Higher-order space time correlations

This review article discusses three aspects of the measurement of higher-order space-time correlations (principally 2nd and 3rd order) in a turbulent flow by hot-wire anemometry: (1) sources of error, (2) basic calculation methods, and (3) physical interpretations. Since 3rd and 4th order correlations are associated with large signal amplitudes, they are more affected by nonlinearities than 2nd order correlations. A spectral diversification is also noted. The two-point 3rd order correlations are used in certain 2nd order correlation equations, and are essential for modeling these equations numerically. The 3rd order correlations can be interpreted in terms of dominant perturbations distinguishing the signs of the fluctuations. Three-point higher-order correlations make it possible to delimit, at least in one direction, the statistical size of the region of coherence of the perturbations.