This paper presents results of a study on the flow and noise generated by two-dimensional step elements attached to a flat plate. The step elements used in this study are equivalent to a forward-backward facing step pair and have length to height ratio of l/h = 8, 4 and 2.7. Aerodynamic and acoustic measurements have been taken in an anechoic wind tunnel at the University of Adelaide. Numerical simulations of turbulent boundary layer flow over the step with l/h = 2.7 are also presented. The data given in this paper provide fundamental information on how a sub-boundary layer step element affects the noise and flow field.

High pressure gas venting operations, known as blowdowns, produce significant noise. The simplest means of reducing blowdown noise is to reduce the jet velocity, however, this is often infeasible and/or undesirable in practise. Therefore, the capacity to design devices which provide noise abatement without significantly influencing venting velocities, is of practical interest. One device which has shown some potential for noise abatement is a hemispherical noise reduction reflector, however the influence of these devices on the jet velocity is unknown. Therefore, the present study aims to experimentally investigate the influence of hemispherical noise reduction reflectors on transonic jet flows. Flow measurements found the addition of a reflector did not significantly influence the resulting jet, beyond a slight increase in jet spreading, and therefore a slight reduction in peak velocity as the jet dissipates downstream, attributed to reduced flow entrainment.

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