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 Kiri February 22, 1999 17:08

Entropy

Here's a thermo Q, not really related to CFD. Responses will be much appreciated. (Even references.)

I'm looking for a simple engineering type (based on some thermodynamic model of course) approximation that will allow me to determine the entropy difference between the free stream and the inside of a boundary layer (on a flat plate, for example). We can assume: (1.) No temp loss from plate to edge of b.l. (2.) No pressre loss in transverse dirn to flow (3.) 2-D model (Unidirectional flow)

Simple, but not simplistic, expression (in other words, if I plug in numbers of variables, I must get a value for my delta_s :) and dimensionally correct.

Supersonic flow before the flat plate; two cases: a) Expression w/ shock b)Exp ignoring shock.

More than the expressions themselves, I'd like to know how and where one starts on this.

Many thanks in advance.

 Sergei Chernyshenko February 22, 1999 17:59

Re: Entropy

Hi, Kiri.

In case Pr=1, which might be a reasonable approximation for crude estimates, there is a similarity between the energy and momentum equations in the boundary layer. Therefore, sometimes (depending on the boundary conditions) the question about the entropy distribution reduces to the question about velocity distribution for which it is easier to find answers. The good point to start is the book by Shlichting, 'Boundary layer theory'. (May be, I misspell the name, it can be Schlichting or similar. Sorry, I remember the spelling in Russian only and do not have the book handy, but it is quite famous book, really.)

Note especially integral methods there, they include approximations for various quantities in the boundary layer.

In a hope to help, Yours Sergei.

 Kiri February 24, 1999 10:42

Re: Entropy

Thanks, Sergei. I did get useful information from it.

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