| Popis: |
Spectral analysis of a low-boom axisymmetric external compression inlet has been performed using Schlieren video and experimental unsteady surface pressure readings as a function of mass flow rates. The experimental data was obtained for fixed inlet Mach number in the 8’ x 6’ supersonic wind tunnel at the NASA Glenn Research Center. A 5 kHz sampling rate is used for surface pressure transducer readings while the shock motion was captured with Schlieren video frames at 2,000 frames per second, and processed using image-threshold analysis to determine fluctuations in external shock position. Power spectral density plots are used to reveal the dominant excitation modes for both the normal shock and surface pressure fluctuations. These fluctuations are minimal at the design mass flow rate case of 98.5% mass flow ratio (MFR). However, substantial oscillations were observed for a MFR of about 95.5%, indicating a small buzz region can occur at a relatively high mass flow rate. For the normal shock oscillations, these are primarily focused at frequencies of about 20 Hz, 31 Hz and 70 Hz. The pressure fluctuations indicated similar frequencies but were a strong function of pressure tap location. |
