Numerical and experimental investigation of the near zone flow field in an array of confluent round jets

Numerical simulations, using three different turbulence models (i.e., standard k-epsilon, RNG k-epsilon and Reynolds Stress Model [RSM]) is performed in order to predict mean velocity field as well as turbulence characteristics in the near zone of a 6 x 6 in-line array of unconfined confluent round jets. The numerical results are compared with experimental data acquired by Particle Image Velocimetry (PIV). All the turbulence models used are able to reproduce the mean velocity field and the development of turbulent kinetic energy of the confluent round jets, but in general, the standard k-epsilon and RSM model show better agreement with experimental data than the RNG model. In terms of mean velocity the second-order closure model (RSM) is not found to be superior to the less advanced standard k-epsilon model in spite of the mean flow curvature present in the flow field. The RSM model, however, provides information on individual Reynolds stresses. RSM show satisfactory agreement of streamwise normal Reynolds stress and shear stress, but generally underpredicts the normal Reynolds stress in the spanwise direction. In comparison with plane twin jets, confluent round jets show a longer merging region. Within the merging region the maximum velocity of the confluent jets decay linearly. As the jets enter the combined region confluent jets have hardly any velocity decay, which leads to a higher maximum velocity for a combined confluent jet than a single round jet. The jet's position within the configuration has a substantial impact on the velocity decay, length of the potential core, and the lateral displacement of the confluent jets. Side jets show faster velocity decay, shorter potential core and higher turbulence level compared to central jets. Side jets are also deformed and has a kidney shaped cross-section in the merging region. Corner jets interact less with neighboring jets compared to side jets, thereby extending the potential core and reducing the velocity decay in the merging region compared to side jets. (C) 2014 Elsevier Inc. All rights reserved.