Structure of the temperature field downwind of a line source in grid turbulence

Abstract

A Lagrangian stochastic model is used in conjunction with detailed wind-tunnel measurements to examine the structure and development of the temperature field behind a line source in grid turbulence. It is shown that on the scale of these experiments molecular diffusion and viscosity have an important influence on temperature fluctuations (particularly on the intensity of these fluctuations) and must be explicitly modelled. The model accounts for a wide range of the measured properties of the temperature field and provides a unified treatment of temperature fluctuations through all stages of the development of the temperature field. This development is discussed in terms of a simple physical picture in which the hot plume is initially smooth and is moved about bodily by the turbulence, but gradually develops increasing internal structure or patchiness as it grows with distance downstream until a self-similar state is reached in which this internal structure maintains the temperature fluctuations.

Measurements of turbulent diffusion in uniformly sheared flow

“…Examples of investigations of turbulent diffusion in the environment include early observations of anti-aircraft shell-bursts (Roberts 1923;Sutton 1932) and plumes of lycopodium spores released in the atmosphere (Hay & Pasquill 1959) and dyes released in a lake (Csanady 1963). Examples of relevant laboratory studies include investigations of diffusion behind a line source in grid turbulence (Warhaft 1984;Anand & Pope 1985;Stapountzis et al 1986), a line source in uniformly sheared flow (Tavoularis & Corrsin 1981;Karnik & Tavoularis 1989), a line source in channel flow (Lepore & Mydlarski 2011), a point source in uniformly sheared flow (Nakamura et al 1986), and a point source in channel flows (Webster et al 2003;Rahman & Webster 2005). In these actual turbulent flows, the turbulent kinetic energy and lengthscale would generally evolve downstream and so would the diffusivities of superimposed scalar plumes.…”

Direct Numerical Simulation of Turbulence with Scalar Transfer around Complex Geometries Using the Immersed Boundary Method and Fully Conservative Higher-Order Finite-Difference Schemes

“…The code employed is based on the code presented in this section, along with the immersed boundary method for handling complex wall geometries (Fadlun et al 2000). Grid-generated turbulence has been widely used to generate quasi-isotropic turbulence in wind tunnels and water channels and has been applied to investigate the heat transfer in a wind tunnel (Warhaft & Lumley 1978;Sreenivasan et al 1980;Budwig et al 1985), mass transfer in a water channel (Huq & Britter 1995), scalar diffusion from line and point sources (Stapountzis et al 1986;Nakamura et al 1987), turbulent transport of small particles in a wind tunnel (Gad-el-Hak & Morton 1979), heat and mass transfer in stable density stratification (Stillinger et al 1983;Lienhard & Van Atta 1990;Jayesh et al 1991;Komori & Nagata 1996;Nagata & Komori 2001), mass transfer in unstable density stratification (Nagata & Komori 2000), and mass transfer with a chemical reaction (Komori et al 1993;Nagata & Komori 2000;Ito et al 2002). Grid-generated turbulence is also considered in turbulence analysis (Nagata et al 2006(Nagata et al , 2010.…”

Effects of Turbulence on Mass Transfer of Cylindrical Disks

“…Mean and fluctuating velocities were measured with Pitot-static tubes and hot wires. It is known, [10] , that the intensity i decays with distance from the grid, while the turbulence length scale L xu increases, which means that the turbulence is nearly homogeneous and isotropic in the transverse direction, but inhomogeneous in the x direction. For constant Re number, the mass transfer is expected to be influenced by changes in both the intensity and the turbulence length scale necessitating the use of many grids.…”