Richard Smith's blog

Ludwig Prandtl: Real Fluids Explained

Prior to Ludwig Prandtl (1875 - 1953), analytic analysis of fluids with an early form of Computational Fluid Dynamics (CFD), confined to paper and pencil, assumed ideal inviscid potential flow. However, this approach was less than ideal at predicting drag (d'Alembert's paradox) and airfoil stall, which was a pressing problem for engineers at the dawn of powered heavier-than-air flight. Prandtl developed practical theories for real fluids that found favor with aircraft designers. Also, like Osborne Reynolds before him, Prandtl had a non-dimensional number, the Prandtl Number, named after him.

The Life and Times of Ludwig PrandtlTold by Eberhard Bodenschatz

Osborne Reynolds: A Giant in Fluid Dynamics

If you have performed simulations with industrial Computational Fluid Dynamics (CFD) and thereby solved the Reynolds-Averaged Navier-Stokes (RANS) equations, or if you have compared scaled fluid dynamic experiments with their full size counterparts using the Reynolds Number, then you have benefited from the groundbreaking work of Osborne Reynolds (1842 - 1912).

The Life and Times of Osborne ReynoldsTold by Brian Launder (himself a giant in turbulence modeling)

Sliver Treatment Strategies for CFD

Extremely thin, high-aspect-ratio geometry faces (also known as slivers) can cause problems for meshing and adversely affect Computational Fluid Dynamics (CFD) simulation stability. Learn some strategies to identify and deal with slivers to maximize your CFD productivity.

Sliver SurfaceSliver SurfaceProduces poor surface mesh elements (blue)

How to Fix Small Acute Angles for CFD

Small acute angles in your geometry, such as those found where a tangential surface meets a cylindrical surface, can lead to poor results from your Computational Fluid Dynamics (CFD) simulation. Keep reading to learn how to identify and remedy acute angles.

Small Acute Angled Geometry FeatureSmall Acute Angled Geometry FeatureProduces poor mesh elements

Small Feature Removal for CFD

In preparing geometry for a Computational Fluid Dynamics (CFD) simulation you will sometimes find small geometry features (edges and faces) that are irrelevant for your simulation. To resolve a small irrelevant feature would require a large number of small mesh cells that would be a waste of precious computing resources. Keep reading to find out how to detect and remove such features.

Small Feature Causing Unnecessary Mesh ClusterSmall Feature Causing Unnecessary Mesh Cluster

Fluid Visualization in Nature

On the rare occasions that CFD-ers unhitch from their Matrix and venture outdoors, it is only to see that nature is copying the visualization techniques we take for granted in Computational Fluid Dynamics (CFD).

Flowing Stream Visualization Via SiltFlowing Stream Visualization Via Silt

Design is Compromise

Rare is the occasion when you can design a new widget without constraints, in fact I'd argue that it's not only rare but it's never. Engineering design is all about compromise. Take a Formula 1 car as an example, its success on the race track is overwhelmingly governed by the efficiency of its aerodynamics - yet even though it's so important the external aerodynamics for F1 cars is an exercise in compromise. Compromise to satisfy regulations, which are in place to actually slow cars down for safety's sake. Compromise to ensure that the wheels are supported correctly relative to the road. Compromise to ensure that the engine gets enough inlet air, cooling air, and a path to eject exhaust. Compromise in terms of the driver's safety structure. Compromise after compromise. No one element of a design can be optimized without considering the effect on the overall design.

F1 is a Compromise: 2007 Honda F1 CarF1 is a Compromise: 2007 Honda F1 Car

CFD Is Not Enough

Although most Computational Fluid Dynamics (CFD) software vendors would have you believe otherwise, a CFD tool alone does not a successful product make. Consider that Computer Aided Engineering (CAE) tools, such as CFD, are widely available yet some engineering organizations succeed and others fail. An excellent example is Formula 1, where all the teams use the latest state-of-the-art CFD tools, but some teams routinely win while others struggle. Clearly the governing factor is not the CFD tool they are using. The difference is the overall design and development process that encompasses CFD and, in no small part, the ingenuity of the engineers driving the process.

CFD Simulation of an Open Wheel RacecarCFD Simulation of an Open Wheel Racecar

All CFD Should Be Upfront CFD

There is a category of Computational Fluid Dynamics (CFD) called Upfront CFD. It typically refers to CFD software embedded in and launched from within CAD systems. Upfront, the term, also implies that it is something that happens before something else, maybe prior to detailed design in the design process - even during the concept design phase. I think the use of the term Upfront CFD is great marketing, but a poor differentiator of the actual CFD software.

Concept Design Phase CFDConcept Design Phase CFDParametric study of pipe diameter

Speed Up CFD with Symmetry and Cyclic Conditions

Symmetry (or planar symmetry) and cyclic (or rotational symmetry) boundary conditions for Computational Fluid Dynamics (CFD) can often save you 50% or more in simulation turnaround time. Alternatively you can use the freed up memory to run more accurate simulations with more mesh cells clustered in areas of interest. Clearly these simulations are worth considering if your model satisfies the symmetry or cyclic criteria.

Symmetric Flow Volume for the External Aerodynamic CFD Analysis of a CarSymmetric Flow Volume for the External Aerodynamic CFD Analysis of a CarSingle symmetry plane

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