The wakes behind a variety ofaxisymmenic bodies were investigated with flow visualization and hot-wire measurements. The main objective of this study was to correlate changes in the time-averaged features of the wake with changes in the characteristics of the coherent large-scale structure resulting from changing the solidity of the wake generator or by introducing periodic disturbances to force the wake. The use of an axisymmenic probe holder permitted instantaneous decomposition of the axialvelocity field into temporal and azimuthal Fourier modes. Increases in the body solidity resulted in nearly proportional increases in the size of the mean wake boundary. For the non-shedding (low body solidity) wakes, flow visualization shows that the amplitude of discernible large-scale structure is small in comparison to the wake diameter, and there is no evidence of a recirculation region. For the shedding wakes, flow visualization reveals large-scale structure with amplitude that is comparable in size to the wake diameter, and a recirculation region is observed that oscillates in axial extent Fourier analysis of velocity measurements discloses that the temporal scale of the coherent large-scale structure for a non-shedding wake decreases in value with downstream distance while the corresponding scale for a shedding wake is constant Significant changes in the both the time-averaged features of the wake and in the large-scale structure usually occurred only when the forcing frequency was near the natural shedding frequency (within ± 25%). Those time-averaged features changed by forcing include the drag, the mean- and variance-profile shapes, and the size of the wake. The mean profile was observed to change from a regular shape to that which resembles a variance profile. Forcing results in a number of peaks being present in 2-D spectra plots, most of which are the result of non-linear interactions of the forcing wave with the natural shedding frequency. The flow visualization reveals that those peaks which are harmonics or subharmonics of the forcing frequency may be more prominent than the forcing frequency if they are closer to the natural shedding frequency of the unforced wake.

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The low Reynolds number aerodynamics of the flapping wing Micro-Air Vehicle (MAV) developed at NPS by Max Platzer and Kevin Jones was studied numerically. The dynamic mesh simulation model of the full multi-wing configuration, which consists of a fixed wing and a pair of aft position, opposed pitch/ plunge flapping wings was developed using an advanced CFD code that is available commercially. The unsteady flow fields, wake structures and forces were determined by solving the incompressible Navier-Stokes equations, and the results were compared to past experimental observations. The results were encouraging and provided impetus for future computational optimization studies on the NPS flapping wing MAV.

Approved for public release, distribution unlimited / During launch of aircraft off of a carrier deck, steam leakage is sometimes ingested into the aircraft's engine and may cause a compressor stall or 'pop-stall'. As the US Navy prepares to field the single engine F-35C Joint Strike Fighter, it becomes necessary to investigate the phenomenon known as 'pop-stall'. In the present study, steady-state as well as transient measurements prior to and during a steam induced rotating stall were taken. Changes to the honeycomb altered the performance characteristics of the Transonic Compressor Rig and needed to be remapped in order to determine a new stall line as well as a peak performance criterion. Data was taken at 90 percent design speed as well as during a 70 percent steam induced stall with the aide of 9 Kulites at varying positions along the case wall. Data was reduced and analyzed through the use of a data acquisition and data reduction system. / US Navy (USN) author.

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