The purpose of this instrumentation grant was to purchase equipment to be used in conjunction with an ongoing ARO-funded research grant entitled "Experimental Studies of High-Speed Separated Flows." The research efforts of this program are focused on experimental investigation of the fluid dynamic mechanisms and interactions within separated flow regions embedded in high-speed compressible flows. The fundamental objective is to improve understanding of the detailed flow processes in the near-wake of missile and projectile-type base flows with the long-term goal of optimizing and controlling these flows to derive flight vehicle performance benefits. The funds were used to repair the heads of two Nd:YAG lasers that are used heavily in particle image velocimetry, Rayleigh/Mie scattering, and planar laser-induced fluorescence (PLIF) experiments. These replacements/repairs will extend the lives of these lasers for at least 5 years. The department also used the equipment funds to purchase an intensified CCD array camera system that may be used for experiments with low signal levels (e.g., for ongoing acetone PLIF experiments). Finally, funds were used to purchase a state-of-the-art pressure transducer calibration dead-weight tester. In all cases, purchase of this equipment will help to maintain and strengthen the department's ability to make significant contributions to the research area of compressible, separated flows, which is of significant importance to the U.S. Army. The specific pieces of equipment, vendors, and purchase prices are detailed.

This final report describes the results of a four-year research effort that performed experimental studies in the general area of high. speed separated flows. The motivation for this research effort was to investigate in detail high-speed base flows that are similar in nature to those occurring for missiles and projectiles, so that they can be better understood, predicted, and controlled. The research program consisted of two inter-related tasks: (1) planar visualization and measurement of axisymmetric, supersonic base flows; and (2) three-dimensional, supersonic base flows. The research approach consisted of detailed separated flow experiments employing both conventional instrumentation, such as schlieren and shadowgraph photography, surface streakline visualization, and mean and fluctuating pressure measurements, with major emphasis on non-intrusive optical diagnostic techniques, including laser Doppler velocimetry, particle image velocimetry, planar Rayleigh/Mie scattering visualization, planar laser/induced fluorescence, and pressure. sensitive paint. We believe that this research effort has contributed significant fundamental understanding of the fluid dynamic mechanisms in separated flows, in addition to the direct relevance of this program to applications of importance to the U.S. Army.

Summary: An experimental and theoretical study has been made of the two-dimensional transonic flow past a 12° wedge airfoil with lower surface inclined 13° to the air stream. The experimental portion of the study consists of surveys of the flow field about the leading edge in a closed throat tunnel near choking Mach number by means of an X-ray densitometer. From these surveys various features have been determined; namely, the location of the stagnation point, the location of the sonic line, the size of the separation bubble on the upper surface, and the value of the Mach number at the bubble edge. These features were relatively insensitive to changes in Reynolds number in the range from 1X106 to 3X106 based on chord. The theoretical portion of the study consists of the calculation by relaxation methods of an unbounded, inviscid, two-dimensional flow about a portion of the same body at a free-stream Mach number of exactly unity. The calculations yield a separation bubble on the upper surface which has a shape shown to be compatible with known theoretical conditions for viscous attachment to the upper surface of the body. Agreement between theoretically calculated and the experimentally determined features of the flow was good in regions where the local Mach number was 2 or less. In regions of higher local Mach number the agreement was fair. The theoretically determined Mach number on the bubble edge was 2.80 whereas the experimentally determined value was 2.30. The theoretically determined length of the separation bubble was 1.54-percent chord whereas the experimentally determined length was about 5-percent chord. The theoretically determined location of the stagnation point was 0.16-percent chord from the leading edge whereas the experimentally determined location was at 0.56-percent chord. The experience gained in studying the flow suggests the possibility that the solution obtained is not unique and that another solution in better agreement with experiment might exist.