💥💥💥 How to model pressure drop in Ansys Fluent?

Pressure drop is the difference in pressure between two points in a fluid flow. It is caused by friction, turbulence, bends, valves, fittings, or other obstacles in the flow path. Pressure drop can affect the performance, efficiency, and safety of fluid systems, such as pipes, ducts, pumps, compressors, turbines, heat exchangers, etc.

There are different ways to calculate pressure drop in Ansys Fluent, depending on the type of flow, the boundary conditions, and the model assumptions. Some of the common methods are:

• Using the Darcy-Weisbach equation, which relates the pressure drop to the friction factor, the density, the velocity, the length, and the diameter of the pipe. This equation is valid for laminar and turbulent flows in smooth and rough pipes. You can use the Moody chart or the Colebrook equation to find the friction factor for a given Reynolds number and relative roughness. You can also use the Swamee-Jain equation or the Haaland equation to estimate the friction factor more easily. For more details, please see this video.
• Using the Bernoulli equation, which relates the pressure drop to the change in kinetic and potential energy of the fluid. This equation is valid for inviscid, incompressible, and steady flows along a streamline. You can use the Euler equation to extend the Bernoulli equation to rotational flows. You can also use the energy equation to account for the heat transfer and viscous dissipation in the flow. For more details, please see this guide.
• Using the porous media model, which relates the pressure drop to the permeability and the inertial resistance of the porous medium. This model is valid for flows in porous materials, such as filters, catalysts, packed beds, etc. You can use the Ergun equation or the Forchheimer equation to find the permeability and the inertial resistance coefficients for a given porosity and particle diameter. You can also use the core porosity model to define the pressure drop parameters and the effectiveness of a heat exchanger zone. For more details, please see this guide.
• Using the user-defined function (UDF), which allows you to write your own code to specify the pressure drop function based on your own criteria. This method is useful for cases where the existing models are not suitable or accurate enough for your simulation. You can use the DEFINE_PRESSURE_DROP macro to define the pressure drop across a boundary or an interface. You can also use the DEFINE_PROFILE macro to define the pressure drop as a function of the spatial coordinates. For more details, please see this forum post.

How to define flow resistance (pressure drop) at outlet in Ansys Fluent?

One way to define flow resistance at an outlet in Ansys Fluent is to use the outlet vent boundary condition. This boundary condition allows you to specify a loss coefficient that represents the pressure drop across the vent. The pressure drop is calculated as follows¹:

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Another way to define flow resistance at an outlet in Ansys Fluent is to use a user-defined function (UDF). This allows you to write your own code to specify the outlet boundary condition based on your own criteria. For example, you can use a UDF to define a pressure outlet boundary condition with a variable pressure drop that depends on the flow rate or the Reynolds number. You can find some examples of UDFs for outlet boundary conditions in this forum post and this forum post.

Is there possibilty to define pressure drop on contact between two domains in Ansys Fluent ?

Yes, there is a possibility to define pressure drop on contact between two domains in Ansys Fluent. One way to do this is to use the interface boundary condition and specify the jump option. This option allows you to define a pressure jump or a loss coefficient across the interface between two domains. You can also use a user-defined function (UDF) to define a custom pressure drop function across the interface. For more details, please refer to this guide or this forum post.

How to calculate  a loss coefficient, where fluid density is 1.2 kg/m3 , pressure drop is 40000 Pa and velocity is 20 m/s

💥💥💥 How to define free inlet and outlet in Ansys Fluent?

 A free inlet is a type of boundary condition that allows the fluid to enter or exit the domain depending on the pressure difference. It is suitable for external or unconfined flows, such as wind tunnel simulations or open channel flows.

To define a free inlet in Ansys Fluent, you can use the pressure inlet boundary condition and set the total (stagnation) pressure to zero. This will allow the fluid to flow in or out of the domain depending on the local pressure gradient. You will also need to specify the total temperature, turbulence parameters, and other scalar properties of the flow at the inlet. For more details, please refer to this guide.

Alternatively, you can use the velocity inlet boundary condition and set the velocity magnitude to zero. This will also allow the fluid to flow in or out of the domain depending on the pressure difference. However, you will need to use a user-defined function (UDF) to update the velocity direction at each time step, based on the local flow direction. For more information, please see this forum post.

How to define free outlet in Ansys Fluent?

A free outlet is a type of boundary condition that allows the fluid to exit the domain freely without any restriction. It is suitable for external or unconfined flows, such as jet flows or exhaust flows.

To define a free outlet in Ansys Fluent, you can use the pressure outlet boundary condition and set the gauge pressure to zero. This will allow the fluid to flow out of the domain based on the local pressure gradient. You will also need to specify the backflow properties of the flow at the outlet, such as temperature, turbulence parameters, and other scalar quantities. For more details, please refer to this guide.

