Selection Of Turbulence Model Research Articles

패널법과 전산유동해석법의 결합을 이용한 날개단면 주위 점성유동 해석

Panel methods are essential tools for analyzing a fluid-flow problem around complex three dimensional bodies, but they lack ability to solve viscous effects. On the other hand, CFD methods are considered as powerful tools for analyzing fluid-flow characteristics including viscosity. However, they also have short falls, requiring more computing time and showing different results depending on the selection of turbulence models and grid systems. In this paper a hybrid scheme combining a panel method and a CFD method is suggested. The scheme adopts a panel method for far-field solution where viscous effects are negligible and a CFD method for the solution of RANS equations in near-field where viscous effects are relatively strong. The intermediate region between the far-field and near-field is introduced where the calculated field point velocities by the panel method are given as boundary velocities for the CFD method. To verify the scheme, calculated results, by a panel method, a CFD method and the hybrid scheme, for a two dimensional foil section are compared. The suggested hybrid scheme gives reasonable results, while computation time and memory can be dramatically reduced. By using the hybrid scheme efforts can be concentrated for the local flow near the leading and trailing edges, by providing more dense grid system, where detailed flow characteristics are required.

초임계 압력하의 기체수소-액체산소 화염에 대한 난류모델을 이용한 해석에서 수치기법 평가

Turbulent flow and thermal fields of gaseous hydrogen/liquid oxygen flames at supercritical pressure are investigated by turbulence models. The modified Soave-Redlich-Kwong (SRK) EOS is implemented into the flamelet model to realize real-fluid combustions. For supercritical fluid flows, the modified pressure-velocity-density coupling are introduced. Based on the algorithm, the relative performance of six convection schemes and the predictions of four turbulence models are compared. The selected turbulence models are needed to be modified to consider various characteristics of real-fluid combustions.

The Effect of the Numerical Wind Tunnel Simulation Results of Arched Roof for Different Turbulence Models

Using the FLUENT software, this paper taking the wind load shape coefficient in the current code for the design of building structures as the comparison standard, have numerical wind tunnel simulation of the wind the surface wind pressure on arch roof. It focused on the effect of the different turbulence models on the numerical simulation, such as Spalart-Allmaras, Standard k ε, RNGk ε, Realizablek ε, Standard k ω, SST k ωand RSM. It provided reasonable reference for selection of turbulence model.

Study of natural circulation in a VHTR after a LOFA using different turbulence models

Natural convection currents in the core are anticipated in the event of the failure of the gas circulator in a prismatic gas-cooled very high temperature reactor (VHTR). The paths that the helium coolant takes in forming natural circulation loops and the effective heat transport are of interest. The heated flow in the reactor core is turbulent during normal operating conditions and at the beginning of the LOFA with forced convection, but the flow may significantly be slowed down after the event and laminarized with mixed convection. In the present study, the potential occurrence and effective heat transport of natural circulation are demonstrated using computational fluid dynamic (CFD) calculations with different turbulence models as well as laminar flow. Validations and recommendation on turbulence model selection are conducted. The study concludes that large loop natural convection is formed due to the enhanced turbulence levels by the buoyancy effect and the turbulent regime near the interface of upper plenum and flow channels increases the flow resistance for channel flows entering upper plenum and thus less heat can be removed from the core than the prediction by laminar flow assumption.

Application of CFD Simulation to Predicting Upper‐Room UVGI Effectiveness

This study outlines the potential for Computational Fluid Dynamics (CFD) simulation to be used to predict upper-room ultraviolet germicidal irradiation (UVGI) effectiveness to aid system design and the development of future guidance. A numerical study of two wall-mounted UVGI lamps in a mechanically ventilated test chamber is used to assess the influence of modeling parameters on prediction of dose distribution and microorganism inactivation. Irradiance fields for both UVGI fixtures are obtained via radiometry and implemented in the model. A series of sensitivity studies consider the importance of UVGI field accuracy and computational grid and turbulence model selection. Results show that 2D irradiance fields are sufficient for calculating dose and in-activation, whereas a 1D field is inadequate for modeling purposes. Further parametric studies consider the effects of ventilation parameters, UVGI lamp configuration and microorganism susceptibility. These demonstrate the feasibility of modeling the interaction of the airflow and UV field in a room to quantify the dose distribution. Microorganism in-activation can also be accomplished by employing passive scalars and species transport models, however, further validation data are necessary before this can be used to make reliable quantitative predictions.

The Influence of Turbulence Model Selection and Leakage Considerations on CFD Simulation Results for a Centrifugal Pump

A commercial CFD software was used to simulate and predict a centrifugal pump performance. In this paper，the influences on the numerical simulation results using different turbulence models and different leakage flow assumptions were studied. The simulations are based on RANS with the and SST turbulence models. It is found that SST turbulence is better. Also the influence of the leakage flow was studied.

