Nt1310 Unit 6 Lab

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The power spectral densities ($PSD$) of the gas jet centerline $C^*(t)$ for the tests in Tab.\ref{Table} were computed via $FFT$, and collected in Fig.\ref{Spectra}. For plotting purposes, the frequency domain $f_j$ is limited to $f_j=150 Hz$, and the $PSD$ in each graph is normalized with respect to the maximum $PSD$ detected within the three tests. Regardless of the stand-off distance $\hat{Z}$, for $\hat{Y}=0$ the response of the jet to the membrane motion is the superimposition of a harmonic response $f_h$ and a higher frequency $f_f$, which is not affected by the membrane motion. Noteworthy, $f_f$ scales with the standoff distance and leads to a constant Strouhal number $St_Z=f_f Z/U_j\approx 0.08$, not far from the $St_Z=0.12$ \cite{Vshape}

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