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Experiments in Fluids
Erschienen in: Experiments in Fluids 2/2009

01.08.2009 | Research Article

Experimental analysis of low-Reynolds number free jets

Evolution along the jet centerline and Reynolds number effects

verfasst von: Valentino Todde, Pier Giorgio Spazzini, Mats Sandberg

Erschienen in: Experiments in Fluids | Ausgabe 2/2009

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Abstract

The present paper analyzes the features of a low-Reynolds number free submerged jet with special regard to statistical quantities on the jet centerline. Measurements in an environment with very low disturbances allowed to observe details of turbulence and higher-order moments. Some peculiar features of the measured (natural) jet are shown to be in correspondence to observations referring to forced higher-Reynolds number jets. In particular, it is shown that, at low Reynolds numbers, the initial region of the jet is dominated by well-defined vortices in the shear layer. This result is substantiated by both the statistical moments and the spectral analysis. The presence of two distinct regimes is evidenced and discussed from a physical standpoint, also in relation to the mathematical analysis of the jet structure from the bibliography.
Vorheriger Artikel Investigation of binary drop rebound and coalescence in liquids using dual-field PIV technique
Nächster Artikel The application of stereoscopic PIV to measure the flow of air into an enclosure containing a fire

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Fußnoten
1
Nominal outlet velocities of 0.5, 1.0, 1.5 and 2.0 m/s.
 
2
Data were cut at U/U 0 ≈ 0.1, for the same reasons described above, also for numerical integrations.
 
3
The virtual origin is defined as the point where the extrapolation of 1/U * reaches a value of 0.
 
4
Because of data rectification (the SHW cannot discriminate the flow direction), the measured velocity distribution is more skewed towards the positive side than the actual velocity distribution.
 
5
The main difference being that the abscissa where the regularity of the time trace begins to decay changes with the exit velocity.
 
6
The T u value in this case will correspond to the RMS value of a sinusoid, which is the maximum deviation from the average times \(\sqrt{2}\). It can be easily verified that this relationship is respected in the early region of the jet.
 
7
In principle, the helical structure should induce a constant velocity on the axis. But in practice, small imperfections in the placement of the hot-wire sensor on the axis of the jet, or slight deviations of the jet from a perfectly straight path, would cause a fluctuation in the signal because of the different distance of the sensor from the various parts of the helix, though the amplitude of this fluctuation should be modest and quite uniform.
 
8
From a mathematical standpoint, other helical modes can be unstable, but it was demonstrated that they would never actually appear in a flow.
 
Literatur
Abramovich GN (1963) The theory of turbulent jets. 1st edn. Massachussetts Institute of Technology, Cambridge
Barlow JB, Rae WHJ, Pope A (1999) Low-speed wind tunnel testing. 3rd edn. Wiley, New York
Becker HA, Massaro TA (1968) Vortex evolution in a round jet. J Fluid Mech 31:435–448CrossRef
Boguslawski L, Popiel CO (1979) Flow structure of the free round turbulent jet in the initial region. J Fluid Mech 90:531–539CrossRef
Burattini P, Antonia RA, Rajagopalan S, Stephens M (2004) Effect of initial conditions on the near-field development of a round jet. Exp Fluids 37:56–64CrossRef
Crow SC, Champagne FH (1971) Orderly structure in jet turbulence. J Fluid Mech 48:547–591CrossRef
Dimotakis PE, Miake-Lye RC, Papantoniou DA (1983) Structure and dynamics of round turbulent jets. Phys Fluids 26(11):3185–3192CrossRef
Ho CM, Huerre P (1984) Perturbed free shear layers. Annu Rev Fluid Mech 16:365–424CrossRef
Hussain AKMF, Clark AR (1981) On the coherent structure of the axisymmetric mixing layer: a flow-visualization study. J Fluid Mech 104:263–294CrossRef
Hussain AKMF, Zaman KBMQ (1980) Vortex pairing in a circular jet under controlled excitation. Part 2. Coherent structure dynamics. J Fluid Mech 101:493–544CrossRef
Hussain AKMF, Zaman KBMQ (1981) The ‘preferred mode’ of the axisymmetric jet. J Fluid Mech 110:39–71CrossRef
Hussein HJ, Capp SP, George WK (1994) Velocity measurements in a high-Reynolds number, momentum-conserving, axisymmetric, turbulent jet. J Fluid Mech 258:31–75CrossRef
Lau JC, Fisher MJ (1975) The vortex-street structure of ‘turbulent’ jets. Part 1. J Fluid Mech 67:299–337CrossRef
Malmstrőm TG, Kirkpatrick AT, Christensen B, Knappmiller KD (1997) Centerline velocity decay measurements in low-velocity axisymmetric jets. J Fluid Mech 246:363–377CrossRef
Mattingly GE, Chang CC (1974) Unstable waves on an axisymmetric jet column. J Fluid Mech 65:541–560MATHCrossRef
Michalke A, Hermann G (1982) On the inviscid instability of a circular jet with external flow. J Fluid Mech 114:343–359MATHCrossRef
Morel T (1975) Comprehensive design of axisymmetric wind tunnel contractions. J Fluids Eng 97:225–233
O’Neill P, Soria J, Honnery D (2004) The stability of low Reynolds number round jets. Exp Fluids 36:473–483CrossRef
Plaschko P (1979) Helical instabilities of slowly divergent jets. J Fluid Mech 92:209–215MATHCrossRef
Spazzini PG, Todde V, Sandberg M (2007) Low-speed measurements using a hot-wire anemometer. In: Proceedings of the 14th international flow measurement conference (FLOMEKO14). Johannesburg
Spazzini PG, Todde V, Sandberg M (2009) Two-variables calibration of a hot wire probe. J Flow Meas Instrum (submitted for publication)
Xu G, Antonia RA (2002) Effect of different initial conditions on a turbulent round frfee jet. Exp Fluids 33:677–683
Zaman KBMQ, Hussain AKMF (1980) Vortex pairing in a circular jet under controlled excitation. Part 1. General jet response. J Fluid Mech 101:449–491CrossRef
Metadaten
Titel
Experimental analysis of low-Reynolds number free jets
Evolution along the jet centerline and Reynolds number effects
verfasst von
Valentino Todde
Pier Giorgio Spazzini
Mats Sandberg
Publikationsdatum
01.08.2009
Verlag
Springer-Verlag
Erschienen in
Experiments in Fluids / Ausgabe 2/2009
Print ISSN: 0723-4864
Elektronische ISSN: 1432-1114
DOI
https://doi.org/10.1007/s00348-009-0655-0

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