Convergence of Parareal for the Navier-Stokes equations depending on the Reynolds number
Identifies a practical limitation of Parareal for convection-dominated flows, relevant to computational fluid dynamics practitioners.
The paper analyzes Parareal's convergence for Navier-Stokes equations, showing that decreasing viscosity (higher Reynolds number) degrades convergence, with the effect strongly depending on spatial resolution.
The paper presents first a linear stability analysis for the time-parallel Parareal method, using an IMEX Euler as coarse and a Runge-Kutta-3 method as fine propagator, confirming that dominant imaginary eigenvalues negatively affect Parareal's convergence. This suggests that when Parareal is applied to the nonlinear Navier-Stokes equations, problems for small viscosities could arise. Numerical results for a driven cavity benchmark are presented, confirming that Parareal's convergence can indeed deteriorate as viscosity decreases and the flow becomes increasingly dominated by convection. The effect is found to strongly depend on the spatial resolution.