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Old 09-11-2013, 03:17 PM   #9 (permalink)
aerohead
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transition and L

Quote:
Originally Posted by julien.decharentenay View Post
Yes. To keep it in the spirit of the forum



No. It is intended as a fun and quick experiment with shape and analysis, not a vehicle design.



Thanks for explanation as I was not familiar with closed-course. You can assume that it is operated on a closed-course. Since it is modelling based, you need to be aware that the model uses a turbulence model. I would be interested to see the difference in model prediction between a profile optimized for laminar flows and one optimized for transitioning/turbulent flows. I am assuming that the model will indicate that the latter is better - another limit of modelling...



Sounds good. Re = rho x U x L / mu where
rho = 1.205 kg/m3 and mu = 1.8e-5 kg/m.s
U is the travelling speed selected for the analysis
What is L ??? It could be a characteristic length taken as the longer of the height, width or length or based on the frontal area (L = sqrt(frontal area))?
For road vehicles,the source flow is considered already fully turbulent and the vehicle totally immersed in a turbulent boundary layer.Which is good,as the TBL can feed kinetic energy in,in a hostile region of adverse pressure gradient over the aft-body,helping to prevent reverse-circulation and ensuing separation in this 3-D domain.
In a protected,closed-course environment,with a lone vehicle on the course at a time on a calm day,it might be able to get a bit of laminar boundary layer up to the first minimum pressure position,then transition over.But vehicles have such little surface area compared to say an aircraft,the skin friction is insignificant compared to pressure drag.
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With respect to the Rn,yes L=body length as we treat it with vehicles.
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