Alternatively, you can use the outflow boundary condition and set the mass flow rate to zero. This will also allow the fluid to flow out of the domain without any restriction. However, you will need to ensure that there is no reverse flow at the outlet, as the outflow boundary condition does not account for backflow. For more information, please see this forum post.

What is the difference between pressure outlet and outflow?

The difference between pressure outlet and outflow boundary conditions in Ansys Fluent is that:

• Pressure outlet allows you to specify the static (gauge) pressure at the outlet, and the software will calculate the mass flow rate based on the pressure gradient. You also need to define the backflow properties in case of reverse flow at the outlet. This boundary condition is suitable for cases where the outlet pressure is known or important for the simulation results.
• Outflow assumes a zero diffusion flux for all flow variables except the pressure, and the software will calculate the pressure at the outlet based on the mass conservation. You do not need to define the backflow properties, but you need to ensure that there is no reverse flow at the outlet. This boundary condition is suitable for cases where the flow is fully developed and the outlet pressure is not known or important for the simulation results.

For more information, please refer to this guide or this forum post.

What is the difference between pressure inlet and velocity inlet?

The difference between pressure inlet and velocity inlet boundary conditions in Ansys Fluent is that:

• Pressure inlet allows you to specify the total (stagnation) pressure at the inlet, and the software will calculate the mass flow rate based on the pressure gradient. You also need to define the backflow properties in case of reverse flow at the inlet. This boundary condition is suitable for cases where the inlet pressure is known or important for the simulation results¹.
• Velocity inlet allows you to specify the velocity magnitude and direction at the inlet, and the software will calculate the total pressure based on the mass conservation. You do not need to define the backflow properties, but you need to ensure that there is no reverse flow at the inlet. This boundary condition is suitable for cases where the inlet velocity is known or important for the simulation results².

For more information, please refer to this guide or this forum post.

💥💥💥 What is Helyx-OS and what is used for ?

Helyx-OS is an open-source graphical user interface (GUI) for OpenFOAM, a free and open-source computational fluid dynamics (CFD) software¹. It allows users to perform pre-processing tasks such as meshing, case definition and solver execution. It supports both OpenFOAM and OpenFOAM+, and works on Linux and Windows platforms².

Helyx-OS is designed to facilitate the usage of the standard OpenFOAM libraries, by removing the complexity of text based case definition in favour of an intuitive easy-to-use graphical user interface. It is intended for academic use and entry-level CFD work¹. If you are looking for an enterprise CFD solution for industrial applications, you can check out HELYX, a more advanced CFD software product developed by ENGYS³.

Is Helyx-os completely free?

Yes, Helyx-OS is completely free for academic use and entry-level CFD work. It is released to the public under the GNU General Public License¹. However, if you are looking for an enterprise CFD solution for industrial applications, or if you require technical support and/or training for Helyx-OS and OpenFOAM, you may need to pay for those services². You can contact ENGYS, the developer of Helyx-OS, for more information³.

Can I use Helyx-OS for commercial purposes?

According to the developer of Helyx-OS, ENGYS, the software is intended for academic use and entry-level CFD work, and it is delivered to the public under the GNU General Public License¹. This means that you can use Helyx-OS for commercial purposes, as long as you comply with the terms and conditions of the license². However, you may not receive any technical support or documentation from ENGYS, unless you pay for those services¹. If you are looking for an enterprise CFD solution for industrial applications, you may want to consider HELYX, a more advanced CFD software product developed by ENGYS³. HELYX is not free, but it offers more features, reliability and support than Helyx-OS².

What is difference between Helyx-os  and HELYX ?

The main difference between Helyx-OS and HELYX is that Helyx-OS is an open-source graphical user interface (GUI) for OpenFOAM, a free and open-source computational fluid dynamics (CFD) software, while HELYX is a comprehensive general purpose CFD software package for engineering analysis and design optimisation of enterprise applications, based on ENGYS’ own open-source CFD simulation engine¹².

Helyx-OS is intended for academic use and entry-level CFD work, and it is delivered to the public under the GNU General Public License. It supports both OpenFOAM and OpenFOAM+, and works on Linux and Windows platforms. It allows users to perform pre-processing tasks such as meshing, case definition and solver execution. It does not provide any technical support or documentation from ENGYS, unless users pay for those services¹³.

HELYX is a unified, off-the-shelf CFD software product compatible with most Linux and Windows platforms, including high-performance computing systems. It features an advanced hex-dominant automatic mesh algorithm with polyhedra support, a wide range of physical models, and a Generalised Internal Boundaries method to support complex boundary motions. It also incorporates an extensive set of ancillary services to facilitate the deployment and usage of the software in any working environment. It offers more features, reliability and support than Helyx-OS, but it is not free²⁴.

Can I modify Helyx-OS for my own purposes?

