Simulations of high‐aspect‐ratio jets

Abstract

???The definitive version is available at www3.interscience.wiley.com '. Copyright John Wiley and Sons Ltd. DOI: 10.1002/fld.340 [Full text of this article is not available in the UHRA]There are many practical situations when jets are emanating from non-axis-symmetric apertures, yet numerical simulations of such three-dimensional jets are scarce and most of them have failed to reproduce some of the unique flow features. Examples of this type of jets are gas leaks from flanges. These can be treated as jets issuing from high aspect ratio rectangular orifices. The present work consists of a series of large eddy simulations typifying such jets using different inflow boundary conditions. Good agreement with available experiments was observed provided appropriate boundary conditions were present. A discrete method for formulating turbulence data with a known energy spectrum for an inflow condition is outlined and evaluated with three other inflow conditions???a steady uniform profile, a steady parabolic profile and pseudo-random noise. The implementation of the new inlet condition results in a more realistic centreline velocity decay where the division between the end of the potential core region and the start of the characteristic decay region is clearly visible. Large velocity oscillations are also observed in the final quarter of the domain (15???20 slot widths downstream). Similar oscillations have been observed in real jets. Off-centre mean velocity peaks are present along the major axis 10 slot widths downstream of the exit in all the simulations. The peaks are approximately 3% of the centreline velocity. The presence of the off-centre peaks are proved to be independent of jet inflow boundary conditions and an explanation for the mechanism causing the off-centre peaks is given

On the effect of inflow conditions in simulation of a turbulent round jet

“…Most of the numerical simulations conducted so far have failed in predicting these flow features, particularly in the near-field region. The same differences between numerical and experimental results are observed in all shapes of nozzle including round, planar, and rectangular nozzles [20,21]. These differences can be seen especially in the near-field region.…”

Reduced basis simulations as a tool for generating turbulent inlet‐data for two opposing jets

“…The rapid increase in turbulence energy shows that the production mechanisms are present in the inlet turbulence. If not realistic turbulence is given as boundary conditions, the energy has a tendency to decrease before the turbulence reorganizes, becomes self-sustained and can start to grow again (see Figure 2 and also References [7,8]). Figure 5 shows mean velocity W , rms-proÿles and turbulent shear-stress uw of the merged jet.…”

Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: the influence of small aspect ratio

“…Wilson and Demuren [14] performed a finite-difference numerical simulation on a three-dimensional rectangular jet with an aspect ratio of 2:1, using three different turbulence conditions at the jet inlet. Holdo and Simpson [15] examined a rectangular turbulent jet with an aspect ratio of 10:1 using large eddy simulation. When compared with the experimental results of Quinn et al [8], the results of Holdo and Simpson show a good agreement in the far-field region, but they do not show the initial acceleration of the jet in the stream-wise direction within the first five equivalent diameters of the flow field.…”