Quote:
Originally Posted by kach22i
I'm assuming downwash and or upwash is not equal to attached flow because of what the surrounding air is doing.
That is to say: if the downwash attachment is being caused by a giant drag causing vortex, then you do NOT have clean pressure or evidence of attached flow.
Yes or no on the assumption and description above.
Pressure attachment Vs Flow attachment.
Is there an article on this?
........................part II of post.
In general the objections I have about template use is the it's shadow obscuring adjacent subjects.
Sure we take time to discuss air curtains, air tabs, diffusers and testing methods, but that shadow hovers overhead.
We need not destroy or perforate the template in order to shine light on other topics.
However, sometimes we have to shove it off to the side so we can look around and see what the real world is doing. And they are doing some cool things with air management that were never dreamed of in the 1930's because they didn't have the tools the industry has today.
Us novice type folks and Ecomodders do not have these industry tools.
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Hucho shared the research of Ahmed et al., with respect to vortex-induced drag as a function of aft-body downslope. Results are extremely conditional, contextual.
An example is Figure 4.10, on page 114 of the 2nd-Edition.
1) A simple prismatic model is modified.
2) Drag coefficient of a Cd 0.272 square-back is the baseline.
3) The last 28.8 % of the body length is the single area of investigation.
4) By conversion to a fastback, the drag drops to a minimum of Cd 0.23, @ 15-degrees down slope, immediately rises, reaching a peak drag of Cd 0.33 at 30-degrees, then falls again to Cd 0.2738 @ 40-degrees, the end of the investigation.
5) For this particular length of slope, as compared to total body length, 15-degrees is the 'sweet-spot.'
6) By going beyond 15-degrees, attached, longitudinal vortices form, responsible for up to Delta- Cd 0.10 of drag. ( this is what the Porsche 912/911 faced )
7) Buchheim et al. investigated a range of slope-length-to-body-length variability, generating a 'template' table from which a minimum drag could be selected for any slope size.
8) No such table is provided for 'curved' roof vehicles. Except the effective fineness ratio table. But don't go looking at that or you'll catch hell.