Large Scale Flow Characteristics of Multiple Annular Impinging Jets within a Cylindrical Chamber

Abstract

The thesis presents a systematic study of the flow structure within a cylindrical chamber generated by multiple isothermal jets, under conditions relevant to a wide range of practical applications, including confined swirl combustors, ventilation systems and concentrated solar thermal devices. The system comprises a symmetric arrangement of four jets with a tangential component relevant to the Hybrid Solar Receiver Combustor (HSRC) under development at the University of Adelaide. The geometrical configuration of the HSRC is simplified here to a cylindrical cavity with four inlet jets (representing four burners), which are configured in an annular arrangement and aligned at an inclination angle to the axis with a tangential component to generate a swirl in the chamber. The use of a simple jet configuration also makes these results relevant to more complex burner arrangements, such as those comprising a central fuel jet and a co-annular air jet, by considering the total momentum associated with the combined jet. However, the greater complexity of multiple-jets over the single round jet issuing into a quiescent environment, including the additional parameters and experimental challenges, means many gaps in understanding remain. Hence, this thesis presents a detailed characterisation of the flow velocity within a Multiple Impinging Jets in a Cylindrical Chamber (MIJCC) that has geometrical relevance to the HSRC. A joint experimental and numerical methodology was used to characterise the large-scale flow field within the MIJCC configurations, under fully turbulent flow condition with a constant nozzle Reynolds number of ReD = 10500. A range of MIJCC devices was manufactured from acrylic and fully submerged into a water tank to provide laser access and minimise optical distortion. Particle image velocimetry was used to measure the instantaneous velocity field within the experimental MIJCC configurations, while the numerical modelling employed Reynolds-Averaged Navier-Stokes methods to provide qualitative information of the flow field in the region of the flow for which experimental data were not available. The annular arrangement of multiple-jets was found to form a resulting jet flow downstream from the jet merging point, while the location of this point depends strongly on jet angles. The flow-field reveals strong similarity to single free and swirling jet flows downstream from the merging point, but retains significant differences upstream from this point. The key controlling parameters of multiple annular impinging jets (i.e., jet angles, number of jets and geometrical aspect ratio) were found to significantly influence the mean and turbulent velocity fields, the position and strength of the external and central recirculation zones, and also the degree of flow unsteadiness within the MIJCC configurations. In addition, the dependence of the key qualitative flow features on these controlling parameters was analysed by presenting the corresponding flow regime maps, while configurations of greatest relevance to solar thermal environments and combustion regimes were proposed. The key results and findings of the present study have been presented in four peer review papers, which have been published by the journal of “Physics of Fluids”.