Test flow disturbances in an expansion tube

Paull A. and Stalker R.J. (1992) Test flow disturbances in an expansion tube. Journal of Fluid Mechanics, 245 493-521. doi:10.1017/S0022112092000569

Author Paull A.
Stalker R.J.
Title Test flow disturbances in an expansion tube
Journal name Journal of Fluid Mechanics   Check publisher's open access policy
ISSN 1469-7645
Publication date 1992-01-01
Sub-type Article (original research)
DOI 10.1017/S0022112092000569
Volume 245
Start page 493
End page 521
Total pages 29
Subject 2210 Mechanical Engineering
2211 Mechanics of Materials
3104 Condensed Matter Physics
Abstract The operation of an expansion tube is investigated with particular attention given to the test flow disturbances which have limited their utility in the past. Theoretical bounds for the duration of uniform test flow are first explored using one-dimensional ideal-gas relations, together with shock-tube boundary-layer entrainment effects. It is seen that test flow duration is limited either by the arrival of the downstream edge of the test-gas unsteady expansion or by the arrival of the upstream edge of this expansion after it has been reflected from the driver-test gas interface. These bounds are seen to be in good agreement with measurements made with large driver-gas expansion ratios. For small expansion ratios additional disturbances are observed in the test gas. Similar disturbances are also observed in the driver gas. It is postulated that these disturbances first appear in the driver gas and are transmitted into the test gas before the test gas is expanded. These disturbances remain with the test gas as it is expanded and subsequently produce unsteady conditions at the test section. Theoretical calculations for the range of frequencies which occur in the test gas before the expansion are obtained by modelling the disturbances as acoustic waves. It is shown that only the high-frequency components of the disturbances in the driver gas can penetrate the driver-test gas interface and this provides a mechanism for suppressing disturbances in the test gas. Additional analytical calculations for the shift in frequency produced as an acoustic wave traverses an unsteady expansion are also presented and it is shown that all frequencies of a given acoustic wave mode converge to one frequency. This focusing of frequencies is seen to occur in three different facilities.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
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Created: Sat, 09 Jul 2016, 17:07:03 EST by System User