Richard Smith's blog

Physics and Solver Setup for CFD

A Computational Fluid Dynamics (CFD) simulation requires that you configure physics and solver values based on your knowledge of your fluid application. Primarily this setup stage requires defining your fluid state, reference values (e.g., velocity), initial values, boundary conditions, and solver parameters. Follow along as I describe each stage and relate it to a CFD simulation of the external airflow over an idealized car.

CFD Simulation of the External Airflow Over an Idealized CarCFD Simulation of the External Airflow Over an Idealized CarPressure iso-surfaces

Meshing in a Single, Integrated Simulation Environment

Meshing in a single, integrated simulation environment (e.g., Caedium) for Computational Fluid Dynamics (CFD) is different, in a good way, from meshing in a dedicated mesh or post-processing tool. An integrated CFD simulation environment has the standard meshing tools, but in addition upstream you have a full geometry engine to create and modify geometry as needed, and downstream you can use the same meshing tools for visualization, such as seeds for streamlines and surfaces for results interpolation. You are not forced into a linear progression through the CFD simulation process, because often it requires multiple visits backwards and forwards (non-linear) through the tool chain to get to a final result. Also the visualization of mesh metrics (e.g., surface mesh quality) is identical to general flow field visualization (e.g., pressure), which minimizes the number of concepts you need to learn.

Single, Integrated CFD Simulation EnvironmentSingle, Integrated CFD Simulation Environment

CFD Geometry Creation

Given the option, it is often better to create geometry specifically for your Computational Fluid Dynamics (CFD) simulations. It is even better if your CFD system supports geometry creation. Then you can stay within a single integrated simulation environment for your entire task without the need to learn or purchase additional software packages.

Two Flow Volumes Created Ready For CFD SimulationTwo Flow Volumes Created Ready For CFD Simulation

CFD Prefers NURBS Over STL

Let me explain why, given the option, you should prefer analytic geometry (e.g., NURBS) over faceted geometry (e.g., STL) for Computational Fluid Dynamics (CFD).

CFD Mesh for a Faceted WheelCFD Mesh for a Faceted WheelNote spurious flat spots

DIY CFD

If fluid flow is a primary driver for your design project then Computational Fluid Dynamics (CFD) is likely to be a cost effective way to help meet your goals. You could outsource your CFD to consultants, but in the long run it usually pays to do it yourself.

Dust Collector CFD SimulationDust Collector CFD Simulation

How to Control Your CFD Simulations in Caedium

The Caedium Simulation Control Toolbar provides the controls to initialize and run your Computational Fluid Dynamics (CFD) simulations. Take a moment to learn how to use these simulation controls effectively.

Caedium CFD SimulationCaedium CFD SimulationAfter a single step of iterations

How to Control Your CFD Mesh in Caedium

The Caedium Accuracy tool is largely responsible for determining the accuracy of your Computational Fluid Dynamics (CFD) simulations by imposing constraints on the underlying computational mesh or grid. Therefore, it's worth spending a moment to learn how the Accuracy tool in Caedium works.

Volume Mesh ElementsVolume Mesh Elements

Walkalong Tumblewing Meets CFD

To complete this series of Computational Fluid Dynamics (CFD) on simple rotating paper wings, we now turn our attention to the walkalong tumblewing.

CFD Simulation of a Walkalong TumblewingCFD Simulation of a Walkalong TumblewingVelocity vectors at 0 degrees

Tumblewing Meets CFD

Although a sheet of paper can be made to fly by spinning, it isn't always reliable. By adding winglets and flaps with 4 simple folds we can improve the stability of the wing and in so doing produce a tumblewing. How do the aerodynamics of a tumblewing compare with a sheet of paper? It just so happens Computational Fluid Dynamics (CFD) can help, just as it did with the simulation of the spinning sheet of paper.

CFD Simulation of a Rotating TumblewingCFD Simulation of a Rotating TumblewingPressure iso-surfaces at 90 degrees

Spinning Paper Sheet Meets CFD

I don’t think anyone would argue with the fact that paper airplanes are simple (and fun!), but what is the simplest paper airplane that can still fly? I give you a single rectangular piece of paper without any folds that will gently spin around its longest horizontal axis if released with a long edge parallel to the ground. Next, what is the simplest Computational Fluid Dynamics (CFD) method that can capture the essence of the spinning paper? I give you the Moving Reference Frame (MRF, also known as the frozen rotor method) option for CFD. Combine the two and you arrive at an interesting simulation of a simple phenomenon.

CFD Simulation of a Rotating Paper SheetCFD Simulation of a Rotating Paper SheetVelocity vectors at 90 degrees

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