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Old 03-12-2013, 05:56 PM   #10 (permalink)
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Originally Posted by Blue Angel View Post
I've seen several references to a "bubble effect" that apparently happens on the leading face of a vehicle where a recessed feature can cause air to build up in front of it, hindering airflow. Examples would be:

-Recessed grille openings
-Recessed fog light bezels
-Recessed headlights

Generally, it seems, placing a smooth sheet over these features will streamline airflow. If I am headed in the wrong direction, please point me straight!

My question is this: How "flush" behind a grille does a grille block need to be for maximum effectiveness?

My Cruze Eco has an upper grille that's mostly blocked. It has a hexagonal grille pattern that is blocked, leaving the pattern exposed at the front. The center section of the grille has the same hexagonal pattern, but the holes go through. See this pic:

Chevrolet Cruze Eco 2011 2011 Chevrolet Cruze Eco - Grille View

If I was to design a variable shutter grille block, the simplest thing I could do would be to build a box structure behind the grille with shutters in the back of the box. This, however, would leave a large air "pocket" between the grille and the shutters when the shutters are closed.

Would it be worth the extra effort to build something that sat closer to the grille to minimise the amount of air between the grille and shutters?
A recessed depression isn't necessarily a liability.If it's non-aspirated,like a foglight,as long as there is ample radius around it,the surrounding airflow will go past the stagnant pool of air trapped in the bucket as if it was already faired in flush.
In a crosswind,there might be premature separation,but that might be viewed by some as a positive when yawing moments are concerned.
As far as the grille block itself,you'll want enough radius where the air is passing through or you'll have turbulence right there.
To visualize bad flow,check out 'vena contracta,submerged vena contracta,or Borda mouthpiece.' Bad! Really bad!
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