The Turbulent Flow Model Selection for Numerical Wind Tunnel Simulation of the Low Layer Double Slope Roof

Using the FLUENT software, this paper taking the current code for the design of building structures as the comparison standard, have numerical wind tunnel simulation of the wind the surface wind pressure on low layer double slope roof. It focuses on the analysis of the effects of turbulence model selection on the numerical simulation results, such as Spalart-Allmaras、Standard k −ε、RNG k −ε、Realizable k −ε、Standard k −ω、SST k −ω and RSM, to provide a basis for the reasonable selection of turbulence models.

Considerations on the Numerical Modeling and Performance of Axial Swirlers Under Relight Conditions

Numerical modeling of aero engine combustors under relight conditions is a matter of continuously increasing importance due to the demanding engine certification regulations. In order to reduce the complexity and the cost of the numerical modeling, common practice is to replace the atomizer’s swirlers with velocity profiles boundary conditions, very often scaled down from nominal operating conditions assuming similarity of the swirler flowfield. The current numerical study focuses on the flowfield characteristics of an axially swirled atomizer operating within a windmilling engine environment. The scalability of the velocity profile from higher power settings is examined. Observations on the performance of the axial swirler under relight conditions are also made. Experimental data was used as a validation platform for the numerical solver, after a grid sensitivity study and a turbulence model selection process. Boundary conditions for simulating the windmilling environment were extracted from experimental work. The swirler axial and tangential velocity profiles were normalized using the swirler inlet velocity. Results showed that both profiles are only scalable for windmilling conditions of high flight Mach number (≥ 0.5). At low flight Mach numbers, the actual profile had a lower velocity than that predicted through scaling. The swirl number was found to deteriorate significantly with the flight velocity following a linear trend, reducing significantly the expected flame quality. As a consequence the burner is forced to operate at the edge of its stability loop with low certainty regarding its successful relight.

LES and RANS simulations of cryogenic liquid nitrogen jets

Turbulent flows of liquid nitrogen jets at near-critical and supercritical pressures are investigated by turbulence models (RANS) and a large eddy simulation (LES). To consider real-fluid effects, two real-fluid equations of state (EOS) are implemented into the numerical procedure and the normalized static enthalpy is introduced to describe the turbulent mixing under supercritical conditions. The pressure–velocity–density coupling is obtained by the modified PISO algorithm. The relative performance of six convection schemes and the predictions of four turbulence models for the different EOSs are compared with the available data. From the results, the suitable adoption of real-fluid EOS is more significant than the selection of turbulence model for the numerical performance. Additionally, the effects of SGS models are examined for the LES predictions using the different EOSs. The importance of real-fluid EOS is similarly found in the LES results. The coherent structures are strongly dependent on the different EOSs than SGS models. The results display that the selected RANS models need to be extended for supercritical fluid flows. Finally, the effects of turbulence models and SGS models on the jet spreading rate are discussed.

Comparative study of turbulence models performance for refueling of compressed hydrogen tanks

Compressed hydrogen gas is a popular mode of fuel storage for hydrogen powered vehicles. When hydrogen gas is filled at high pressure, the gas temperature increases. The maximum gas temperature should be within acceptable safety standards. Numerical studies can help optimize the filling process. There is a high level of turbulence in the flow as the high velocity inlet jet is penetrating the nearly stagnant gas in the tank. Selection of a suitable turbulence model is important for accurate simulation of flow and heat transfer during filling of hydrogen tanks. In the present work, a comparative study is performed to identify suitable turbulence model for compressed hydrogen tank filling problem. Numerical results obtained with different turbulence models are compared with available experimental data. Considering accuracy, convergence and the computational expenses, it is observed that the realizable k-ε model is the most suitable turbulence model for hydrogen tank filling problem.

Transport and Deposition of Micro-and Nano-Particles in Human Tracheobronchial Tree by an Asymmetric Multi-Level Bifurcation Model

Transport and deposition of particles in the upper tracheobronchial tree were analyzed using a multi-level asymmetric lung bifurcation model. The first three generations of tracheobronchial tree were included in the study. The laryngeal jet at the trachea entrance was modeled as an effective turbulence disturbance, and the study was focused on how to accurately simulate the airflow and predict the motion of the inhaled particles. Downstream in the lower level of the bronchial region, a laminar flow model was used, as smoother flow condition was expected. Transport and deposition of nano- and micro-scale spherical particles in the range of 0.01 μm to 30 μm were evaluated. The particle local deposition pattern and deposition rate in the lung bifurcation was discussed. The proposed multi-level asymmetric lung bifurcation model was found to be flexible, easy to use and computationally highly efficient. It was also shown that the selection of the anisotropic Reynolds stress transport turbulence model (RSTM) was appropriate, and the use of the enhanced two-layer model boundary treatment was needed for accurate simulation of the turbulent airflow conditions in the upper airways.