Yes, you can modify Helyx-OS for your own purposes, as long as you comply with the terms and conditions of the GNU General Public License¹. Helyx-OS is an open-source graphical user interface (GUI) for OpenFOAM, a free and open-source computational fluid dynamics (CFD) software². The source code of Helyx-OS is available on GitHub³, where you can also find instructions on how to compile it on your own⁴. However, if you modify Helyx-OS, you may not receive any technical support or documentation from ENGYS, the developer of Helyx-OS, unless you pay for those services². You may also want to check out the FAQ page of Helyx-OS for more information.

What is difference in functionaity between Helyx-os and HELYX for CFD simulations ?

The difference in functionality between Helyx-OS and HELYX for CFD simulations is mainly related to the following aspects:

• Meshing: Helyx-OS uses SnappyHexMesh, an automatic mesh generator for complex geometries based on hexahedral cells¹. HELYX uses an advanced hex-dominant automatic mesh algorithm with polyhedra support, which can run in parallel and generate large computational grids².
• Solvers: Helyx-OS supports a subset of solvers and boundary conditions available in OpenFOAM, a free and open-source CFD software¹. HELYX supports a wide range of physical models, such as single- and multi-phase turbulent flows, thermal flows, radiation, compressible and incompressible flows, etc. It also incorporates a Generalised Internal Boundaries method to handle complex boundary motions².
• GUI: Helyx-OS provides a graphical user interface (GUI) for pre-processing tasks such as meshing, case definition and solver execution. It also allows users to monitor the simulation progress and visualize the results¹. HELYX provides a more comprehensive and user-friendly GUI, with client-server support for remote and cloud-based operation. It also offers more features and options for case setup, simulation control and post-processing².
• Support: Helyx-OS is delivered to the public under the GNU General Public License, and does not provide any technical support or documentation from ENGYS, the developer of Helyx-OS, unless users pay for those services¹. HELYX is a commercial product, and provides first-class user support, code maintenance and documentation from ENGYS².

In summary, Helyx-OS is a free and open-source GUI for OpenFOAM, intended for academic use and entry-level CFD work. HELYX is a comprehensive and cost-effective CFD software package for engineering analysis and design optimisation of enterprise applications, based on ENGYS’ own open-source CFD simulation engine.

💥💥💥 New year - new challenges - "OpenFoam project" part 2 (main differences between OpenFoam and Ansys Fluent)

 OpenFoam and Ansys Fluent are both software tools for computational fluid dynamics (CFD) simulations, but they have some key differences. Here are some of the main ones:

• 
  OpenFoam is an open-source software, which means it is free to use and modify, while Ansys Fluent is a commercial software, which requires a license fee to use¹².
• OpenFoam is based on a finite volume method, while Ansys Fluent can use both finite volume and finite element methods³⁴.
• OpenFoam has a more flexible and customizable solver structure, which allows users to create their own solvers and models, while Ansys Fluent has a more user-friendly and standardized interface, which makes it easier to set up and run simulations¹².
• OpenFoam has a steeper learning curve and requires more programming skills, while Ansys Fluent has more tutorials and documentation available and requires less coding¹².
• OpenFoam has a larger and more active community of users and developers, who contribute to the software development and provide support, while Ansys Fluent has more professional and technical support from the company¹².

How do I choose between OpenFoam and Ansys Fluent?

Choosing between OpenFoam and Ansys Fluent depends on several factors, such as your budget, your skill level, your problem type, and your preference. Here are some general guidelines that may help you decide:

• If you have a limited budget or you want to modify the source code, you may prefer OpenFoam, as it is free and open-source¹².
• If you want a more user-friendly and standardized interface, or you need professional and technical support, you may prefer Ansys Fluent, as it has more tutorials and documentation available and a company behind it¹².
• If you need to use both finite volume and finite element methods, or you want to use a specific solver or model that is not available in OpenFoam, you may prefer Ansys Fluent, as it has more options and features³⁴.
• If you want to create your own solvers and models, or you want to use a more flexible and customizable solver structure, you may prefer OpenFoam, as it allows you to program your own equations and algorithms¹².
• If you have a complex or large-scale problem that requires high accuracy and performance, you may need to compare the results of both software, as they may differ depending on the problem and the settings¹²⁵.

Ultimately, the best way to choose between OpenFoam and Ansys Fluent is to try them both and see which one suits your needs and preferences better. 

Which one is better for simulating turbulence?

