Abstract

Statistically unsteady jets and plumes are prevalent in many areas of engineering, owing to natural and man-made temporal variability in sources of momentum and buoyancy. We will discuss the physics and modelling of unsteady turbulent jets and plumes by considering several canonical cases. An energy-based framework will be described and used to explain how the structure of the governing integral equations depends on the assumptions one makes about the radial dependence of the longitudinal velocity, turbulence and pressure. We consider the behaviour of the characteristic radius of the flow, the response of the flow to harmonic source perturbations and the relative balance of buoyancy and inertia in propagating waves. Using the framework, we have developed a well-posed model for unsteady jets and plumes, whose predictions are in good agreement with results from direct numerical simulation.