Realizable Turbulence Model Research Articles

Numerical analysis of flow in a highly efficient flotation column

AbstractFor the purpose of optimization by numerical analysis, a highly efficient flotation column named cyclonic‐static micro‐bubble flotation apparatus, which is widely used in mineral processing, was simulated with computational fluid dynamics to study the distributions of velocity magnitude, pathlines, turbulent intensity, and turbulent kinetic energy under different discretization schemes, turbulence models, and rotational speeds of pump. This simulation was based on the volume of fluid multiphase and multiple reference frame models. Spatial discretization scheme had an obvious effect on the velocity distribution in the column and revolving flotation sections, especially in the former. The introduction of a turbulence model changed the velocity distribution, the turbulence state, and the pathlines in the column and revolving flotation sections. Moreover, the standard, renormalization group (RNG), and realizable k‐epsilon turbulence models had numerous differences. Among these models, the RNG and realizable turbulence models had the most similar results. As the rotational speed of pump increased, velocity and turbulence field intensified. The flow field in the column flotation section differed from that in the revolving flotation section. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Influence of Swirling Air on Ignition and Combustion Characteristics in Boron-Based Ducted Rocket

Three-dimensional two-phase flow in the typical double downside 90°afterburning chamber of boron based ducted rocket is numerically simulated by means of Realizable turbulence model, one-step eddy-dissipation combustion mode1 and the ignition and combustion mode of boron particles of KING with considering the film moving effect in the high-speed flow. The results show that co-swirl and counter-swirl air in the double side of inlet enters into afterburning chamber to make mixture of air and gas more fully and combustion efficiency increases with the increase of swirl number. Boron particles and total combustion efficiency with co-swirl is higher than counter-swirl when the swirl number is less than 0.179. On the contrary, the counter-swirl is higher than co-swirl when the swirl number greater than 0.385, the co-swirl is balance to the counter-swirl when the swirl number is about 0.2; the ignition time of boron particles is reduced with swirling air, its minimum can be attained when swirl number is 0.385.

Numerical Simulation of Turbulent Flow in Carbon Steel Pipes Leading to Flow Accelerated Corrosion

In the present study, turbulent flow fields in diverse carbon steel pipe components leading to flow accelerated corrosion (FAC) are analyzed using the Realizable turbulence model. The present study is inspired by the detailed case studies of flow accelerated corrosion in nuclear power plants around the globe. The Numerical study is conducted with the main objective of analyzing the flow around the recirculation regions arising in different piping components, such as sudden expansion, double elbow, orifice and T-bend, since these components are known to be more susceptible to FAC. Employed Realizable k-e turbulence model and the flow simulations are validated with the Experimental and Numerical results available in the literature. The topological consistency is verified by means of a topological invariance relation of the flow based on the Euler number. The calculated reattachment length increased, but the concentration of ferrous ions decreased or remained almost constant at the corner recirculation regions as a function of Reynolds number. As the shear stress distribution is one of the most important factors in predicting the local regions of pipes that are highly susceptible to FAC, this distribution was calculated in the considered geometries. These results would help to select the components that are more susceptible to FAC. In addition, the locations of the maximum wall shear stress are identified in each component. It is observed that the double elbow and orifice are two components that are more susceptible to FAC among all the considered components.

Numerical Simulation on the Performance of Vertical Jet Flowmeter of Natural Gas

In this paper, SimpleC algorithm and Realizable turbulence model are applied to simulate the detailed flow field of oscillator, which is the key component of the vertical drainage jet flowmeter. Based on analyzing the pressure fluctuation of fluid in the feedback channels of the oscillator at different flowrates, the results indicate that there is an obviously linear relationship between velocity and oscillation frequency of static pressure in the vertical feedback channels within a certain range of flowrate. The achievements can be helpful to the optimization the design of vertical drainage jet flowmeter.

Numerical Study of Water Control with Downhole Oil-Water Separation Technology

The maturing oil fields with increasing water production can pose a challenging produced water handling and disposal issues. This paper presents a numerical study of a motorless hydrocyclone to enhance understanding of the downhole oil-water separation. The turbulence of fluid flow is obtained using K- Realizable Turbulence model for complex swirl dominated flow, while the interface between hydrocarbon and water is described using the Discrete Phase model. In this approach, factors which contribute to the hydrocyclone separation instability were discussed. Discussion is then extended to the relationship of residence time with pressure difference between overflow and underflow. These pressure differences are able to relate to pressure condition for high water cut well which require downhole separation.

