Quote:
Originally Posted by KamperBob
In Hucho 4th Ed 1998 page 204 is figure 4.101 showing the corner radius effect work of D.M. Waters 1969. The same figure in German appears in Peschke & Mankau 1982 which is available as a Google Book.
Waters' work was based on a (camper) trailer (my area of interest) towed behind a car so the flow field conditions are not quite the same as a bus but I see a feature worth noting. The solid curve shows marginal diminishing return from nose rounding. The dashed curve shows much more dramatic improvement for a rectangular block with all corners radiused not just the front. I'd love to sink my teeth into Water's original paper. 
Meanwhile, the rounded rump of a vintage bus seems pretty beneficial. A lot of Airstream trailers and other brands benefit from a similar shape by all accounts I have found (mostly owner reports comparing rounded to boxy units). |
SAE Transactions,Volume 70,1962: General Motor's Chevrolet Truck Division did similar research.
*The 'oval',a 56-inch radius on a semi-trailer COE tractor had lowest drag,@ ---------------------------------Cd 0.547.
* 18-inch radius on same tractor= Cd 0.562
* 12-inch radius ---------------- Cd 0.562
* 6-inch radius------------------ Cd 0.725
* 45-degree chamfer------------ Cd 0.74
* square leading edges---------- Cd 0.88