Turbulence Simulation: Outer Scale Effects on the Refractive Index Spectrum

Report No. ARL-TR-548
Authors: Tofsted, David H.
Date/Pages: November 2000; 50 pages
Abstract: An analysis of the commonly used refractive index power spectrum indicates that its method of simulating outer scale effects is deficient in two aspects: it approaches a nonzero value at zero frequency and is ambiguous regarding definition and usage of the outer scale in its functional form. To resolve these problems, a modified form of the refractive index spectrum is proposed which properly models the behavior of the spectrum at zero frequency and simulates the energy-containing eddy region. In support of this analysis, outer scale is defined such that it is independent of the mathematical form used to describe the refractive index spectrum. Based on reported experimental data, a new equation for outer scale as a function of stability conditions is proposed, revealing dependence of the outer scale on both height above the surface and the stability-related Monin-Obukhov length.
Distribution: Approved for public release
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Last Update / Reviewed: November 1, 2000