Quote:
Originally Posted by ERTW
I stopped babysitting the solver after a couple of nights  I've logged over 70 CFD hours in the last week, 50 in the last few days. Watching the solver is actually nerve racking...like watching the ticker of your stock  Just hoping it'll move the way you want it.
I finished the "template" prism. Instead of rotating the body, I extruded it. The side edges have a 5" radius.
LWH 241.1" x 78.74" x 55"
ground clearance (hG) 5"
A = 2.540 mē
v = 30 m/s
Cd = 0.161
Cz =0.083
I have observed snow falling on cars and creating sharp edges along the roof. I was curious if a sharp edge was better, and somehow impeded streamlines from wrapping up along the sides and creating vortices. nope. It seems the DP at sharp edges is highest at sharp edges, and wreaks havoc.
Cx = 0.175
Cz = 0.099
So it not only hurts drag, but lift as well (drag induced by lift, aka vortex drag). It's still only 150 lb of lift on a, say, 3500 lb vehicle; it's not a stability or safety issue.
Phil, I was perfectly happy with my simple extrusions and revolutions. Now you're telling me I need to work in surfaces?! Without at least 3 views it's not possible to model it accurately. Dimensions would help too.
When I go to SAE congress next month, I'll see if I can steal the boxfish solid model  |
ERTW,your doing plenty good without me! I apologize for the incompleteness of the thread.
Since it was intended as an aft-body streamlining aid,I figured that folks would just work with what they had dimension wise, 'n try 'n make the most with what they had to work with.
There's been some interest in boat-tails and I was following Hucho's criteria for a minimum structure which still respected separation-free architecture.I settled on the 2.5:1 streamline body partly because Hucho showed it in one of his tables,it had Cd 0.04 (which is close to a theoretical minimum )in free air,which would translate into Cd 0.08 in mirror-image ground reflection ( after Prandtl/Rumpler).
When wheels are added to these 'pumpkin seeds' it is typical for the Cd to jump to at least 0.12.
It wasn't supposed to be a body-in-white.I added 'features' to the original drawing to make it look more like an automobile.
I have an underside view which is close,and an end view which is kind of like a wire frame model,depicting what bulkhead stations might be like if you were doing a mockup.
I'll try 'n get 'busier'!
The CFD is really impressive and I've got to tip my hat to you and others that can just wade in.The isobaric contours really help one visualize what the pressures are doing.And that's the name of the game.
Have a blast at SAE! That should be a riot.I hope they stagger presentations enough that you can take in all the sessions you're interested in.
Too much fun!