Although a free jet is a well investigated problem in literature, there are still some aspects that are discussed controversially. Especially the Reynolds number Re dependence of the propagation behaviour is an open question. This problem was addressed on the basis of experimental investigations of compressible, transient, subcritical, round air jets. For this purpose, the velocity field of sudden horizontal vessel discharges were considered experimentally for the first time with a phase Doppler anemometer in the range of up to 60 times the outlet diameter. The determination of the particle size in addition to the velocity provided an important basis for validation. This ensured that only particles with an almost perfect following behaviour exhibiting the gas velocity were considered. Statistical analyses show a significant influence of the Reynolds number Re on the decay rate K1,u with a significance value p = 1.703 ⋅ 10-4 and spreading rate K2,u with p = 1.453 ⋅ 10-6 in the investigated range of Reynolds number 30 000 ≤ Re ≤ 400 000. With increasing Reynolds number Re, the decay rate increases K1,u and the spreading rate K2,u decreases. This disproves the theory that the propagation of free jets is independent of the Reynolds number Re. Since the influence of the Reynolds number is relatively small, the specification of an average value and a quasi-self-similar behaviour seems to be appropriate. The average decay constant is K1,u = 5.86 and the average spreading rate is K2,u = 0.096.
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