Abstract
In this paper the oscillations of pseudo-shock waves in a straight rectangular duct when the flows are choked at the duct exit have been investigated by wall pressure fluctuation measurements at five measuring points along the duct. The pressure signals are statistically analysed using a micro computer. The results show ; (1) The wall pressure at the first shock of a λ-type pseudo-shock wave oscillates with an amplitude of 0.35ΔPpsw and low frequencies below 40 Hz, where ΔPpsw is the whole pressure rise due to a pseudo-shock wave. (2) The wall pressure at the first shock of an X-type pseudo-shock wave oscillates with an amplitude of 0.5 to 0.6ΔPpsw and with low frequencies below 100 Hz and high frequencies of 150 to 250 Hz. (3) The wall pressure fluctuations in pseudo-shock waves are always induced by the pseudo-shock wave oscillations. (4) The frequencies of the pseudo-shock wave oscillations obtained experimentally are nearly the same as those of the oscillations of air columns in straight ducts behind the pseudo-shock waves.
