Characteristics of swirling and precessing flows generated by multiple confined jets

Shen Long,Alfonso Chinnici,Timothy C W Lau,Zhao Feng Tian,Bassam B Dally,Graham J Nathan

doi:10.1063/1.5089904

Abstract

An experimental study is reported of the interaction between multiple isothermal jets within a cylindrical chamber under conditions relevant to a wide range of engineering applications, including the confined swirl combustors, industrial mixers, and concentrated solar thermal devices. The particle image velocimetry technique was used to investigate the swirling and precessing flows generated with four rotationally symmetric inlet pipes at a fixed nozzle Reynolds number of ReD = 10 500 for two configurations of swirl angle (5° and 15°) and two alternative tilt angles (25° and 45°). The measurements reveal three distinctive rotational flow patterns within the external recirculation zone (ERZ) and the central recirculation zone (CRZ) for these configurations. It was found that the mean and root-mean-square flow characteristics of the swirl within the chamber depend strongly on the relative significance of the ERZ and CRZ, with the swirling velocity being higher in the CRZ than that in the ERZ. A precessing vortex core was identified for all experimental conditions considered here, although its significance was less for the cases with a dominant CRZ.

Highlights

Devices that utilize multiple-jets within a confined environment are commonly used in a wide range of scientific and industrial applications, such as gas turbine engines[1], solar cavity receivers[2], separated-jet combustors[3] and ventilation systems[4]
For the case of Regime I, the mean flow spirals outward from the center to the near-wall region in each case, with a magnitude that is greatest at x/Lc = 0.36 and decreases with axial distance x/Lc ≥ 0.45. It can be seen from the color scale that there is a trend for the magnitude of Uθ within the outer regions of the chamber to decrease with axial distance from x/Lc = 0.36 to x/Lc = 0.63
In conclusion, new qualitative and quantitative information have been provided to the swirling and precessing flows generated by the Multiple Impinging Jets in a Cylindrical Chamber (MIJCC) with the inclination and azimuthal angles: 1. The new findings of the three distinctive flow regimes (Regimes I, II and III) are as follows: a) The magnitude of tangential velocity Uθ is the strongest [(Uθ/Ue)max ≈ 0.12] and is almost independent from the axial locations throughout the chamber for Regime III where a dominant central recirculation zone (CRZ) occurs, while the value of Uθ is relatively weak [(Uθ/Ue)max ≈ 0.04] and decays much faster along the axis for the cases where a dominant external recirculation zone (ERZ) is present (e.g., Regime I, αj = 25° and θj = 5°). This indicates that the swirl strength is much stronger and remains higher value for the CRZ than that for the ERZ

Summary

Introduction

Devices that utilize multiple-jets within a confined environment are commonly used in a wide range of scientific and industrial applications, such as gas turbine engines[1], solar cavity receivers[2], separated-jet combustors[3] and ventilation systems[4]. The details of the flow-field within them can have a significant influence on their system performance and thermal efficiency. Despite their importance, the internal flow within these systems has not been well characterized due to their greater complexity relative to a single round free jet[5]. The present investigation aims to address key gaps in understanding of these classes of flow through detailed measurements of the flow velocity within a Multiple Impinging Jet in a Cylindrical Chamber (MIJCC), which has geometrical relevance to the Hybrid Solar Receiver Combustor (HSRC) under development at the University of Adelaide[6,7,8, 10,11,12]

Objectives

Results

Conclusion