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Vibrational spectra are reported for cubane, cubane-t/i, .rym-cubane-ti/2, Ym-cubane-í/6, and cubane-t/g-Infrared spectra are from 400 to 3600 cm-1 for CS2 and CCI4 solutions, and for a solid deposited from the vapor at ~100 K. Raman spectra are for the same solutions and for the polycrystalline solid at room temperature. Vibrational assignments have been made for all the fundamentals of all five compounds, 120 modes in all. The fortuitous crystal structure of cubane and cubane-/g was an important aid. Of the 18 fundamentals of cubane, only one or two are not certain. The spectra show almost no effect of the severe bond angle strain. Also there are no low molecular modes; the lowest for cubane is 617 cm'1.

Multiple peaks of comparable strength in unsteady pressure autospectra often characterize compressible flowinduced cavity oscillations. Yet it is unclear whether these peaks (i.e., Rossiter modes) coexist or are the result of a mode-switching phenomenon. The cause of additional peaks in the spectrum, particularly at low frequency, is also unknown. This paper describes the analyses of unsteady pressure data in a cavity using time-frequency methods, namely the Short Time Fourier Transform (STFT) and the continuous Morlet wavelet transform, and higher-order spectral techniques. The STFT and wavelet analyses clearly show that the dominant mode switches between the primary Rossiter modes. This hypothesis is also verified by instantaneous schlieren images. Furthermore, the Rossiter modes experience some degree of low-frequency amplitude modulation. An estimate of the modulation frequency, obtained from the wavelet analysis, matches the low-frequency peak seen in the autospectrum. Polyspectra are used to investigate potential quadratic nonlinear interactions. Significant nonlinearities are present in a L/D -2 cavity at Mach 0.4, while nonlinear effects are much smaller in a L/D -4 cavity at Mach 0.6. These results lead to the hypothesis that when three Rossiter modes (f c >fb> fa) are present and satisfy the relation f c -(f a +fh) = Af~ 0, significant nonlinear coupling can occur between the modes, leading to a low-frequency amplitude modulation of the primary modes at f m = Af and larger than normal SPL. Even when this condition is not satisfied, the difference interactions between the primary modes, namely (f a , -fa), (fb, -fb) and (£, -f c ), create a low-frequency mode that appears in the power spectrum and amplitude modulates the Rossiter modes.

A current NASA Research Announcement (NRA) project being conducted by Georgia Tech Research Institute (GTRI) personnel and NASA collaborators includes the development of Circulation Control (CC) blown airfoils to improve subsonic aircraft high-lift and cruise performance. The emphasis of this program is the development of CC active flow control concepts for both high-lift augmentation, drag control, and cruise efficiency. A collaboration in this project includes work by NASA research engineers, whereas CFD validation and flow physics experimental research are part of NASA's systematic approach to developing design and optimization tools for CC applications to fixed-wing aircraft. The design space for CESTOL type aircraft is focusing on geometries that depend on advanced flow control technologies that include Circulation Control aerodynamics. The ability to consistently predict advanced aircraft performance requires improvements in design tools to include these advanced concepts. Validation of these tools will be based on experimental methods applied to complex flows that go beyond conventional aircraft modeling techniques. This paper focuses on recent/ongoing benchmark high-lift experiments and CFD efforts intended to provide 2-D CFD validation data sets related to NASA's Cruise Efficient Short Take Off and Landing (CESTOL) study. Both the experimental data and related CFD predictions are discussed.