arXiv subjects

Philipp Bahavar

Publications and source records attributed to Philipp Bahavar.

4 recordsLinked to original sources

arXiv2026

Influence of passenger head-position uncertainty on infection risk predictions

We investigate the influence of natural head movement on the infection risk posed by airborne pathogens using a CFD-based forward risk prediction model. Quasi-Monte-Carlo simulations are used to obtain the resulting infection risk distributions by representing head movement via probability distributions of parameters describing the position and orientation of each passenger's breathing zone. A significant impact of fore/aft and lateral head position on infection risk was found and should be accounted for to increase robustness when predictions of local, seat-specific infection risks are used to guide design and policy decisions. Unlike the sampling-based Monte Carlo approach, estimates of the statistical moments of the risk distributions and sensitivities, calculated using first-order second-moment and higher-order methods, were found to inadequately capture the dependencies between head movement components and infection risk.

q-bio.QM↗

arXiv2025

Curvature-based energy spectra revealing flow regime changes in Rayleigh-B\'enard convection

We use the local curvature derived from velocity vector fields or particle tracks as a surrogate for structure size to compute curvature-based energy spectra. An application to homogeneous isotropic turbulence shows that these spectra replicate certain features of classical energy spectra such as the slope of the inertial range extending towards the equivalent curvature of the Taylor microscale. As this curvature-based analysis framework is sampling based, it also allows further statistical analyses of the time evolution of the kinetic energies and curvatures considered. The main findings of these analyses are that the slope for the inertial range also appears as a salient point in the probability density distribution of the angle of the vector comprising the two time evolution components. This density distribution further exhibits changing features of its shape depending on the Rayleigh number. This Rayleigh number evolution allows to observe a change in the flow regime between the Rayleigh numbers $10^6$ and $10^7$. Insight into this regime change is gathered by conditionally sampling the salient time evolution behaviours and projecting them back into physical space. Concretely, the regime change is manifested by a change in the spatial distribution for the different time evolution behaviours. Finally, we show that this analysis can be applied to measured Lagrangian particle tracks.

physics.flu-dyn↗

arXiv2022

Sessile condensate droplets as quasi-static wall deformations in direct numerical simulations of channel flow with condensation

Condensation is an important aspect of many flow applications due to the universal presence of humidity in the air at ambient conditions. For direct numerical simulations of such flows, simulating the gas phase as a mixture characterized by temperature and humidity coupled by the release and absorption of latent heat has been shown to yield results consistent with multiphase direct numerical simulations at reduced costs. Modeling sessile droplets as quasi-static deformations based on the underlying condensation rates at the surface extends the single-phase approach to include the interaction between droplets and flow while retaining the advantages of simulating the gas phase only. The results of simulations of turbulent flow through a cooled, vertical channel with and without droplets show increased turbulent transport of heat and vapor due to the presence of condensate droplets, both in the immediate vicinity of the droplets and for the channel as a whole. In particular, the breaking of the symmetry of the wall shifts condensation from the surrounding areas onto the droplet surfaces.

physics.flu-dyn↗

arXiv2020

Condensation-induced flow structure modifications in turbulent channel flow investigated in direct numerical simulations

The turbulent flow of a fluid carrying trace amounts of a condensable species through a differentially cooled vertical channel geometry is simulated using single-phase direct numerical simulations. The release of latent heat during condensation is modeled by interdependent temperature and vapor concentration source terms governing the relation between the removal of excess vapor from the system and the associated local increase in fluid temperature. A coupling between condensation and turbulence is implemented via solutal and thermal buoyancy. When compared to simulations of an identical system without phase transition modeling, the modifications of the subcooled boundary layer due to the transient and highly localized release of latent heat could be observed. A separate analysis of fluid before and after phase transition events shows a clear increase in post-interaction streak spacing, with the release of latent heat during condensation events opposing the cooling effect of the channel wall and the associated damping of turbulence.

physics.flu-dyn↗