2차원 단순 물체의 초공동 유동에 대한 수치해석

In this paper, a numerical analysis is carried out to study the characteristics of supercavitating flows and the drag of relatively simple two-dimensional and axisymmetric bodies which can be used for supercavity generation device, cavitator, of a high-speed underwater vehicle. In order to investigate the suitability of numerical models, cavity flows around the hemispherical head form and two-dimensional wedge are calculated with combinations of three turbulence models(standard , realizable , Reynolds stress) and two cavitation models(Schnerr-Sauer, Zwart-Gerber-Belamri). From the results, it is confirmed that the calculated cavity flow is more affected by the turbulence model than the cavitation model. For the calculation of steady state cavity flows, the convergence in case of the realizable model is better than the other turbulence models. The numerical result of the Schnerr-Sauer cavitation model is changed less by turbulence model and more robust than the Zwart-Gerber-Belamri model. Thus the realizable turbulence model and the Schnerr-Sauer cavitation model are applied to calculate supercavitating flows around disks, two dimensional and wedges. In case of the disk, the cavitation number dependences of the cavity size and the drag coefficient predicted are similar to either experimental data or Reichardt`s semi-empirical equations, but the drag coefficient is overestimated about 3% higher than the Reichardt`s equation. In case of the wedges, the cavitation number dependences of the cavity size are similar to experimental data and Newman`s linear theory, and the agreement of the cavity length predicted and Newman`s linear theory becomes better as decreasing cavitation number. However, the drag coefficients of wedges agree more with experimental data than those of Newman`s analytic solution. The cavitation number dependences of the drag coefficients of both the disk and the wedge appear linear and simple formula for estimating the drag of supercavitating disks and wedges are suggested. Consequently, the CFD scheme of this study can be applied for numerical analysis of supercavitating flows of the cavitator and the cavitator design.

Multi-objective aero acoustic optimization of rear end in a simplified car model by using hybrid Robust Parameter Design, Artificial Neural Networks and Genetic Algorithm methods

In this paper, optimization of rear end of a simplified car model is performed considering aerodynamic and acoustic objectives. Slant angle, rear box angle, boat tail angle, and rear box length are considered as main variables of the rear end. For numerical simulation of flow around the model and studying aerodynamic noise, realizable turbulent model and broad band noise model are used, respectively. Simulation results are validated by the experimental results reported in the literature. To reduce number of simulations to reach optimum values of parameters, Taguchi method has been used. The results of Taguchi are in good agreement with simulation results. Then, the results of Taguchi have been used to obtain a relation between parameters and objectives employing Artificial Neural Networks. Optimization of the model has been conducted by the Neural Network and Multi Objective Genetic Algorithm methods. Finally, flow around the optimized model has been studied by numerical simulation and results have been reported.

Numerical Investigation of Combined Top and Lateral Blowing in a Peirce-Smith Converter

Abstract Typical current operation of lateral-blown Peirce-Smith converters (PSCs) has the common phenomenon of splashing and slopping due to air injection. The splashing and wave motion in these converters cause metal losses and potential production lost time due to intermittent cleaning of the converter mouth and thus reduced process throughput. Understanding of the effect of combined top and lateral blowing could possibly lead to alternative technology advancement for increased process efficiency. In this study, computational fluid dynamics (CFD) simulations of conventional common practice (lateral blowing) and combined (top and lateral blowing) in a PSC were carried out, and results of flow variables (bath velocity, turbulence kinetic energy, etc.) were compared. The two-dimensional (2-D) and three-dimensional (3-D) simulations of the three-phase system (air–matte–slag) were executed utilizing a commercial CFD numerical software code, ANSYS FLUENT 14.0. These simulations were performed employing the volume of fluid and realizable turbulence models to account for multiphase and turbulent nature of the flow, respectively. Upon completion of the simulations, the results of the models were analysed and compared by means of density contour plots, velocity vector plots, turbulent kinetic energy vector plots, average turbulent kinetic energy, turbulent intensity contour plots and average matte bulk velocity. It was found that both blowing configuration and slag layer thickness have significant effects on mixing propagation, wave formation and splashing in the PSC as the results showed wave formation and splashing significantly being reduced by employing combined top- and lateral-blowing configurations.

