽  
Turbulence Models ◽  
Complete Separation ◽  
Solid Particles ◽  
Flow Rates ◽  
Separation Device ◽  
Coupling Technique ◽  
Laminar And Turbulent Flows

Abstract The transfer of particles in laminar and turbulent flows has many applications in combustion systems, biological, environmental, nanotechnology. In the present study, a Combined Baffles Quick-Separation Device (CBQSD) is simulated numerically using the Eulerian-Lagrangian method and different turbulence models of RNG k-ε, k-ω, and RSM for 1–140 μm particles. A two-way coupling technique is employed to solve the particles’ flow. The effect of inlet flow velocity, the diameter of the splitter plane, and solid particles’ flow rate on the separation efficiency of the device is examined. The results demonstrate that the RSM turbulence model provides more appropriate results compared to RNG k-ε and k-ω models. Four thousand two hundred particles with the size distribution of 1–140 µm enter the device and 3820 particles are trapped and 380 particles leave the device. The efficiency for particles with a diameter greater than 28 µm is 100%. The complete separation of 22–28 μm particles occurs for flow rates of 10–23.5 g/s, respectively. The results reveal that the separation efficiency increases by increasing the inlet velocity, the device diameter, and the diameter of the particles.

Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows

1995 ◽  
Vol 48 (4) ◽  
pp. 189-212 ◽  
Author(s):  
G. J. Brereton ◽  
R. R. Mankbadi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Modeling ◽  
Unsteady Flows ◽  
Turbulence Models ◽  
Research Area ◽  
Transition To Turbulence ◽  
Measurement Technology ◽  
Internal Flows ◽  
Recent Advances ◽  
The Many

Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.

Influence of Marine Propeller Geometry on Turbulence Model Selection for CFD Simulations

2021 ◽  
Vol 55 (2) ◽  
pp. 150-164
Author(s):  
Mohamed R. Shouman ◽  
Mohamed M. Helal
Keyword(s):  
Turbulent Flows ◽  
Small Diameter ◽  
Turbulence Models ◽  
Dynamics Simulation ◽  
Geometrical Parameters ◽  
Test Case ◽  
Transition Model ◽  
Transient Flows ◽  
Marine Propellers ◽  
Numerical Predictions

Abstract One of the big challenges yet to be addressed in the numerical simulation of wetted flow over marine propellers is the influence of propellers' geometry on the selection of turbulence models. Since the Reynolds number is a function of the geometrical parameters of the blades, the flow type is controlled by these parameters. The majority of previous studies employed turbulence models that are only appropriate for fully turbulent flows, and consequently, they mostly caused high discrepancy between numerical predictions and corresponding experimental measurements specifically at geometrical parameters generating laminar and transient flows. The present article proposes a complete procedure of computational fluid dynamics simulation for wetted flows over marine propellers using ANSYS FLUENT 16 and employing both transition-sensitive and fully turbulent models for comparison. The K-Kl-ω transition model and the fully turbulent standard K-ε model are suggested for this purpose. The investigation is carried out for two different propellers in geometrical features: the INSEAN E779a model and the Potsdam Propeller Test Case (PPTC) model. The results demonstrate the effectiveness of the K-Kl-ω transition model for the INSEAN E779a propeller rather than the PPTC propeller. This can be interpreted as the narrow-bladed and small-diameter propellers have more likely laminar and transient flows over its blades.

Computational Fluid Dynamics Evaluation of Heat Transfer Correlations for Sodium Flows in a Heat Exchanger

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Seok-Ki Choi ◽  
Seong-O Kim ◽  
Hoon-Ki Choi
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Cross Flow ◽  
Turbulence Models ◽  
Parallel Flow ◽  
Sst Model ◽  
Heat Transfer Correlations

