Estimating the integral length scale on turbulent flows from the zero crossings of the longitudinal velocity fluctuation

Mora, Daniel Odens; Obligado, Martín

doi:10.1007/s00348-020-03033-2

Cited by 29 publications

(23 citation statements)

References 29 publications

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“…The experiments were performed in a close-circuit wind tunnel 'Lespinard ' in the Laboratoire des Écoulements Géophysiques et Industriels (LEGI) at Université Grenoble Alpes. This facility has been regularly employed to study particle clustering under decaying homogeneous isotropic turbulence (HIT) conditions [3,[32][33][34]. A sketch of our experimental setup is depicted in figure 1.…”

Section: A Experimental Setup Detailsmentioning

confidence: 99%

Effect of Reλ and Rouse numbers on the settling of inertial droplets in homogeneous isotropic turbulence

et al. 2021

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We present an experimental study on the settling velocity of dense sub-Kolmogorov particles in active-grid-generated turbulence in a wind tunnel. Using phase Doppler interferometry, we observe that the modifications of the settling velocity of inertial particles, under homogeneous isotropic turbulence and dilute conditions (i.e., small liquid fraction φv ≤ O(10) −5 ), is controlled by the Taylor-Reynolds number Re λ of the carrier flow. Meanwhile, we did not find a strong influence of the ratio between the fluid and gravity accelerations on the particle settling behavior. Remarkably, we find that that the degree of hindering experienced by the particles (i.e., the measured particle settling velocity is smaller in magnitude than its respective one in still fluid conditions) increases with Re λ . This observation is contrary to previous works at intermediate values of Re λ that report the opposite effect: settling enhancement. Nonetheless, our trend is observed at all particle sizes investigated, and when previous experimental data is included into the analysis, our data suggest that the particle settling behavior may be non-monotonic with Re λ : inducing enhancement at moderate values of Re λ , and at promoting hindering at higher values of Re λ . Moreover, at the highest Re λ studied, the settling enhancement regime ceases to exist. Finally, we find that the difference between the measured particle settling velocity (Vp) and the particle terminal velocity in still fluid conditions (VT ), normalized by the carrier phase rms fluctuations, (Vp − VT )/u scales linearly with the Rouse number Ro = VT /u (i.e., the ratio between the particles settling velocity and the fluid rms fluctuations). However, such behavior (Vp − VT )/u ∼ −Ro appears only to be valid for moderate values of the Rouse number.

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Section: A Experimental Setup Detailsmentioning

confidence: 99%

Effect of Reλ and Rouse numbers on the settling of inertial droplets in homogeneous isotropic turbulence

et al. 2021

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“…For wall-bounded turbulence, several studies have shown that the distributions of the persistence time scales can be interpreted as equivalent to the streamwise size distributions (by applying Taylor's hypothesis) of the turbulent structures in such flows [30,16,29,25]. In convective ASL flows, Chowdhuri et al [6,11] have illustrated that the persistence analysis is an effective tool to provide a structural description behind the intermittent fluctuations in velocity and temperature, and in the associated heat and momentum fluxes.…”

Section: Persistence Analysismentioning

confidence: 99%

The characterization of turbulent heat and moisture transport during a gust-front event over the Indian peninsula

2021

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The ramifications of gust-front on atmospheric surface layer (ASL) turbulence is a vexing issue, with nearly no information available over the Indian region where such events are not uncommon. Over the Indian peninsula, Chowdhuri et al. (Environ. Fluid Mech. 21(1):263-281, 2021) have shown that, the cold pool associated with the gust-front creates two distinct regimes in ASL turbulence, where the temperature fluctuations display contrasting behavior. To evaluate the corresponding impacts on the moisture fluctuations and turbulent heat and moisture transport, we extend our analysis by using the same field-experimental dataset of Chowdhuri et al. (2021). We discover that, the topology of the turbulent structures which govern the temperature and moisture fluctuations clearly exhibit a regime-wise distinction. In the first regime, the structures in temperature and moisture fluctuations are significantly inclined in the vertical, while demonstrating a self-similarity in their time scales by being related through a power-law distribution. However, in the second regime, the vertical inclination disappears for the temperature structures with hardly any change observed for the moisture. Moreover, the power-law exponents of the turbulent temperature time scales remain sensitive to the regimes, although no such effect is visible in the power-law character of the moisture time scales. Additionally, the dissimilarity in the heat and moisture transport is investigated through a novel polar-quadrant based approach that separates the phases and amplitudes of the flux-transporting motions.

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“…8. The integral length scale can be estimated via the zero crossings proposed by Mora and Obligado (2020). To verify that zero crossing are well resolved the signal has to be filtered with a low-pass filter with a characteristic length η c .…”

Section: Estimation Of Fundamental Turbulence Length Scalesmentioning

confidence: 99%

“…Figure 8: Standard deviation (normalized) of the Voronoi cells as a function of the characteristic length η c of a low-pass filter for estimating the integral length scale with the method according to Mora and Obligado (2020).…”

Section: Estimation Of Fundamental Turbulence Length Scalesmentioning

confidence: 99%

An open source Matlab package for stochastic data analysis in the context of Fokker-Plank Equation and Integral Fluctuation Theorem

Fuchs¹,

Kharche²,

Wächter³

et al. 2021

Preprint

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We present a user-friendly open-source Matlab package for stochastic data analysis. This package enables to perform a standard analysis of given timeseries like scaling analysis of structure functions and energy spectral density, estimation of correlation functions or investigation of the PDF&#8217;s of increments including Castaing fits. Also, this package can be used to extract the stochastic equations describing scale-dependent processes, such as the cascade process in turbulent flows, through Fokker-Planck equations and concepts of non-equilibrium stochastic thermodynamics. This stochastic treatment of scale-dependent processes has the potential for a new way to link to fluctuation theorems of non-equilibrium stochastic thermodynamics and extreme events (small scale intermittency, structures of rogue waves).&#160;The development of this user-friendly package greatly enhances the practicability and availability of this method, which allows a comprehensive statistical description in terms of the complexity of time series. It can also be used by researchers outside of the field of turbulence for the analysis of data with turbulent like complexity, including ocean gravity waves, stock prices and inertial particles in direct numerical simulations. Support is available: github.com/andre-fuchs-uni-oldenburg/OPEN FPE IFT, where questions can be posted and generally receive quick responses from the authors.This package was developed by the research group Turbulence, Wind energy and Stochastics (TWiSt) at the Carl von Ossietzky University of Oldenburg. We acknowledge funding by Volkswagen Foundation.&#160;

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Estimating the integral length scale on turbulent flows from the zero crossings of the longitudinal velocity fluctuation

Cited by 29 publications

References 29 publications

Effect of Reλ and Rouse numbers on the settling of inertial droplets in homogeneous isotropic turbulence

Effect of Reλ and Rouse numbers on the settling of inertial droplets in homogeneous isotropic turbulence

The characterization of turbulent heat and moisture transport during a gust-front event over the Indian peninsula

An open source Matlab package for stochastic data analysis in the context of Fokker-Plank Equation and Integral Fluctuation Theorem

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