Simulating turbulence is a challenging task that depends on the type and complexity of the flow, the accuracy and stability of the numerical methods, and the suitability and validity of the turbulence models. Therefore, there is no definitive answer to which software is better for simulating turbulence, as it may vary from case to case. However, some general considerations are:

• OpenFoam has a larger variety of turbulence models than Ansys Fluent, including some advanced models such as large eddy simulation (LES), detached eddy simulation (DES), and scale-adaptive simulation (SAS)¹². However, some of these models may require more computational resources and expertise to use properly³.
• Ansys Fluent has a more user-friendly and standardized interface for setting up and running turbulence simulations, as well as more tutorials and documentation available¹². However, some of the settings and options may be hidden or simplified, which may limit the user’s control and understanding of the simulation⁴.
• Both software have different numerical methods and solvers, which may affect the accuracy and performance of the turbulence simulations. For example, OpenFoam uses a finite volume method, while Ansys Fluent can use both finite volume and finite element methods³⁴. Moreover, OpenFoam uses a conjugate gradient solver, while Ansys Fluent uses an algebraic multigrid solver². These methods may have different advantages and disadvantages depending on the problem and the mesh⁵.

The best way to compare the software for simulating turbulence is to run the same problem with the same settings and mesh, and compare the results in terms of accuracy, convergence, and computational time. You can also consult the literature and the web for more information and examples of turbulence simulations with OpenFoam and Ansys Fluent¹²³⁴⁵. 

Which one is better for simualting Conjugate Heat Transfer ?

Conjugate heat transfer (CHT) is the process of heat transfer between a solid and a fluid, or between different solids, in contact with each other¹. Simulating CHT requires solving the energy equation for both the fluid and the solid domains, and applying appropriate boundary conditions at the interface².

Both OpenFoam and Ansys Fluent are capable of simulating CHT, but they have some differences in their approaches and features. Here are some of the main ones:

• OpenFoam uses a single solver, called chtMultiRegionFoam, for CHT simulations, which can handle multiple fluid and solid regions, and couple them using a regionCouple boundary condition³. Ansys Fluent uses different solvers for different types of CHT simulations, such as pressure-based or density-based solvers, and couples the fluid and solid regions using a coupled-wall boundary condition⁴.
• OpenFoam requires the user to create separate meshes for each fluid and solid region, and to define the interface between them in a regionProperties file³. Ansys Fluent allows the user to create a single mesh for the whole domain, and to specify the fluid and solid regions using cell zones and cell types⁴.
• OpenFoam has a more flexible and customizable solver structure, which allows the user to modify the source code and create their own models and algorithms, while Ansys Fluent has a more user-friendly and standardized interface, which makes it easier to set up and run simulations¹².
• OpenFoam has a larger variety of turbulence models and numerical schemes than Ansys Fluent, which may affect the accuracy and performance of the CHT simulations¹². However, some of these models and schemes may require more computational resources and expertise to use properly³.
• Ansys Fluent has more options and features for CHT simulations, such as radiation, phase change, porous media, and moving/deforming mesh⁴. However, some of these options and features may be hidden or simplified, which may limit the user’s control and understanding of the simulation².

💥💥💥 New year - new challenges - "OpenFoam project" - part 1 (installation)

 There are different ways to install OpenFoam on Windows, depending on your preferences and needs. One option is to use the Windows Subsystem for Linux (WSL), which allows you to run Linux applications on Windows 10. Another option is to use a virtual machine (VM), such as VirtualBox, which creates a separate Linux environment on your Windows system. Here are some brief steps for each option:

• 
  WSL: You need to activate WSL and install the Ubuntu distribution from the Microsoft Store. Then, you can download the OpenFoam package for Ubuntu and install it using the commands provided in the OpenFOAM website. You also need to install some additional dependencies and configure your bash shell to run OpenFOAM. To enable graphical applications, such as ParaView, you need to install an X server software, such as VcXsrv¹²³.
• VM: You need to download and install VirtualBox, and then create a new virtual machine with Ubuntu as the operating system. Then, you can follow the same steps as for WSL to install OpenFOAM on Ubuntu. Alternatively, you can download a pre-configured VM image with OpenFOAM from the OpenFOAM website and import it into VirtualBox⁴⁵.

Is threre possibilty to install OpenFoam directly on Windows ?

No, there is no possibility to install OpenFoam directly on Windows, as OpenFoam is a Linux-based software that requires a Linux environment to run. However, as I mentioned before, you can use WSL or VM to create a Linux environment on your Windows system and install OpenFoam there. These methods are well-documented and supported by the OpenFoam community¹²³. 

How to install OpenFoam on Windows by the WSL method?

To install OpenFoam on Windows by the WSL method, you need to follow these steps:

• Activate Windows Subsystem for Linux (WSL) and install the Ubuntu distribution from the Microsoft Store¹.
• Launch the Ubuntu distribution through WSL and download the OpenFoam package for Ubuntu using the commands provided in the OpenFOAM website.
• Install some additional dependencies and configure your bash shell to run OpenFOAM¹.
• Install an X server software, such as VcXsrv, to enable graphical applications, such as ParaView¹²³.

What is the difference between WSL and VM?

