A Methodology for Simulating Compressible Turbulent Flows

2003 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Fine Grid ◽  
Local Flow ◽  
Wide Range ◽  
Unsteady Rans ◽  
Grid Points

A Flow Simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modelling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for RANS) and scaling of the model terms with a “contribution function”. The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This “physical” resolution is determined 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 modelling if the computation is locally well resolved so that it approaches a DNS in the fine-grid limit and such that it provides modelling of all scales in the coarsegrid limit and thus approaches an unsteady RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modelling for the unresolved scales while the larger (resolved) scales are computed as in traditional LES. However, FSM is distinctly different from LES in that it allows for a consistent transition between (unsteady) RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a traditional LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step at low Mach number and a supersonic, axisymmetric baseflow. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for a wide range of compressible flows.

A Methodology for Simulating Compressible Turbulent Flows

2005 ◽  
Vol 73 (3) ◽  
pp. 405-412 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Bluff Body ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Fine Grid ◽  
Local Flow

A flow simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modeling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for Reynolds averaged Navier-Stokes (RANS)) and scaling of the model terms with a “contribution function.” The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This physical resolution is determined 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 it approaches direct numerical simulations (DNS) in the fine-grid limit and such that it provides modeling of all scales in the coarse-grid limit and thus approaches a 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 large eddy simulation (LES). However, FSM is distinctly different from LES in that it allows for a consistent transition between RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step and a plane wake behind a bluff body, both at low Mach number, and supersonic axisymmetric wakes. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for simulations of turbulent compressible flows for complex geometries.

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.

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.

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart–Shur Correction Term

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Transport Model ◽  
Wide Range ◽  
Sst Model ◽  
The One

A rotation-curvature correction suggested earlier by Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) for the one-equation Spalart–Allmaras turbulence model is adapted to the shear stress transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and direct numerical simulations (DNS) data, on the one hand, and with the corresponding results of the original SST model and advanced Reynolds stress transport model (RSM), on the other hand. It is found that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Development of a Spectral Element DNS/LES Method for Turbulent Flow Simulations

2007 ◽  
Author(s):  
Xu Zhang ◽  
Dan Stanescu ◽  
Jonathan W. Naughton
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Compressible Flows ◽  
Time Integration ◽  
Flow Simulation ◽  
Spectral Element ◽  
Order Of Accuracy ◽  
Eddy Simulation ◽  
Large Eddy

This paper describes a turbulent flow simulation method, which is based on combination of spectral element and large eddy simulation (LES) technique. The robust, high-order discontinuous Galerkin (DG) spectral element method for large-eddy simulation of compressible flows allows for arbitrary order of accuracy and has excellent stability properties. A local spectral discretization in terms of Legendre polynomials is used on each element of the (possibly unstructured) mesh, which allows for high-accurate simulations of turbulent flows. Discontinuities across the interfaces of the elements are resolved using a Riemann solver. An isoparametric representation of the geometry is implemented, with boundaries of the domain discretized to the same order of accuracy as the solution, and explicit low-storage Runge-Kutta methods are used for time integration. Large eddy simulation has proven to be a valuable technique for the calculation of turbulent flows. An element based filtering technique is used in conjunction with the standard Smagorinsky eddy viscosity model to estimate the effect of sub-grid scales stresses in this paper. The recently developed nonlinear model [1] will also be added in the future. The final aim of this project is to use the LES methodology in swirling jet flow simulation. As a first step towards these simulations, simulations of compressible turbulent mixing layer and back-facing step are also performed to evaluate the robust method. Initial results based on both DNS and large eddy simulations are presented in this paper. Future work will be to validate the code.

Optical Validation of Ejector Flow Characteristics Predicted by Computational Analysis

2012 ◽  
Author(s):  
Adrienne B. Little ◽  
Yann Bartosiewicz ◽  
Srinivas Garimella
Keyword(s):  
Large Scale ◽  
Waste Heat ◽  
Turbulence Models ◽  
Ideal Gas ◽  
Computational Simulations ◽  
Design Data ◽  
Local Flow ◽  
Wide Range ◽  
Flow Features ◽  
Flow Phenomena

Passive, heat actuated devices can offer simple and energy-efficient options for a variety of end uses. An ejector pump is one such device that provides reasonable pressure head with no electrical input or moving parts. Useful for a wide range of applications from nuclear reactor cooling to vapor compression in waste-heat-driven heat pumping and work recovery systems, the flow phenomena inside an ejector must be understood to achieve improvements in component design and efficiency. In an effort to obtain insights into the flow phenomena inside an ejector, and to evaluate the effectiveness of commonly used computational tools in predicting these conditions, this study presents a set of shadowgraph images of flow inside a large-scale air ejector, and compares them to computational simulations of the same flow. On-design and off-design conditions are considered where the suction flow is choked and not choked, respectively. The computational simulations used for comparison apply k-ε RNG and k-ω SST turbulence models available in ANSYS FLUENT to 2D, locally-refined rectangular meshes for ideal gas air flow. Experimental and computational results show that on-design ejector operation is predicted with reasonable accuracy, but accuracy with the same models is not adequate at off-design conditions. This is attributed to an inability of turbulence models to predict shock/expansion interaction with the motive jet boundary, as well as the strength and position of flow features. Exploration of local flow features shows that the k-ω SST model predicts the location of flow features, as well as global inlet mass flow rates, with greater accuracy. It is concluded that to provide a rigorous validation of turbulence models for the application of modeling ejector flow, it is necessary to rely on off-design data where more complex phenomena occur, such as flow separation, strong boundary layer/shock interaction, and unsteady flow. Such validation will help refine turbulence models for future ejector design purposes, and allow for more efficient ejector operation.

