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Consider the flat-walled diffuser in Fig. 6.26a, where section 1 is the inlet and section 2 the exit. Application of Bernoulli’s equation (6.112) to this diffuser predicts that or V2
1 p2 Cp,frictionless p01 1 1
2 p1 1
V1 p02 2 (6.114) Meanwhile, steady one-dimensional continuity would require that
Q V1A1 V2A2 (6.115) Combining (6.114) and (6.115), we can write the performance in terms of the area ratio AR A2/A1, which is a basic parameter in diffuser design:
Cp,frictionless 1 (AR) 2 (6.116) | v v A typical design would have AR 5 1, for which Eq. (6.116) predicts Cp 0.96, or
nearly full recovery. But, in fact, measured values of Cp for this area ratio  are only
as high as 0.86 and can be as low as 0.24. | e-Text Main Menu | Textbook Table of Contents | Study Guide 6.9 Experimental Duct Flows: Diffuser Performance 383
pressure Fig. 6.27 Diffuser performance:
(a) ideal pattern...
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- Spring '08