CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   Main CFD Forum (https://www.cfd-online.com/Forums/main/)
-   -   Basic Fluid mechanics (https://www.cfd-online.com/Forums/main/117411-basic-fluid-mechanics.html)

 mouli1991 May 8, 2013 03:51

Basic Fluid mechanics

Hello everyone
I have very bad knowldege in fluid mechanics..Explain me about Newtanion fluid.I need the derivation for the topic called "CONSTITUTIVE EQUATIONS FOR NEWTONION FLUID"(or viscous fluid)..some 6 equations like
towxx=2M(mu)(du/dx)
similar for yy and zz
include xy,yz and zx..
explain me pls

 Rami May 29, 2013 05:01

Hi Sayee Chandrasekara Mouli,

Newtonian fluid means there is a linear relation between the stress and the strain-rate tensors (analogous to elasticity, where the stress is proportional to the strain). This is written (in tensor notation) as
Sik = -p * Iik +lambda * Emm * Iik + 2*mu * Eik
where Sik is the stress, Eik is the strain-rate, p is the pressure, Iik is the identity tensor, mu is the viscosity, muv is the bulk viscosity (usually assumed 0, i.e., Stokesw assumption) and lambda=muv - 2/3* mu is similar to Lame constant in elasticity.

The viscous stress, Tik, is defined as
Tik = Sik + p * Iik

The stain-rate is related to the velocity vector Ui through
2*Eik = Ui,k + Uk,i

From these relations you can easily derive the relations you asked about.

Rami

 All times are GMT -4. The time now is 00:45.