Boundary Lyer Theory

230
XI. Axinlly symmctricnl and three-dinicnsionnl bonndnry layers
the boundary layrr cxtends considorably higher than in the example with the disk
rotating in a fluid at rest (Scc. Vb). If thc boi~&r?/-hyer thickness 8 is defined as the
height for which thr drviation of thc pcriphrral vclocity is cq~~al to 2 prr ccnt , wc
for the stationary fluid.
shall obtain 8 = 8 1/ v/w as against 8 = 4 d q
The cxa~njtlc of t,11c mot.ion of a vor1.c~ sourcc hl.wccr~ t,wo pzrallcl walls consiclcretl
by U. Vogclpohl [I201 is rel:it,ctl 10 somo cxtcnt to thc prcscnt cam. For
very small ltcynolds numbers thc velocity distribution deviates little from the
parabolic curve of Poisc~~illc flow. For large Rcynoltls numhcm thc velocity profile
approachcs a rectangular tlistribntion, and a boundary laycr is sccn to bc forming.
The corrcsponding case of turl)ulcnt flow was discussed by C. I'fleidercr [%I. In this
conncxion t,hc papcr hy R. Bccker [F1 may also be consulted.
Similnr phnno~ncnn cnn bc found in swirling flow through n conical funncl-like channel
investigated by I