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Underexpansion jet to cavity flow induced pressure
oscillation inside the cavity tube and the induced temperature
increasing on the bottom of the tube has been investigated based
on three parameters of nozzle pressure ratio, nozzle exit to
cavity distance and the cavity tube length. Two major flow modes
named as regurgitant mode and screeching mode were observed. The
measured major frequency on the pressure oscillation inside
cavity tube is very closed to the theoretical fundamental
frequency of the flow system or its multiplier. Instead of a
solid cavity tube end, as replacing it with a sponge-end or a
open-end, it has been observed that the amplitude of the
pressure oscillating reduced to a negligible level, however, the
major frequency remains on the same characteristics. It is
concluded that the major mechanism for the pressure oscillating
inside cavity tube is owing to the pressure wave reflection
between the solid end surface and the inlet surface of the
cavity tube. On some regurgitant modes the amplitude of the
pressure oscillation can be as high as 70 psia, with a frequency
closed to the fundamental frequency. Due to the accumulation of
the entropy on the cavity tube end on the pressure oscillation
processes in regurgitant mode, an obviously temperature rising
has been measured on the end of the cavity tube.
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