Numerical Simulation and Experimental Validation of Three-Dimensional Unsteady Multi-Phase Flow in Flushing Process of Toilets

In order to predict the flush performances of digital toilet products before mass production, a numerical simulation for a three-dimensional unsteady multi-phase flow in the flushing process of a wash-down toilet is carried out by using FLUENT software. The finite volume method (FVM) is used to discrete the three governing equations in space and time. The discrete equations are solved by using the first-order upwind discretization scheme and the PISO pressure-velocity coupling scheme. The realizable turbulence model is chosen as the viscous model to treat the fluid flow with large bending curvature wall. The volume of fluid (VOF) model is applied to solve the transient free-surface problem. First, a two-phase flow was simulated on the assumption that there is not sewage but water in the trap seal. Then, by simplifying the mixture of sewage and water in the trap seal as the third phase with high viscosity, a three-phase flow was simulated. Moreover, in order to validate the simulated results, a flushing testing was conducted to test the flush range, and a target type flow meter was designed, calibrated and applied to test the flush velocity. The comparisons show a good agreement between the numerical and experimental results. Based on the verified simulation results, the flush performances of the digital wash-down toilet, such as flush range, flush velocity and sewage replacement ability, can be predicted and evaluated.

Heat transfer and vortical structures around a rotating cylinder with a spanwise disk and low-velocity crossflow

In this paper, we study the flow field characteristics and heat transfer of a rotating cylinder with a spanwise disk attached and subjected to low-velocity crossflow with a disk-cylinder diameter ratio, Dd/Dc=3.06. Reynolds Averaged Navier–Stokes (RANS) simulations using the k-∊ realizable turbulence model with enhanced wall treatment were performed for various crossflow and rotational velocities. We were particularly interested in the case of a rotating cylinder, with a spanwise disk attached, in an air stream with a crossflow Reynolds number, ReU=23,560, and rotational Reynolds numbers, ReΩ, ranging from 5500 to 109,800. Large-eddy simulations (LES) using the dynamic kinetic energy subgrid-scale model were performed for ReΩ=54,900 and 109,800. Heat transfer results from the RANS simulations were compared to results from previous studies. Flow statistics computed from the LES calculations were compared to results measured by particle image velocimetry experiments. Unsteady flow patterns and thermal behaviours are discussed with reference to the instantaneous LES results.

A Numerical Study of Both Internal and External Two-Phase Flows of a Rotating Disk Atomizer

In this paper, a numerical study has been carried out to model and simulate the air-liquid two-phase flows both inside and around a rotating disk atomizer, which is fitted with multiple spray nozzles. The physical problem was simulated with an Eulerian multiphase model in a single computational domain. The realizable two-equation turbulence model was used for the turbulent flow. The governing equations were solved with a finite-volume-based numerical method. The rotary frame method was used for the spinning disk. Numerical simulation was conducted in a rotational disk speed range of 1000 to 10000 rpm and a liquid feed flow rate range of 100 to 175 gpm for the liquid feeder. Both uniform and non-uniform liquid distribution conditions were considered. Detailed results about flow velocity and volume fraction fields inside and outside of the atomizer are presented and discussed. It was found that when liquid is nonuniformly distributed through the distributors, some of the nozzles could reach flooding conditions at lower rotational disk speeds and liquid feed volume flow rates, as compared to uniform distribution cases.

Experimental and numerical study of turbulent flow and heat transfer inside hexagonal duct

Flow and heat transfer characteristics in transition and turbulent regions are studied experimentally and numerically in a horizontal smooth regular hexagonal duct under constant wall temperature boundary condition covering a range of Reynolds number from 2.3 × 103 to 52 × 103. Two types of k-omega (standard and shear stress transport (SST)) and three types of k-e (standard, renormalization (RNG), and realizable) turbulence model are employed for transition and turbulent regions, respectively. Both average and fully developed Darcy friction factor and Nusselt number are presented as a function of Reynolds number. It is seen that k-omega SST and k-e realizable turbulence models gave the best agreement with the experimental data in transition and turbulent regions, respectively. All the experimental results are correlated within an accuracy of ±13 % and ±7 % for Nusselt number and Darcy friction factor, respectively. Results obtained in this study are compared with circular duct results using hydraulic diameter.

