scholarly journals Numerical Simulation of Bubble Coalescence and Break-Up in Multinozzle Jet Ejector

2016 ◽  
Vol 2016 ◽  
pp. 1-19
Author(s):  
Dhanesh Patel ◽  
Ashvinkumar Chaudhari ◽  
Arto Laari ◽  
Matti Heiliö ◽  
Jari Hämäläinen ◽  
...  
Keyword(s):  
Bubble Size ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Interfacial Area ◽  
Industrial Applications ◽  
Bubble Coalescence ◽  
Ansys Fluent ◽  
Numerical Predictions ◽  
Size Groups ◽  
Rans Models

Designing the jet ejector optimally is a challenging task and has a great impact on industrial applications. Three different sets of nozzles (namely, 1, 3, and 5) inside the jet ejector are compared in this study by using numerical simulations. More precisely, dynamics of bubble coalescence and breakup in the multinozzle jet ejectors are studied by means of Computational Fluid Dynamics (CFD). The population balance approach is used for the gas phase such that different bubble size groups are included in CFD and the number densities of each of them are predicted in CFD simulations. Here, commercial CFD softwareANSYS Fluent 14.0is used. The realizablek-εturbulence model is used in CFD code in three-dimensional computational domains. It is clear that Reynolds-Averaged Navier-Stokes (RANS) models have their limitations, but on the other hand, turbulence modeling is not the key issue in this study and we can assume that the RANS models can predict turbulence of the carrying phase accurately enough. In order to validate our numerical predictions, results of one, three, and five nozzles are compared to laboratory experiments data for Cl2-NaOH system. Predicted gas volume fractions, bubble size distributions, and resulting number densities of the different bubble size groups as well as the interfacial area concentrations are in good agreement with experimental results.

Numerical Simulation of a Three-Dimensional Axisymmetric Hill: Performance Evaluation of Hybrid RANS-LES Models

2021 ◽  
Author(s):  
Tausif Jamal ◽  
Varun Chitta ◽  
Dibbon K. Walters
Keyword(s):  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Dynamics Simulation ◽  
Recirculation Region ◽  
Mean Flow ◽  
Large Eddy ◽  
Rans Models

Abstract Computational fluid dynamics simulation of flow over a three-dimensional axisymmetric hill presents a unique set of challenges for turbulence modeling. The flow past the crest of the hill is characterized by boundary layer separation, complex vortical structures, and unsteady wake flow. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly for this benchmark test case. Recent studies have focused on the use of large-eddy simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, several different HRL models are investigated and results from the different models are evaluated relative to each other, to an eddy-viscosity RANS model, and to previously documented high-fidelity large-eddy simulations and experimental data. Results obtained from the simulations in terms of mean flow statistics, surface pressure distribution, and turbulence characteristics are presented and discussed in detail. Results indicate that HRL models can significantly improve predictions over RANS models, but only when the development of turbulent velocity fluctuations in the separated shear layer and recirculation region are well resolved.

Thermofluid Characteristics of Czochralski Melt Convection Using 3D URANS Computations

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Sudeep Verma ◽  
Anupam Dewan
Keyword(s):  
Turbulence Modeling ◽  
Three Dimensional ◽  
Comparative Assessment ◽  
Navier Stokes ◽  
Thermal Gradients ◽  
Melt Flow ◽  
Turbulent Characteristics ◽  
Eddy Structures ◽  
Rans Models ◽  
Reynolds Averaged Navier Stokes

Turbulent characteristics of Czochralski melt flow are presented using the unsteady Reynolds-averaged Navier–Stokes (URANS) turbulence modeling approach. Three-dimensional, transient computations were performed using the Launder and Sharma low-Re k-ε model and Menter shear stress transport (SST) k-ω model on an idealized Czochralski setup with counterrotating crystal and crucible. A comparative assessment is performed between these two Reynolds-averaged Navier–Stokes (RANS) models in capturing turbulent thermal and flow behaviors. It was observed that the SST k-ω model predicted a better resolution of the Czochralski melt flow capturing the near wall thermal gradients, resolving stronger convective flow at the melt free surface, deciphering more number of characteristics Czochralski recirculating cells along with predicting large number of coherent eddy structures and vortex cores distributed in the melt and hence a larger level of turbulent intensity in the Czochralski melt compared with that by Launder and Sharma low-Re k-ε model.

scholarly journals Numerical simulation of liquid fuel prechamber ignition

2021 ◽  
Author(s):  
Levon Larson
Keyword(s):  
Turbulence Modeling ◽  
Spray Angle ◽  
Navier Stokes ◽  
Discrete Phase Model ◽  
Lean Burn ◽  
Penetration Length ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Discrete Phase ◽  
Rans Models

A Computational Fluid Dynamics (CFD) model was built that simulates the transient, compressible, reacting, multi-phase environment that exists within a reciprocating engine's combustion chamber(s). ANSYS Fluent v13.0 was used with the Euler-Lagrangian Discrete Phase Model (DPM), the Shell autoignition model, and the Large Eddy Simulation (LES) method of turbulence modeling. Validation of the spray dynamics was performed by comparing simulation results with experiments of liquid and vapour penetration length of an n-Heptane spray experiment done by Sandia National Laboratories. It was found that LES produced more accurate results than several Reynolds Averaged Navier-Stokes (RANS) models. The Shell autoignition model was coded to function with C10.17H19.91 and compared with experimental ignition results in a Rapid Compression Machine (RCM) environment. All of the above models were then combined to simulate a directly-fueled lean-burn combustion prechamber configuration wherein the effects of spray angle, timing, and duration were studied.

