Hot-wire measurements in compressible subsonic flows using Hilbert spectral analysis

The application of the multiple overheats method together with Hilbert spectral analysis to evaluate the intensity and the spectral composition of the flow fluctuation characteristics in wind tunnels with limited running time is considered. The peculiarities of the hot-wire technique in operation for transonic wind tunnel are discussed. By using the band-pass technique with the method of the hot-wire fluctuations diagram technique, the intensity of the mass flow and total temperature fluctuations, correlation coefficients and their frequency spectra at the free-stream Mach numbers M_∞=0.4, 0.6, 0.76 were obtained. It is shown that the acoustic fluctuations are predominant in the flow at all Mach numbers. It is found that the data are almost stationary at low frequencies and they become more non-stationary with frequency increasing.