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

We report a systematic study of the interaction between four rotationally symmetric jets within a cylindrical chamber obtained with particle image velocimetry, under conditions relevant to a wide range of practical applications including the hybrid solar receiver combustor. The geometry consists of a cylindrical cavity with four inlet jets (representing four burners), which are configured in an annular arrangement and aligned at an inclination angle (alpha(j)) to the axis with a tangential component (azimuthal angle theta(j)) to generate a swirl in the chamber. The configurations of alpha(j) = 25 degrees were assessed with two azimuthal angles theta(j) = 5 degrees and 15 degrees, a range of chamber aspect ratios (L-c/D-c), and a fixed nozzle Reynolds number of Re-D = 10 500. The experimental results reveal a significant dependence of the mean and turbulent flow-fields on the aspect ratio L-c/D-c for the values of alpha(j) and theta(j) considered here. Three different flow regimes and their controlling parameters were identified within the range 1 <= L-c/D-c <= 3. The dependence of the flow characteristics on the chamber length L-c was weak within 1.5 < L-c/D-c <= 3, but significant for 1 <= L-c/D-c <= 1.5. It was also found that the value of L-c/D-c has a controlling influence on the position and strength of large-scale recirculation regions, together with the extent of flow unsteadiness, although this influence is reduced as theta(j) is increased. Published by AIP Publishing.