A numerical study for the evaluation of heat transfer correlations for sodium flows in a heat exchanger of a fast breeder nuclear reactor is performed. Three different types of flows such as parallel flow, cross flow, and two inclined flows are considered. Calculations are performed for these three typical flows in a heat exchanger changing turbulence models. The tested turbulence models are the shear stress transport (SST) model and the SSG-Reynolds stress turbulence model by Speziale, Sarkar, and Gaski (1991, “Modelling the Pressure-Strain Correlation of Turbulence: An Invariant Dynamical System Approach,” J. Fluid Mech., 227, pp. 245–272). The computational model for parallel flow is a flow past tubes inside a circular cylinder and those for the cross flow and inclined flows are flows past the perpendicular and inclined tube banks enclosed by a rectangular duct. The computational results show that the SST model produces the most reliable results that can distinguish the best heat transfer correlation from other correlations for the three different flows. It was also shown that the SSG-RSTM high-Reynolds number turbulence model does not deal with the low-Prandtl number effect properly when the Peclet number is small. According to the present calculations for a parallel flow, all the old correlations do not match with the present numerical solutions and a new correlation is proposed. The correlations by Dwyer (1966, “Recent Developments in Liquid-Metal Heat Transfer,” At. Energy Rev., 4, pp. 3–92) for a cross flow and its modified correlation that takes into account of flow inclination for inclined flows work best and are accurate enough to be used for the design of the heat exchanger.

Assessment of Certainty of Ventilation Processes Mathematical Modeling

2015 ◽  
Vol 725-726 ◽  
pp. 1255-1260
Author(s):  
Tamara Daciuk ◽  
Vera Ulyasheva
Keyword(s):  
Mathematical Modeling ◽  
Turbulent Flows ◽  
Turbulence Models ◽  
Field Measurements ◽  
Heat Emission ◽  
Emission Sources ◽  
Wide Range ◽  
Calculation Results ◽  
Definition Of ◽  
Semiempirical Models

Numerical experiment has been successfully used during recent 10-15 years to solve a wide range of thermal and hydrogasodynamic tasks. Application of mathematical modeling used to design the ventilation systems for production premises characterized by heat emission may be considered to be an effective method to obtain reasonable solutions. Results of calculation performed with numerical solution of ventilation tasks depend on turbulence model selection. Currently a large number of different turbulence models used to calculate turbulent flows are known. Testing and definition of applicability limits for semiempirical models of turbulence should be considered to be a preliminary stage of calculation. This article presents results of test calculations pertaining to thermal air process modeling in premises characterized by presence of heat emission sources performed with employment of different models of turbulence. Besides, analysis of calculation results and comparison with field measurements data are presented.

scholarly journals Unravelling turbulence near walls

2009 ◽  
Vol 630 ◽  
pp. 1-4 ◽  
Author(s):  
IVAN MARUSIC
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Turbulent Flows ◽  
Direct Numerical Simulations ◽  
Aircraft Wing ◽  
Physical Mechanisms ◽  
Drag And Lift

Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for example. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct numerical simulations have contributed significantly towards this understanding.

On the Oscillatory Instability of Closed-Loop Thermosyphons

1985 ◽  
Vol 107 (4) ◽  
pp. 826-832 ◽  
Author(s):  
K. Chen
Keyword(s):  
Turbulent Flows ◽  
Closed Loop ◽  
Numerical Solutions ◽  
Angular Frequency ◽  
Oscillatory Instability ◽  
Neutral Stability ◽  
Horizontal Segment ◽  
Aspect Ratios ◽  
The Stability ◽  
Laminar And Turbulent Flows

The stability of natural convection flows in single-phase closed-loop thermosyphons is investigated. The thermosyphons considered in the present analysis are fluid-filled tubes bent into rectangular shapes. The fluid is heated over the lower horizontal segment and cooled over the upper horizontal segment. Analytical and numerical solutions are presented for a range of loop aspect ratios and radii for both laminar and turbulent flows. It is found that the steady-state results for thermosyphons with different aspect ratios and radii can be expressed in terms of a single dimensionless parameter. When this parameter is less than a critical value, the flow is always stable. Above this critical point, oscillatory instability exists for a narrow range of a friction parameter. The calculated neutral stability conditions show that the flow is least stable when the aspect ratio of the loop approaches unity. The frequency of the convection-induced oscillation is slightly higher than the angular frequency of a fluid particle traveling along the loop.

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