Experimental evaluation of a subsonic Ludwieg tube

On mechanisms of choked gas flows in microchannels

“…No theories up to now can perfectly explain the significant pressure drop from the channel outlet (p o ) to the reservoir (p o ) for a subsonic gas flows. Yet the NASA report [39] found that an expansion wave may form and propagate pressure information even in subsonic gas flows. Although the expansion wave has not been caught in our simulations, it is reasonable to believe that it is the expansion wave downstream the channel outlet that holds the effective pressure ratio (p i /p o ) when the outlet pressure p o decreases lower than the critical value.…”