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Decay of a coherent scalar disturbance in a turbulent flow
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Nakano, T. Kerr, R. M. Nelkin, M. |
| Copyright Year | 1985 |
| Description | The time evolution of an initially coherent, sinusoidal passive-scalar disturbance is considered when the wavelength q is less than the length scale of the surrounding isotropic turbulent flow. In 64 sup 3 direct numerical simulations a Gaussian prescription for the average scalar amplitude breaks down after a timescale associated with the wavenumber of the disturbance and there is a transition to a new characteristic decay. The Gaussian prescription is given by exp(-(1/2) q-squared w(t)), where a form for w(t), the Lagrangian mean square displacement of a single fluid particle, is proposed. After the transition the decay is given by exp(-t/tau), where tau is the new characteristic timescale. If q k(sub K), then 1/tau = 1/tau(sub D) + 1/tau(sub K), where k(sub K) is the Kolmogorov wavenumber, tau(sub D) is the diffusive timescale and tau(sub K) is the Kolmogorov timescale. An experiment originally proposed by de Gennesis considered in which the evolution of a coherent laser-induced pattern is read by a diffracting laser. The theory of this experiment involves the dispersion of particle pairs, but it is shown that in a certain limit it reduces to the single Fourier-mode problem and can be described in terms of single particle diffusion. The decay of a single mode after the transition in the simulation best describes the experiment. |
| File Size | 973731 |
| Page Count | 33 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19850021932 |
| Archival Resource Key | ark:/13960/t4dn91812 |
| Language | English |
| Publisher Date | 1985-06-01 |
| Access Restriction | Open |
| Subject Keyword | Fluid Mechanics And Heat Transfer Normal Density Functions Mean Square Values Turbulent Flow Computational Fluid Dynamics Reynolds Number Flow Characteristics Turbulent Diffusion Navier-stokes Equation Simulation Scalars Isotropic Turbulence Kolmogorov Theory Laser Applications Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Technical Report |