Closure Laws for the Transport Equation of Interfacial Area in Dispersed Flow

2002 ◽  
Author(s):  
X. Rioua ◽  
J. Fabrea ◽  
C. Colin
Keyword(s):  
Transport Equation ◽  
Size Distribution ◽  
Bubble Size ◽  
Interfacial Area ◽  
Bubble Size Distribution ◽  
Bubble Coalescence ◽  
Size Distributions ◽  
Mean Diameter ◽  
The Mean ◽  
Two Fluid

Derivation of a transport equation for the interfacial area concentration. In two-phase flows, the interfacial area is a key parameter since it mainly controls the momentum heat and mass transfers between the phases. An equation of transport of interfacial area may be very useful, especially for the two-fluid models. Such an equation should be able to predict the transition between the flow regimes. With this aim in view, we shall focus our attention on pipe flow. Besides in a first step, our study will be limited to dispersed flows. Different models are used to predict the evolution of bubble sizes. Some models use a population balance that provides a detailed description of the bubble size distributions, but they require as many equations as diameter ranges (Coulaloglou & Tavlarides1). Some others use only one equation for the transport of the mean interfacial area (Hibiki & Ishii2). In that case the bubble size distribution is treated as it would be monodispersed, its mean diameter being equal to the Sauter diameter. An intermediate approach was proposed by Kamp et al.3, in which polydispersed size distributions can be taken into account. It is the starting point of the present study in which: • The choice of an interfacial velocity is discussed. • The sink and source terms due to bubble coalescence, break-up or phase change are established. The model of Kamp et al. consists of transport equations of the various moments of the density probability function P(d) of the bubble diameter. In many experimental situations, P(d) is well predicted by a log-normal law (with two characteristic parameters d00 the central diameter of the distribution and a width parameter): The different moments of order ? of P(d) may be calculated: Sγ=n∫P(d)dγd(d)(1) where n is the bubble number density, S1/n, the mean diameter and S2/?, the interfacial area. A transport equation can be written for each moment: ∂Sγ∂t+∇·(uGSγ)=φγ(2) The lhs of (2) is an advection term by the gas velocity uG and the rhs is a source or sink term due to bubble coalescence, break-up or mass transfer. Since the bubble size distribution is characterised by the two parameters d00 and σˆ, only two transport equations (for S1 and S2) have to be solved to calculate the space-time evolution of the bubble size distribution. These two equations are still too cumbersome for a two-fluid model. Under some hypotheses (σˆ ∼ constant), they are lead to a single equation for the interfacial area. In its dimensionless form the interfacial area ai+ (ai+ = π S2 D, where D is the pipe diameter) reads: d/dt+(ai+)=f(RG,Re,We,ai+)(3) where RG is the gas fraction, Re is the Reynolds number of the mixture, We the Weber number of the mixture and t+ a dimensionless time.

scholarly journals Numerical Modelling of Horizontal Oil-Water Pipe Flow

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5042 ◽  
Author(s):  
Thomas Höhne ◽  
Ali Rayya ◽  
Gustavo Montoya
Keyword(s):  
Water Flow ◽  
Interfacial Area ◽  
Industrial Applications ◽  
Ansys Fluent ◽  
Ansys Cfx ◽  
Simon Bolivar ◽  
Oil Water ◽  
Interfacial Area Density ◽  
And Performance ◽  
The University

The purpose of this work is modeling of a horizontal oil–water flow with and without the Algebraic Interfacial Area Density (AIAD) model. Software and hardware developments in the past years have significantly increased and improved the accuracy, flexibility, and performance of simulations for large and complex problems typically encountered in industrial applications. At Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the focus has been concentrated on the R&D of new modeling capabilities for Euler–Euler approach where interfaces exist. In this research paper, the applicability of the AIAD model for a horizontal oil–water flow is investigated. The comparison between the standard ANSYS Fluent Eulerian Interface Capabilities (namely Multi-Fluid VOF) without AIAD and ANSYS CFX with AIAD implemented via user functions for the oil–water flow was performed. Thereafter, the obtained results were compared with existing experimental data produced by the Department of Thermodynamics and Transport Phenomena of the University Simon Bolivar (USB) in Caracas, Venezuela. The results of the simulations show that horizontal oil–water flow can be modelled with rather acceptable accuracy when using regime transition capabilities as those offered by the AIAD model.

scholarly journals Numerical investigation on the performance of coalescence and break-up kernels in subcooled boiling flows in vertical channels

