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Since the front produce most drag it has been the most urgent part to optimise.
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Huh
The "streamlining a brick" tests showed quite something else.
On Figures 19 and 20 , does anyone have a clue as to what causes the different values for apparently the same test conditions are ?
It can't be the different VGs (see Table 2) as the legend says these are tests without VG.
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6 Conclusions
These results indicate that it doesn’t seems to be any point in mounting VGs just behind the shoulder of a diffuser as described by figure 2. The most beneficial approach in reducing bluff body drag seems to be to equip it with a 50° boat-tail.
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Yet Figure 20 shows some variation of their 40° test to be even more beneficial !
Also see appendix 3 p34 : 20° is better than 40° up to about 35 m/s - 126 kph - 78 mph , but it's not reported.
Yet 20° is already steep compared to the 12-15° boattail / Kammback angle recommendations often made on ecomodder
Figure 19 shows either an anomaly that wasn't filtered out of the reporting, or a pretty useful angle at 23-30 m/s (83-108 kph / 51-67 mph)
If this study - which I don't rate really high based on its reporting - indicates anything, it is that wrongly sized and placed VG can be massive drag generators !
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