Effects of helicity on dissipation in homogeneous box turbulence

TL;DR

This paper investigates how the helicity of external forcing influences the dissipation rate in homogeneous turbulence, revealing a reduction of up to 10% in the dissipation coefficient, supported by theoretical bounds and numerical simulations.

Contribution

It demonstrates that helicity in the forcing reduces the dissipation coefficient and validates this effect through upper bound theory and numerical results.

Findings

Helicity reduces the dissipation coefficient by up to 10%.

Upper bound theory accurately predicts the helicity dependence.

Implications for turbulence modeling and large eddy simulations.

Abstract

The dimensionless dissipation coefficient $\beta=\varepsilon L/U^3$ is an important characteristic of statistically stationary homogeneous turbulence. In studies of $\beta$, the external force is typically isotropic and large-scale, and its helicity $H_f$ either zero or not measured. Here, we study the dependence of $\beta$ on $H_f$ and find that it decreases $\beta$ by up to 10$\%$ for both isotropic forces and shear flows. The numerical finding is supported by static and dynamical upper bound theory. Both show a relative reduction similar to the numerical results. That is, the qualitative and quantitative dependence of $\beta$ on the helicity of the force is well captured by upper bound theory. Consequences for the value of the Kolmogorov constant and theoretical aspects of turbulence control and modelling are discussed in connection with the properties of the external force. In particular, the eddy viscosity in large eddy simulations of homogeneous turbulence should be decreased by about 10$\%$ in case of strongly helical forcing.