Numerical investigation on high-pressure convergent nozzle by comparative and statistical analysis method

Water jet is a kind of technology which is using nozzle structure to transform high pressure water into high velocity water jet beam. For high velocity water flow into low velocity water flow, it is extremely complicated because of the existence of velocity gradient. In this paper, convergent nozzle structure is chosen as simulation prototype and investigational region is selected as the water jet flow can fully develop, the mesh scheme of investigational region is structured mesh and numerical simulation results is independent with the grid number, various kinds of turbulence model are employed. Combining theory, experimental data and different kinds of turbulence model's computational results of the velocity distribution and flow pattern, we can figure out that k-epsilon realizable turbulent model is more suitable than any other kinds of turbulent simulation models for simulation water jet. It is useful for the application of CFD technology in water jet field and helpful for understanding the interior filed of water jet flow, at the same time, this work can also provide reference for further investigation and discussion about using turbulent model to simulate water jet flow.

Convection heat transfer of supercritical pressure carbon dioxide in a vertical micro tube from transition to turbulent flow regime

This paper presents experimental investigations of the convection heat transfer of carbon dioxide at supercritical pressures in a vertical tube with inner diameter of 99.2μm for various Reynolds numbers, heat fluxes and flow directions. The effects of buoyancy and flow acceleration due to heating and pressure drop are evaluated and analysed. The results show that the effects of flow acceleration are significant and the local wall temperature varies non-linearly for both upward and downward flows at the pressures in the vicinity of critical point and low inlet Reynolds numbers when the heat fluxes are relatively high. The buoyancy effect on the heat transfer is negligible in micron scale tubes at inlet Reynolds (from 2600 to 6700) and various heat fluxes (from 85kW/m2 to 748kW/m2). The flow acceleration due to heating and pressure drop can strongly influence the turbulence and reduce the heat transfer for high heat fluxes and low inlet Reynolds. Comparison of numerical predictions with the experimental data showed that the AKN low Reynolds number turbulence model gave better agreement than the k–ε realizable turbulence model with the enhanced wall treatment.

Numerical Simulation of Multiphase Transport Phenomena During Impinging Stream Drying of a Particulate Material

The objective of the present study was to employ an existing three-dimensional computational fluid dynamic model to investigate the multiphase transport phenomena in a coaxial impinging stream dryer. The continuous-phase equations were solved in the Eulerian frame, while the discrete-phase equations were solved in the Lagrangian frame. Two-way coupling between the continuous and dispersed phases was taken into account in the model. Standard k-ϵ and realizable k-ϵ turbulence models were compared in order to decide which model could better represent the turbulent behavior of the flow in the ISD, while the stochastic approach was used to treat the effect of turbulence on the particle motion. Simulated mean particle moisture content and air humidity ratio at the dryer outlet as well as the particle mean residence time were compared with the experimental data. The results indicated that the model could predict the experimental results within ±10%, with the realizable turbulence model performing better than the standard model. The effects of various parameters including the inlet air velocity, inlet air temperature, material feed flow rate, and impinging distance on the transport and performance behavior of the dryer were then numerically investigated and discussed.

Numerical Investigations of Solid-Liquid Two-Phase Turbulent Flows through Francis Turbine

This work is to investigate solid-liquid flows inside entire passage of a large Francis turbine unit and a modified algebraic model is proposed to take the solid-phase turbulent viscosity into consideration based on realizable turbulence model for the liquid phase and further development of the commercial CFD software. The energy conversion between the pressure and velocity, and the sedimentation distribution characteristics around all the hydraulic parts are simulated. The calculated velocity and sedimentation concentration distributions inside the runner are not uniform due to the effect of the centrifugal and Coriolis force. In addition, the calculated eccentric vortex rope in the draft tube causes vortex cavitation and vibration to the turbine unit, which leads to the eccentric sedimentation distribution. The simulation results (i.e., the mixture pressure, velocity and sedimentation distributions) are in good agreement with the natural rule, suggesting that the simulation strategies are capable to handle two-phase flows over complex geometries. The computational results can provide the useful information for hydraulic turbine designs. Future work will focus on the optimizations of hydraulic impeller designs using simulated results.