CFD Simulation of Forced Flow Within the THAI Model Containment

2009 ◽  
Author(s):  
Armin Zirkel ◽  
Guido Doebbener ◽  
Eckart Laurien
Keyword(s):  
Turbulent Flows ◽  
Cfd Simulation ◽  
Complex Geometry ◽  
Turbulence Models ◽  
Severe Accident ◽  
Forced Flow ◽  
Primary Circuit ◽  
Reference Case ◽  
Fine Grid ◽  
Advection Schemes

This paper presents the current state of an ongoing analysis and validation of turbulence models for three dimensional numerical simulations (CFD-simulations) within containments of nuclear reactors. A severe accident flow inside a containment could be caused by a leak in the primary circuit of the reactor. It is characterized by different velocities, mass transport, the anisotropy and time dependency of the turbulence field as well as the transition between laminar and turbulent flows. Another issue is the complex geometry of a containment with different rooms and obstacles. The analysis is using the experimental data of the THAI model containment, using the TH18 experiment as the reference case. In order to investigate the numerical error, different advection schemes were used and a grid-dependency study was carried out within a half model of the geometry. On a sufficiently fine grid transient simulations were performed by using the Shear Stress Transport and the Reynolds Stress turbulence models. The results of the simulations are showing different deviations from the experiment. Along with the results, a guide for future work is discussed.

A Method for Conjugate Heat Transfer With Unsteady RANS Simulation

2014 ◽  
Author(s):  
Takashi Yamane ◽  
Yuhi Tanaka
Keyword(s):  
Heat Transfer ◽  
Time Scale ◽  
Thermal Conduction ◽  
Conjugate Heat Transfer ◽  
Turbulence Modeling ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Solid Materials ◽  
Rans Simulation ◽  
Unsteady Rans

The conjugate heat transfer simulation is expected to simulate precise temperature distributions of turbine cooling structures and contribute to the reduction of cooling air usage. This method has mainly been used to predict steady state temperature because of the large difference of time scale between RANS flow simulation and thermal conduction in solid materials, thus the accuracy of temperature estimation depends on the modeling of the turbulence. Despite many efforts to improve turbulence models, an inherent limitation of RANS and turbulence modeling and the necessity of unsteady simulation for better accuracy in heat transfer simulations have been pointed out. The aim of this study is to combine the unsteady RANS simulation with the steady thermal conduction of solid materials. The “Time Smoothing” method was introduced to compensate the large time scale difference between fluid and solid, then the effectiveness of the method was confirmed through conjugate heat transfer simulations around a pipe shape object where strong flow unsteadiness prevails.

An explicit algebraic Reynolds stress model for incompressible and compressible turbulent flows

2000 ◽  
Vol 403 ◽  
pp. 89-132 ◽  
Author(s):  
STEFAN WALLIN ◽  
ARNE V. JOHANSSON
Keyword(s):  
Turbulent Flows ◽  
Reynolds Stress ◽  
Compressible Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
New Developments ◽  
The Individual

Some new developments of explicit algebraic Reynolds stress turbulence models (EARSM) are presented. The new developments include a new near-wall treatment ensuring realizability for the individual stress components, a formulation for compressible flows, and a suggestion for a possible approximation of diffusion terms in the anisotropy transport equation. Recent developments in this area are assessed and collected into a model for both incompressible and compressible three-dimensional wall-bounded turbulent flows. This model represents a solution of the implicit ARSM equations, where the production to dissipation ratio is obtained as a solution to a nonlinear algebraic relation. Three-dimensionality is fully accounted for in the mean flow description of the stress anisotropy. The resulting EARSM has been found to be well suited to integration to the wall and all individual Reynolds stresses can be well predicted by introducing wall damping functions derived from the van Driest damping function. The platform for the model consists of the transport equations for the kinetic energy and an auxiliary quantity. The proposed model can be used with any such platform, and examples are shown for two different choices of the auxiliary quantity.

scholarly journals Assessment of Cavitation Models for Compressible Flows Inside a Nozzle

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 134 ◽  
Author(s):  
Aishvarya Kumar ◽  
Ali Ghobadian ◽  
Jamshid M. Nouri
Keyword(s):  
Experimental Data ◽  
Compressible Flows ◽  
Flow Simulation ◽  
Ideal Gas ◽  
Cavitating Flows ◽  
Local Pressure ◽  
Local Flow ◽  
Ideal Gas Law ◽  
Cavitation Region ◽  
The Ideal

This study assessed two cavitation models for compressible cavitating flows within a single hole nozzle. The models evaluated were SS (Schnerr and Sauer) and ZGB (Zwart-Gerber-Belamri) using realizable k-epsilon turbulent model, which was found to be the most appropriate model to use for this flow. The liquid compressibility was modeled using the Tait equation, and the vapor compressibility was modeled using the ideal gas law. Compressible flow simulation results showed that the SS model failed to capture the flow physics with a weak agreement with experimental data, while the ZGB model predicted the flow much better. Modeling vapor compressibility improved the distribution of the cavitating vapor across the nozzle with an increase in vapor volume compared to that of the incompressible assumption, particularly in the core region which resulted in a much better quantitative and qualitative agreement with the experimental data. The results also showed the prediction of a normal shockwave downstream of the cavitation region where the local flow transforms from supersonic to subsonic because of an increase in the local pressure.

Sign in / Sign up

Export Citation Format

Share Document