Accession Number : ADA267266


Title :   Transmission of Light through a Turbulent Mixing Layer


Descriptive Note : Final rept. 30 Sep 89-30 Jun 92,


Corporate Author : CALIFORNIA INST OF TECH PASADENA GRADUATE AERONAUTICAL LABS


Personal Author(s) : Roshko, Anatol ; Wissler, John


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a267266.pdf


Report Date : 14 Aug 1992


Pagination or Media Count : 5


Abstract : Light transmission through incompressible gaseous turbulent mixing layers was investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments were done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considered both the unequal density (high-speed He and low-speed N2) and equal density (high-speed N2 and low-speed He-Ar) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers ranged between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics were first studied qualitatively using a network of thin sheets of short-exposure (approx. l microsec) white light which were aberrated by the mixing layer and then imaged directly onto photographic film. Light transmission characteristics were then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wandered under the influence of the passing coherent structures. The study found that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high- speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the spanwise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs. ...Aero-optics, Turbulent structure.


Descriptors :   *TURBULENT BOUNDARY LAYER , *LIGHT TRANSMISSION , VELOCITY , ANGLES , DENSITY , OPTICAL PROPERTIES , OPTICS , HIGH PRESSURE , LASER BEAMS , WHITE LIGHT , INCOMPRESSIBLE FLOW , REYNOLDS NUMBER , STATIC PRESSURE , VALUE , TRANSITIONS , PHOTOGRAPHIC FILM , MIXING , PRESSURE VESSELS , TRAILING EDGES , UNIFORMS , GAS FLOW , PLATES , VORTICES , INTERACTIONS , INTERFACES , EDGES , LIGHT , DEFLECTION


Subject Categories : Aerodynamics
      Optics


Distribution Statement : APPROVED FOR PUBLIC RELEASE