On the time required to reach fully developed flow in pulsed supersonic free jets

A new and simple model is presented for estimating the minimum pulse duration ("valve open time") required for a pulsed nozzle to produce a supersonic beam comparably "cold" to that obtained from a continuous source. The model is based on the notion that cooling will be complete if the leading edge of the beamlet reaches the terminal temperature prescribed by the steady state flow equations before the sound wave created at the back of the pulse by the nozzle's closing catches up with the leading edge. The times predicted from this model for reasonable stagnation conditions are all ≲10μs. © 1983 American Institute of Physics.