Turbulent dispersion from line sources in grid turbulence
نویسندگان
چکیده
Probability density function PDF calculations are reported for the dispersion from line sources in decaying grid turbulence. The calculations are performed using a modified form of the interaction by exchange with the conditional mean IECM mixing model. These flows pose a significant challenge to statistical models because the scalar length scale of the initial plume is much smaller than the turbulence integral scale. Consequently, this necessitates incorporating the effects of molecular diffusion in order to model laboratory experiments. Previously, Sawford Flow Turb. Combust. 72, 133 2004 performed PDF calculations in conjunction with the IECM mixing model, modeling the effects of molecular diffusion as a random walk in physical space and using a mixing time scale empirically fit to the experimental data of Warhaft J. Fluid Mech. 144, 363 1984 . The resulting transport equation for the scalar variance contains a spurious production term. In the present work, the effects of molecular diffusion are instead modeled by adding a conditional mean scalar drift term, thus avoiding the spurious production of scalar variance. A laminar wake model is used to obtain an analytic expression for the mixing time scale at small times, and this is used as part of a general specification of the mixing time scale. Based on this modeling, PDF calculations are performed, and comparison is made primarily with the experimental data of Warhaft on single and multiple line sources and with the previous calculations of Sawford. A heated mandoline is also considered with comparison to the experimental data of Warhaft and Lumley J. Fluid Mech. 88, 659 1978 . This establishes the validity of the proposed model and the significant effect of molecular diffusion on the decay of scalar fluctuations. The following are the significant predictions of the model. For the line source, the effect of the source size is limited to early times and can be completely accounted for by simple transformations. The peak centerline ratio of the rms to the mean of the scalar increases with the Reynolds number approximately as R 1/3 , whereas this ratio tends to a constant approximately 0.4 at large times independent of R . In addition, the model yields a universal long-time decay exponent for the temperature variance. © 2008 American Institute of Physics. DOI: 10.1063/1.3006069
منابع مشابه
Large-eddy simulation of turbulent flow over an array of wall-mounted cubes submerged in an emulated atmospheric boundary-layer
Turbulent flow over an array of wall-mounted cubic obstacles has been numerically investigated using large-eddy simulation. The simulations have been performed using high-performance computations with local cluster systems. The array of cubes are fully submerged in a simulated deep rough-wall atmospheric boundary-layer with high turbulence intensity characteristics of environmental turbulent fl...
متن کاملHistory of Lagrangian Stochastic Models for Turbulent Dispersion
Lagrangian Mode Geophysical Mon © 2012. American 10.1029/2012GM This article briefly summarizes the historical evolution of the modern Lagrangian stochastic (LS) class of models for the calculation of fluid element (or particle) paths in turbulence. The fundamental advantages of a “first-order” LS model relative to alternative descriptions of turbulent dispersion are (1) its ability to correctl...
متن کاملComparison of Turbulent Particle Dispersion Models in Turbulent Shear Flows
This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993)), in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and...
متن کاملThermohydrodynamic Characteristics of Journal Bearings Running under Turbulent Condition
A thermohydrodynamic (THD) analysis of turbulent flow in journal bearings is presented based on the computational fluid dynamic (CFD) techniques. The bearing has infinite length and operates under incompressible and steady conditions. In this analysis, the numerical solution of Navier-Stokes equations with the equations governing the kinetic energy of turbulence and the dissipation rate, couple...
متن کاملApplication of the Schwarz-Christoffel Transformation in Solving Two-Dimensional Turbulent Flows in Complex Geometries
In this paper, two-dimensional turbulent flows in different and complex geometries are simulated by using an accurate grid generation method. In order to analyze the fluid flow, numerical solution of the continuity and Navier-Stokes equations are solved using CFD techniques. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid by means of...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2008