January 4

ANSYS CFX: Everything to Know

ANSYS CFX: Everything to Know

Sohaib Alam

ANSYS comes with two different state-of-the-art computational fluid dynamics software for process and product design optimization. One is ANSYS Fluent while other is the ANSYS CFX. In this section, we will be looking into the designs and features of ANSYS CFX and what makes this software great.

Table of Contents (click to navigate)

What is ANSYS CFX?

ANSYS CFX is a general-purpose high-performance computational fluid dynamics program that is used to solve complex wide range fluid problems for over two decades now. At the heart of the ANSYS CFX is its innovative solver technology that is the main driving force to achieve highly reliable and accurate results in a much more efficient manner as compared to other CFD solvers. ANSYS CFX advanced solver lays the foundation of the users to abundant choices of physical models to virtually capture any type of phenomenon that is connected with fluid flow. Let it be turbulent to laminar flow or fully compressible to incompressible fluid or let is be combusting or non-reacting fluids, ANSYS CFX solver capabilities covers almost all the spectrum of fluid dynamics simulations. 

But ANSYS CFX is more than just an advanced and powerful computational fluid dynamics code. ANSYS CFX integrated with ANSYS Workbench, greatly benefits the users with bi-directional connections to a variety of CAD systems. The geometry modifications with the ANSYS SpaceClaim, and the fast meshing with ANSYS Meshing, the users can link all these with the ANSYS CFX and get the most of their product in one single go.  

Key physical models in ANSYS CFX model

ANSYS CFX comes packed with many different industrial-grade physical models and working capabilities, some of the most prominent of those are as follows;

Rotating Machinery

From the very beginning, ANSYS CFX has been a global leader in the CFD simulation and processing for rotating machinery, and in the latest version of ANSYS, the CFX capabilities have become even better. ANSYS CFX now has a full suite of models to capture the interactions between the stationary and rotating components that are completely tailored to the pre- and post-processing environments of turbomachinery. ANSYS CFX is complemented by the ANSYS TurboGrid™ and ANSYS BladeModeler™.

Turbomachinery CFD in ANSYS CFX

Radiation and heat transfer

Beyond the solving capabilities of the convective transport of energy via fluid flow, ANSYS CFX now includes a CHT (Conjugate Heat Transfer) capabilities to solve the radiation and the thermal conduction in all states of matter. The models supplied by the radiation and heat transfer in ANSYS CFX allows the users to capture all types of radiative heat exchanges.

Combustion

Whether you are carrying out the simulation of combustion design in a gas turbine, coal-fired engines or a turboprop aircraft engine, ANSYS CFX a dense framework to carry out the modeling for the combustion and the chemical reactions with the fluid flow. ANSYS CFX can provide the user with the combustion models from anything between turbulent to laminar flows as well as slow to fast chemical kinetics. 

Multiphase

ANSYS CFX has more than two years of experience in multiphase modeling. ANSYS CFX allows for the modeling and simulation of multiple fluid streams, droplets, bubbles, particles, and free surface flows. The Lagrangian transport model in CFX allows for the simulation of one or more discrete particles within a continuous phase. ANSYS CFX also has an efficient statistical model for particle-particle collision and quasi-static wall film model. ANSYS CFX also comes packed with the Eulerian multiphase model for user to have a wealth of options to capture the exchange of energy, momentum, mass, and change of states of matter. Multiple size group (MUSIG) model is also available to process and simulate the coalescence and breakup of dispersing phases in the poly-dispersed multi-phase flows.

ANSYS CFX interface

Turbulence

Most of the industrial flows are turbulent. Therefore, ANSYS CFX has always focused on providing advanced turbulence models to cater to the demands of the industry by fully capturing the effects of the turbulence accurately and efficiently. Along with the common RANS models of turbulence such as SST, Reynolds-Stress models, k-epsilon and k-omega, ANSYS CFX provides other numerous turbulence models. These models include the SST model to capture the effects of streamline curvature, the Menter-Langtry model and the novel SAS (Scale-Adaptive Simulation ™) model for fluid flow under unsteady turbulence models. 

Turbulence modeling and processing in CFX

Fluid-Structure Interface (FSI)

FSI is an important feature of CFD solvers. ANSYS CFX combines its technologies and the capabilities to provide the most advanced simulation for the interaction between the solids and fluids. In CFX, both one-way and two-way Fluid-Structural Interfaces are possible ranging from the setting up of problem to the advanced post-processing. 

Fluent vs. CFX, which one shall I use?

Both the ANSYS Fluent and ANSYS CFX are equally good computational fluid solvers. The preference on which one to use depends completely over the physics of the flow as well as the familiarity of the user with the solver. Below are some of the most prominent differences between the two solvers;

  • In ANSYS CFX, the mesh adaption capabilities are significantly weaker as compared with the ANSYS Fluent. CFX, on the other hand, has ‘Adaptive Meshing’ for single domains with no General Grid Interfaces (GGI). 
  • Fluent allows the user to carry out simulation acceleration with a GPU for simulations requiring high processing power. CFX cannot benefit from simulation acceleration
  • CFX cannot carry out simulation having a true 2D mesh; it can handle a pseudo-2D mesh having at least one element thickness. However, Fluent can easily work over the 2D meshes.
  • Fluent carries out its simulation via a cell-centered approach while CFX makes use of a vertex-centered approach to generate its results. 
  • CFX can easily handle tetra and hexa mesh topologies whereas; Fluent is capable of handling uncut polyhedral meshes 
  • Fluent is a better option for high Mach number flow which includes hypersonic and supersonic airflows
  • ANSYS CFX allows the users to generate detailed performance maps unlike Fluent, where are maps are basic
  • CFX can reliably capture cavitation without user tuning or empirical parameters. ANSYS Fluent requires high user inputs to capture the cavitation in a diverse application such as diesel fuel injectors, hydro pumps and rocket fuel system 
  • CFX is much more advanced as compared to Fluent in turbomachinery

Though ANSYS Fluent might be more diverse in terms of its working capabilities, ANSYS CFX has unmatched capabilities in turbomachinery and simulation of industry-grade turbulent fluid flow models. If you want to read about ANSYS Fluent in-depth, please check out our article, “Everything you need to know about ANSYS Fluent” here.

Summary

ANSYS CFX powerful pre- and post-processing capabilities are not based on single product features. What makes CFX great and powerful is a combination of leading-edge and proven technologies in all elements of the software that provides the users with speed, reliability, accuracy, and flexibility. ANSYS CFX capabilities combined with the ANSYS Workbench platform opens the doors to even possibilities and levels of efficiencies in engineering simulation. 

References

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About the Author

Sohaib Alam is an Undergraduate at the University of Sunderland specializing in Mechanical Engineering. Sohaib specializes in Physics among many other engineering subject matter. He focuses his writing on ANSYS and AutoCAD Inventor.

Sohaib Alam

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