MULTIFRACTAL CHARACTERISTICS OF AXISYMMETRIC JET TURBULENCE INTENSITY FROM RANS NUMERICAL SIMULATION

다국어 초록 (Multilingual Abstract)

<P>A turbulent jet bears diverse physical characteristics that have been unveiled yet. Of particular interest is to analyze the turbulent intensity, which has been a key factor to assess and determine turbulent jet performance since diffusive and mixing conditions are largely dependent on it. Multifractal measures are useful in terms of identifying characteristics of a physical quantity distributed over a spatial domain. This study examines the multifractal exponents of jet turbulence intensities obtained through numerical simulation. We acquired the turbulence intensities from numerical jet discharge experiments, where two types of nozzle geometry were tested based on a Reynolds-Averaged Navier-Stokes (RANS) equations. The <TEX>$ k$</TEX>-<TEX>$ \varepsilon $</TEX> model and <TEX>$ k$</TEX>-<TEX>$ \omega $</TEX> model were used for turbulence closure models. The results showed that the RANS model successfully regenerates transversal velocity profile, which is almost identical to an analytical solution. The RANS model also shows the decay of turbulence intensity in the longitudinal direction but it depends on the outfall nozzle lengths. The result indicates the existence of a common multifractal spectrum for turbulence intensity obtained from numerical simulation. Although the transverse velocity profiles are similar for two different turbulence models, the minimum Lipschitz-Hölder exponent <TEX>$ (\alpha _{\min })$</TEX> and entropy dimension <TEX>$ (\alpha _{1})$</TEX> are different. These results suggest that the multifractal exponents capture the difference in turbulence structures of hierarchical turbulence intensities produced by different turbulence models.</P>