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Boundary Lyer Theory

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710 XXIII. l'urhnlrnt. honntlnry lnycrn in rornprrmihlo flow<br />

In order to apply the preccding equation to particular cases it is still necessary<br />

to malzc a suitable ass~~mption about the ratio of thc mcan velocity at tho outer<br />

edge of the laminar suh-laycr to that in the free stream t. In the particular casc when<br />

P = 1, thc I'randtl-Taylor equation (23.18) reduces to Reynoltls's cquntion (23.16).<br />

In clcriving tho Prar~tlt~l-Taylor equation (23.18) it was supposed that tllc bountlary<br />

laycr coulcl bc sharply divitlcd into a turbulcnt laycr and a laminar sob-layer.<br />

In actual fact onc merges intp thc othcr in a continuous way antl it is possible to<br />

discern the cxistcnce of an inkrmcdiatc, or I~uCfer layer in which thc mngnit~~rlcs<br />

of tlic molccl~lar and tml)ulcnt cxchangc arc comparable. 'S?Il. vo11 I

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