Quantitative evaluation of PIV peak locking through a multiple Δt strategy: relevance of the rms component

Nogueira, J.; Lecuona, A.; Nauri, Sara; Legrand, Mathieu; Rodríguez, Pedro

doi:10.1007/s00348-011-1094-2

Cited by 20 publications

(25 citation statements)

References 16 publications

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“…a Symmetrical image deformation, b non-symmetrical image deformation error PL is not expected to change significantly for a certain d real when several particles contribute to the correlation signal. The main variation due to the contribution of N particles in the interrogation window corresponds to the rms of the peak-locking error r PL , which is expected to change with N -0.5 , as commented in Nogueira et al (2011). The factor N -0.5 corresponds to a linear effect; thus, it is just a gross approximation, because PIV may present several non-linear effects coming from particles overlap, group-locking effects, etc……”

Section: Peak-locking 1-d Modelingmentioning

confidence: 90%

“…pos is the particle image fractional location in the first CCD frame with respect to the entire pixel (i.e., the location of the particle image center with respect to the pixel border), as explained in the literature (e.g., Nogueira et al 2011). As shown in Eq.…”

Section: Peak-locking 1-d Modelingmentioning

confidence: 99%

“…But the random part of peak-locking error is much less documented, although Willert et al (1998) and Raffel et al (1997) already mentioned it; later Nogueira et al (2011) showed that peak locking do not only bias the measurement ensemble average, but also originate a strong rms component that affects the measurement of velocity fluctuations. In addition, Nogueira et al (2009) reveal another error type, identifying the existence of significant readout errors from contemporary 12-bit CCD cameras, and quantifying it for some PIV applications.…”

Section: Introductionmentioning

confidence: 99%

“…In the previous works (Nogueira et al 2009(Nogueira et al , 2011, the authors took advantage of this property in order to assess these errors separately using a multiple Dt strategy. Instead of the classical procedure involving a constant Dt for a measurement series, the only difference when this technique is applied consists on acquiring two or more subseries, each with a specific Dt.…”

Section: Introductionmentioning

confidence: 99%

“…Nogueira et al (2009) reviewed different sources of peak locking: subpixel peak-fitting algorithms (Lourenco and Krothapalli 1995), insufficient resolution to describe the particle images (Westerweel 1998), truncation of the particles at the window border (Nogueira et al 2001), and image interpolation algorithms (Astarita and Cardone 2005). A later work, Nogueira et al (2011), showed that peak locking may correspond only to bias error, only to rms error, or that both may be present. Those works can be consulted for insight into these issues, but the methods proposed here are of general application, independently of the source.…”

Section: Introductionmentioning

confidence: 99%

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Simultaneous assessment of peak-locking and CCD readout errors through a multiple Δt strategy

et al. 2011

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The multiple Dt strategy is an inexpensive procedure that can be implemented with any usual particle image velocimetry (PIV) set up. The only requirement is acquiring different series of PIV image pairs, setting a different time between laser pulses for each series. With this additional information, robust procedures for error assessment are possible. Within this strategy, this paper offers new discoveries that correct and complement previous works by the authors. Nogueira et al. (Meas Sci Technol 20-7:074001, 2009) addressed the tasks of assessing CCD readout and peak-locking bias errors separately. In this paper, a new approach, of general application to PIV, is proposed for assessing both errors simultaneously. Additionally, it unveils the effect of the flow variability on the local amplitude of the peak-locking bias. In a different work, Nogueira et al. (Exp Fluids. doi: 10.1007/s00348-011-1094-2, 2011) have focused on assessing peak-locking rms error. That paper achieved only order of magnitude estimations of the rms error because one of its components was overlooked. Here, the new term is included and the assessment obtained is good enough to correct rms systematic errors, improving the measurement of the turbulent kinetic energy or similar flow magnitudes. After describing the strategies, the application to selected synthetic and real cases is presented, validating the modeling of the errors behavior when dealing with turbulent flows. The results indicate the possibility to assess bias errors in the range from 0.01 to 0.2 pixels for both sources (peak locking and CCD readout) simultaneously. Furthermore, the previous works simply assessed the magnitude of the errors, but the results of the new procedures proposed here, in some cases, are good enough to correct the measurement itself. In addition, the determination of zones where these errors are not the dominant ones is presented.

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Section: Peak-locking 1-d Modelingmentioning

confidence: 90%

Section: Peak-locking 1-d Modelingmentioning

confidence: 99%