WSL and VM are two different ways to run Linux applications on Windows. WSL stands for Windows Subsystem for Linux, and VM stands for Virtual Machine. Here are some of the main differences between them:

• WSL uses the Windows kernel to implement Linux system calls, while VM uses a separate Linux kernel running on a hypervisor¹².
• WSL has better performance and integration with Windows, while VM has better compatibility and isolation with Linux¹².
• WSL is more lightweight and easy to set up, while VM is more flexible and customizable¹²³.
• WSL supports only command-line applications, while VM supports both command-line and graphical applications¹²⁴.

What are the advantages of using WSL over VM?

Some of the advantages of using WSL over VM are:

• WSL is more lightweight and easy to set up than VM, as it does not require allocating resources from the host machine or installing heavy ISO files¹².
• WSL has better performance and integration with Windows than VM, as it uses the Windows kernel to implement Linux system calls instead of a separate Linux kernel running on a hypervisor³⁴.
• WSL is faster to launch and more convenient to use than VM, as it does not need to boot a full Linux system or switch between different machines⁴².
• WSL supports most of the Linux command-line tools, languages, and compilers that developers need, while VM supports both command-line and graphical applications³⁴.

What are the advantages of using VM over WSL?

Some of the advantages of using VM over WSL are:

• VM is more compatible and isolated with Linux than WSL, as it uses a separate Linux kernel running on a hypervisor instead of the Windows kernel to implement Linux system calls¹².
• VM is more flexible and customizable than WSL, as it allows you to configure virtual devices, allocate resources, and install different operating systems on the same machine²³⁴.
• VM supports both command-line and graphical applications, while WSL supports only command-line applications (although Microsoft promises support for GUI apps in WSL in the future)¹²⁵.
• VM gives you a more authentic Linux experience than WSL, as it runs a full Linux system with all the processes and features that Linux has to offer²⁵.

💥💥💥 What is k-epsilon model in Ansys Fluent and what is used for ?

 The k-epsilon model is a type of turbulence model that is used in computational fluid dynamics (CFD) simulations. It is based on two transport equations for the turbulence kinetic energy (k) and its dissipation rate (epsilon). The k-epsilon model can capture the effects of mean velocity gradients, buoyancy, compressibility, and heat and mass transfer on the turbulent flow. It is one of the most widely used turbulence models in engineering applications because of its robustness, economy, and reasonable accuracy for a wide range of flows¹².

Ansys Fluent is a software package that allows users to perform CFD simulations using various turbulence models, including the k-epsilon model. Ansys Fluent provides three variants of the k-epsilon model: the standard, the RNG, and the realizable k-epsilon models. Each variant has different methods of calculating the turbulent viscosity, the turbulent Prandtl numbers, and the generation and destruction terms in the epsilon equation³. The k-epsilon model in Ansys Fluent can be used for modeling internal and external flows, separated flows, jets, flows with high-pressure gradients, and flows through curved geometries⁴⁵.

Source:

(1) ANSYS FLUENT 12.0 User's Guide - 33.3.3 Viscous Model Dialog Box - ENEA. https://www.afs.enea.it/project/neptunius/docs/fluent/html/ug/node1022.htm.

(2) 12.4.1 Standard k Model Overview - University of Washington. https://courses.washington.edu/mengr544/handouts-10/Fluent-k-epsilon.pdf.

(3) ANSYS FLUENT 12.0 User's Guide - 12.4 Steps in Using a Turbulence Model. https://www.afs.enea.it/project/neptunius/docs/fluent/html/ug/node411.htm.

(4) Difference between K-epsilon and K-omega Turbulence Model - Ansys .... https://forum.ansys.com/forums/topic/difference-between-k-epsilon-and-k-omega-turbulence-model/.

(5) k-epsilon and Laminar differrence - Ansys Learning Forum. https://forum.ansys.com/forums/topic/k-epsilon-and-laminar-differrence/.

What are the limitations of k-epsilon model?

The k-epsilon model is a popular and widely used turbulence model, but it also has some limitations that affect its accuracy and applicability. Some of the limitations are:

- It assumes that the turbulence is isotropic, which means that the ratio between Reynolds stress and mean rate of deformation is the same in all directions. This is not true for flows with strong anisotropy, such as swirling, rotating, or curved flows²³.

- It requires a high Reynolds number, which means that the inertial forces are much larger than the viscous forces. This is not true for flows near the wall, where the viscous effects are important. Therefore, the k-epsilon model needs a near-wall treatment, such as wall functions or low-Reynolds number corrections, to account for the wall effects¹².

- It does not capture the effects of history and rapid distortion on the turbulence. This means that the model cannot handle flows with large adverse pressure gradients, boundary layer separation, or shock waves. Therefore, the k-epsilon model may under-predict the extent of recirculation zones or over-predict the turbulent kinetic energy at stagnation points¹⁴⁵.

