Puff turbulence in the limit of strong buoyancy

TL;DR

This paper numerically validates a phenomenological theory describing the statistical properties of turbulent puffs, especially in buoyancy-dominated regimes, extending classical turbulence theories with excellent simulation agreement.

Contribution

It introduces a validated theory for buoyancy-dominated turbulent puffs, generalizing classical turbulence models with numerical confirmation.

Findings

Excellent agreement between theory and direct numerical simulations.

Validation of scaling laws for velocity and temperature differences.

Identification of a buoyancy-dominated turbulence regime.

Abstract

We provide a numerical validation of a recently proposed phenomenological theory to characterize the space-time statistical properties of a turbulent puff, both in terms of bulk properties, such as the mean velocity, temperature and size, and scaling laws for velocity and temperature differences both in the viscous and in the inertial range of scales. In particular, apart from the more classical shear-dominated puff turbulence, our main focus is on the recently discovered new regime where turbulent fluctuations are dominated by buoyancy. The theory is based on an adiabaticity hypothesis which assumes that small-scale turbulent fluctuations rapidly relax to the slower large-scale dynamics, leading to a generalization of the classical Kolmogorov and Kolmogorov-Obukhov-Corrsin theories for a turbulent puff hosting a scalar field. We validate our theory by means of massive direct numerical simulations finding excellent agreement.