dear all

u1 means du/dx; u2 means du/dy; u3 means du/dz

<.> means time average.

in impressible homogeneous isotropic flow, what relations among u1,u2 and u3? for example, u1=u2? what relations among u1,v1 and w1? u1=v1=w1?? in compressible flow?

best regards

u(t)=Umean+u*(t)

isotroppic flow means that the kinetic energy of the fluctuating velocity (turbulence) is equaly distributed in the three directions: < u*2 >=< v*2 >=< w*2 >, where * indicates the fluctuating part of the velocity.

The mean flow can be anisotropic, but the fluctuations not.

in a paper i had read, there is the eq. <Sij*Sij>=15/2.*<(u1)^2>. Sij is strain stress. How obtained the results? why not <(v2)^2> or (w3)^2 ? could you advise some books about it? thanks

in isotropic turbulence <(u1)^2> =<(v2)^2> = (w3)^2 ...so no mystery....

thanks

in isotropic turbulence <(u1)^2> =<(v2)^2> = (w3)^2

in isotropic turbulence <(u2)^2> =<(v3)^2> = (w1)^2 ? regards