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Research Papers

Vaneless Diffuser Advanced Model

[+] Author and Article Information
Oleg Dubitsky, David Japikse

 Concepts NREC, 217 Billings Farm Road, White River Jct., VT 05001

J. Turbomach 130(1), 011020 (Jan 28, 2008) (10 pages) doi:10.1115/1.2372781 History: Received October 01, 2004; Revised February 01, 2005; Published January 28, 2008

A new vaneless diffuser model is presented. Upon thorough examination of the change in average total pressure, the average static pressure and the average flow angle through a vaneless diffuser, it was discovered that existing models fail to provide useful integrity. Consequently, a new model was built. It was learned that it was necessary to use a two-zone model of the flow entering the vaneless diffuser and to carefully model the two-zone degradation as the flow passes through the vaneless diffuser. The new model is presented with detailed testing. The impact upon future design is outlined, and the expectation is established that various future designs will require the integrity of the new model; old models can be used in limited cases with care.

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Figures

Grahic Jump Location
Figure 5

A comparison of total pressure (a) and flow angle (b) data with a new periodic vaneless diffuser performance model. Resultant cumulative Cf coefficient is also shown (c). Static pressure (only) is a forced match to data for each model. New model gives good p¯0 and α¯ agreement. The Eckardt rotor B case with traverse data at four different radii. This matching permits a definitive evaluation of δ2p=−1.98°, δ2s=15°, χ=0.197 and Cf(r) (CCN7).

Grahic Jump Location
Figure 6

A comparison of total pressure (a) and flow angle (b) data with a new periodic vaneless diffuser performance model. The resultant cumulative Cf coefficient is also shown (c). Static pressure (only) is a forced to data for each model. The new model gives good p¯0 and α¯ agreement. Concepts NREC case CCN103 with traverse data at two different radii. This matching permits a definitive evaluation of δ2p=−5.93°, δ2s=17.4°, χ=0.064 and Cf(r) (CCN103).

Grahic Jump Location
Figure 7

Composite of all traverse based local Cf trends with diffuser length Re number, Rex=Cx∕v, where x is the flow pathlength based on a log spiral through the diffuser. The resultant model fit gives the cumulative value of Cf as 0.11∕Rex0.2 or Cf=0.5∕Rex0.3, where these values can only be used with the periodic model.

Grahic Jump Location
Figure 1

The Dean and Senoo (9) comparison between theory and their pressure rise dataset for one operating point (replotted from the original)

Grahic Jump Location
Figure 2

The Dean and Senoo (9) comparison between theory and their estimated flow angle dataset for one operating point (replotted from the original)

Grahic Jump Location
Figure 3

A comparison of total pressure (a) and flow angle (b) data with a new periodic vaneless diffuser performance model and the Stanitz model. The resultant cumulative Cf coefficient is also shown (c). Static pressure (only) is a forced match to data for each model. The new model gives good p¯0 and α¯ agreement. An Eckardt rotor O case with traverse data at four different radii are shown. This matching permits a definitive evaluation of δ2p−15.95°, δ2s=12.4°; χ=0.13 and Cf(r) (CCN5).

Grahic Jump Location
Figure 4

A comparison of total pressure (a) and flow angle (b) data with a new periodic vaneless diffuser performance model. The resultant cumulative Cf coefficient is also shown (c). Static pressure (only) is a forced match to data for each model. The new model gives good p¯0 and α¯ agreement. The Eckardt rotor A case with traverse data at four different radii. This matching permits a definitive evaluation of δ2p=−1.98°, δ2s=15°, χ=0.227 and Cr(r) (CCN6).

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