Originally Posted by pauledg
The other surprise is that the Fluence, which is large, heavy and surely not designed with aerodynamics in mind, does so well range-wise. It makes me think all this advertising garbage about airflow, funny headlight covers and shiny paint on wing mirrors is just that, advertising garbage that has negligible effect. And since when did streamlining really work at the sort of speeds we are talking about in one of these cars?
Au contraire. The Fluence (much to Leaf owners' surprise, I expect) is more
aerodynamic than the Leaf. This may be more out of happy-coincidence rather than design intent, because if you extend the boot to a narrow cross-section then you can really improve the Cd of a car (and, also, it is more aerodynamically stable at higher speeds). So maybe it was a happy outcome, rather than planned design.
The Fluence has a reported Cd of 0.25 (which is the same as the latest Prius, which is a Cd that Toyota have no hesitation in shouting about, yet Renault remain mute), whereas the Leaf has a Cd of 0.28.
Now, the actal aerodynamic cross-sections are about the same, SCx = 0.66m^2 for Leaf (smaller car), 0.67 for Fluence. However, the way aerodynamics works is that you can't model the drag of a car from the bald figures alone - because the Cd is lower on the Fluence then it will gain on aerodynamic efficiency quicker than the Leaf as the speed picks up. The SCx figure is an approximation at particular [lower] speeds. (It's to do with Reynolds numbers and complicated stuff, I think.)
(The Zoe has a SCx of 0.75m^2 ... yeah, wierd, the Fluence has a smaller aerodynamic cross-section than the Zoe!)
It's not altogether a hugh surprise - remember that the Fluence is quite low because the battery is not wedged under the floor (like every
other EV?) but is added to the car's length. For aerodynamics, the 'flatter' the cross-section, the better.
The other issue for the Leaf is that it has a permanent magnet motor. I reckon that it is over its V/Hz regime by about 30 mph, so for most of its life, the Leaf motor will be in field weakening, which saps its efficiency (and at very high light loads, can actually demagnetise the magnets). Whereas the rotor coil of the Renault ZEs don't suffer this effect. They may even ramp down the current for the rotor excitation, and get an increase, rather than decrease, in efficiency.