Computational Fluid Dynamics (CFD)

What is Computational Fluid Dynamics (CFD)?

Computational fluid dynamics is an engineering analysis method used to understand how fluids flow in or around an object [1]. CFD analysis uses theoretical fluid dynamics models obtained from the Navier-Stokes equation to simulate how a specific fluid will flow around an object [1]. Other CFD software use the Lattice Boltzmann Method to solve CFD simulations [2]. By doing CFD analysis on a part you can drastically reduce the amount of prototypes and lower the development cost of the final product [1]. CFD has many applications as it can be used for anything that involves a fluid in motion. CFD can be used to simulate incompressible flow, compressible flow, laminar flow, turbulent flow, mass transport, and thermal transport [2]. The most common applications of CFD are HVAC, aerodynamics, heat transfer, turbomachinery, high-performance computing (HPC), electronics cooling, cleanrooms, and pipes and valves [2].

*SimScale Compressible Flow Analysis [2]*

Computational Fluid Dynamics Software

The 6 most popular CFD software from highest to lowest popularity are Ansys, OpenFOAM, PowerFLOW, SimScale, COMSOL Multiphysics, and Autodesk CFD [3]. The most accessible CFD software for University of Waterloo students is flow simulation in Solidworks. For projects that require a high degree of accuracy, it would be best to use a dedicated CFD software such as Ansys or OpenFOAM.

Ansys

In Ansys, you can perform CFD simulations using Ansys Fluent. Ansys offers free software for students with a 64 bit version of Windows [4]. For detailed tutorials and information on how to perform CFD simulations in Ansys consult the Fluent learning modules on SimCafe's Confluence page [5].

Solidworks

In Solidworks, you can perform flow simulations on parts and assemblies. There are 2 modules that can be added to the base Solidworks Flow Simulation package that add more types of flow simulations [6]. The base Solidworks Flow Simulation package has head conduction in solids, radiation, time-dependent, gravity, rotation, and free surface simulation features. The HVAC Module adds heating, cooling, and ventilation tools for simulating HVAC systems and radiation [6]. The Electronics Cooling Module adds thermal management tools for simulating printed circuit boards (PCBs) and enclosures [6]. The Student Edition of Solidworks appears to come with the base Solidworks Flow Simulation package.

Starting a Flow Simulation in Solidworks

Navigate to the Solidworks Add-Ins tab and click Solidworks Flow Simulation. Once it appears select the Flow Simulation tab.

Wizard

After selecting the wizard command, follow its instructions by naming the study, selecting a configuration, selecting a unit system, entering unit precision, selecting internal or external analysis, selecting simulation features, select fluid(s), selecting wall conditions and roughness, selecting initial simulation parameters, and then selecting finish to close the wizard. Internal analysis is for simulating inside enclosed parts and assemblies and external analysis are for other parts and assemblies. If you select certain gases you can choose to add humidity to the simulation and if you add specific liquids you can add cavitation to the simulation.

Computational Domain

The computational domain is the region where the simulation will occur. This area is illustrated by a transparent box around the part or assembly. The simulation will calculate the flow in this region only, so it should be close to the size of the region you want to simulate because an excessively large region will require more time to calculate. Once the computational domain is properly sized, hide it by right clicking it in the projects tree and selecting hide.

Fluid Subdomains

If you selected multiple fluids for your simulation you must select the subdomains of where each fluid will be in the simulation.

Boundary Conditions

Boundary conditions allow the user to further define the simulation conditions. There are flow openings, pressure openings, and wall conditions. The flow opening conditions are inlet mass flow, inlet mass flux, inlet volume flow, inlet velocity, inlet mach number, outlet mass flow, outlet mass flux, outlet velocity, and outlet mach number. The pressure opening conditions are environment pressure, static pressure, and total pressure. The wall conditions are real wall and ideal wall.

Rotating Region

If you select a rotating simulation you must select the region that will rotate. Creating a rotating simulation can be quite difficult in Solidworks because you have to select a region that will rotate as you cannot select the part you want to rotate. To use a rotating region there are many small things that must be done correctly, so I would recommend viewing the centrifugal supercharger example shown below. To insert a rotating region, you must create a part that will go around the part that you want to rotate. This separate rotating region part should be constrained so it can still rotate how you would like it to in the simulation. If you are going to use a rotating region, add a velocity of 0.1m/s in the wizard going into the rotating region how you want it to flow. This will help the flow trajectories exit the rotating region.

Rotating Region Comparison Chart

*Centrifugal Supercharger Simulation Result of Patterned Points at 10000rpm and with no Inlet Velocity*	*Centrifugal Supercharger Simulation Result of Patterned Points at 10000rpm and with an Inlet Velocity of 0.1m/s*	*Centrifugal Supercharger Simulation Result of Selected Points at 10000rpm and with an Inlet Velocity of 0.1m/s*	*Centrifugal Supercharger Simulation Result of Patterned Points at 20000rpm and with an Inlet Velocity of 0.1m/s*	*Centrifugal Supercharger Simulation Result of Patterned Points at 10000rpm and with an Inlet Velocity of 0.5m/s*	*Centrifugal Supercharger Simulation Result of Patterned Points at 10000rpm and with an Inlet Velocity of 1m/s*

Goals

Goals are the parameters that you can measure during the simulation that can be plotted after running the simulation.

Results

Once the simulation is defined, run the simulation. After the results have been calculated, they will load into the flow simulation. It can take several minutes to calculate the flow simulation.

Flow Trajectories

Once the results have been calculated, you can create flow trajectories to visually demonstrate how the fluid will flow in your simulation. To create flow trajectories, you create the starting points of the flow lines and the simulation will calculate the flow. First, select if you want to use a pattern, manual selection, coordinates, or a pattern on shapes to select flow trajectory start points. After you have selected your points, you can change the appearance of the flow lines, select what data the lines show, and constrain them. To view flow lines inside a part without using section view, select the feature tree and change part transparency. To view an animation of the flow lines, right click on the flow trajectories you have made and select run. To change the scale of the flow trajectories, left click on either the top and bottom values of the scale and enter new ones.

Goal Plots

The goals selected eailier can be plotted and then exported in an Excel spreadsheet.

Gravity Flow Simulation of an Exhaust Header	Rotating Region Flow Simulation of a Centrifugal Supercharger

References

[1] SimScale. What is CFD? | Computational Fluid Dynamics?. Accessed on: Mar. 11, 2021. [Online]. Available: https://www.simscale.com/docs/simwiki/cfd-computational-fluid-dynamics/what-is-cfd-computational-fluid-dynamics/

[2] SimScale. Computational Fluid Dynamics: CFD Software. Accessed on: Mar. 15, 2021. [Online]. Available: https://www.simscale.com/product/cfd/

[3] TEC. Top Computational Fluid Dynamics (CFD) Software. Accessed on: Mar. 15, 2021. [Online]. Available: https://www3.technologyevaluation.com/sd/category/computational-fluid-dynamics-cfd

[4] Ansys. Ansys for Students. Accessed on: Mar. 29, 2021. [Online]. Available: https://www.ansys.com/academic/students

[5] SimCafe, FLUENT Learning Modules, Cornell University, Confluence, July 7, 2008. Accessed on: Mar. 29, 2021. [Online]. Available: https://confluence.cornell.edu/display/SIMULATION/FLUENT+Learning+Modules

[6] Solidworks. Solidworks Flow Simulation, Dassault Systemes. Accessed on: Mar. 16, 2021. [Online]. Available: https://www.solidworks.com/product/solidworks-flow-simulation

Contributors:

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Mayurakhi Khan	931 days ago
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srossign@uwaterloo.ca