Experiments on the Flow Field and Acoustic Properties of a Mach number 0·75 Turbulent Air Jet at a Low Reynolds Number

Slot, Harmen; Moore, Peter; Delfos, R.; Boersma, Bendiks Jan

doi:10.1007/s10494-009-9212-4

Cited by 5 publications

(3 citation statements)

References 37 publications

(47 reference statements)

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“…While the jet is weakly compressible near the nozzle, downstream at the measurement location the Mach number has reduced to \0.1 so that incompressibility can be assumed again. Further details on the settling chamber and the shape of the nozzle are given by Slot et al (2009). The PIV experiment was designed on the basis of a preliminary characterization of the jet flow, which was performed using constant temperature hot-wire anemometry (CTA).…”

Section: The Design Of the Experimentsmentioning

confidence: 99%

“…A schematic of the experimental apparatus producing the turbulent air jet under investigation is shown in figure 3 of Fiscaletti et al (2014b). Further details on the settling chamber and the shape of the nozzle are given by Slot et al (2009). The jet flow was characterized with hot-wire anemometry (HWA) in a constant temperature configuration.…”

Section: The Turbulent Flowmentioning

confidence: 99%

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Long-range μPIV to resolve the small scales in a jet at high Reynolds number

2014

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The investigation of flows at high Reynolds number is of great interest for the theory of turbulence, in that the large and the small scales of turbulence show a clear separation. But, as the Reynolds number of the flow increases, the size of the Kolmogorov length scale (g) drops almost proportionally. Aiming at achieving the adequate spatial resolution in the central region of a selfsimilar round jet at high Reynolds numbers (Re k % 350), a long-range lPIV system was applied. A vector spacing of 1:5g was achieved, where the Kolmogorov length scale was estimated to be 55 lm. The resulting velocity fields were used to characterize the small-scale flow structures in this jet. The autocorrelation maps of vorticity and k ci (the imaginary part of the eigenvalue of the reduced velocity gradient tensor) reveal that the structures of intense vorticity have a characteristic diameter of approximately 10g. From the autocorrelation map of the reduced (2D) rate of dissipation, it is inferred that the regions of intense dissipation tend to organize in the form of sheets with a characteristic thickness of approximately 10g. The regions of intense dissipation have the tendency to appear in the vicinity of intense vortices. Furthermore, the joint pdf of the two invariants of the reduced velocity gradient tensor exhibits the characteristic teapot-shape. These results, based on a statistical analysis of the data, are in agreement with previous numerical and experimental studies at lower Reynolds number, which validates the suitability of longrange lPIV for characterizing turbulent flow structures at high Reynolds number.

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Section: The Design Of the Experimentsmentioning

confidence: 99%

Section: The Turbulent Flowmentioning

confidence: 99%

Long-range μPIV to resolve the small scales in a jet at high Reynolds number

2014

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“…3 of Fiscaletti et al (2014b). Further details on the settling chamber and the shape of the nozzle are given by Slot et al (2009). The jet flow was characterized with hot-wire anemometry (HWA) in a constant temperature configuration.…”

Section: The Turbulent Flowmentioning

confidence: 99%

Tomographic long-distance µPIV to investigate the small scales of turbulence in a jet at high Reynolds number

et al. 2021

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The small scales of turbulence in a high-Reynolds-number jet ( Re ≈ 350 ) are investigated with a µPIV setup to overcome the optical limitations of conventional tomographic PIV setups. With the aim of validating the performances of tomographic long-distance µPIV, analyses are carried out involving statistical aspects of the small scales of turbulence. The technique is assessed and the data are bench-marked to be applied to the analysis of any three-dimensional small-scale phenomena in large-scale flow domains.

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Amplitude and frequency modulation of the small scales in a jet

2015

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The present study is an experimental investigation of the relationship between the large- and small-scale motions in the far field of an air jet at high Reynolds number. In the first part of our investigation, the analysis is based on time series of hot-wire anemometry (HWA), which are converted into space series after applying the Taylor hypothesis. By using a spectral filter, two signals are constructed, one representative of the large-scale motions ($2{\it\lambda}_{T}-L$, where ${\it\lambda}_{T}$ is the Taylor length scale, and $L$ is the integral length scale) and the other representative of the small-scale motions ($1.5{-}5{\it\eta}$, where ${\it\eta}$ is the Kolmogorov length scale). The small-scale signal is found to be modulated both in amplitude and in frequency by the energy-containing scales in an analogous way, both at the centreline and around the centreline. In particular, for positive fluctuations of the large-scale signal, the small-scale signal is locally stronger in amplitude (amplitude modulation), and it locally exhibits a higher number of local maxima and minima (frequency modulation). The extent of this modulation is quantified based on the strength of the large-scale fluctuations. The response of the small-scale motions to amplitude modulation can be considered instantaneous, being on the order of one Kolmogorov time scale. In the second part of our investigation we use long-range ${\it\mu}$PIV to study the behaviour of the small-scale motions in relation to their position in either high-speed or low-speed regions of the flow. The spatially resolved velocity vector fields allow us to quantify amplitude modulation directly in physical space. From this direct estimation in physical space, amplitude modulation is only 25 % of the value measured from HWA. The remaining 75 % comes from the fixed spectral band filter used to obtain the large- and small-scale signals, which does not consider the local convection velocity. A very similar overestimation of amplitude modulation when quantified in the time-frame is also obtained analytically. Furthermore, the size of the structures of intense vorticity does not change significantly in relation to the large-scale velocity fluctuation, meaning that there is no significant spatial frequency modulation. The remaining amplitude modulation in space can be explained as a statistical coupling between the strength of the structures of vorticity and their preferential location inside large-scale high-velocity regions. Finally, the implications that the present findings have on amplitude and frequency modulation in turbulent boundary layers (TBLs) are discussed.

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Experiments on the Flow Field and Acoustic Properties of a Mach number 0·75 Turbulent Air Jet at a Low Reynolds Number

Cited by 5 publications

References 37 publications

Long-range μPIV to resolve the small scales in a jet at high Reynolds number

Long-range μPIV to resolve the small scales in a jet at high Reynolds number

Tomographic long-distance µPIV to investigate the small scales of turbulence in a jet at high Reynolds number

Amplitude and frequency modulation of the small scales in a jet

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