D. Lo Jacono

Chaotic vortex induced vibrations

This study investigates the nature of the dynamic response of an elastically mounted cylinder immersed in a free stream. A novel method is utilized, where the motion of the body during a free vibration experiment is accurately recorded, and then a second experiment is conducted where the cylinder is externally forced to follow this recorded trajectory. Generally, the flow response during both experiments is identical. However, particular regimes exist where the flow response is significantly different. This is taken as evidence of chaos in these regimes.

Flow behind a cylinder forced by a combination of oscillatory translational and rotational motions

The flow behind a cylinder undergoing forced combined oscillatory motion has been studied. The motion consists of two independent oscillations: cross-stream translation and rotation. Previous studies have extensively investigated the effect of these motions individually on cylinder wakes; however, the investigation of their combined effect is new. The motivation lies in its application to vortex-induced vibration and its suppression and to biomimetic motion. The focus is on the effect of the phase difference between the two motions. The results show that there is an unexpected loss of synchronization of the wake for a finite range of phase differences.

Spatially localized binary fluid convection in a porous medium

The origin and properties of time-independent spatially localized binary fluid convection in a layer of porous material heated from below are studied. Different types of single and multipulse states are computed using numerical continuation, and the results related to the presence of homoclinic snaking of single and multipulse states.

The three-dimensional wake of a cylinder undergoing a combination of translational and rotational oscillation in a quiescent fluid

Previous two-dimensional numerical studies have shown that a circular cylinder undergoing both oscillatory rotational and translational motions can generate thrust so that it will actually self-propel through a stationary fluid. Although a cylinder undergoing a single oscillation has been thoroughly studied, the combination of the two oscillations has not received much attention until now. The current research reported here extends the numerical study of Blackburn et al. [Phys. Fluids 11, L4 (1999)] both experimentally and numerically, recording detailed vorticity fields in the wake and using these to elucidate the underlying physics, examining the three-dimensional wake development experimentally, and determining the three-dimensional stability of the wake through Floquet stability analysis. Experiments conducted in the laboratory are presented for a given parameter range, confirming the early results from Blackburn et al. [Phys. Fluids 11, L4 (1999)]. In particular, we confirm the thrust generation abil...

Spatially localized magnetoconvection

Numerical continuation is used to compute branches of time-independent, spatially localized convectons in an imposed vertical magnetic field focusing on values of the Chandrasekhar number Q in the range 10 < Q < 103. The calculations reveal that convectons initially grow by nucleating additional cells on either side, but with the build-up of field outside owing to flux expulsion, the convectons are able to transport more heat only by expanding the constituent cells. Thus, at large Q and large Rayleigh numbers, convectons consist of a small number of broad cells.

Flow and particles deposition in anatomically realistic airways

The aerosol particles present in our environment are identified as increasingly risk factors for the human health. In particular, small particles that reach the surface of gas exchange in the alveolar region of lungs are considered most harmful to health

Evolution and breakdown of helical vortex wakes behind a wind turbine

The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable.

Flow and Particles Deposition in Rabit and Rat Airways Under Realistic Inflow Rate

The understanding of the flow structures and the particle transport/deposition across the human bronchial system remains a challenge to achieve because of the complexity of the geometry of human lungs. This work relies a strong collaboration between physicians, medical imaging researchers, fluid mechanics researcher and CFD researchers. Four configurations of airways (the generic Weibel model, the Human model proposed by Hiroko Kitaoka, a realistic Rat lung obtained by \(\mu \)-CT and a realistic rabbit geometry obtained by a synchrotron based CT) have been generated, meshed and simulated using the CFD commercial package CFD-ACE. Both steady and realistic inflow rates have been studied as well as the associated transport and deposition of particles.

Fibre Bragg Grating use in Fluid Dynamic Studies

The application of fibre Bragg grating sensors for strain and force measurements in fluid dynamic experimental studies is presented. In the first example, a fibre Bragg grating is used as both a tether and a strain gauge for studies of neutrally buoyant spheres. The measured strains on the tether were found to agree well with the theory for the flow rates tested (0.14 to 0.33 m/s). In the second example a Bragg grating sensor has been used to monitor the forces acting on a cylinder as a function of flow rate and when the cylinder is translated in a stationary fluid. Excellent agreement was found between the vibration frequencies of the cylinder as measured by the Bragg grating and with a camera use to record the motion of the cylinder.