Accession Number:

ADA243470

Title:

Transmission of Thin Light Beams Through Turbulent Mixing Layers

Descriptive Note:

Doctoral thesis

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s):

• Wissler, John B.

Report Date:

1991-09-06

Pagination or Media Count:

122.0

Abstract:

Light transmission through incompressible gaseous turbulent mixing layers is 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 are 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 considers both the unequal density high-speed Helium and low-speed Nitrogen 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 range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure about 1 microsec white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin Helium-Neon laser beam as it wanders under the influence of the passing coherent structures. The study finds 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 layers 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.

Descriptors:

• *LIGHT TRANSMISSION
• *TURBULENT FLOW
• CORES
• LAYERS
• STRUCTURES
• COHERENCE
• LIGHT
• DEFLECTION
• HIGH PRESSURE
• VORTICES
• LASER BEAMS
• NITROGEN
• GASES
• LOW VELOCITY
• SHEETS
• PRESSURE
• FLUIDS
• THINNESS
• MIXING
• PHOTOGRAPHIC FILM
• TRANSITIONS
• HELIUM
• HELIUM NEON LASERS
• DISTORTION
• REYNOLDS NUMBER
• BOTTLES
• WHITE LIGHT
• TRAILING EDGES
• DENSITY
• OPTICAL PROPERTIES

Subject Categories:

• Lasers and Masers
• Optics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE