Showing posts from 2024

Three-Dimensional Flow Fields

Every day, it seems, I understand something new I had failed to grasp before—especially in aerodynamics. For example, take this statement:   "Once again, it is necessary to remember that road vehicles and their air flow patterns are highly three-dimensional " (Barnard 15, emphasis added).   This always bothered me a little. Of course the flow over cars is 3-dimensional, I thought; how on earth can something be more or less , let alone highly 3D? Isn’t flow just...3D or not 3D?   Well, a few weeks ago in an Incompressible Flow lecture I finally understood it. Now you can too. Investigating the veracity of Barnard's claim. I've done this before, and have yet to find him wrong. Flow Fields   A field is a region of space where properties vary as a function of position within that space. The flow field around a car is the 3-dimensional space where the seven properties needed to completely characterize a flow (pressure, density, temperature, viscosity, and three compo

Testing a Smooth Engine Undertray

When I investigated the effects of a splitter on my Prius , I discovered something unusual: gauge pressures on the stock engine undertray were a lot higher than I expected. Julian Edgar’s Vehicle Aerodynamics: Testing, Modification & Development includes several examples of engine undertrays with measured pressures much less than atmospheric. My test showed that the Prius undertray was developing pressures at atmospheric or higher. What was going on? Gauge pressure at 80 kph. Left: no splitter. Center: with splitter. Right: difference. Hypothesis and Testing   So, I’ve got a problem here I want to investigate: high pressures on the engine undertray where most examples I’ve read about have lower pressures. Where to begin?   When you investigate something like this, a good place to start is fundamental principles. I know that velocity and pressure are related, and that as pressure goes down, velocity goes up. So the velocity under my car’s engine undertray must be slower than on