Abstract. We study a system consisting of the elliptic-parabolic Keller-Segel equations coupled to Stokes equations by transport and gravitational forcing. We show global-in-time existence of solutions for small initial mass in 2D. In 3D we establish global existence assuming that the initial L 3/2 -norm is small. Moreover, we give numerical evidence that for this extension of the Keller-Segel system in 2D, solutions exist with mass above 8π, which is the critical mass for the system without fluid.Key words. Keller-Segel, chemotaxis, Stokes, global existence, blow-up.AMS subject classifications. 35K55, 35Q92, 35Q35, 92C17.
MotivationThe Keller-Segel system modelling chemotaxis is a very well studied model in mathematical biology. In the following, we investigate a system consisting of the elliptic-parabolic Keller-Segel equations coupled to Stokes equations:Here c denotes the concentration of a chemical, n a cell density, and u a fluid velocity field described by Stokes equations. The fluid couples to n and c through transport and gravitational forcing modelled by ∇φ. The pressure P can be seen as the Lagrange multiplier enforcing the incompressibility constraint. The chemical c diffuses, it is produced by the cells and it degrades. The cell density diffuses and it moves in the direction of the chemical gradient. The constant a 1 ≥ 0 measures self-degradation of the chemical and the constants a 2 ≥ 0, η > 0 determine the evolution undergone by u.The motivation for this model comes from experiments described in [21,30,33] for the case of bacteria consuming the chemical. There the authors observed large-scale convection patterns in a water drop sitting on a glass surface containing oxygensensitive bacteria, oxygen diffusing into the drop through the fluid-air interface and they proposed this model:The idea behind this paper is to take these equations and change consumption of the chemical to production i.e. make it the mathematically more interesting case of *