Quote:
Originally Posted by mikesheiman
How much effect does lots of low pressure air in the engine area have (particularly in EV conversions with lots of open air space under the hood draining pressure into wheel wells?
One part of me figures the low pressure would pull back on the hood, the other says it would push forward on the front of the dashboard behind the hood and equalize the net effect.
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Typically,for streamlining purposes,and aerodynamicist,or aerodynamic engineer would be concerned with cooling system drag.
A garden-variety car of the 1960s might have a cooling system which constituted 12% of the car's overall drag.
Fully-ducted race cars of the same period had 2%-loss cooling systems.
Today,with variable grille-shutters,the drag will vary as a function of engine heat flux.
An EV with sealed grille would essentially have an 'engine' compartment at whatever the ambient barometric pressure was.All surfaces inside there would 'see' the same pressure.
Even if it were open to the outside somewhere,if it was non-porous,it would just be an area of dead air.
Given that,the flow around the car would all be at a lower pressure and the hood would want to blow off if unsecured.
Since most production engine bays are an aerodynamic torture-chamber,any thing you can do to minimize flow there cuts drag.
Some very low-drag ICE concept cars move the radiator to the rear of the car and use the inlets back there as suction slots,and the exits as blown slots.
The Ford Probe-IV can be driven at 2.5-mph on the blast from it's cooling fan.
The EV has an advantage of shunting more air around the vehicle,better energizing the boundary layer,and with less internal turbulence,has more kinetic energy to harvest as pressure recovery in the aft-body,for lower drag.