These limitations can be overcome by using more advanced turbulence models, such as Reynolds stress models, large eddy simulation, or detached eddy simulation, which can account for the effects of anisotropy, compressibility, history, and distortion on the turbulence. However, these models are also more complex, computationally expensive, and sensitive to initial and boundary conditions. Therefore, the choice of the turbulence model depends on the trade-off between accuracy and efficiency for a given flow problem.

Source: 

(1) The k-ε Turbulence Model - COMSOL Multiphysics. https://doc.comsol.com/5.5/doc/com.comsol.help.cfd/cfd_ug_fluidflow_single.06.088.html.

(2) OpenFOAM: User Guide: k-epsilon. https://www.openfoam.com/documentation/guides/latest/doc/guide-turbulence-ras-k-epsilon.html.

(3) K-epsilon turbulence model - Wikipedia. https://en.wikipedia.org/wiki/K-epsilon_turbulence_model.

(4) Validation and analysis of turbulence modeling in pipe elbow under .... https://link.springer.com/article/10.1007/s40430-022-03899-9.

(5) Limitations and empirical extensions of the k-epsilon model as applied .... https://ntrs.nasa.gov/search.jsp?R=19840035309.

Is k-epsilon model good for low quality meshes ?

The k-epsilon model is not very suitable for low quality meshes, especially near the wall regions. This is because the k-epsilon model requires a high Reynolds number, which means that the inertial forces are much larger than the viscous forces. This is not true for flows near the wall, where the viscous effects are important. Therefore, the k-epsilon model needs a near-wall treatment, such as wall functions or low-Reynolds number corrections, to account for the wall effects¹². However, these treatments are sensitive to the mesh quality and resolution, and may not work well for coarse or skewed meshes³⁴.

A better alternative for low quality meshes is the k-omega model, which is more robust and accurate for near-wall flows. The k-omega model does not require a high Reynolds number, and can handle flows with large adverse pressure gradients, boundary layer separation, or shock waves. The k-omega model is also good in resolving internal flows, separated flows and jets and flows with high-pressure gradient and also internal flows through curved geometries³. However, the k-omega model may be more computationally expensive and sensitive to initial and boundary conditions than the k-epsilon model². Therefore, the choice of the turbulence model depends on the trade-off between accuracy and efficiency for a given flow problem.

Source: 

(1) K-epsilon Turbulence Model | Global Settings | SimScale. https://www.simscale.com/docs/simulation-setup/global-settings/k-epsilon/.

(2) K-epsilon turbulence model - Wikipedia. https://en.wikipedia.org/wiki/K-epsilon_turbulence_model.

(3) Difference between K-epsilon and K-omega Turbulence Model. https://forum.ansys.com/forums/topic/difference-between-k-epsilon-and-k-omega-turbulence-model/.

(4) k-epsilon model: which criteria do I have to meet for the near wall mesh?. https://forum.ansys.com/forums/topic/k-epsilon-model-which-criteria-do-i-have-to-meet-for-the-near-wall-mesh/.

What is the difference between k-epsilon and k-omega models?

The k-epsilon and k-omega models are both types of turbulence models that are used in computational fluid dynamics (CFD) simulations. They are based on two transport equations for the turbulence kinetic energy (k) and either its dissipation rate (epsilon) or its specific dissipation rate (omega). The main difference between them is that the k-epsilon model is more suitable for flow away from the wall, while the k-omega model is more accurate for near-wall flow regions¹².

The k-epsilon model assumes that the turbulence is isotropic, which means that the ratio between Reynolds stress and mean rate of deformation is the same in all directions. This is not true for flows with strong anisotropy, such as swirling, rotating, or curved flows. The k-epsilon model also requires a high Reynolds number, which means that the inertial forces are much larger than the viscous forces. This is not true for flows near the wall, where the viscous effects are important. Therefore, the k-epsilon model needs a near-wall treatment, such as wall functions or low-Reynolds number corrections, to account for the wall effects. However, these treatments are sensitive to the mesh quality and resolution, and may not work well for coarse or skewed meshes¹².

The k-omega model does not assume isotropy, and can handle flows with large adverse pressure gradients, boundary layer separation, or shock waves. The k-omega model does not require a high Reynolds number, and can resolve the viscous layer without wall functions. The k-omega model is also good in resolving internal flows, separated flows, jets, flows with high-pressure gradients, and flows through curved geometries¹³. However, the k-omega model may be more computationally expensive and sensitive to initial and boundary conditions than the k-epsilon model².

A common variant of the k-omega model is the SST (shear stress transport) model, which blends the k-epsilon and k-omega models to achieve the best of both worlds. The SST model uses the k-omega formulation in the near-wall region and switches to the k-epsilon formulation in the free-stream region. The SST model can capture the effects of mean velocity gradients, buoyancy, compressibility, and heat and mass transfer on the turbulent flow. The SST model is one of the most widely used turbulence models in engineering applications because of its robustness, economy, and reasonable accuracy for a wide range of flows¹⁴.

