SPH simulations of turbulence in fixed and rotating boxes in two dimensions with no-slip boundaries

TL;DR

This study uses SPH simulations to analyze decaying turbulence in two-dimensional fixed and rotating boxes with no-slip boundaries, revealing how boundary conditions and rotation influence turbulence decay and vortex structures.

Contribution

It demonstrates the effects of fixed versus freely rotating boundaries on turbulence decay and vortex evolution in 2D SPH simulations, extending prior work with new insights on angular momentum.

Findings

Angular momentum varies over time in fixed boundaries due to viscous stresses.

In freely rotating boxes, the change in fluid angular momentum is significantly smaller.

Rotation speed does not affect decay in the rotating frame, but influences vortex structures when rotation is free.

Abstract

In this paper we study decaying turbulence in fixed and rotating boxes in two dimen- sions using the particle method SPH. The boundaries are specified by boundary force particles, and the turbulence is initiated by a set of gaussian vortices. In the case of fixed boxes we recover the results of Clercx and his colleagues obtained using both a high accuracy spectral method and experiments. Our results for fixed boxes are also in close agreement with those of Monaghan1 and Robinson and Monaghan2 obtained using SPH. A feature of decaying turbulence in no-slip, square, fixed boundaries is that the angular momentum of the fluid varies with time because of the reaction on the fluid of the viscous stresses on the boundary. We find that when the box is allowed to rotate freely, so that the total angular momentum of box and fluid is constant, the change in the angular momentum of the fluid is a factor ~ 500 smaller than is the case for the fixed box, and the final vorticity distribution is different. We also simulate the behaviour of the turbulence when the box is forced to rotate with small and large Rossby number, and the turbulence is initiated by gaussian vortices as before. If the rotation of the box is maintained after the turbulence is initiated we find that in the rotating frame the decay of kinetic energy, enstrophy and the vortex structure is insensitive to the angular velocity of the box. On the other hand, If the box is allowed to rotate freely after the turbulence is initiated, the evolved vortex structure is completely different.