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Old 06-03-2020, 04:58 PM   #19 (permalink)
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Originally Posted by aerohead View Post
1) Flow separation occurs on all cars, except streamlined cars. It's the reason they don't have as low as Cd 0.12. Hucho clearly explains this. And the rules haven't changed in the last 20-30-years.
2) The low base pressure of modern cars is a function of the local pressure at the separation line. It has absolutely nothing to do with 'airflow wrapping over the body.' That doesn't even happen on wings.
3) The only way your four professional aerodynamicists could be factually correct, with respect to low pressures over the aft-body is, that the intense,fastback, long-lived, attached, counter-rotating longitudinal vortices are inducing a downwash, which impells the 911's tufts to 'adhere' to the rear slope, which in no way demonstrates 'attached flow'. The low pressure originates from the low local pressure at the separation line at the base of the backlight, where the body contour exceeds 23-degrees off the horizon, which would show up in smoke flow visualization. Your premise is incorrect.

3) Until you study and master the Bernoulli Theorem you're never going to understand the ramification of flow separation as it relates to pressure at the separation point(s), how that impacts base pressure, pressure drag,and overall drag.
4) Current literature has not overturned fluid dynamic principles.
5) The models and understandings I present are founded in empirical research leading back to the 18th-century. Ram-tubes, static tubes, and manometers aren't a recent technology. Nor are moving-floor wind tunnels.
6) As to measuring pressures, the protocol would include 42-pressure taps and manometers, photo-recorded, simultaneously, in a laboratory, where atmospheric conditions could be closely monitored, and all results corrected for standard SAE atmosphere. If you're in an income bracket which can absorb the cost of 42-Dwyer Magnehelics, good for you!
7) Looking at your measurements for the 1979, Mercedes-Benz 230 sedan, and averaging the six pressure points listed, it looks like the top of the car produces 0.00625 atmospheres difference at 100-miles per hour. And it's quite odd that Jaguar placed the top of the XE's spoiler right on the 'template' line.
8) In 1969, one of the car magazines found that they could eliminate any front or rear lift with a couple dollars worth of sheet metal or plastic. Hucho later basically claimed the issue wasn't worth fretting over, unless people drove like you do. Which is completely illegal in the US, and considered 'homicide' in some states.
9) As to the 'template,' the streamline body of revolution (torpedo) from which it is derived, produces zero-lift. (Goro Tamai,MIT, The Leading Edge).
10) The streamline half-body from which the 'template' is further derived, 'could' generate lift, however this depends upon its inclination (angle -of-attack ) which,so far, you haven't researched.[ At 135-miles per hour, the Spirit of developed 30-pounds front downforce, and 22-pounds rear lift ( with a compromised belly and diffuser), on a 4,280-pound vehicle. Using the velocity-square law, you can see that driving even at 85-mph (the highest legal speed in the United States) would produce 'meaningless' 'lift.' Essentially, the 'template' produces a zero-lift body (measured in a laboratory under controlled conditions).
11) It is the roof 'camber' which helps decelerate and increase the pressure of the flow. The further the flow is from the suction peak ahead of the windscreen header, the higher the local pressure, and higher the base pressure once the flow does separate. On the 'template'(s) body side camber and boat-tailing, this is taken to the extreme, providing the entire deceleration ramp (twice the length of the acceleration ramp), which experiences zero separation, full pressure recovery (in light of the surface friction losses), producing the lowest possible drag.
None of this will mean anything to you until you get Bernoulli behind you. Ask your 'experts.'
It's an odd world you live in when tufts showing attached flow aren't really showing attached flow, and where measured on-road aero pressures can't really be measured pressures! Much better to sit at a keyboard and make stuff up about what, according to you, should be happening.

I think I'll go on what I can measure, and on what some of the top aerodynamacists in the world tell me. Both have vastly more credibility than 'Aerohead' on a discussion forum.

Last edited by JulianEdgar; 06-03-2020 at 05:58 PM..
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