INTERACTION OF TWO PLANE PARALLEL TURBULENT JETS

Abstract

Analytical and experimental investigations were carried out to study an interaction of two plane parallel turbulent jets which were issued from two parallel free-standing (ventilated) nozzles into stagnant surroundings. Analytical expressions for the resultant velocity distributions were derived by superposing the single jet solutions of Gortler and Reichardt . The analytical results for the mean velocity profiles and the rate of jet spreads are then compared with the available experimental results for the single and combined jet, and the discrepancies are discussed in light of the assumptions made in the analysis. Experiments were then carried out to obtain detailed measurements of mean and fluctuating longitudinal and lateral velocity components using single and cross hot-wires at several streamwise locations in the converging, merging and combined regions of two interacting plane parallel turbulent jets. The results obtained for mean velocity and turbulent intensities distributions, shear stress profiles, probability density function and associated higher order moments of the velocity components, auto-and cross-correlations and their Fourier transforms are presented and discussed. The locations of the merging and confluent points and the spread of the jet were identified from the velocity profiles. The longitudinal turbulent intensities are greater than the lateral intensities in most part of the flow field, indicating that the flow is highly non-isotropic. Along the centreline in the merging region, the lateral turbulent intensities are greater than the longitudinal intensities due to the interaction of the two jets. The flow is chaotic and heterogeneous in the converging region. In the middle part of the merging and combined regions the flow is quite homogeneous, while towards the edge of the jet the flow is intermittent and spotty. The turbulent properties of the combined jet in the combined region are self-similar and agree well with the single jet results. The self-preservation of the turbulent intensities is obtained after about 120 nozzle widths in the streamwise direction. The integral length scales obtained from auto-correlation also suggest that the flow field is non-isotropic in most part of the combined jets. The interaction between adjacent vortices from the opposite sides of the centreline gives rise to small values of co spectrum and coherence in the vicinity of the centreline. In most part of the combined jet, the lateral velocity component leads the longitudinal velocity component by about 180 degrees at the dominant frequency. A significant increase in the value of cospectrum and coherence away from the centreline indicates lie existence of strong vortical coherent structures extending up to the edge of the jet.