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Unformatted text preview: with good performance; (b) actual measured pattern
with boundary-layer separation and
resultant poor performance. “Stalled”
(b) | v v The basic reason for the discrepancy is flow separation, as sketched in Fig. 6.27.
The increasing pressure in the diffuser is an unfavorable gradient (Sec. 7.4), which
causes the viscous boundary layers to break away from the walls and greatly reduces
the performance. Theories can now predict this behavior (see, e.g., Ref. 20).
As an added complication to boundary-layer separation, the flow patterns in a diffuser are highly variable and were considered mysterious and erratic until 1955, when
Kline revealed the structure of these patterns with flow-visualization techniques in a
simple water channel.
A complete stability map of diffuser flow patterns was published in 1962 by Fox
and Kline , as shown in Fig. 6.26c. There are four basic regions. Below line aa
there is steady viscous flow, no separation, and moderately good performance. Note
that even a very short diffuser will s...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08