D'Angelo, Cristina (2025) Experimental investigation of the fluid dynamic behaviour and heat transfer performance of sweeping and precessing jets. [Tesi di dottorato]

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Abstract

Turbulent jets play a crucial role in a wide range of industrial applications, from propulsion systems to flow control and heat transfer enhancement. Among the various jet configurations studied over the years, sweeping and precessing jets have recently attracted significant attention due to their unsteady flow characteristics, which can promote flow entrainment and enhance mixing performance. This thesis investigates the flow field and heat transfer behaviour of impinging sweeping jets, with particular attention to the effects of the nozzle-to-plate distance and of key geometric parameters of the fluidic oscillators, namely the mixing chamber length and the feedback-channel minimum passage width. Building on these results, the precessing motion of a conventional precessing jet is stabilized by applying the feedback-channel mechanism of two-dimensional sweeping jets. To this end, a novel nozzle design is introduced, in which helical feedback channels are wrapped around the mixing chamber of a conventional precessing jet nozzle. The flow field of the resulting free precessing jets, as well as their heat transfer performance in the impinging configuration, are investigated. Finally, a parametric analysis is carried out to assess the influence of the angular displacement between the inlet and outlet sections of the feedback channels.

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