Flow phenomena basic to separated flows are being experimentally investigated. Nonintrusive measurement techniques based on laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and Mie/Rayleigh scattering are being used. Under investigation are plume-induced separated flows, supersonic, axisymmetric base bleed flows, and incompressible and compressible mixing layers. These experimental data will provide new information and insight into mechanisms governing separated flow phenomena.

A particle image velocimeter (PIV) system for use in high-speed flows is under development. PIV is a technique for visualizing and quantifying the instantaneous velocity field in an entire plane in the flow. The principle of operation is to use two pulses of a laser beam, expanded into a plane, to obtain a photographic double exposure of seed particles suspended in the flow. The method is currently being applied to planar incompressible and compressible shear layers.

A nonintrusive, optical measurement technique is being developed to make spatially well-resolved pressure measurements on surfaces in aerodynamic flows. The method is based on applying a ruthenium-based compound on the surface of interest, illuminating the compound with the proper wavelength of light, and detecting the resulting luminescence intensity. This luminescence signal is known to be inversely proportional to static pressure resulting from quenching by oxygen. Development and use of the technique will allow measurement of the mean and time-resolved pressure distributions on the various aerodynamic surfaces with excellent spatial resolution.

This research focuses on the computation of the unsteady, large-scale, three-dimensional structures present in supersonic base flows. Computations are performed using very large eddy simulations (VLES) which allow modeling of the large-scale turbulence. Current computations indicate that the large structures present in supersonic shear layers, similar to the shear layers present in base flows, can accurately be modeled and captured using VLES. The accuracy of the supersonic base flow computations will be verified using experimental data. These computations will provide better understanding of the fundamental physics of supersonic base flows.

Flow fields produced by sonic circular and elliptical jets injected transversely into supersonic streams are investigated experimentally in a new facility at Wright-Patterson AFB. Experimental techniques employed include planar Mie/Rayleigh scattering, and pressure and concentration probe measurements. Mie/Rayleigh scattering images offer detailed information concerning the instantaneous and time-averaged structural organization of the flows. The probe data yields measurements of stagnation pressure losses and mixing. The motivation for this work is to improve understanding of the fluid dynamic mechanisms within the flow fields.

An experimental study is being conducted to examine the existence, role, and dominance of large-scale structures in the free shear layer, recompression, reattachment, and redevelopment regions of a compressible separated flow. The experimental technique employed is planar Mie/Rayleigh scattering from condensed ethanol droplets seeded in the flow. This research effort will result in improved understanding of the role of large structures in these flows with the future goal of manipulating them for optimum performance in various applications.

The objective of this research program is the development of new nonintrusive optical techniques for spatially and temporally resolved measurements of pressure, temperature, and density in high-speed separated flows. Two new coherent anti-Stokes Raman scattering (CARS) techniques are proposed: simultaneous detection of vibrational and pure rotational Raman signals using dual-pump CARS and high-resolution pure rotational CARS. In the high-resolution pure rotational CARS technique, the CARS signal from two nearly overlapping transitions, the nitrogen S(9) line and the oxygen S(13) line, will be spectrally resolved using a high-finesse solid etalon.

A MacCormack-based computer program has been developed for time-integration of the unsteady compressible flow equations with multiple domains. The objective of this research is to study the large-scale structures of com pressible flow over a flat plate. Calculations are in progress for various Reynolds numbers and Mach numbers.

* Denotes principal investigator.