# Richard Smith's blog

## CFD Flow Volumes and Solid Models

Solid modeling is the dominant form of virtual object representation underpinning nearly all 3D Computer-Aided Design (CAD) systems. The strength of a solid model is that it defines a water tight (manifold) unambiguous object which implicitly delineates between the inside and the outside of an object simply by the alignment of the boundaries (B-rep or BREP) that define it. This makes solid modeling an ideal basis for virtual analysis techniques, e.g., stress analysis and Computational Fluid Dynamics (CFD). Also solid modeling provides a relatively straightforward path to manufacture through CNC machines and, more recently, 3D printing.

Boundary Representation (B-rep or BREP)

## Sports, Fluid Flow, and Spheres

Given how easy it is to define a sphere with a single value (radius) you'd think the fluid flow around a sphere would be simple too, right? However, as with many innocuous looking fluid problems, our intuition is wrong. The resulting flow characteristics, especially the drag variation with fluid velocity, are wild. Why does this matter? One word - sports.

Reynolds number 10,000, large unsteady asymmetric recirculation

## Laminar vs Turbulent Flow Over Airfoils

Which is more efficient: laminar or turbulent flow over an airfoil? Find out in this simple Computational Fluid Dynamics (CFD) study.

Velocity Magnitude Contours

## 12 CFD Tips for a Productive New Year

To make best use of Computational Fluid Dynamics (CFD) software there are a number of key concepts to keep in mind. Based on my experiences and those of Caedium Professional users here's a selection of the important issues to consider while you prepare and perform your own CFD simulations.

## Underwater Kites Generate Electricity

There are some fascinating proposals for power generation using tethered kites and balloons, so why not investigate the equivalent of underwater kites for generating power? Why not indeed, because that is exactly what two independent teams of researchers are doing, one from Minesto, Sweden and the other from Worcester Polytechnic Institute, USA [Source: Discovery News].

## CFD Explains Santa's Whereabouts

For Santa to meet his aggressive toy delivery schedule on Xmas eve it would appear that he has to travel impossibly fast. Yet there are often sightings of Santa on his rounds, which seems to contradict this high speed hypothesis. The only way to explain Santa's whereabouts is that he uses a Reality Distortion Field (RDF). Santa's special projects division (known as Elf Works) is responsible for the RDF and it remains tight lipped on how it works. However, with the help of Computational Fluid Dynamics (CFD) we have pieced together how the RDF might work.

Iso-surfaces of velocity magnitude

## Elephant Literally Collapses into a Puddle

What happens if by suspending the laws of physics an elephant was to instantaneously transform into water? Given that approximately 70% of an elephant is already water we just need to magically convert the remaining 30% - I'll leave that as your homework assignment. Then the results would probably look something like this Volume Of Fluid (VOF free-surface) Computational Fluid Dynamics (CFD) simulation.

Elephant collapses into a puddle

## Flying Jellyfish

It seems that a day doesn't go by without the announcement of a new and innovative flying drone. Joining the throng we have researchers from New York University (NYU) who have developed a drone that flies like a jellyfish, but without the sting! Their work was showcased at the 2013 APS Division of Fluid Dynamics Meeting.

## Airplane + Helicopter + Hovercraft + Airship = ESTOLAS

What do you get if you cross an airplane with a helicopter, with a hovercraft, with an airship? The European Commission's Extremely Short Take Off and Landing on Any Surface (ESTOLAS) project.

## Inspiration from Spinning Maple Seeds

Looking to nature for inspiration (biomimicry) is nothing new. I've already covered turbine blades inspired by humpback whale fins and drag-reducing textures that mimic shark skin, so next up we have the elegant spinning maple seed.

Leading edge vortex shown by streamlines

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## Recent blog posts

- CFD Benefits From 3D Printing
- Cutting Planes Reveal Yet More Hidden CFD Secrets
- Clipping Planes Reveal Even More Hidden CFD Secrets
- Symmetry Reveals More Hidden CFD Secrets
- No Colorful Fluid Dynamic Paint Yet
- Colorful Fluid Dynamic Paint
- Transparency Reveals Hidden CFD Secrets
- Challenging Orthodox Truck Design
- Caedium CFD Sneak Peek: Conjugate Heat Transfer
- 10 Design Rules For Fluid Dynamics