Source: 

(1) Which Turbulence Model Should I Choose for My CFD Application?. https://www.comsol.com/blogs/which-turbulence-model-should-choose-cfd-application/.

(2) Use of k-epsilon and k-omega Models - CFD Online. https://www.cfd-online.com/Forums/main/75554-use-k-epsilon-k-omega-models.html.

(3) Difference between K-epsilon and K-omega Turbulence Model. https://forum.ansys.com/forums/topic/difference-between-k-epsilon-and-k-omega-turbulence-model/.

(4) What is the difference between k-epsilon and k-omega model .... https://rampfest-hudson.com/what-is-the-difference-between-k-epsilon-and-k-omega-model/.

(5) What is the difference between k-epsilon and K-Omega?. https://vidque.com/what-is-the-difference-between-k-epsilon-and-k-omega/.

🎅 🎅 🎅 What are the main differences between Ansys Fluent and CFX ?

Ansys Fluent and CFX are both powerful computational fluid dynamics (CFD) solvers, but they have some differences in their features, capabilities, and applications. Here are some of the main differences between them:

- Fluent uses a cell-centered approach while CFX uses a vertex-centered approach. This means that Fluent can handle more complex mesh topologies, such as polyhedral and cutcell meshes, while CFX is limited to tetrahedral and hexahedral meshes¹².

- Fluent has post-processing capabilities of its own while CFX needs a dedicated post-processor, such as CFD-Post¹². Fluent also has more options for mesh adaption and simulation acceleration with a GPU².

- CFX has a built-in expression language (CEL) that allows users to define algebraic equations and monitor them during the run¹². Fluent requires user-defined functions (UDFs) for customization, which can be more challenging for beginners¹.

- CFX is more suitable for turbomachinery applications, as it has specialized features for rotating machinery, such as frozen rotor and transient blade row models²³. Fluent is more preferred for high Mach number flows, such as supersonic and hypersonic flows².

Source: 

(1) What are the differences between CFX and Fluent? - Ansys Learning Forum. https://forum.ansys.com/forums/topic/what-are-the-differences-between-cfx-and-fluent/.

(2) Compare Ansys CFX vs. Ansys Fluent | G2. https://www.g2.com/compare/ansys-cfx-vs-ansys-fluent.

(3) Reply To: What are the differences between CFX and Fluent?. https://forum.ansys.com/forums/reply/58903/.

(4) What are the differences between CFX and Fluent? - Ansys Learning Forum. https://forum.ansys.com/forums/topic/what-are-the-differences-between-cfx-and-fluent/.

(5) Compare Ansys CFX vs. Ansys Fluent | G2. https://www.g2.com/compare/ansys-cfx-vs-ansys-fluent.

(6) Reply To: What are the differences between CFX and Fluent?. https://forum.ansys.com/forums/reply/58903/.

(7) Getty Images. https://www.gettyimages.com/detail/news-photo/in-this-photo-illustration-the-ansys-logo-seen-displayed-on-news-photo/1212478964. 

Which one is more popular in industry?

That's a good question, but it's not easy to answer. The popularity of Ansys Fluent and CFX may depend on the industry, the region, the application, and the preference of the users. According to some sources, Fluent is more widely used than CFX in general, especially in the aerospace, automotive, and chemical industries¹². However, CFX has a strong presence in the power generation and turbomachinery sectors¹³. Ultimately, both solvers have their strengths and weaknesses, and the best choice may depend on the specific problem and the user's experience.

Source: 

(1) What are the differences between CFX and Fluent? - Ansys Learning Forum. https://forum.ansys.com/forums/topic/what-are-the-differences-between-cfx-and-fluent/.

(2) Ansys CFX or Ansys Fluent : r/CFD - Reddit. https://www.reddit.com/r/CFD/comments/yp3vf0/ansys_cfx_or_ansys_fluent/.

(3) Compare Ansys CFX vs. Ansys Fluent | G2. https://www.g2.com/compare/ansys-cfx-vs-ansys-fluent.

Which one  is more accurate on Conjugate Heat Transfer analysis? Ansys Fluent or CFX?

Conjugate heat transfer (CHT) analysis is a type of simulation that models the heat transfer within and between fluids and solids¹. The accuracy of CHT analysis depends on many factors, such as the mesh quality, the boundary conditions, the solver settings, and the physical models²³. Therefore, it is not possible to say which solver, Ansys Fluent or CFX, is more accurate in general, as the results may vary depending on the specific problem and the user's expertise.

