Engineering topics
Publications and source records attributed to Tam, Christopher K. W..
The stochastic model theory of TAM (1987, 1989) for broadband shock associated noise was extended to include the effects of forward flight. The theory was applied to the forward flight simulation experiments of Norum and Shearin (1984, 1986, and 1988). Good agreement is found between calculated and measured far-field noise spectra over the flight Mach number range of 0.0 to 0.4.
An analytical and computational study of the normal-mode small-amplitude waves of high-speed jets is presented. Three families of instability waves have been identified: (1) the familiar Kelvin-Helmholtz instability waves; (2) supersonic instability waves; and (3) subsonic waves. It is demonstrated that the computed wave patterns and propagation characteristics of these three wave types are consistent with the findings of Oetel (1979, 1980, 1982). The subsonic waves are shown to be unstable only for jets with mixing layers of finite thickness.
Recent experiments conducted at NASA Langley show that twin supersonic jets separating by a distance of approximately two nozzle diameters (center to center) exhibit resonant oscillations under a wide range of operating conditions. In this paper the mechanism responsible for the synchronized resonant oscillations is investigated. A vortex sheet jet model is used in the analysis. The model shows that kinematically two modes of twin jet resonance can occur. One mode involves flapping motion of both jets symmetric with respect to the mid-plane separating the two jets. The other mode involves antisymmetric flapping motion. The symmetric mode is consistent with experimental observations. The vortex sheet jet model is, however, unable to provide quantitative estimates of the shift in screech frequency (as compared to a single jet) due to the resonance phenomenon. The reason for this is discussed. Possible improvement of the model and directions for future work are indicated.