Averaging intervals for spectral analysis of nonstationary turbulence

We formulate a method for determining the smallest time interval Δ Tover which a turbulence time series can be averaged to decompose it intoinstantaneous mean and random components. From the random part the method defines the optimal interval (or averaging window) AW over which this part should be averaged to obtain the instantaneous spectrum. Both Δ T and AW vary randomly with time and depend on physical properties of the turbulence. Δ T also depends on the accuracy of the measurements and is thus independent of AW. Interesting features of the method are its real-time capability and the non-equality between AW and Δ T.[PUBLICATION ABSTRACT]