Characterization of the Impingement Region in an Axisymmetric Turbulent Jet

Abstract

A conceptual model is presented for submerged, axisymmetric, turbulent impinging jets which allows for fluid entrainment and, thus, variable flow conditions before deflection. Flow in the impingement region becomes a function of nozzle height, and measured axial velocities and pressure distributions can be generalized for similar jet profiles. Mean velocity in the deflecting jet near the centerline can be approximately described by an inviscid solution. Wall transfer processes are predicted by properly scaling previous boundary layer solutions and measured pressure distributions.

Discussion on “CFD analysis of the effect of nozzle stand-off distance on turbulent impinging jets”

“…If a linear trend is assumed in this region, a decay slope of 0.07 is found from the experimental results for water jets. This is in very good agreement with the CFD computations and with the work of Giralt et al (1977) who proposed that this slope should be 0.077.…”

“…It can be seen that jets with a different issuance velocity produce different lengths of core decay, which in turn are different from those obtained from Giralt et al (1977) and from the CFD computations for air jets.…”

“…The paper provides interesting results of CFD simulation of turbulent circular jets impinging vertically on a flat plate. Three different models were used, the realizable k-model, the k-SST model, and the RSM model, and compared to experimental data from Rajaratnam et al (2010) and Giralt et al (1977). Many characteristics of the impinging jet were reproduced in good agreement with the experimental data.…”

“…It has to be mentioned that, according to the Authors, computations were performed with incompressible RANS equations. Also in the free jet region, the Authors call the attention to rather different behavior between the experimental data from Rajaratnam et al (2010) and Giralt et al (1977). They correctly suggest that this might be due to different nozzle designs that affect jet evolution.…”

“…For air jets, Beltaos and Rajaratnam (1977) proposed that the impingement region starts at x i = 1.2D from the obstacle, while Giralt et al (1977) suggested that this result is valid for nozzle heights of less than H/D = 6.8, and for larger values: x i /D = 0.153(1 + H/D). This suggests that the impingement zone has different limits for air and water jets.…”