Global weak solutions in a three-dimensional chemotaxis-Navier-Stokes system

TL;DR

This paper proves the existence of global weak solutions for a three-dimensional chemotaxis-Navier-Stokes system modeling bacteria-fluid interactions, under mild initial conditions and structural assumptions on the system functions.

Contribution

It establishes the first global existence result for weak solutions in 3D for this complex coupled system, extending previous results limited to 2D or simplified models.

Findings

Global weak solutions exist under mild assumptions.

Results apply to biologically relevant functions like linear chemotaxis sensitivity.

Extends mathematical understanding of bacteria-fluid interaction models.

Abstract

The chemotaxis-Navier-Stokes system linking the chemotaxis equations \[ n_t + u\cdot\nabla n = \Delta n - \nabla \cdot (n\chi(c)\nabla c) \] and \[ c_t + u\cdot\nabla c = \Delta c-nf(c) \] to the incompressible Navier-Stokes equations, \[ u_t + (u\cdot\nabla)u = \Delta u +\nabla P + n \nabla \Phi, \qquad \nabla \cdot u = 0, \] is considered under homogeneous boundary conditions of Neumann type for $n$ and $c$, and of Dirichlet type for $u$, in a bounded convex domain $\Omega\subset R^3$ with smooth boundary, where $\Phi\in W^{1,\infty}(\Omega)$, and where $f\in C^1([0,\infty))$ and $\chi\in C^2([0,\infty))$ are nonnegative with $f(0)=0$. Problems of this type have been used to describe the mutual interaction of populations of swimming aerobic bacteria with the surrounding fluid. Up to now, however, global existence results seem to be available only for certain simplified variants such as e.g.the two-dimensional analogue, or the associated chemotaxis-Stokes system obtained on neglecting the nonlinear convective term in the fluid equation. The present work gives an affirmative answer to the question of global solvability in the following sense: Under mild assumptions on the initial data, and under modest structural assumptions on $f$ and $\chi$, inter alia allowing for the prototypical case when \[ f(s)=s \quad {for all} s\ge 0 \qquad {and} \qquad \chi \equiv const., \] the corresponding initial-boundary value problem is shown to possess a globally defined weak solution.