Finite control volume and scalability effects in velocimetry for application to aeroacoustics

Saltzman, Ashley J.; Lowe, K. Todd; Ng, Wing F.

doi:10.1007/s00348-021-03138-2

Cited by 3 publications

(2 citation statements)

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“…This issue is especially relevant to multi-point, planar measurement techniques such as particle image velocimetry (PIV), where the pixel resolution and working distance of the camera and lens hardware prescribe the minimum and maximum extents of the size of resolved turbulence features. An attenuation of turbulence statistics due to coarse instrument resolution has been observed in many experimental studies, not just in PIV [1][2][3][4]. However, comparisons of data measured via PIV and single-point measurement techniques such as hot-wire anemometry (HWA) have shown that PIV requires a much stricter tolerance of resolution to match that equivalent in single-point measurement techniques, in part due to the finite-volume averaging done within the interrogation windows of the PIV images [3].…”

Section: Introductionmentioning

confidence: 99%

“…Gamba & Clemens (2011) determined that, without an anti-aliasing filter, the spatial averaging inherent of the PIV algorithm results in a rapid decrease of the energy spectrum, where the effects are more prominent in the higher wavenumber limits of the resolved spectrum [6]. The effect of control-volume size in measurements made with Doppler global velocimetry (DGV) (akin to the interrogation window size in PIV) by Saltzmann et al (2021) showed similar attenuation in the higher wavenumber portion of their spectra, but concluded that the impact to the larger scales was minimal and mostly depended on inherent measurement uncertainties [2]. Several studies have offered insight into correction methods, typically using computational fluid dynamics (CFD), usually in the form of direct numerical simulations (DNS), for a priori estimates of the flow behavior ( [7][8][9][10]).…”

Section: Introductionmentioning

confidence: 99%

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Spatial Resolution Limitations of Particle Image Velocimetry in High Reynolds Number Turbulent Boundary Layers

Vishwanathan

Fritsch

Devenport

et al. 2022

Preprint

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Particle image velocimetry (PIV) has become a standard technique in turbulence experiments for its non-intrusive ability to simultaneously measure multiple points in a flow field. However, inherent volume averaging of the interrogation windows as well as fixed limitations of camera spatial resolution and related hardware set the minimum and maximum scales of structures that can be resolved with this measurement technique. Resolution limitations present themselves as an attenuation of the measured turbulence statistics, seen particularly in the Reynolds wall-normal stress components. This experimental study investigates the impact of hardware-level resolution limitations on the resolved turbulence statistics of PIV measurements made of both rough and smooth wall turbulent boundary layers influenced by external pressure gradients. Velocity fields are measured with PIV using two lens magnifications; one with a baseline lens and one with the addition of a teleconverter lens to view the same flow-field with double magnification (i.e. a finer spatial resolution). A comparison of the turbulence statistics between the rough and smooth wall, components of velocity, and pressure gradient magnitudes are analyzed. The smooth wall turbulence data consistently show a much higher sensitivity to the spatial resolution, particularly for the wall-normal component, due to the smaller eddy length-scales. A fixed camera resolution limits the measured range of scales which affects comparative magnitudes of turbulence for flows with different local Reynolds numbers. The rough wall data measurements show a variable sensitivity to the camera resolution depending on local Reynolds number and streamwise flow history. A statistical convergence study based on the anistropy of turbulence scales is necessary in experimental design for the study of turbulent boundary layers.

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