Turbulent convective velocities (broadband and wavenumber dependent) in a plane jet

Goldschmidt, Victor; Young, Michael; Ott, E. S.

doi:10.1017/s0022112081003236

Cited by 63 publications

(34 citation statements)

References 43 publications

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“…One way is adopted by Wills [22], in which he searched for the maximum of the frequency spectrum along a constant wavenumber, or say, the maximum for the time correlation at a given space separation. Alternative way is adopted by Hussain et al [23] and Goldschmidt et al [24], in which they searched for the maximum of the wavenumber spectrum along a constant frequency, or say, the maximum for the space correlation at a given time delay. From Eq.…”

Section: Characteristic Parametersmentioning

confidence: 99%

TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

2014

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The present experimental work is devoted to investigate a new space-time correlation model for the turbulent boundary layer over a flat and a wavy walls. A turbulent boundary layer flow at Re θ = 2 460 is measured by tomographic time-resolved particle image velocimetry (Tomo-TRPIV). The space-time correlations of instantaneous streamwise fluctuation velocity are calculated at 3 different wall-normal locations in logarithmic layer. It is found that the scales of coherent structure increase with moving far away from the wall. The growth of scales is a manifestation of the growth of prevalent coherent structures in the turbulent boundary layer like hairpin vortex or hairpin packets when they lift up. The resulting contours of the space-time correlation exhibit elliptic-like shapes rather than straight lines. It is suggested that, instead of Taylor hypothesis, the elliptic model of the space-time correlation is valid for the wallbounded turbulent flow over either a flat wall or a wavy wall. The elliptic iso-correlation curves have a uniform preferred orientation whose slope is determined by the convection velocity. The convection velocity derived from the space-time correlation represents the velocity at which the large-scale eddies carry small-scale eddies. The sweep velocity represents the distortions of the small-scale eddies and is intimately associated with the fluctuation velocity in the logarithmic layer of turbulent boundary layers. The nondimensionalized correlation curves confirm that the elliptic model is more proper for approximating the space-time correlation than Taylor hypothesis, because the latter can not embody the small-scale motions which have non-negligible distortions. A second flow over a wavy wall is also recorded using TRPIV. Due to the combined effect of shear layers and the adverse pressure gradient, the space-time correlation does not show an elliptic-like shape at some specific heights over the wavy wall, but in the outer region of the wavy wallbounded flow, the elliptic model remains valid.

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Section: Characteristic Parametersmentioning

confidence: 99%

TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

2014

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“…Most of the classical methods are based on analyzing the premultiplied Φ(k x , ω) spectrum, or equivalently, the time-space correlation, and have been reviewed by Goldschmidt, et.al. 15 The methods include looking for: a maximum in the temporal spectrum at each streamwise separation, a maximum in the streamwise spectrum at each frequency, or a line of maxima along k x ωΦ(k x , ω), all of which can give different results. 15 Here we will consider the third method.…”

Section: Resultsmentioning

confidence: 99%

“…15 The methods include looking for: a maximum in the temporal spectrum at each streamwise separation, a maximum in the streamwise spectrum at each frequency, or a line of maxima along k x ωΦ(k x , ω), all of which can give different results. 15 Here we will consider the third method. In Figure 5, k x ωΦ(k x , ω) is presented for each wall parallel plane with the local mean velocity indicated by a solid black line.…”

Section: Resultsmentioning

confidence: 99%

A Study of Convection Velocities in a Zero Pressure Gradient Turbulent Boundary Layer

LeHew

Guala

McKeon

2010

40th Fluid Dynamics Conference and Exhibit

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Time-resolved DPIV measurements performed in wall parallel planes at several wall normal locations in a turbulent boundary layer (TBL) are used to illuminate the distribution of wall parallel velocities in a three-dimensional energy spectrum over streamwise, spanwise, and temporal wavelengths. To our knowledge, this is the first time this type of spectral distribution has been reported. Slices of the 3D spectrum can give insight into the propagation of different scales in the flow as well as the streamwise and spanwise extent of dominant scales. Measurements were performed at three wall normal locations, y + = 34, 108, and 278, in a zero pressure gradient TBL at Reτ = 470 . Two high speed cameras placed side-by-side in the streamwise direction give a 10δ streamwise field of view with a time step of ∆t + = 0.5 between consecutive fields. Far from the wall the convection velocities of all scales are very close to the local mean velocity in agreement with the work of Dennis and Nickels, 1 while at y + = 34 it was found that all measured scales in the flow convect faster than the local mean in agreement with Krogstad et. al.2 The variation of the convection velocity with scale and distance from the wall will be discussed.

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“…Several schemes [41][42][43][44] have been proposed to define the convection velocity. We determine the convection velocity U c based on…”

Section: Space Time Correlationmentioning

confidence: 99%

Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry

Wang¹,

Guan²,

Jiang³

2014

Chinese Phys. B

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The present experimental work focuses on a new model for space-time correlation and the scale-dependencies of convection velocity and sweep velocity in turbulent boundary layer over a flat wall. A turbulent boundary layer flow at Re θ = 2460 is measured by tomographic particle image velocimetry (tomographic PIV). It is demonstrated that arch, cane, and hairpin vortices are dominant in the logarithmic layer. Hairpins and hairpin packets are responsible for the elongated low-momentum zones observed in the instantaneous flow field. The conditionally-averaged coherent structures systemically illustrate the key roles of hairpin vortice in the turbulence dynamic events, such as ejection and sweep events and energy transport. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated and confirm the new elliptic model for the space-time correlation instead of Taylor hypothesis. The convection velocities derived from the space-time correlation and conditionally-averaged method both suggest the scaling with the local mean velocity in the logarithmic layer. Convection velocity result based on Fourier decomposition (FD) shows stronger scale-dependency in the spanwise direction than in streamwise direction. Compared with FD, the proper orthogonal decomposition (POD) has a distinct distribution of convection velocity for the large-and small-scales which are separated in light of their contributions of turbulent kinetic energy.

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Turbulent convective velocities (broadband and wavenumber dependent) in a plane jet

Cited by 63 publications

References 43 publications

TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

A Study of Convection Velocities in a Zero Pressure Gradient Turbulent Boundary Layer

Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry

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