Characterizing flows with an instrumented particle measuring Lagrangian accelerations

We present in this article a novel Lagrangian measurement technique: an instrumented particle which continuously transmits the force/acceleration acting on it as it is advected in a flow. We develop signal processing methods to extract information on the flow from the acceleration signal transmitted by the particle. Notably, we are able to characterize the force acting on the particle and to identify the presence of a permanent large-scale vortex structure. Our technique provides a fast, robust and efficient tool to characterize flows, and it is particularly suited to obtain Lagrangian statistics along long trajectories or in cases where optical measurement techniques are not or hardly applicable.Comment: submitted to New Journal of Physic

Stochastic dynamics of particles trapped in turbulent flows

The long-time dynamics of large particles trapped in two nonhomogeneous turbulent shear flows is studied experimentally. Both flows present a common feature, a shear region that separates two colliding circulations, but with different spatial symmetries and temporal behaviors. Because large particles are less and less sensitive to flow fluctuations as their size increases, we observe the emergence of a slow dynamics corresponding to back-and-forth motions between two attractors, and a super-slow regime synchronized with flow reversals when they exist. Such dynamics is substantially reproduced by a one-dimensional stochastic model of an overdamped particle trapped in a two-well potential, forced by a colored noise. An extended model is also proposed that reproduces observed dynamics and trapping without potential barrier: the key ingredient is the ratio between the time scales of the noise correlation and the particle dynamics. A total agreement with experiments requires the introduction of spatially nonhomogeneous fluctuations and a suited confinement strength

Characterization of flow contributions to drag and lift of a circular cylinder using a volume expression of the fluid force

International audienceA 2D numerical simulation of the flow around a circular cylinder is investigated during the onset of unsteadiness within the range of Reynolds numbers between 50 and 400. Using the recent formulation of Wu, Lu and Zhuang [J. Fluid Mech. 576, (2007)], the fluid force is successfully approximated by a volume integral of a force density over a small flow domain surrounding the cylinder. The domain does contain neither the detached vortices in the wake nor the vortex formation region. Using the vorticity laplacian, the domain is dynamically divided into two regions: the external flow region containing the two separated vortex layers and the back-flow region between these two vortex layers. The integration of the force density on either the separated vortex layers or the back-flow region gives two instantaneous contributions to the total force. For the mean drag it is found that the back-flow contribution increases from almost 0% of the total drag at Re = 50 to 20% of the total drag at Re = 400. The separated vortex layers contribution is found to decrease as (a + bRe −1/2). Concerning the force fluctuations, both regions contribute similarly to the lift oscillations, while only the back-flow region is responsible for the drag oscillations. This alternative comprehension of the fluid force origin is discussed and compared to that of the classical pressure/viscous formulation

Mesure de l'accélération Lagrangienne à l'aide de particules instrumentées

International audienceAccessing and characterizing a flow imposes a number of constraints on the employed measurement techniques; in particular, optical methods require transparent fluids and windows in the vessel. Whereas one can adapt the apparatus, fluid and methods in the laboratory to these constraints, this is hardly possible for industrial mixers. In this paper, we present a novel measurement technique which is suitable for opaque or granular flows: consider an instrumented particle, which continuously transmits the force/acceleration acting on it as it is advected in a flow. Its density is adjustable for a wide range of fluids and because of its small size and its wireless data transmission, the system can be used both in industrial and in scientific mixers, allowing for a better understanding of the flow within. We demonstrate the capabilities and precision of the particle by comparing its transmitted acceleration to alternative measurements, in particular in the case of a turbulent von Kármán flow. Our technique proves to be an efficient and fast tool to characterize flows

How and When May Technostress Impact Workers’ Psycho-Physical Health andWork-Family Interface? A Study during the COVID-19 Pandemic in Italy

Although a growing body of research has analyzed the determinants and effects of technostress, it is still unclear how and when technostress would impact workers’ psycho-physical health and work-family interface during the pandemic. To fill this gap, this study tests the mediating mechanisms and the boundary conditions associated with the impact of technostress on workers’ psycho-physical well-being and work-family conflict. A total of 266 Italian workers completed online questionnaires measuring (traditional vs. remote) working modalities, technostress, fear of COVID-19, working excessively, psycho-physical distress, work-family conflict, loss of a loved one due to COVID-19, and resilience. Structural equation models were performed. Results indicated that technostress was positively related to psycho-physical distress and work-family conflict, as mediated by fear of COVID-19 and working excessively, respectively. The loss of a loved one exacerbated the effects of fear of COVID-19 on psycho-physical health, while resilience buffered the effects of working excessively on work-family conflict. Since numerous organizations intend to maintain remote working also after the COVID-19 emergency, it is crucial to study this phenomenon during its peaks of adoption, to prevent its potential negative outcomes. The implications of these findings for theory and practice are discussed