Improved estimator for the slotted autocorrelation function of randomly sampled LDA data

Maanen, H.R.E. van; Nobach, Holger; Benedict, L. H.

doi:10.1088/0957-0233/10/1/002

Cited by 47 publications

(19 citation statements)

References 4 publications

(5 reference statements)

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“…The sampling frequency varies in [14][15][16][17][18][19][20][21][22][23][24] kHz range and 800,000 bursts are stored for each acquisition points. A slotting method including a weight scheme is coded to post-process the stochastic signal issuing from the LDV system [26].…”

Section: Methodsmentioning

confidence: 99%

Capabilities of the dielectric barrier discharge plasma actuator for multi-frequency excitations

Bénard¹,

Moreau²

2010

J. Phys. D: Appl. Phys.

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Abstract:The natural instability mechanisms are inherent in most of the laminar and turbulent flow configurations. Usually, these instabilities result in the formation of flow structures occurring at diverse spatial and time scales. An effective control requires an actuator able to bring momentum transfer over a wide range of frequency to act on these instabilities. Promising results are expected for such control strategy because, according to stability theory, a small amplitude perturbation can be large enough to produce significant effects even at high Reynolds number. Moreover, simultaneous production of small perturbations at several frequencies can enhance or cancel non linear interactions; this opens alternative methods for flow control. The focus of the present study is to demonstrate the ability of plasma actuators to introduce flow perturbations at single and dual frequencies by simply adjusting the waveform of the voltage applied to the plasma actuator. The flows produced by a dielectric barrier discharge supplied by burst, superposition and ring modulations are described in temporal and frequential domains. The results confirm the potential of non-thermal plasma actuators to produce highly unsteady flows at single, double or multiple frequencies.

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Section: Methodsmentioning

confidence: 99%

Capabilities of the dielectric barrier discharge plasma actuator for multi-frequency excitations

Bénard¹,

Moreau²

2010

J. Phys. D: Appl. Phys.

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“…Various methods have been reviewed in Benedict et al (2000). A preliminary study was conducted on present data to compare several algorithms, including basic interpolation schemes, the refined Sample and Hold with correction from Nobach et al (1998), the fuzzy Slotting algorithm from Van Maanen et al (1999), or the arrival time quantization from Nobach (2016), taking the hot-wire spectrum at z = 1.5h and z = 5h as reference. Based on this preliminary study, it was decided to use the Refined Sample and Hold Algorithm from Nobach et al (1998) for the analysis of our database.…”

Section: Algorithms To Estimate Power Spectral Density From Lda Datamentioning

confidence: 99%

Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using laser Doppler anemometry

et al. 2018

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao. Abstract Laser Doppler anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of + = 32,300 . The boundary layer thickness to cube height ratio ( ∕h = 22.7 ) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy ( z = h∕4 , h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy.

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“…Formula (12) loses its accuracy only if irregular observations are found more often within one slot width. In principle, this bias of shifting time instants to a grid can be made as small as desired by using denser and denser grids, with a smaller slot width w. The limiting value is the aliasing bias that follows with (10). The disadvantage of smaller slots is that the number of grid points increases for the same number of irregular observations, and more grid points are left empty.…”

Section: Bias Of Multi-shift Slotted Nn Resamplingmentioning

confidence: 99%

“…Some improvements have been introduced, local normalization [9] and fuzzy slotting [10], where every contribution is distributed over the two nearest lags. The spectral variance has been reduced further with variable windows [9].…”

Section: Introductionmentioning

confidence: 99%

Time series models for spectral analysis of irregular data far beyond the mean data rate

Broersen¹

2007

Meas. Sci. Technol.

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Slotted resampling transforms an irregularly sampled process into an equidistantly sampled signal where data are missing. Equidistant resampling always causes spectral bias, due to aliasing and to shifting of the observation times. The shift bias can be diminished by using a slot width that is smaller than the resampling time step. A special approximate maximum likelihood time series estimator has been developed to estimate the power spectral density and the autocorrelation function of multi-shift slotted nearest-neighbour resampled data sets with missing observations. The algorithm estimates several time series models and selects the best model order and model type from a number of candidates. It is tested with benchmark data. It can estimate spectra up to frequencies more than a thousand times higher than the mean data rate. It can be applied to various irregularly sampled data, including bubbly turbulent flow and very sparse climate or atmospheric data.

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Improved estimator for the slotted autocorrelation function of randomly sampled LDA data

Cited by 47 publications

References 4 publications

Capabilities of the dielectric barrier discharge plasma actuator for multi-frequency excitations

Capabilities of the dielectric barrier discharge plasma actuator for multi-frequency excitations

Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using laser Doppler anemometry

Time series models for spectral analysis of irregular data far beyond the mean data rate

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