Iso-thermal flow characteristics of rotationally symmetric jets generating a swirl within a cylindrical chamber

Abstract

We present a systematic experimental study of the interaction between four rotationally symmetric jets within a cylindrical chamber, under conditions relevant to a wide range of engineering applications, including the technology of a Hybrid Solar Receiver Combustor (HSRC). The HSRC geometry 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 (azimuthal angle) to generate a swirl in the chamber. In this study, the jet inclination angle (αj) was varied over the range of 25°–45°, while the jet azimuthal angle (θj) was varied from 5° to 15°. The inlet Reynolds number for each injected jet and the number of jets were fixed at ReD = 10 500 and 4, respectively. Measurements obtained with Particle Image Velocimetry were used to characterise the large-scale flow field within selected configurations. The results reveal a significant dependence of the mean and root-mean-square flow-fields on the jet azimuthal angle (θj) and the jet inclination angle (αj). Three different flow regimes with distinctive flow characteristics were identified within the configurations investigated here. It was also found that θj can significantly influence (a) the position and strength of an external recirculation zone and a central recirculation zone, (b) the extent of turbulence fluctuation, and (c) the flow unsteadiness. Importantly, the effect of αj on the flow characteristics was found to depend strongly on the value of θj.

The influence of aspect ratio on the iso-thermal flow characteristics of multiple confined jets

“…The experimental studies of Boushaki and Sautet 4 employing Particle Image Velocimetry (PIV) showed that an increase in α j from 0 • to 30 • leads to a significant increase in the magnitude of mean and turbulent velocity fields within the jet merging region. Similarly, the PIV measurements of Long et al 10,11 found a strong dependence on jet angles (α j and θ j ) of the instantaneous and mean flow-fields generated with multiple symmetric jets. However, to the best of our knowledge, little or no information is available for the key geometrical parameters (e.g., L c and D c ) of the confined space for multiple jet configurations, although the aspect ratio of geometry has been found to have a significant influence on the flow-fields of free jet impingement [17][18][19] and cavity flow.…”

“…Another limit of these studies is that they have been performed almost exclusively for a single jet, which makes it difficult to directly apply to multiple confined jets. In our previous work, Long et al 11 revealed the presence of both an external and internal recirculation zone (ERZ and CRZ) within these configurations. The ERZ and CRZ regions are associated with the entrainment rate (or the recirculation rate) within the chamber, which is important for combustion stabilization and thermal efficiency.…”

“…7 Of particular interest here are those configurations featuring multiple jets of relevance to the Hybrid Solar Receiver Combustor (HSRC) under development at the University of Adelaide. [8][9][10][11][12] This device features a cavity that is operable as either a solar receiver or a combustion chamber equipped with multiple burners to direct fuel and air into the main cavity and tubular heat exchangers to transfer the thermal energy to the heat transfer fluid. The burners are configured in an annular ring and aligned at an inclination angle (α j ) relative to the axis of the cavity and/or at an azimuthal angle (θ j ) relative to the axis of the burner, resulting in a swirling flow within the main cavity.…”

“…Previous investigations of the flow-fields within the HSRC revealed a significant effect of the jet angles (α j and θ j ) on the strength and position of the large-scale recirculation which is critical for achieving desirable flow regimes. 10,11 In addition, the aspect ratio of L c /D c has a strong influence on thermal efficiency and a) Author to whom correspondence should be addressed: shen.long@adelaide. edu.au capital cost.…”

“…Previous studies of flow-fields generated with multiple symmetric jets within a confined space revealed that the flow structure depends strongly on the arrangement and geometrical features of jets. 3,4,10,11,[13][14][15][16] Chammem et al 3 defined the flow structure downstream from the jet impingement point (P i ) as the "resulting jet flow" and that upstream as the "upstream reverse flow" noting that these flow features are significantly influenced by α j . The experimental studies of Boushaki and Sautet 4 employing Particle Image Velocimetry (PIV) showed that an increase in α j from 0 • to 30 • leads to a significant increase in the magnitude of mean and turbulent velocity fields within the jet merging region.…”