2016 ◽  
Vol 9 (2) ◽  
pp. 71-85 ◽  
Author(s):  
Sara Vahaji ◽  
Sherman CP Cheung ◽  
Lilunnahar Deju ◽  
Guan Yeoh ◽  
Jiyuan Tu
Keyword(s):  
Size Distribution ◽  
Bubble Size ◽  
Bubble Dynamics ◽  
Interfacial Area ◽  
Bubble Size Distribution ◽  
Heated Wall ◽  
Bubble Coalescence ◽  
Two Phase ◽  
Interfacial Area Concentration ◽  
Break Up

In order to accurately predict the thermal hydraulic of two-phase gas–liquid flows with heat and mass transfer, special numerical considerations are required to capture the underlying physics: characteristics of the heat transfer and bubble dynamics taking place near the heated wall and the evolution of the bubble size distribution caused by the coalescence, break-up, and condensation processes in the bulk subcooled liquid. The evolution of the bubble size distribution is largely driven by the bubble coalescence and break-up mechanisms. In this paper, a numerical assessment on the performance of six different bubble coalescence and break-up kernels is carried out to investigate the bubble size distribution and its impact on local hydrodynamics. The resultant bubble size distributions are compared to achieve a better insight of the prediction mechanisms. Also, the void fraction, bubble Sauter mean diameter, and interfacial area concentration profiles are compared against the experimental data to ensure the validity of the models applied.

Flow Past a Circular Cylinder: A Comparison Between RANS and Hybrid Turbulence Models for a Low Reynolds Number

2015 ◽  
Author(s):  
Filipe S. Pereira ◽  
Guilherme Vaz ◽  
Luís Eça
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Substantial Improvement ◽  
Computational Domain ◽  
Numerical Predictions ◽  
Flow Past ◽  
Rans Models ◽  
Domain Width

Several offshore applications deal with highly unsteady and detached flows, dominated by three dimensional effects. On such conditions, the usage of scale-resolving simulation (SRS) turbulence models has increased due to the well-known limitations of common RANS models. However, some of these offshore applications, such as flows past cylinders or raisers, present highly complex non-turbulent phenomena which, if not properly resolved, may pollute the outcome of any turbulence model. Therefore, it is crucial to mimic the flow conditions of the problem, the physical settings, and fulfil the numerical requirements of such problems to obtain reliable and accurate predictions. This paper assesses RANS and hybrid turbulence models, focusing on the dependence of the numerical predictions on the physical settings. To this end, the flow past a circular cylinder at a Reynolds number of 3900 is simulated using RANS, DDES and XLES models. The obtained results reveal a large dependence on the grid spatial resolution and physical settings, in particular on the computational domain width and boundary conditions. A substantial improvement of RANS predictions is found when a 3D computational domain is used. As expected, the hybrid models, DDES and XLES, lead to a better agreement with the experiments.

Numerical and Experimental Study of the Flow Around Two Ship Sections Side-by-Side

2014 ◽  
Author(s):  
Tufan Arslan ◽  
Jan Visscher ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson ◽  
Chittiappa Muthanna
Keyword(s):  
Three Dimensional ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Ansys Fluent ◽  
Circulating Water ◽  
Eddy Simulation ◽  
Numerical Predictions ◽  
Large Eddy ◽  
Close Proximity ◽  
Cross Current

This paper reports calculations of three dimensional (3D) unsteady cross flow over two ship sections in close proximity and compares the results with measurements. The ship sections have different breadth and draft, and represent typical situations in a ship-to-ship marine operation in a cross current. The behavior of the vortex-shedding around the two different ship hull sections is investigated numerically by CFD methods and experiments. For the two sections, simulations are done for several Reynolds numbers by using the dynamic Smagorinsky Large Eddy Simulation (LES) turbulence model. Finally the cross flow past the ship sections in side-by-side position is simulated and vortex interaction between the sections is found by using the software (Ansys) FLUENT. The numerical predictions are compared with PIV results taken in a circulating water tunnel.

scholarly journals Numerical simulation of liquid fuel prechamber ignition

2021 ◽  
Author(s):  
Levon Larson
Keyword(s):  
Turbulence Modeling ◽  
Spray Angle ◽  
Navier Stokes ◽  
Discrete Phase Model ◽  
Lean Burn ◽  
Penetration Length ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Discrete Phase ◽  
Rans Models

A Computational Fluid Dynamics (CFD) model was built that simulates the transient, compressible, reacting, multi-phase environment that exists within a reciprocating engine's combustion chamber(s). ANSYS Fluent v13.0 was used with the Euler-Lagrangian Discrete Phase Model (DPM), the Shell autoignition model, and the Large Eddy Simulation (LES) method of turbulence modeling. Validation of the spray dynamics was performed by comparing simulation results with experiments of liquid and vapour penetration length of an n-Heptane spray experiment done by Sandia National Laboratories. It was found that LES produced more accurate results than several Reynolds Averaged Navier-Stokes (RANS) models. The Shell autoignition model was coded to function with C10.17H19.91 and compared with experimental ignition results in a Rapid Compression Machine (RCM) environment. All of the above models were then combined to simulate a directly-fueled lean-burn combustion prechamber configuration wherein the effects of spray angle, timing, and duration were studied.

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