Quote:
Originally Posted by JulianEdgar
So, the diagram on Page 49 shows flow nothing like that on any modern car. Nor does the quote in Hucho actually mention the template, nor any shape like it. You are yet again misquoting.
You didn't bother quoting Hucho Page 52, that talks about the "considerable difference" between an idealised model using inviscid fluid and the real world.
I can't see any mention of inviscid on page 59.
Aerodynamics of Road Vehicles (5th edition) has a major section on inviscid flow - much too big to summarise here.
However, a key point made early in the section (Page 94) is that where airflow wraps around a curve ("where the streamlines are curved") a force is developed that acts outwardly (an "outward oriented centrifugal force").
So yes, I have learnt something - inviscid flow is responsible for the low pressures we can measure where attached airflow wraps around curves.
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It seems like miscomprehension on your part:
1) the figure is probably the only one in the book to address a 'streamlined ' shape and lift, of which you've expressed interest.
2) the streamlines depicted are exactly as they'd be in the real world.
3) it is the pressure distribution which would be 'qualitative', however perfectly accurate for the first 92% of body length, and within 90% of what's depicted for the last 8% of body, ads it's a 'streamlined body we're discussing.
4) there is no considerable difference between an idealized model and a streamlined body in the real world and Hucho knows that. You may come to learn that.
5) I can't address page 59 until Friday. Sorry! I left both your book and Hucho's by my front door when I left for town this morning.
6) as to 'inviscid' I re-read every word of Hucho's book since last Friday. Word for word. I'll be posting an addendum to the 'Subject index' on Friday. I found dozens of critical terms that never made it into the index. One would have to read the entire book, hoping to stumble upon a topic of particular interest. Very disappointing!
7) air is a gas and has mass. It has inertia. It has momentum when it's moving. It should come as no surprise that it would exhibit centripetal / centrifugal force when moving in any acceleration, which it would be within a 'curve,'
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* As to inviscid flow / pressure, you're off base. Here's a checklist:
1) the body determines the streamlines.
2) streamlines determine local velocity at any point.
3) velocity is responsible for pressure.
4) pressure determines whether the boundary layer will be attached or not.
5) even a turbulent boundary layer can sustain only so much pressure rise in the direction of flow.
6) if that threshold is crossed, the boundary layer will separate from the contour, beginning the turbulent wake.
7) pressure behind the separation line will be the pressure at which separation occurred.
8) the closer the separation line is to the suction peak, the lower the pressure over the aft-body.
9) if airflow 'wrapped' over a body, the streamlines would diverge, velocity slow, and pressure increase. You'd have the highest pressure attainable. Your Porsche 911 would have Cd 0.303, not 0.40, just by having a 'template' roofline. Dig Kamm or Fachsenfeld up and ask them. Your general theory of 'wrapped' flow is riddled with physical inconsistencies, and is not supported by scientific observation.
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There is a 'CONTEXT' about your 'lift' concept, and we will examine this. I'm compiling a list of spoiler'd cars which fit the conditions of your logic. You're so close to 'getting it' that I hope you'll hang on for the ride. The only hitch right now is your need of a universal, absolute with respect to lift. It doesn't exist. There's no one-size-fits-all, generalized rule governing lift. Hucho expresses this specifically.