Measured Reynolds stress distributions and energy budgets of a fully pulsed round air jet

Abstract

A detailed experimental examination of the turbulent kinetic energy budgets in a fully pulsed air jet exhausting into still air is presented. Through the pulse hot-wire anemometer measurements were made to obtain estimates of all measurable terms in the energy budget of the intrinsic or phase averaged turbulent kinetic energy. The region of measurements ranged from 50≤x/d≤70 which was previously identified to be the transition from pulse domination to steady jet behaviour. Pulsing was at very low Strouhal numbers to be in the quasi-steady jet regime. Measurements identified significant regions of negative production of turbulent kinetic energy as well as a domination of the energy budget by the time dependent term which is balanced by the advection term during the pulse. The pressure diffusion term is seen to play a significant role, changing from a positive contribution to a negative one as downstream distance increases. Axial diffusion of turbulent energy varies strongly with x/d but radial diffusion is almost self-similar for the region investigated. Results obtained have significant implications for application of turbulence models which have not yielded satisfactory predictions to date. This may be partly due to the finding that the ratio of production of turbulent kinetic energy to dissipation rate is much higher during the pulse dominated part of a cycle than is the case for steady jets thus invalidating a quasi-steady jet assumption which is contained in many model equations.