rear wheel arch

[damunk]

it has been proven that big gap within front wheel arch can produce alot of drag.

what about the rear arch , is it worth modyfying that ;

I am planning on securing properly foam on the underside of the front arch.
70mm thickness all the way around;

The rear arch there is huge voids in there. 200mm gap within the arch at the top of the rear wheels.

Is alot of drag created on the rears?

I have lowered the car but I don;t want it looking boy racer-ish therefore prefer to fill the underside of the arches.

[freebeard]

it has been proven....

[citation needed]

Front wheelwells are exposed to a positive pressure gradient, and require more volume to accomodate steering angles.

I have lowered the car but I don;t want it looking boy racer-ish therefore prefer to fill the underside of the arches.

What kind of car? What do these 'boy-racers' think about fender skirts?

[damunk]

Originally Posted by freebeard

[citation needed]

Front wheelwells are exposed to a positive pressure gradient, and require more volume to accomodate steering angles.



What kind of car? What do these 'boy-racers' think about fender skirts?

an interrogation. how do I block you from my screen.

[freebeard]

I have no idea.

[aerohead]

If this link works, it will bring you to the WS-12 aerodynamic research conducted in England in 2012.
A number of the wind tunnel studies included complete 'skirting' of the rear wheels, and some blanking of the wheelhouse opening underneath the vehicles.
It's most prudent to consider vehicles on a case-specific-basis, as they're all a bit different from one another.
If any of the test vehicles are geometrically similar to yours, it may suggest a 'trend' that you might also experience.
https://studylib.net/doc/12731012/ws...gs-21-february

[freebeard]

That's an awesome find. It includes the offset base plate as well as boxed cavity.

[Phase]

Originally Posted by aerohead

If this link works, it will bring you to the WS-12 aerodynamic research conducted in England in 2012.
A number of the wind tunnel studies included complete 'skirting' of the rear wheels, and some blanking of the wheelhouse opening underneath the vehicles.
It's most prudent to consider vehicles on a case-specific-basis, as they're all a bit different from one another.
If any of the test vehicles are geometrically similar to yours, it may suggest a 'trend' that you might also experience.
https://studylib.net/doc/12731012/ws...gs-21-february

Can you explain how their box cavity reduces drag?

[aerohead]

Originally Posted by Phase

Can you explain how their box cavity reduces drag?

I'm presuming that you're discussing Coventry University's Audi A2 modifications?
If so, then, looking from behind, the rear-extending panels, which follow the perimeter of the cavity, combined with blocking plates, which separate each cell of the cavity, around the periphery, loosely define where an actual boat-tail would terminate, at that distance behind the Audi. 'IF' the newly-created 'contour' is 'streamlined.'
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When the flow separates at the original location, it reattaches by the new trailing edge, capturing a 'locked'-vortex' which continually circulates within the confines of each cell, fed by momentum interchange from the local streamline into the turbulent boundary layer. This constitutes a cannibalistic loss.
The outer 'inviscid' flow 'skips' over the vortex as if it were a phantom surface.
Since the new trailing edge is at a smaller cross-section, the inward rushing flow experiences an acceptable level of deceleration as the streamlines diverge, causing the pressure recovery, which is responsible for all meaningful drag reduction.
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According to Mair's research, where an actual boat-tail would provide a negative Cd 0.099 drag reduction, a box-cavity of the same 'elongation' will provide a negative Cd 0.053 reduction ( 46.4% less efficient ).
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If the box-cavity were to be 'skinned' at a later date, creating an actual 'boat-tail', then the performance would improve by 46.4%.