A numerical study of the effects of a winglet on airfoils

The purpose of this research is to investigate the effects of a winglet on aerodynamic noise of an airfoil. For simplicity, Reynolds Averaged Navier-Stokes equations combined with Realizable turbulence model are used to solve the turbulent flow. In order to verify the accuracy of flow field analysis, a uniform flow past a three-dimensional rectangular airfoil is analyzed and tracks the center line of the tip vortex. The agreement between the simulated and measured center line is good. For the sound field analysis, the flow induced noise around a rectangular airfoil is computed by the Broadband Noise Source (BNS) model. Proudman's formula was used to evaluate acoustic power per unit volume of aerodynamic noise. This study focuses on the sound power of aerodynamic noise generated by tip vortex when the flow passes through an airfoil and an airfoil with winglet. In order to understand the effects of the winglet on the aerodynamic noise, the different winglet characteristics are investigated and discussed. It is found that with a winglet the dynamic coefficient is improved and the generated sound power is also reduced by about 5.4 dB in this study.

Research of Distribution and Dynamic Characteristic of Particle Group in the Structural Flow Passage

Because of the liquid phase’s driving action, particles would be collided the surface and impacted with each other in the flow passage, the surface will be machined though the continuous action of impact force and friction force. The finishing results of structural surface is related to the collision frequency and the pressure, abrasion situation in different area of the structural surface can be analyzed obviously by investigating dynamic characteristic and distribution of particle group. Based on coupled wave theory of liquid-solid two phases flow, using mixture model which belongs to Euler-Euler multiphase flow model and realizable turbulence model, turbulence effects of liquid-solid two-phase flow in the wall is numerical simulated and some parameters such as turbulent velocity and turbulent energy are calculated with different particles concentration in the flow passage which has V-shaped texture and semicircular cross-section. The simulation results show that the disorder degree of turbulence can be improved by assembling V-shaped constrained component, because V-shaped passage is benefit of eddy current’s generation. As the concentration of particles being enhanced, the velocity of particle would be increased in a certain range, turbulence energy reduces gradually, fluctuation margin of particle volume fraction is smaller and smaller, and curves of every kind of parameters change as continuous oscillation, area of surface corresponded with crest of the curve. The concentration of particles should be selected properly and different particles distribution and finishing performance would be obtained with different particles concentration.

Investigation of G4-73 Centrifugal Fan Airfoil Stall Characteristics

It’s of great significance for safe and reliable operation of fan to research on the stall characteristics of the airfoil. The 2D non-compressible Reynolds-Averaged Navier-Stokes equations was built to simulate the flow around the airfoil of G4-73No.8D centrifugal fan, a detailed numerical simulation under different angles has been carried out which based on the Realizable turbulence model with Fluent. The numerical results show that the smaller of the flow rate, the bigger incidence angle is, when the incidence angle is bigger than the critical incidence angle, the suction side stall appears. According simulation the airfoil stall appears when the incidence angle is -28°, with the increasing of the negative incidence angle, the separation point gradually moves to the leading edge. There is a strong vortex which locates at suction side =0.5,the alternating stress on the blade which caused by vortex will make the blade fatigue. If the incidence angle is less than -20°,there is no flow separation, therefore, to ensure the safe operation of the fan, the incidence angle should be less than -20°.

Influence of Convalescence on Soil Temperature Field around a Vertically Buried Single-U-Tube Ground Heat Exchanger

The mathematical physical model of the heat and moisture transfer in the single-U-tube heat exchanger of a ground source heat pump (GSHP) is validated using observed data from the practical rock-soil thermal response test on a resident district in Taiyuan, the soil is layered according to the geological structure of an actual drill in the depth direction in this model. Inputting the dynamic design cooling and heating load of the district into the Realizable turbulent model in Fluent, the temperature fields of a single well in the GSHP project running for 1 year in 2 conditions in which convalescence is considered and not, are simulated numerically. It shows that it rather necessary to take the influence of convalescence into consideration while predicting the soil temperature field of a GSHP system running for a long term, or may not correspond to the reality and make a wrong theory guide to the practical engineering.