New Analysis in 3D-Synthetic Jets Within Numerical Investigation Using CFD Validation Code: Moving Boundary Techniques

The synthetic jets have been identified as a promising technique for various fields of both dynamic fluid and aerodynamics, by using different numerical simulations which recently have been played an important role in their development. In the aim to provide the flow mechanisms by influencing both their visualization and their theoretical analysis provided by the implementation of the different validation code, several passive and active techniques have been studied to explore particularly their characteristics. The present work investigates the performance of the Moving Boundary technique which is one of many different computational tools implemented to reproduce the flow behavior of a 3D synthetic jet. The experimental work is a well stabilized test case used as a CFD benchmark by the CFDVAL 2004 workshop. The main feature of the present work is in use of a moving boundary implemented by use of generating computational mesh at every time step of the unsteady computation. Results are first intended to calibrate versus the measurement in order to be sure that phases are accordance. Several points and lines positions are chosen to compare the averaged velocity components. The preliminary results are encouraging and allow reproducing at least qualitatively the flow behavior animations of the synthetic jet. Nevertheless further improvements have to be added, mainly in grid generation and probably in turbulence model selection. The results given in this paper will be used for validating perspective computational studies to control the boundary layer separation.

Selection of Suitable Turbulence Models for Numerical Modelling of Hydrocyclones

The capability of Computational Fluid Dynamics (CFD) alternates the interest of researcher from the empirical models into the numerical approaches for studying hydrocyclones. This paper presents a comprehensive survey on the influences of turbulence model options in the 3D simulation of the hydrocyclone flow pattern. The required grid resolution was selected through a grid independency study. Four categories of turbulence models involving models based on the Boussinesq hypothesis, the Reynolds Stress Model (RSM), the Large Eddy Simulation (LES) model, and the Detached Eddy Simulation (DES) model were investigated for prediction of velocity components within the hydrocyclone. The methodology was validated by experimental data. The results confirm that both RSM and LES models are efficient turbulent model choices for the simulation of swirling flow of hydrocyclones.

Analysis of turbulent flow through a square-sectioned duct with installed 90-degree elbow

This paper presents the results of a theoretical and experimental investigation of the flow of air through a square-sectioned duct with installed bend. A special test stand was built which allowed testing two different bends with dimensionless mean radius values 2.01 and 1.5. To measure the volumetric flow rate, a measuring orifice plate was installed for control purposes. Additionally, numerical integration of the continuity equation, equations of motion, and equations of selected turbulence models was carried out using FLUENT. As a result of the numerical calculations, time-averaged velocity fields, pressures, and components of the turbulent stress tensor in a developing hydrodynamic flow through a square-sectioned duct with installed bend were determined. The numerical results obtained were subjected to detailed verification by comparison with experimental results obtained on the constructed test stand and those available in the literature.

The Effect and Application of Different Turbulence Models on the Design of Inertial Stage

The numerical simulation of the resistance characteristics of the inertial stage had been researched with different turbulence models, and the resistance characteristic computation curves of the inertial stage with different turbulence models have been obtained. Then curves contrasted with the actual value from experiments. The results show that the error of the Standard model is a little larger, but results of the RNG and Reynolds Stress are comparatively accurate. It has provided the reference frame of the turbulence model selection when the numerical simulation of the inertial stage is conducted.

Model evaluation of roadside barrier impact on near-road air pollution

Abstract Roadside noise barriers are common features along major highways in urban regions and are anticipated to have important effects on near-road air pollution through altering the dispersion of traffic emissions and resulting downstream concentrations. A 3-dimensional computational fluid dynamics (CFD) 6-lane road model has been developed to simulate roadside barrier effects on near-road air quality and evaluate the influence of key variables, such as barrier height and wind direction. The CFD model matches an existing wind tunnel road model and comparison with the wind tunnel data guided the selection of the optimal turbulence model (Realizeable k–ɛ turbulence model with a Schmidt number of 1.0). Under winds perpendicular to the road, CFD model simulations show that roadside barriers reduce the concentration of an inert gaseous tracer (χ), relative to a no-barrier situation, vertically up to approximately half the barrier height and at all horizontal distances from the road. At 20 m (3.3H, where H = 6 m) from the road, barriers of heights ranging from 0.5H to 3.0H reduce the maximum concentrations by 15–61% relative to a no-barrier case, with the location of the maximum shifted to occur near the top of the barrier. The near-road reduction comes at a penalty for on-road air pollutant concentrations: on-road pollution is projected to increase by a factor of 1.1–2.3 corresponding to barriers ranging from 0.5H to 3.0H. When the noise barrier is downwind of the road, a stagnant zone is formed behind the barrier and minor road emissions (e.g., 5% of the highway emissions strength) in this zone, such as a moderately traveled service road, have a magnified effect on concentrations immediately behind the barrier. Wind direction and barrier termination also play a critical role, with a spill-over of accumulated emissions upwind of the barrier strongly increasing near-road concentrations at one end of the barrier. These results imply that roadside barriers may mitigate near-road air pollution, although local meteorology, the barrier structure, and the degree of lee-side emission sources are critical factors determining the outcome.

