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# GROUND EFFECTS DIFFUSERS DATA

## GROUND EFFECTS DIFFUSERS DATA

(OP)

I’ve searched the internet for a long time for hard data on ground effects diffuser design. Finally I found what I thought was a gold mine: Ground Effects Aerodynamics of Race Cars.

SITE:http://eprints.soton.ac.uk/42969/1/GetPDFServlet.pdf

Actually it’s a review of many ground effects experiments in university wind tunnels, many with moving ground planes. Good stuff.

So I went to page 41, and there it was, the GOLD!: two charts showing lift and drag curves (in the Y axis) as a function of h/d (in the X axis). The variable h is defined (p40, fig. 12) as the vertical dimension of the diffuser entrance, AKA ride height. What about the variable “d” ? No definition or explanation is given, as far as I can tell. Do any of the pros on this site have a clue what “d” is? Thanks, Paul6

### RE: GROUND EFFECTS DIFFUSERS DATA

"d" is probably a dimension - say the width of the diffuser would be my guess???

### RE: GROUND EFFECTS DIFFUSERS DATA

(OP)
Mike, I think you're right. It is very likely to be a dimension. From the diagram on page 40, the only important missing dimension is the height of the diffuser exit. If this were to be the mysterious "d", h/d would be the inverse of the expansion ration, a very important factor. But why the inverse?

Paul6

### RE: GROUND EFFECTS DIFFUSERS DATA

(OP)
Correction, I meant expansion ratio.

### RE: GROUND EFFECTS DIFFUSERS DATA

NO idea - it was just a guess

### RE: GROUND EFFECTS DIFFUSERS DATA

h/d could effectively be a typo for h/Ld Ld=length of duct, or from the next section h/theta d

Cheers

Greg Locock

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