Efficient estimation of power spectral density from laser Doppler anemometer data

Nobach, Holger; Müller, Erika; Tropea, Cameron

doi:10.1007/s003480050199

Cited by 56 publications

(21 citation statements)

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“…The power spectral density investigation was performed at several positions within the flow through the evaluation of the data rate of the (LDA) signal. Within the scope of this work, the "Refined Sample and Hold" method based on Nobach et al [23], and the real auto correlation function was employed. In this case, the autocorrelation function is determined as follows:…”

Section: Pvc Characterisation and Insightsmentioning

confidence: 99%

Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle

Fokaides

Weiß

Kern

et al. 2009

Flow Turbulence Combust

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We report on the experimental and numerical investigation of swirl induced self-excited instabilities in the form of precessing helical structures at the vicinity of an Airblast Atomiser. Within the scope of this work, the increase of the knowledge of the fundamental factors governing the precessing vortex core phenomenon (PVC) (Gupta et al. 1984) by applying dual air-flow Airblast nozzles is aimed. This study concentrates on the experimental investigation of the impact of important parameters of a combustor system on the performance characteristics of this instability. In particular, in terms of this work the properties of the PVC are determined by applying two different Airblast Atomisers, one of them producing an attached swirl flame, and another producing a lifted swirl flame. Measurements are also performed for a confined and a non confined flame, aiming to determine the impact of the confining duct on the performance of the PVC. In order to gain some further knowledge, regarding the impact of this aerodynamic instability on combustion of gaseous fuel, the features of PVC are experimentally identified under reacting conditions, by employing a laser light sheet (LLS) measurement technique. By applying the LLS measurement technique, further investigation on the nature of the PVC is also attempted. The power spectral density (PSD) function of the flow field was determined on the basis of raw data provided by 3D Laser Doppler Anemometry (3D-LDA). In order to validate the measurement technique as well as the nature of the instability, the planar Mie-Scattering of the flow was evaluated by employing a high speed camera performing at 12 kHz. The precessing character of the flow was also confirmed by means of a numerical simulation using the 3D Reynolds Stress Model (3D-RSM). The results of the numerical investigation provided some useful information concerning the onset of the instability within the primary swirler as well as its size and amplitude. According to this analysis, a high 512 Flow Turbulence Combust (2009) 83:511-533 frequency instability was confirmed within a region of about one burner diameter downstream of the burner exit. Finally an evaluation of the (LDA) method in terms of providing accurate (PSD) was performed for the case of a swirl flow field.Keywords Precessing vortex core (PVC) · Swirl flows · Airblast Atomiser · Single helix structure · High frequency instability · Self excited aerodynamic instability Nomenclature D Diameter [m] F Frequency [Hz] k Turbulence kinetic energy [m 2 /s 2 ] L Length [m] · n Mean LDA data rate [Hz] R Radius [m] R Autocorrelation function [-] Re Reynolds-no. [-] S Swirl number [-] Sr Strouhal number [-] St Stokes number [-] T Temperature [K] Tu Turbulence [%] U Axial velocity component [m/s] V Radial velocity component [m/s] · V Volume flow [m 3 /h] W Tangential velocity component [m/s] X Radial coordinate [m] Z Axial coordinate [m]Greek Symbols ρ Density [kg/m 3 ] Equivalence ratio [-]

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Section: Pvc Characterisation and Insightsmentioning

confidence: 99%

Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle

Fokaides

Weiß

Kern

et al. 2009

Flow Turbulence Combust

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“…Furthermore, it is known that LDV measurements can overestimate the energy spectrum at high frequency due to the particle-rate filter effect (Nobach et al 25 demonstrate a clear example). It is possible that the lower rate of decay at higher frequencies, observed by Liu et al 20 ,…”

Section: Experimental Turbulent Energy Spectramentioning

confidence: 99%

Models of Flow-Induced Loading on Blood Cells in Laminar and Turbulent Flow, with Application to Cardiovascular Device Flow

Quinlan

Dooley

2007

Ann Biomed Eng

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Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the energy spectral density measured by Liu et al. (J. Biomech. 34:1361-1364. Results show that in laminar flow, the maximum stress on a cell is approximately equal to 2 N.J. Quinlan and P.N. Dooley the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the energy spectral density.Key words turbulent blood flow -laminar blood flow -prosthetic heart valves -hemolysis -Reynolds stress -energy spectral density

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“…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. Indeed, this algorithm seems to provide the best trade-off between faithfulness, CPU efficiency, and low variance.…”

Section: Algorithms To Estimate Power Spectral Density From Lda Datamentioning

confidence: 99%

“…The temporal auto-correlation is computed from the LDA data using the Refined Sample and Hold algorithm (Nobach et al 1998) already described in Sect. 2.2.…”

Section: Integral Time Scale Of the Flowmentioning

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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Efficient estimation of power spectral density from laser Doppler anemometer data

Cited by 56 publications

References 0 publications

Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle

Experimental and Numerical Investigation of Swirl Induced Self-Excited Instabilities at the Vicinity of an Airblast Nozzle

Models of Flow-Induced Loading on Blood Cells in Laminar and Turbulent Flow, with Application to Cardiovascular Device Flow

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

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