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How to Think About Car Aerodynamics: A Very, Very Basic Overview

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The study of aerodynamics is complicated. If anyone tries to tell you otherwise, run the other direction—it’s a sure sign they don’t know what they’re talking about.   Over the last two years especially, my thinking about aerodynamics and appreciation of its complexity has changed dramatically—a result of my going back to school to get another bachelor’s degree, this time in aerospace engineering where a good working knowledge of airflows is required and education in not just general fluid mechanics but also aircraft aerodynamic design forms a core part of the technical curriculum. I'm in the midst of my last semester now and to clarify my thinking at this point I decided to put some things in writing in the hopes they might help someone else as well as myself, specifically focused on car aerodynamics. A word of warning: I've tried to minimize the amount of math below, but some mathematical relations are unavoidable if you want to build an understanding of fluid flows. If anyth...
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Measuring and Improving Cooling System Performance – Part 8: Modification

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Production car cooling systems are always beholden to styling considerations, packaging issues, and cost constraints (design cost, materials cost, manufacturing cost, etc.). Because of this, most leave room for improvement if your goals and requirements are different than the manufacturer's. We've seen so far that a few simple measurements on your car will give you a lot of information about how well its cooling system works and where it can be made better. If you don't mind getting your hands dirty, you should be able to reduce cooling drag on your car while maintaining or even increasing cooling capacity. How big should inlets be? Outlets? How should they be shaped? How much will internal smoothing reduce drag? How much will mass flow increase if we reduce system losses? Don't try to modify any of these things by guessing! The engineers behind this 2019 Porsche 911 certainly didn't. Modifying Cooling System Flow   As an example, I'll modify the cooling system ...
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The Bernoulli Equation

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In the US, many students' first introduction to aerodynamic principles happens in basic physics or natural sciences coursework with a lesson on the "Bernoulli effect." Unfortunately, for a lot of people this is also the end of their education in aerodynamics, leading to a lot of incorrect understanding, weird theories, and gross oversimplification—like the incorrect idea that a fully streamlined body with no flow separation will have no pressure drag ( it still does ).   You probably recall the gist of it: as the velocity of a stream of air increases, its static pressure is reduced. This qualitative relationship is always true of low speed flows with no energy addition, since (total) pressure is a measure of the (total) energy in a volume of air and, because energy cannot be created or destroyed spontaneously, when more of that energy is used in the kinetic energy of the flow there must be less internal energy (static pressure) available. This is one explanation of how ...
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