Entrainment by turbulent fountains

Abstract

Experimental measurements of entrainment by turbulent fountains from circular sources in quiescent uniform environments are presented. Our results span almost four orders of magnitude in the source Froude number ( $0.004\leqslant \mathit{Fr}_{0}\leqslant 25$

) and thereby encompass the entrainment across all classes of fountain behaviour identified to date. We identify scalings for the entrained volume flux

$Q_{E}$

, in terms of

$\mathit{Fr}_{0}$

and the source volume flux

$Q_{0}$

, within a number of distinct Froude-number bands corresponding to each class of fountain. Additionally we identify a distinct class of new behaviour, as yet unreported, for

$\mathit{Fr}_{0}\lesssim 0.1$

.