Oscillatory flow near the entry of a circular tube

Atabek, H. B.; Chang, C. C.

doi:10.1007/bf01592332

Cited by 93 publications

(38 citation statements)

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“…͓That the time-varying behavior of U J (t) could be determined for the velocity programs considered ͑see Fig. 3͒ from a steady-state calibration was confirmed by comparing the expected results from the calibration with those calculated from the model formulated by Atabek and Chang 16 for unsteady entrance pipe flow.͔…”

Section: Methodsmentioning

confidence: 55%

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The significance of vortex ring formation to the impulse and thrust of a starting jet

2003

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The recent work of Gharib, Rambod, and Shariff ͓J. Fluid Mech. 360, 121 ͑1998͔͒ studied vortex rings formed by starting jets generated using a piston-cylinder mechanism. Their results showed that vortex rings generated from starting jets stop forming and pinch off from the generating jet for sufficiently large values of the piston stroke to diameter ratio (L/D), suggesting a maximization principle may exist for propulsion utilizing starting jets. The importance of vortex ring formation and pinch off to propulsion, however, rests on the relative contribution of the leading vortex ring and the trailing jet ͑which appears after pinch off͒ to the impulse supplied to the flow. To resolve the relative importance of the vortex ring and trailing jet for propulsion, a piston-cylinder mechanism attached to a force balance is used to investigate the impulse and thrust generated by starting jets for L/D ratios in the range 2-8. Two different velocity programs are used, providing two different L/D values beyond which pinch off is observed, in order to determine the effect of vortex ring pinch off. Measurements of the impulse associated with vortex ring formation show it to be much larger than that expected from the jet velocity alone and proportionally larger than that associated with a trailing jet for L/D large enough to observe pinch off. The latter result leads to a local maximum in the average thrust during a pulse near L/D values associated with vortex rings whose circulation has been maximized. These results are shown to be related to the nozzle exit over-pressure generated during vortex ring formation. The over-pressure is in turn shown to be associated with the acceleration of ambient fluid by vortex ring formation in the form of added and entrained mass.

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Section: Methodsmentioning

confidence: 55%

“…5. Comparison of this method for determining I U with the predictions of the model for unsteady pipe flow by Atabek and Chang 16 showed it to be accurate to within 5%. FIG.…”

Section: Impulse and Thrust Measurementsmentioning

confidence: 84%

The significance of vortex ring formation to the impulse and thrust of a starting jet

2003

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“…Atabek and Chang [1961] presented an approximate solution technique for pulsating laminar flow within the entry length of a circular pipe. The equations of flow were linearized by assumptions in respect of the inertial terms of the equations.…”

Section: Conclusion For Laminar and Transitional Monotonic Flowmentioning

confidence: 99%

“…The excellent agreement between the theoretical and experimental work indicated that the premise was valid. Florio and Meuller [1968] adopted the approximate model of Atabek and Chang [1961], in carrying out an investigation into partly developed pulsatile laminar flow. For the range of parameters studied, it was shown that a developing pulsatile flow was composed of a fully developed oscillating component, superimposed upon a monotonically developing flow.…”

Section: Conclusion For Laminar and Transitional Monotonic Flowmentioning

confidence: 99%

The study of unsteady pipe flow and non-uniform channel flow by the use of laser doppler anemometry

Johnson¹

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Steady fluid flow within circular pipelines has been the subject of very extensive research for well over 100 years. However, unsteady flows, particularly those at transitional and higher Reynolds Numbers, have not been nearly so well analyzed.Consequently, although there is now an essentially complete description of the hydraulic and fluids mechanics aspects of steady flow, the understanding of turbulent unsteady flow phenomena is much less certain.The major difficulty in working in the unsteady flow area is the inherent nature of the flow. That is, the unsteadiness of the velocity vector requires a measurement device that does not rely upon time-averaging techniques to produce estimates of the velocity magnitude. For this reason alone, the laser-Doppler anemometer (LDA) is an ideal instrument for analysis of unsteady flows. In addition, it is non-intrusive and so does not affect the structure of the flow during the measurement process.Experimental procedures were developed successfully to enable the accurate measurement of mean velocity and turbulence intensity in monotonically varying unsteady pipe flow. Previous research at the University of Queensland had produced unexpected results in relation to this class of flow, and it was considered that a more detailed experimental analysis would yield important information.More specifically, the concept of quasi-steadiness of the flow was examined. In parallel with the experimental program, theoretical analyses were undertaken to derive methods for determining whether flow at a particular time instant is quasi-steady in nature. A modified simple power law was developed, which enables the flow rate and velocity profile in a steady turbulent flow to be estimated accurately from a single measurement of the centreline velocity. From the same velocity measurement, a law of the wall was used to derive estimates of the friction velocity and hence turbulence intensities over the entire cross-section. niIt was found that velocity profiles in monotonically unsteady turbulent flow were indistinguishable from the corresponding profiles for steady flow at the equivalent Reynolds Number. However, turbulence intensities, in flow under the effect of an acceleration transient, were shown to be significantly smaller than quasi-steady. This is consistent with a lagging process. Under these conditions, it was also found that the onset of laminar-turbulent transition was very significantly delayed (to Re in excess of 100 X 10^). The behaviour around the time of transition was examined in detail, with the conclusion that transition to fully developed turbulent flow occurred much more rapidly in accelerating flow than under steady flow conditions. The LDA was also used to study the behaviour within an open channel flow transition, where the flow area remains constant throughout the transition, but the aspect ratio varies continuously. The channel chosen was such that the width of flow converged as the bed level fell away. Previous research has shown that this form of channel exhib...

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“…The oscillatory flows have a zero mean velocity where the velocity is generally given as u = uosinaot; whereas pulsatile flows with u = uo+sino)t have a non-zero mean velocity. Although several researchers have extensively investigated entrance effects in steady flows (Sparrow et al, 1964;Van Dyke, 1970;Fargie & Martin, 1971;Chen, 1973 andNarang &Krishnamoorthy, 1976) and pulsatile flows (Atabek &Chang, 1961 andKu, 1994) only a few have documented these effects for purely oscillatory flows (Kassianides &Gerrad, 1975 andGoldberg &Folk, 1988). In the current study we develop a semi-analytical model for predicting the entrance losses and use numerical simulations to provide empirical data for the closure of the semi-analytic model.…”

Section: Entrance Length In Oscillatory Slot Flowsmentioning

confidence: 99%

Design Tools for Zero Net Mass flux Devices: CFD Effort

Mittal¹

2005

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Oscillatory flow near the entry of a circular tube

Cited by 93 publications

References 1 publication

The significance of vortex ring formation to the impulse and thrust of a starting jet

The significance of vortex ring formation to the impulse and thrust of a starting jet

The study of unsteady pipe flow and non-uniform channel flow by the use of laser doppler anemometry

Design Tools for Zero Net Mass flux Devices: CFD Effort

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