Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Aerodynamic Streamlining Template: Part-C

s_t · 08-30-2017, 05:06 AM

I've been looking at roof profiles, in relation to a potential motorhome as discussed in this thread: http://ecomodder.com/forum/showthrea...van-35515.html

In the below image are two roof profiles. The primary difference is how rounded they are just after the windscreen. Intuition tells me that the more rounded top would be the lower drag.

However, when I apply the template this thread is about, it tells me that the pointy one is better. Primarily because the downward taper starts significantly closer to the front of the vehicle (by roughly 10-12% of total vehicle length).

Pointy option - could even drop off steeper at the back for small tail cross section:

Rounded one - dropping off too quickly - needs larger tail cross section:

Post #604 in this thread has some modelling showing high pressure at the sharp point above the windscreen, which I think indicates rounding is better? (sure, I realise the front profile is quite different, but same general pattern probably applies)

Is the bluntness /sharpness of the front of the vehicle, and transition to the downward taper, really that insignificant relative to the position of the high point? Any comments/thoughts as to which is better?

08-30-2017, 05:06 AM	#669 (permalink)
s_t EcoModding Lurker Join Date: Aug 2017 Location: Brisbane, Australia Posts: 26 Thanks: 1 Thanked 7 Times in 7 Posts	I've been looking at roof profiles, in relation to a potential motorhome as discussed in this thread: http://ecomodder.com/forum/showthrea...van-35515.html In the below image are two roof profiles. The primary difference is how rounded they are just after the windscreen. Intuition tells me that the more rounded top would be the lower drag. However, when I apply the template this thread is about, it tells me that the pointy one is better. Primarily because the downward taper starts significantly closer to the front of the vehicle (by roughly 10-12% of total vehicle length). Pointy option - could even drop off steeper at the back for small tail cross section: Rounded one - dropping off too quickly - needs larger tail cross section: Post #604 in this thread has some modelling showing high pressure at the sharp point above the windscreen, which I think indicates rounding is better? (sure, I realise the front profile is quite different, but same general pattern probably applies) Is the bluntness /sharpness of the front of the vehicle, and transition to the downward taper, really that insignificant relative to the position of the high point? Any comments/thoughts as to which is better?