Quote:
Originally Posted by MeteorGray
Now, the question I have: The "pressure sensitive" colors on the hood of your car shown in the video seem to imply that the hood is experiencing high pressures not only at the base of the windshield, but also in the center of the hood. The reason I question this is I have installed hood louvers on several of my vehicles, and I have found the centers of my hoods see relative low pressure on the top as compared with higher pressures on the bottom (from the engine bay), which allows excessive heat to flow out and up through the hood at speed (and also when stopped, of course). An exception to this pressure differential would be at the base of the windshield, which does see high pressures due to the windshield vs hood confluence there.
So, are you actually seeing high pressures on the center of the hood as the colors in your video seem to show, or am I misinterpreting it?
|
That view is of the
back of the Jaguar, not the front!
Typically, there is a low pressure across the leading edge of the hood (around the front curve) and a high pressure at the rear of the hood (base of windscreen, as you say). As you'd then expect, there is a gradient from low to high pressure across the hood, and at one zone the pressure on top is the same as ambient.
However, the influence of any yaw (cross wind component) can cause some changes in this pattern, as the airflow wraps around a 'side corner' (ie from the fender onto the hood).
To site hood vents, it's best to use a differential pressure gauge (eg Magnehelic) to measure the pressures under, and over, the hood simultaneously at the different possible vent locations. To vent the engine bay you want the biggest difference (highest under, minus lowest over). In the last car I did this with, a forward location on the hood was best.