Exploring Bayesian olfactory search in realistic turbulent flows

Abstract

The problem of tracking the source of a passive scalar in a turbulent flow is relevant to flying insect behavior and several other applications. Extensive previous work has shown that certain Bayesian strategies, such as "infotaxis," can be very effective for this difficult "olfactory search" problem. More recently, a quasi-optimal Bayesian strategy was computed under the assumption that encounters with the scalar are independent. However, the Bayesian approach has not been adequately studied in realistic flows which exhibit spatiotemporal correlations. In this work, we perform direct numerical simulations (DNS) of an incompressible flow at $\mathrm{Re}_\lambda\simeq150,$ while tracking Lagrangian particles which are emitted by a point source and imposing a uniform mean flow with several magnitudes (including zero). We extract the spatially-dependent statistics of encounters with the particles, which we use to build Bayesian policies, including generalized ("space-aware") infotactic heuristics and quasi-optimal policies. We then assess the relative performance of these policies when they are used to search using scalar cue data from the DNS, and in particular study how this performance depends on correlations between encounters. Among other results, we find that quasi-optimal strategies continue to outperform heuristics in the presence of strong mean flow but fail to do so in the absence of a mean flow. We also explore how to choose optimal search parameters, including the frequency and threshold concentration of observation.