However, some studies have compared the performance of Fluent and CFX for different CHT applications, such as liquid-cooled IGBT assemblies⁴, heat exchangers⁵, and turbomachinery. These studies have shown that both solvers can produce similar results, but they may have different advantages and disadvantages in terms of computational efficiency, convergence behavior, and ease of use. For example, Fluent may have more options for mesh adaption and acceleration with a GPU², while CFX may have more features for rotating machinery and expression language³.

Therefore, the best way to determine which solver is more accurate for your CHT analysis is to try both of them and compare the results with experimental data or analytical solutions, if available. You can also consult the Ansys documentation and forums for more guidance and tips on how to use Fluent and CFX for CHT analysis. 😊

Source:

(1) How does the "Loosely Coupled Conjugate Heat Transfer" function work .... https://forum.ansys.com/forums/topic/how-does-the-loosely-coupled-conjugate-heat-transfer-function-work/.

(2) THERMAL ANALYSIS/CONJUGATE HEAT TRANSFER ANALYSIS IN ANSYS CFX THERMAL .... https://www.youtube.com/watch?v=Jx39uFHtHbs.

(3) CHT analysis using Fluent Solver | Ansys Courses. https://courses.ansys.com/index.php/courses/conjugate-heat-transfer/lessons/cht-analysis-of-liquid-cooled-igbt-assembly/topic/part-3-using-fluent-solver/.

(4) CHT Analysis in Ansys Discovery | Ansys Courses. https://courses.ansys.com/index.php/courses/conjugate-heat-transfer/.

(5) Ansys Fluent Heat Transfer Modeling | Ansys Training. https://www.ansys.com/training-center/course-catalog/fluids/ansys-fluent-heat-transfer-modeling.

(6) CHT Analysis in Ansys Discovery | Ansys Courses. https://courses.ansys.com/index.php/courses/conjugate-heat-transfer/.

(7) Ansys Fluent Heat Transfer Modeling | Ansys Training. https://www.ansys.com/training-center/course-catalog/fluids/ansys-fluent-heat-transfer-modeling.

(8) CHT analysis using Fluent Solver | Ansys Courses. https://courses.ansys.com/index.php/courses/conjugate-heat-transfer/lessons/cht-analysis-of-liquid-cooled-igbt-assembly/topic/part-3-using-fluent-solver/.

(9) CHT analysis using Fluent Solver | Ansys Courses. https://courses.ansys.com/index.php/courses/conjugate-heat-transfer/lessons/cht-analysis-of-liquid-cooled-igbt-assembly/topic/part-3-using-fluent-solver/.

What is the difference between Fluent and Star-CCM+?

Fluent and Star-CCM+ are both commercial computational fluid dynamics (CFD) software packages developed by Ansys and Siemens, respectively. They have some similarities and differences in their features, capabilities, and applications. Here are some of the main differences between them:

- Fluent uses a cell-centered finite volume method while Star-CCM+ uses a vertex-centered finite volume method. This means that Fluent can handle more complex mesh topologies, such as polyhedral and cutcell meshes, while Star-CCM+ is limited to tetrahedral and hexahedral meshes¹².

- Fluent has its own post-processing capabilities while Star-CCM+ requires a separate post-processor, such as CFD-Post or FieldView¹². Fluent also has more options for mesh adaption and simulation acceleration with a GPU².

- Star-CCM+ has a built-in expression language (CEL) that allows users to define algebraic equations and monitor them during the run¹². Fluent requires user-defined functions (UDFs) for customization, which can be more challenging for beginners¹.

- Star-CCM+ is more suitable for turbomachinery applications, as it has specialized features for rotating machinery, such as frozen rotor and transient blade row models²³. Fluent is more preferred for high Mach number flows, such as supersonic and hypersonic flows².

Source: 

(1) Siemens STAR CCM+ Vs. ANSYS Fluent | Resolved Analytics. https://www.resolvedanalytics.com/theflux/comparing-cfd-software-part-4-comprehensive-cfd-software-packages.

(2) Fluent vs Star CCM vs Openfoam -- CFD Online Discussion Forums. https://www.cfd-online.com/Forums/ansys/213810-fluent-vs-star-ccm-vs-openfoam.html.

(3) Compare Ansys Fluent vs. Simcenter STAR-CCM+ | G2. https://www.g2.com/compare/ansys-fluent-vs-simcenter-star-ccm.

(4) Siemens STAR CCM+ Vs. ANSYS Fluent | Resolved Analytics. https://www.resolvedanalytics.com/theflux/comparing-cfd-software-part-4-comprehensive-cfd-software-packages.

(5) Fluent vs Star CCM vs Openfoam -- CFD Online Discussion Forums. https://www.cfd-online.com/Forums/ansys/213810-fluent-vs-star-ccm-vs-openfoam.html.

(6) Comparison of STAR-CCM+ and ANSYS Fluent for Simulating Indoor Airflows. https://engineering.purdue.edu/~yanchen/paper/2018-1.pdf.