CFD modelling of livestock odour dispersion over complex terrain, part I: Topographical modelling

Odour from livestock production is an increasing problem in many countries. To reduce odours and establish the effects of livestock production on their surrounding communities, many studies have been carried out on odour dispersion using diffusion simulations and field experiments. Recently, computational fluid dynamics (CFD) has been effectively used to study odour dispersion. CFD can consider various atmospheric phenomena and topographical conditions to study the occurrence of odours and aerosol dispersions. The ultimate objective of this study was to develop an aerodynamic model to qualitatively and quantitatively predict odour dispersion originating from livestock facilities. This first of two papers, deals with the grid construction method, selection of fundamental design criteria and topographical modelling. A mesh model of complex topography, with a 3.6 km diameter and 2.5 km height, was developed with a fine resolution. Well known, commercially available, computational tools were used for the topographical modelling. An earlier wind tunnel experiment contributed to the selection of the grid size (to ensure grid independence), and the selection of time step and turbulence model for CFD simulation. In the second paper, methodologies for modelling of the dispersion phenomenon are presented. In the future, this model will be used to help ameliorate odour conflicts by predicting odour dispersion according to various meteorological and geographical conditions.

On the performance of linear and nonlinear [formula omitted] turbulence models in various jet flow applications

In this paper, a thorough numerical investigation of the performance of several linear and nonlinear k – ε turbulence model variants in various jet flow applications is carried out. Three k – ε based turbulence models are considered, namely the standard k – ε model, the υ 2 – f model, and the nonlinear k – ε model. The selected turbulence models are applied for the prediction of simple as well as complex jet flow applications to underpin knowledge about the accuracy obtained from the two-equation turbulence models. The numerical code developed by the present authors solves the unsteady RANS equations by using the control volume approach on a non-staggered grid system. Three jet flow applications are selected, namely a turbulent free jet, a turbulent jet impinging on a flat plate, and a turbulent wall jet. In order to validate the numerical results obtained and to investigate the performance of the different turbulence models considered, different experimental measurements from the literature are used. The present work is primarily motivated by the desire to provide a rational way for deciding how complex the turbulence model is required to be for a given application and to find out how the accuracy changes with model complexity. Due to the superior predictive performance of modern turbulence models in a wide range of complex industrial and engineering applications, it was believed that a ‘universal’ turbulence model might exist. In general, that is not true. Simple flows can be analysed using standard two-equation models. The present numerical investigation showed that the linear turbulence model could give good results in simple (non-impinging) jet flows. However, in complicated flows, such as impinging jet problems or wall jet flows, a more elaborate level of modeling is required. In such contexts, nonlinear models are appropriate for predicting the turbulent viscosity structure, namely the inhomogeneous near-wall flow region and the anisotropic Reynolds stresses, which is a vital part of turbulent jet flow prediction.

Shell side CFD analysis of a small shell-and-tube heat exchanger

Abstract The shell side design of a shell-and-tube heat exchanger; in particular the baffle spacing, baffle cut and shell diameter dependencies of the heat transfer coefficient and the pressure drop are investigated by numerically modeling a small heat exchanger. The flow and temperature fields inside the shell are resolved using a commercial CFD package. A set of CFD simulations is performed for a single shell and single tube pass heat exchanger with a variable number of baffles and turbulent flow. The results are observed to be sensitive to the turbulence model selection. The best turbulence model among the ones considered is determined by comparing the CFD results of heat transfer coefficient, outlet temperature and pressure drop with the Bell–Delaware method results. For two baffle cut values, the effect of the baffle spacing to shell diameter ratio on the heat exchanger performance is investigated by varying flow rate.

A method for the accurate numerical prediction of the tip vortices shed from hydofoils

The possibly accurate numerical prediction of the detailed structure of vortices shed from the tips of hydrofoils is an important element of the design process of marine propellers. The concentrated tip vortices are responsible for the propeller cavitation erosion and acoustic emission. The purpose of the project described in this paper was to develop the numerical method for prediction of the tip vortex structure. In the course of the project the numerical calculations were confronted with the results of experimental measurements. This led to creation of the specific method of construction of the computational grid and to selection of the optimum turbulence model. As a result the reliable method for the accurate numerical prediction of the concentrated tip vortices for different hydrofoil geometry and flow conditions has been developed and validated. This method enables elimination of the unfavourable phenomena related to the tip vortices in the course of the propeller design calculations.