View Single Post
Old 06-06-2021, 08:15 AM   #17 (permalink)
vianney
EcoModding Lurker
 
Join Date: Mar 2021
Location: france
Posts: 14

eNV200 - '20 Nissan e-NV200

e-NV200 - '20 Nissan e-NV200
Thanks: 1
Thanked 27 Times in 12 Posts
Quote:
Originally Posted by aerohead View Post
Technically, you want 'curves' not angles, at least until you've transitioned from the straight plank sides into the critical slope angle. Just as you've drawn for the side elevation.
The sides need to be exactly like the top, when viewed from above.
Only you can tell how much the diffuser angle will have to be compromised.
18% body length diffusers are never more than around 4-degrees upsweep.
The low drag diffusers are even 'slower' in angle if 'straight-flat'. They can withstand higher angles if gently and progressively curved, as in the Volkswagen 2000 concept of 1980. Much like your drawing.
I realize that is complicates fabrication by orders of magnitude, but in order to protect the boundary layer, there cannot be any 'kinks' or pressure 'spikes'.
The Evalia is reported at Cd 0.31. It's frontal area is going to be in the neighborhood of 2.9 meters-squared.
It's rated at 165- km highway in 'warm' weather.
391- Wh/mile ( 242.4 Wh/ km )
If we knew the exact speed at which your Evalia registered 242 Wh/km, that would be a good test speed.
------------------------------------------------------------------------------------
Dirty math suggests:
* Cd 0.31 OEM
* Cd 0.304 with rear skirts
* Cd 0.269 with smooth rear belly section and 'slow' diffuser
* Cd 0.17 with boat tail.
* a 45% drag reduction
* maybe 195-km range
You'd have to have the more complex geometry.
Here's how Union-Pacific Railroad handled the more complex surfaces in 1934. See link at top
here is the excel sheet I used to calibrate drag coefficients (rolling resistance, cd, etc)

docs.google.com/spreadsheets/d/1wZTI-nX2AWMz4ppH0gTCxHLHz6gaMt8Z/edit#gid=190811041

average consumption at 103km/h (true speed) is 244Wh/km (avg of 3 measures). The Cd I get is more around 0.37 (actually 0.31 is the Cd of the leaf which is much more aerodynamic than the env200, frontal area set apart, so 0.31 I thought anyway it was a bit underestimated, altough there may be as well some economies of scale).

I will try to tuft-test the undertray to see if flow is detached already at this stage. Problem is that the transverse bar is very low hanging and if I attempt to put a 5° rigid slope upwards I'm pretty sure it will scratch at every bumper . But I could setup something flexible so that it the shape can be designed for target speed and adapt in other situations.
  Reply With Quote
The Following User Says Thank You to vianney For This Useful Post:
aerohead (06-09-2021)