External Intermittency Simulation in Turbulent Round Jets

Abstract

Direct numerical and large eddy simulation (DNS and LES) are applied to study passive scalar mixing and intermittency in turbulent round jets. Both simulation techniques are applied to the case of a low Reynolds number jet with Re=2,400, whilst LES is also used to predict a high Re=68,000 flow. Comparison between time-averaged results for the scalar field of the low Re case demonstrate reasonable agreement between the DNS and LES, and with experimental data and the predictions of other authors. Scalar probability density functions (pdfs) for this jet derived from the simulations are also in reasonable accord,although the DNS results demonstrate the more rapid influence of scalar intermittency with radial distance in the jet. This is reflected in derived intermittency profiles, with LES generally giving profiles that are too broad compared to equivalent DNS results, with too low a rate of decay with radial distance. In contrast, good agreement is in general found between LES predictions and experimental data for the mixing field, scalar pdfs and external intermittency in the high Reynolds number jet. Overall, the work described indicates that improved sub-grid scale modelling for use with LES may be beneficial in improving the accuracy of external intermittency predictions by this technique over the wide range of Reynolds numbers of practical interest.

Numerical simulation and self-similarity of the mean mass transfer in turbulent round jets

“…The full grid validation is reported in [1], where the grid is analyzed in terms of the following variables: i) ratio between sub-grid viscosity and laminar viscosity; ii) ratio between sub-grid kinetic energy and turbulent kinetic energy; iii) ratio between local grid stencil and Kolmogorov length scale; iv) turbulence energy spectra. A flat velocity profile is imposed on the nozzle exit, similarly to the experiments of [29], and previous numerical investigations [13,[30][31]. A no-slip boundary condition is used on the nozzle lip.…”

Near-Field Study of Multiple Interacting Jets : Confluent Jets

“…The intermittent behavior of the near field of a round jet has been investigated in numerical and experimental studies (Gilliland et al, 2012;Ranga Dinesh et al, 2010). Among the turbulence models that consider intermittency, two transition models, the ( ) model (Walters and Cokljat, 2008;Walters and Leylek, 2004) and the TrSST (Menter et al, 2006) model, were selected for this study.…”