Large eddy simulation of flow and scalar transport in a round jet

Abstract

Large eddy simulation (LES) was performed for a spatially developing round jet and its scalar transport at four steps of Reynolds number set between 1200 and 1,000,000. A simulated domain, which extends 30 times the nozzle diameter, includes initial, transitional, and established stage of jet. A modified version of convection outflow condition was proposed in order to diminish the effect of a downstream boundary. Tested were two kinds of subgrid scale (SOS) models: a Smagorinsky model (SM) and a dynamic Smagorinsky model (DSM). In the former model, parameters are kept at empirically deduced constants, while in the latter, they are calculated using different levels of space filtering. Data analysis based on the decay law of jet clearly presented the performance of SGS models. Simulated results by SM and DSM compared favorably with existing measurements of jet and its scalar transport. However, the quantitative accuracy of DSM was better than that of SM at a transitional stage of flow field. Computed parameters by DSM, coefficient for SGS stresses, C R , and SGS eddy diffusivity ratio, Γ SGS , were not far from empirical constants of SM.Optimization of the model coefficient was suggested in DSM so that coefficient C R was nearly equal in the established stage of jet but it was reduced in low turbulence close to the jet nozzle.

Quantitative planar imaging of turbulent buoyant jet mixing

“…The spatial extent of the planar measurements makes the results ideal for assessments of LESs of jet mixing. LES of round jets has been reported by Olsson & Fuchs (1996), Basu & Mansour (1999), Boersma (2004) and Suto et al (2004). LES results are, by definition, grid dependent, meaning that computed quantities such as scalar fluctuations and gradients will depend on the resolution of the grid (or filter) scale used for the simulations.…”

“…Finally, the filtered grid for each window is aligned so that one grid cell in each (radial) row is centred on the flow centreline. For reference, we note that for the previously reported LES of round jets of Basu & Mansour (1999), Boersma (2004) and Suto et al (2004), the relative resolution is r/λ D ≈ 5-7, where r is the computational grid spacing, and so the resolution levels represented here are characteristic of actual LES. (Strictly speaking, the relative resolution, /λ D , measures the degree to which a given grid fails to resolve the finest molecular mixing scale or, in LES, the departure from DNS resolution; it does not directly measure the ability of an LES grid to resolve the energy-containing flow scales.)…”

Experimental and numerical investigation of turbulent jets issuing through a realistic pipeline geometry: Asymmetry effects for air, helium, and hydrogen

“…Of these, significant advances in round jet theory have been made possible from statistical analysis of many physical experiments [5][6][7][8][9][10][11][12][13][14][15][16][17]. Advances in computational resources have also allowed numerical sim-ulation, through large eddy simulation (LES), to prove useful for determining entire flow fields of such round jets [18][19][20][21][22]. In most experiments, data has been collected for air, helium, and CO 2 jets, due to the reactive nature of hydrogen.…”