Applicability of the aero-optic linking equation to a highly coherent, transitional shear layer

We investigate the validity of applying a simplified (under the assumptions of isotropic and homogeneous turbulence) aero-optic linking equation to a flow field that is known to consist of anisotropic and nonhomogeneous turbu lence. The investigation is performed in the near-nozzle region of a heated two-dimensional jet, and the study makes use of a conditional-sampling exp eriment to acquire a spatiotemporal temperature field database for the heat ed-jet flow field. After compensating for the bandwidth limitations of cons tant-current wire temperature measurements, the temperature field database is applied to the computation of optical degradation through both direct an d indirect methods, relying on the aero-optic Linking equation. The simplif ied version of the linking equation was found to provide good agreement wit h direct calculations, provided that the length scale of the density fluctu ations was interpreted as being the integral scale, with the limits of inte gration being the first two zero crossings of the covariance coefficient fu nction. (C) 2000 Optical Society of America OCIS codes: 120.5050, 120.6810, 010.7060.