Experiments giving the mass efflux of a Poiseuille flow over a naturally permeable block are reported. The efflux is greatly enhanced over the value it would have if the block were impermeable, indicating the presence of a boundary layer in the block. The velocity presumably changes across this layer from its (statistically average) Darcy value to some slip value immediately outside the permeable block. A simple theory based on replacing the effect of the boundary layer with a slip velocity proportional to the exterior velocity gradient is proposed and shown to be in reasonable agreement with experimental results.

No abstract

WUF.NICVlm II new book on compres~ible-Huid dynamics appears t·here i~ always a tendency to compare it. wit.h the weIlknown works by Shapiro and hy Liepmanll and Hoshko. Although t.hcse hooks have dominat.ed t.his area for many years, there has heen a growing need recently for a new text. OIl compressihle flows suit.ahle for use at t.he senior and first.-year grad1lI,te level. It is the opinion of this reviewer that I.hi,; book fiIlH t.his need admirably.The hook is qui\(! 10llg, and contains far moJ'(! material t.han ean be ilworporated into a single comse. There arc I I chapters in all, t.llI! first two of which present. all introduetion t.o Huid merhanics alHI t.hermodynumics. This mat.erial rould form t.llI! basis of an introduct.ory course on the foundat.iuns of fluid mcchani(!s probably a), t.he first-year graduale level. The lhird chapt.er ronsist.s of an introduction t.o dimensional analysis and similarit.y. The rompressihle-flow IIlRterial st.ltrl~ It!. Clmpter four wit.h a rather lengt.hy ehapt.er on physical llrollst.ies. The author t.reat.~ aeollst.ics from a Hlliri mechanics point of view, and the mat erial rOllld ea~ily form t.hl! basis for the first. part. of an int.roductory course Oil acollsLirs. There follows an interest.ing little chaptnr 011 the nat.ure of steady compressihle flows, after whieh t.he famili:1l' topies of olw-dimensional and two-riimensional st.eady flows, shock waves, and one-(Iimensional unst.l!ariy flows arc discuHsed. FOllr specific examples of self-similar motions arc c1e~crihed in 1\ clmpter under t.hRt hellding, Imd t.he finIlI chapt.er on analogs in compressihle flow inclndes, among ot.hers, shallow WIlt.er waves and t.raffic flow.The hook is very well writ.ten and illnstrated, and contains II conHiderahle nnmber of relevanl problems t.o be worked hy t.he reader. The main emphasis is claimeri to be on fundamentals, hut there is no short.age of good illustmt.ive examples. An ellgaging feRt,ure of the book is t.he illelusioll of short hi"torical remarks which arc scat. Although t.he aut.hors stat.ed in the Int.roduct.ion that. t.he reader of t.he book is "to be equipJled wit.h a· normal undergraduat.e haggage of Ilwr:hanics, applil!ll mat.lwllIatir:s, and strlldmal engineering," the level of eontents of t.his hook is far n,bove wlmt. an ordinllry graduat(! in engineering, even wit.h arlvtlnc(!(1 riegrees, ean comprehend. 1-linee the suhjects of linear anel nonlinear vibl'll(.ions, eIIlst.ir: waves, probabilit.y and st.at.istirs, opt.imi"ations, ami theory of st.rudllres nil have import.ant applieations in Earthquake Engineering, applieri mechanicians, who are well grounderi on t1l1!se suhjerls, lIlay finel t.his hook ext.remely int.erest.ing. 'Professor,

Experiments were performed to study the laminar flow characteristics and the laminar-turbulent transition in a parallel-plate channel, one of whose bounding walls is a porous medium. The flow regime investigated herein is characterized by parallel, unidirectional, fully developed flows in the channel and the porous medium. The experimental results for the laminar regime were found to be in excellent accord with theoretical predictions based on a model which admits a slip velocity at the surface of the porous material. The effect of the presence of the porous wall is to increase the mass flow and decrease the friction factor relative to the corresponding quantities for a solid-walled channel. In addition, transition to turbulence occurs at a lower Reynolds number owing to the presence of the porous wall.