Secondary flow of second kind in a short channel observed by PIV

Duda, Daniel; Bém, Jindřich; Yanovych, Vitalii; Pavlíček, Petr; Uruba, Václav

doi:10.1016/j.euromechflu.2019.10.005

Cited by 23 publications

(12 citation statements)

References 14 publications

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“…The integration goes from the solid surface (0) to infinity or, practically, "far enough". Its physical interpretation is that it is the shift of an average streamline due to the presence of the solid surface [22,23].…”

Section: Expanding Boundary Layer Approachmentioning

confidence: 99%

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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Several methods of defining and estimating the width of a turbulent wake are presented and tested on the experimental data obtained in the wake past an asymmetric prismatic airfoil NACA 64(3)-618, which is often used as tip profile of the wind turbines. Instantaneous velocities are measured by using the Particle Image Velocimetry (PIV) technique. All suggested methods of wake width estimation are based on the statistics of a stream-wise velocity component. First, the expansion of boundary layer (BL) thickness is tested, showing that both displacement BL thickness and momentum BL thickness do not represent the width of the wake. The equivalent of 99% BL thickness is used in the literature, but with different threshold value. It is shown that a lower threshold of 50% gives more stable results. The ensemble average velocity profile is fitted by Gauss function and its σ-parameter is used as another definition of wake width. The profiles of stream-wise velocity standard deviation display a two-peak shape; the distance of those peaks serves as wake width for Norberg, while another tested option is to include the widths of such peaks. Skewness (the third statistical moment) of stream-wise velocity displays a pair of sharp peaks in the wake boundary, but their position is heavily affected by the statistical quality of the data. Flatness (the fourth statistical moment) of the stream-wise velocity refers to the occurrence of rare events, and therefore the distance, where turbulent events ejected from the wake become rare and can be considered as another definition of wake width. The repeatability of the mentioned methods and their sensitivity to Reynolds’ number and model quality are discussed as well.

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Section: Expanding Boundary Layer Approachmentioning

confidence: 99%

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

2021

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“…We venture to explain this phenomenon by the presence of secondary flows [13] along the ribs [14,15]. This secondary flow takes the form of longitudinal vortices [16,17,18], which, although are weak and disturbed by the surrounding turbulence, can prevent or, at least, delay the development of large-scale toroidal vortices of Kelvin-Helmholtz instability. The presence of stream-wise vortices past the ribs may appear in the averaged vorticity field even in higher distances from the nozzle, see Fig.…”

Section: Discussionmentioning

confidence: 99%

Turbulent jet stability increased by ribs inside the nozzle – Stereo PIV measurement one diameter past the nozzle

et al. 2021

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We observe that decreasing the inner nozzle surface by adding longitudinal ribs increases the jet stability in terms of the amount of turbulent kinetic energy in the near shear layer. We try to explain our observation as a stabilization effect of secondary flow vortices emerging in the corners of the ribs. These stream-wise vortices damage the development of larger-scale structures in the near shear layer. This explanation is supported by autocorrelation function of the stream-wise velocity component, which displays slightly smaller integral length-scale in the case with ribs than in the case of smooth nozzle. The experiment is performed at Reynolds number 2.2 × 105 (based on the nozzle diameter 50 mm); the Stereo-PIV (Particle Image Velocimetry) measurement takes place at the plane perpendicular to the jet axis one diameter past the nozzle exit. Optical 3D scanner controls the real nozzle geometry. This article presents preliminary measurement at single position and single velocity only; further exploration of this problem is needed.

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“…This PIV system has been used for many measurements in the past, for example the flow inside an axial single stage-turbine [3,31], which was not so easy as it sounds [32]. From the laboratory experiments, this system participated in the measurement of secondary flow in a corner of channel [33], measurement of turbulent mixing past a grid [34] and past a strangeshaped counter-swirler [16] or in a turbulent jet [35].…”

Section: Methodsmentioning

confidence: 99%

Particle image velocimetry measurement of turbulent wake past circular cylinder at Reynolds numbers from 2.5·10³to 1.5·10⁴

Sterly

2021

MATEC Web Conf.

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A canonical case of air flow past a circular cylinder is studied by using Particle Image Velocimetry technique. This contribution focus to the ensemble statistics (first and second moment) of the stream-wise and transverse velocity component as well as to the in-plane vorticity component. Although the range of explored Reynolds numbers is narrow, we observe a significant shortening of recirculation bubble within this range.

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Secondary flow of second kind in a short channel observed by PIV

Cited by 23 publications

References 14 publications

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Turbulent jet stability increased by ribs inside the nozzle – Stereo PIV measurement one diameter past the nozzle

Particle image velocimetry measurement of turbulent wake past circular cylinder at Reynolds numbers from 2.5·10³to 1.5·10⁴

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Secondary flow of second kind in a short channel observed by PIV

Cited by 23 publications

References 14 publications

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data

Turbulent jet stability increased by ribs inside the nozzle – Stereo PIV measurement one diameter past the nozzle

Particle image velocimetry measurement of turbulent wake past circular cylinder at Reynolds numbers from 2.5·103to 1.5·104

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Particle image velocimetry measurement of turbulent wake past circular cylinder at Reynolds numbers from 2.5·10³to 1.5·10⁴