Quote:
Originally Posted by donee
Hi All,
I am really starting to think the 2010 Prius has flow seperation issues, in comparison to the 2nd Gen (2004 - 2009). They lowered the rake of the front of the car significantly. The front to back dimension under the hood is much bigger.
I just do not get the coast down performance I was getting from my other car (if you have not heard, my 2006 Prius was totalled by an un-trained SUV driver - lets make SUV drivers pass special training and testing! - and I am now driving a 2010). Even though the low-speed rolling resistance seems just fine, maybe even better! Yea, the car is bigger, but its also a little heavier, and yea its got those big rear-view mirrors, but they have been aero-improved with steped down rim along the back. The 2010 has a nice difuser treatment under the rear bumper. It should be a wash.
On Boundary layers, I think allot depends on vehicle shape. An aero vehicles will have a thin boundary layer, and a bluff body car will have a turbulent boundary layer. So, I think the boundary layer can probably vary by a factor of three from car to car. The thickness of the boundary layer is dependant on the tubulence energy within the air next to the vehicle. Aero-experts does this sound right ?
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donee,I took a factory photo of the 2nd-gen Prius and compared to the Streamlining Template and got a very close match.If there is separation over the backlight I would suspect it to be insignificant.
The boundary layer is a function of vehicle length and velocity,and the pressure profile of the pathway the air is following.It is reported by Hucho that around 20-mph,most cars will be in a turbulent boundary layer.
I have the equation to calculate boundary layer thickness although there doesn't appear to be much interest in the formulas already posted.
Our big challenge is flow separation,reducing it,or eliminating it,and Hucho asserts that this can only be accomplished by extending the length of the vehicle,improving its length/height ratio ( fineness ratio ).