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The NASA Glenn Research Center's rotating rake mode measurement system has been successful in measuring the modal content propagating in hard-wall ducts. This paper proposes an extension of the rotating rake measurement and analysis technique to treated sections by developing basis functions based on wall impedance boundary conditions for flow conditions (i.e. constant duct area and Mach number), where the closed-form analytical solution exists. Analytical equations developed to estimate mode power are incorporated. Using the impedance boundary conditions results in better mode measurement solutions. This method is verified by decomposing and analyzing radial pressure profiles generated numerically by the Eversman propagation code. Several modes, frequencies, and impedances are evaluated. For ducts with soft-walls and mean flow, the radial basis functions must be numerically computed. The linear companion matrix method is used to obtain both the eigenvalues of interest, without the need for an initial guess, and the radial basis functions. The governing equations allow for the mean flow to have a boundary layer at the wall. In addition, a nonlinear least-squares method is used to adjust the wall impedance to best fit the data in an attempt to use the rotating system as an in-duct wall impedance measurement tool. Simulated and measured data are used to show the effects of wall impedance and mean flow on the computed results. Data from an inlet of a low-speed ducted fan with several different impedance conditions on the outer wall were acquired and reduced to determine the best fit to the data. The methodology and analysis documented in this paper were directly inspired by the groundbreaking work of Dr. Edward J Rice. [ABSTRACT FROM AUTHOR]

Time-resolved, particle image velocimetry was used to measure the velocity fluctuation field at three locations along the lipline of two subsonic jets. The time history data within these fields were filtered in the time domain using empirical mode decomposition to produce two signals from the velocity fluctuation measurements. One signal was for the low-frequency, large-scale turbulent eddy component of the velocity fluctuations and represented the computed results of a large-eddy simulation. The other signal was for the high-frequency, small-scale turbulent eddy component of the velocity fluctuations. This represented the missing scales of a large-eddy simulation. The effect of filtering on the statistical properties of the velocity fluctuations relevant to jet noise prediction modeling were studied. Two-point, space-time, cross correlations were computed for the axial velocity fluctuations. Comparisons were made for the second- and fourth- order two-point correlations, the integral phase velocities, length scales, and time scales, and the frequency dependent phase velocities, length scales, and time scales between the total, large-scale, and small-scale velocity fluctuations. [ABSTRACT FROM AUTHOR]