about universality of Kolmogorov k^(5/3) law
Is the Kolmogorov k^(5/3) law for the energie spectrum E(k) in freely decaying turbulence a realy universal law ? I am interested specialy in stratified turbulence, does the law above exist in this case , or does any other laws exist ? can anyone tell me about this subject ?

Re: about universality of Kolmogorov k^(5/3) law
Yes, Kolmogorov k^(5/3) also exists in stratified turbulence. (Ref: Stull R B, an intruduction to Boundary layer Meteo.(1988)). However, it seems to me stratified turbulence is a very hard topic, intermittence, week turbulence, nonequilibrium etc.

Re: about universality of Kolmogorov k^(5/3) law
Sometimes minor intermittency corrections are added to the K^(5/3) law. If the stratification effects are very high (e.g. across thin exothermic flames), then the K^(5/3) law may not hold. If the stratification effects are small compared to the inertial effects, K^(5/3) usually is a good approximation even without any intermittency correction.
Sreenivasan (Physics of fluids, 1995) has done a nice job of gathering data on lots of different types of flows and presenting the spectral scaling for them. Take a look at this paper to see if you can find better answers to your question. 
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