Response of turbulent energy spectrum and flow structures when vortical motion of a certain scale is suppressed by artificial forcing

Abstract

A numerical experiment is conducted to investigate the response of a homogeneous isotropic turbulent field at a statistically equilibrium state when the energy cascade process is abruptly interrupted. Vortex motions of a certain scale in the inertial subrange are extracted using a Fourier bandpass filter and forcibly damped by applying artificial forces to the small regions that are the target vortices. Once the forces are applied, the target vortices immediately disappear from the flow field, which is followed by a slight increase in kinetic energy in the larger scale range and a decrease in the smaller scale range. The decrease in energy in the smaller scale range is likely to be caused by the decrease in the stretching speeds of the vortices of that range. Next, the behaviors of individual vortices whose scales are either four times or twice as large as the target scale are tracked using a method in which each vortex is reconstructed as a group of vortex units. It is found that the vortices that are twice as large as the target vortices show smaller curvatures and longer lifespans in comparison to the case without artificial forces, while no remarkable changes are found for the vortices that are four times larger.