Multi-point measurement techniques used in the study of separated flows

Stokes, Sheldon S.; Glauser, Mark

doi:10.2514/6.1999-3518

Cited by 6 publications

(5 citation statements)

References 4 publications

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“…Also, the TKE production was observed to reach its maximum within the first four step-heights. These were consistent findings with those of Stokes (1999) and Hussein et al (1994) in the backward-facing step and the axisymmetric jet's shear layer, respectively. Cole & Glauser (1998a) also found that the reattachment length was about 9.0 step-heights from the expansion lip.…”

Section: Introductionsupporting

confidence: 89%

“…Also, the TKE production was observed to reach its maximum within the first four step-heights, while the reattachment length was about 9 step-heights from the expansion lip. These findings were consistent with those of Stokes (1999) and Hussein, Capp & George (1994) in the backward-facing step and the axisymmetric-jet shear layer, respectively.…”

Section: Introductionsupporting

confidence: 89%

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Low-dimensional azimuthal characteristics of suddenly expanding axisymmetric flows

et al. 2006

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Two rakes of cross-wire probes were used to capture the two-point velocity statistics in a flow through an axisymmetric sudden expansion. The expansion ratio of the facility is 3, and has a constant geometry. Measurements were acquired at a Reynolds number equal to 54,000 based on centerline velocity and inlet pipe diameter. The two-point velocity correlations were obtained along a plane normal to the flow (r, θ), at eleven downstream step-height positions spanning from the recirculating region, through reattachment, and into the redeveloping region of the flow. Measurements were acquired by means of a flying hot-wire technique to overcome rectification errors near the outer wall of the pipe where flow recirculations were greatest. A mixed application of Proper Orthogonal (in radius) and Fourier Decomposition (in azimuth) was performed at each streamwise location to

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Section: Introductionsupporting

confidence: 89%

Section: Introductionsupporting

confidence: 89%

Low-dimensional azimuthal characteristics of suddenly expanding axisymmetric flows

et al. 2006

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“…Details regarding the SE technique can be found in several studies such as those by Adrian, 5 Guezennec, 7 and Stokes and Glauser, 9 to name a few. Details regarding the SE technique can be found in several studies such as those by Adrian, 5 Guezennec, 7 and Stokes and Glauser, 9 to name a few.…”

Section: Single-point Linear and Quadratic Stochastic Estimationmentioning

confidence: 99%

Stochastic estimation of a separated-flow field using wall-pressure-array measurements

2007

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Concurrent, surface-pressure and planar, particle image velocimetry ͑PIV͒ measurements were obtained in the separating/reattaching flow region downstream of an axisymmetric, backward-facing step at a Reynolds number of 8081, based on step height. The surface-pressure and PIV measurements were used to investigate the evolution of coherent structures in the flow field by employing proper orthogonal decomposition ͑POD͒ and multipoint, linear, stochastic estimation ͑mLSE͒ analysis techniques. POD was used to determine the dominant modes in the pressure signature, while mLSE was used to estimate the dominant flow structures above the wall from the wall-pressure POD modes over a series of time steps. It was found that a large-scale, coherent structure develops in place ͑i.e., temporally͒ at approximately half the reattachment distance. Once this structure reaches a height equivalent to the step, it sheds and accelerates downstream. This growth in place, and then shedding, resembles the evolution of the flow structure in the wake of bluff bodies. Such a "wake mode" has been observed in numerical-simulation studies of long cavities and backward-facing steps, where flow two dimensionality is controllable. The present study shows for the first time evidence for the existence of a wake mode in an experimental study of a backward-facing step. This is believed to relate to the quality of the two dimensionality ͑i.e., axisymmetry͒ of the test geometry and the ability to track the temporal evolution of structural features through mLSE.

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“…Several reconstruction techniques exist to rebuild global information from pointwise measurements, and among them, stochastic estimation (SE) is one of the most widely used in fluid mechanics. Initially introduced by Adrian (1979) as a way to extricate the coherent structures in a turbulent flow, this technique has been extensively used to obtain the instantaneous least-mean-square error estimate of the velocity at various locations, with the sole information of the velocity at a few other points (see for instance Adrian (1979), Tung & Adrian (1980), Guezennec (1989), Cole & Glauser (1998) and Stokes & Glauser (1999)). This requires access to simultaneous unsteady measurements at points of interest.…”

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confidence: 99%

Unsteady flow dynamics reconstruction from mean flow and point sensors: an experimental study

et al. 2017

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This article presents a reconstruction of the unsteady behaviour of a round jet at a Reynolds number equal to 3300, from the sole knowledge of the time-averaged flow field and one pointwise unsteady measurement. The reconstruction approach is an application of the work of Beneddine et al. (J. Fluid Mech., vol. 798, 2016, pp. 485-504) and relies on the computation of the dominant resolvent modes of the flow, using a parabolised stability equations analysis. To validate the procedure, the unsteady velocity field of the jet has been characterised by time-resolved particle image velocimetry (TR-PIV), yielding an experimental reference. We first show that the dominant resolvent modes are proportional to the experimental Fourier modes, as predicted by Beneddine et al. (J. Fluid Mech., vol. 798, 2016, pp. 485-504). From these results, it is then possible to fully reconstruct the unsteady velocity and pressure fluctuation fields, yielding a flow field that displays good agreement with the experimental reference. Finally, it is found that the robustness of the reconstruction mainly depends on the location of the pointwise unsteady measurement, which should be within energetic regions of the flow, and this robustness as well as the quality of the reconstruction can be greatly improved by considering a few pointwise measurements instead of a single one. The effects of other experimental parameters on the reconstruction, such as the size of the interrogation window used for the TR-PIV processing and the accuracy of the positioning of the sensors, are also investigated in this paper.

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Multi-point measurement techniques used in the study of separated flows

Cited by 6 publications

References 4 publications

Low-dimensional azimuthal characteristics of suddenly expanding axisymmetric flows

Low-dimensional azimuthal characteristics of suddenly expanding axisymmetric flows

Stochastic estimation of a separated-flow field using wall-pressure-array measurements

Unsteady flow dynamics reconstruction from mean flow and point sensors: an experimental study

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