Recognizing a random signal
How may I decide if a signal is random or not ? The usual way is to plot the signal versus time and decide if it looks random.
There is a mathematical definition for a random signal ? If I want to analyze numerical a signal how may I decide if it is random ? Thanks in advance. 
Re: Recognizing a random signal
This has nothing to do with cfd, but anyway... You should preform a fast fourier transform on the signal and then plot it (preferably with Matlab or similar software). If it is a random signal no frequence will differ while a nonrandom one will have one or several peaks (one peak for each present frequency).

Re: Recognizing a random signal
Thanks Anders, actually my problem has connection with CFD because I try to analyze the results from a DNS calculation. I need a criteria for identifying for example if the pressure at a certain point is turbulent or not.

Re: Recognizing a random signal
Typically a random signal has a very narrow autocorrelation peak (in either space or time) and the fourier components have no obvious phase relationship to one another. You can also do chisquared tests to evaluate whether the signal obeys a particular statistical distribution (lognormal, gaussian, poisson, etc). Finally you can analyse whether the statistical moments (mean, variance, etc. ) converge as the number of data points increases.

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