Where we observe that helical turbulence prevails over inertial waves in forced rotating flows at high Reynolds and low Rossby numbers

TL;DR

This study investigates the dominance of helical turbulence over inertial waves in forced rotating flows at high Reynolds and low Rossby numbers, revealing how turbulence characteristics change with these parameters.

Contribution

It introduces a validated spectral model for helical turbulence under rotation, extending analysis beyond current DNS capabilities and clarifying the role of inertial waves and helicity.

Findings

Helical turbulence dominates at low Rossby numbers.

Increasing Reynolds number shifts the flow towards turbulence-dominated energy exchanges.

The parameter NC = ReRo effectively characterizes the flow regime.

Abstract

We present a study of spectral laws for helical turbulence in the presence of solid body rotation up to Reynolds numbers Re~1*10^5 and down to Rossby numbers Ro~3*10^-3. The forcing function is a fully helical flow that can also be viewed as mimicking the effect of atmospheric convective motions. We test in the helical case variants of a model developed previously (Baerenzung et al. 2008a) against direct numerical simulations (DNS), using data from a run on a grid of 15363 points; we also contrast its efficiency against a spectral Large Eddy Simulation (LES) (Chollet and Lesieur 1981) as well as an under-resolved DNS. The model including the contribution of helicity to the spectral eddy dissipation and eddy noise behaves best, allowing to recover statistical features of the flow. An exploration of parameter space is then performed beyond what is feasible today using DNS. At fixed Reynolds number, lowering the Rossby number leads to a regime of wave-mediated inertial helicity cascade to small scales. However, at fixed Rossby number, increasing the Reynolds number leads the system to be dominated by turbulent energy exchanges where the role of inertial waves is to weaken the direct cascade of energy while strengthening the large scales. We find that a useful parameter for partitioning the data is NC = ReRo = U2rms/[nu Omega], with Urms, nu and Omega the rms velocity, the viscosity and the rotation rate respectively. The parameter that determines how much the energy cascade is direct or inverse in which case the cascade to small scales is predominantly that of helicity is linked to Ro.