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This Defense Intelligence Reference Document from the Defense Intelligence Agency, dated 20 November 2010, was one of a series of advanced technology reports produced in FY 2010 under the Advanced Aerospace Weapon System Applications (AAWSA) Program. It reviews the theory of subsonic, supersonic and hypersonic flow. It then compares electromagnetic, optical, and acoustic and seismic methods for detecting and tracking hypersonic objects, and it makes four recommendations for progress over the next 30 years.
“Anderson”2 pages
UNCLASSIFIED// I Ok err1e1111t t!l!li!!! 8HLV Boundary Layers Strouhal Eddies or Streamlines Vortices ~Turbulent Wake~ ---------------------<:----!--/----- Projectile Direction of Flow Figure 2. Subsonic Flow Past a Projectile. Visible examples of a "wake" are the contrails observed in the upper atmosphere when water vapor in the exhaust of jet aircraft freezes into ice crystals, highlighting the wake generated by the aircraft and its engines. In still air, the wake can be visible for many miles behind the aircraft. The wake rapidly becomes turbulent as it extends downstream. The Strauhal eddies are detectable and have a shedding frequency that is expressed in terms of the Strauhal number, St= f 0/V, where f is the Strauhal shedding frequency (hz), O is the diameter (m) of the projectile, and V is its velocity (m/s) through the air. The Strauhal number is a function of Reynolds number, as shown in Figure 3. By measuring the Strauhal frequency, the velocity of the projectile can be determined with moderate accuracy. At low speeds, and corresponding low Reynolds numbers, the flow is "laminar" where streamlines move in smooth "laminae" or layers over projectiles. At high Reynolds numbers, the fluid flow becomes unstable and forms a widely distributed set of small eddies defined as "turbulence." In turbulent flow, rapid mixing of the flow in the wake, even in the boundary layers, will occur. 5 UNCLASSIFIED/ ;roR orrtCIAL USE one,
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 46 pages are in the text index: search them above, or from the library's search.