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Unformatted text preview: where ABL is the wall area
blocked, or displaced, by the retarded boundary-layer flow in the inlet (typically
Bt varies from 0.03 to 0.12)
A flat-walled diffuser would require an additional shape parameter to describe its
5. Aspect ratio AS b/W1 Even with this formidable list, we have omitted five possible important effects: inlet
turbulence, inlet swirl, inlet profile vorticity, superimposed pulsations, and downstream
obstruction, all of which occur in practical machinery applications.
The three most important parameters are AR, , and B. Typical performance maps
for diffusers are shown in Fig. 6.28. For this case of 8 to 9 percent blockage, both the
flat-walled and conical types give about the same maximum performance, Cp 0.70,
but at different divergence angles (9° flat versus 4.5° conical). Both types fall far short
of the Bernoulli estimates of Cp 0.93 (flat) and 0.99 (conical), primarily because of
the blockage effect.
From the data of Ref. 14 we can determine that, in...
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- Spring '08