Technical Article

# A Look Into Computational Fluid Dynamics

February 22, 2021 by Sara McCaslin

## Learn about computational fluid dynamics and how it is used in various sectors across the manufacturing industry.

Computational fluid dynamics is used in a variety of industries and applications.

From engineering efficient ways to keep an SoC (System on a Chip) cool enough to function properly to helping race cars shave a few more seconds of their time, computational fluid dynamics remains a powerful tool for simulation and optimization.

### What is Computational Fluid Dynamics?

Computational fluid dynamics (often abbreviated CFD) is a numerical simulation and modeling tool based on fluid dynamics principles. It leverages numerical methods and algorithms to solve problems that involve the flow of fluids.

As part of this explanation, it is important to keep in mind that fluids are not limited to liquids and include gases like air. In fact, CFD can be used to simulate fluid flow, chemical reactions, phase changes, heat and mass transfer, and liquids, gases, and solids as they flow through a system.

#### Governing Equations and Key Variables

The primary governing equations involved are the continuity equation (conservation of mass), Newton’s Second Law (conservation of momentum), and the First Law of Thermodynamics (conservation of energy). The key variables are velocity, pressure, and absolute temperature, along with density, thermal conductivity, enthalpy, and viscosity.

##### Flow simulation can provide streamlines the clearly illustrate the flow of fluid particles through a system as they interact with both solids, other liquids, and heat. Image courtesy of Autodesk.

CFD simulation aims to know the velocity, pressure, and temperature at every point within the flow regime.

#### Results of CFD Modeling

CFD modeling results can be post-processed to provide informative visualizations that can include streamlines representing the velocity (speed and direction) of fluid flow, maps showing temperature distributions, and particle tracing that shows the movement of a single fluid particle (to name a few).

With the continuing increase in computing power and graphics capabilities, visualizations can be manipulated in 3D and used to generate compelling images and videos, and animations to help users interpret the data and share it with non-technical audiences.

### What is the Most Widely Used Computational Fluid Dynamics Model?

The most widely used model in CFD is FVM, which stands for Finite Volume Model. Strictly speaking, it is a discretization method whereby the fluid volume is divided into finite control volumes. These individual control volumes are centered around a node located at the centroid of the volume.

The differential form of the model’s governing equations is integrated, and the variable of interest between the centroids is obtained using interpolation profiles. The resulting equation, known as the discretization or discretized equation, then expresses the conservation principle for the variable inside the control volume.

FVM is quite popular because of its versatility and the fact that the solution will satisfy the conservation of quantities such as energy, species, momentum, or mass. Conservation is exactly satisfied for both individual control volumes and the entire computational domain.

##### CFD finds extensive application in thermal management of electronics, as in this example of a modular chassis used for mission-critical applications. Image courtesy of ANSYS.

Other methods include the Finite Element Method (FEM), typically associated with solid mechanics, and Finite Element Analysis (FEA) but can also be used with CFD.

There is also the FDM or Finite-Different Method; this particular method is not as widely used for CFD as FVM and FEM but does find extensive application in weather calculations, seismology, and special effects for films and television.

### What is Computational Fluid Dynamics Used For?

In a general sense, computational fluid dynamics optimize, analyze, and verify designs involving fluid flow before expensive prototypes are manufactured. Costly physical tests are performed on those prototypes.

More specifically, CFD can be used for:

• Battery simulation
• Electric motor cooling
• Rheology
• Energy efficiency
• Thermal management
• Fluid-structure interaction
• Shape optimization
• Turbulence modeling
• HVAC
• Aircraft / Aerospace design
• Automotive design

More specifically, CFD is being used to:

In addition, CFD can be used with FEA (Finite Element Analysis) to capture complex interactions among fluids, thermodynamics, heat, electricity, magnetism, and structural analysis.

### Computational Fluid Dynamics Software

There are a wide variety of CFD software packages on the market. For example, ANSYS Fluent and CFX are two well-known CFD software packages. There is also PTC Creo Simulation, Siemens Simcenter STAR-CCM+, Flotherm, and Autodesk CFD.

However, not all CFD packages are commercial: OpenFOAM is a free, open-source CFD package that runs on Linux, macOS, and Windows 10. In addition, there are browser-based CFD systems such as SimScale, which happens to be based on OpenFOAM.There are also powerful post-processing tools such as Ceetron Desktop Components that bring life to CFD solution data.

CFD is used in many different industries, assisting in optimizing designs and saving time and money when it comes to prototyping and physical testing.

From fuel nozzles in jet engines and race car bodies to soft robotics and data center air cooling systems, CFD has proven invaluable time and time again during the engineering process.

When done properly, it can reveal the behavior of fluids and how they interact with solids, heat, phase changes, and chemical reactions.

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