RESONANCE OF CIRCULAR SHOCK-WAVES

In supersonic centrifugal compressor or disc MHD power generators, oscillation modes of the circular shock wave can be caused by the static change or the dynamic change of the back pressure. While previous studies, which included only the former effects, were carried out both experimentally and theoretically, the latter effects of forced oscillation are considered here. The excitation of the back pressure fluctuation in a downstream stagnation chamber was accomplished by rotating a butterfly valve. The pressure fluctuation was measured to investigate the resonance of the circular shock wave at concentric positions in the vicinity of the first shock and in the downstream stagnation chamber. A-D converted signals were statistically correlated to extract the spacial oscillation modes. Resonance was confirmed to occur when the excitation frequency was near the natural frequency of mode 0. Furthermore, the small pertubation of the higher harmonic modes in the downstream stagnation chamber influenced the oscillation modes of the circular shock wave.