Abstract
Studies of unsteady flows about pitching airfoils and flows with unsteady freestream components require a consistent method of nonstationary data analysis for proper characterization of unsteady turbulent behavior. A method has been developed for data analysis of flows composed of high-frequenc y turbulence fluctuations superimposed upon a time-dependent low-frequency component or ensemble-averaged mean velocity with the goal of establishing a consistent method for the presentation of results from varying tests and flow situations. A nonstationary mean was determined by ensemble-aver aging and frequency-domain low-pass filtering. Turbulence intensities were calculated based on a local mean using frequency-domain low-pass filtering methods. A nonstationary power spectral density estimator was developed to estimate the time-varying spectral characteristics of a turbulent boundary layer subjected to an unsteady freestream disturbance. A discussion concerning the choice of cutoff frequencies and digital filters is included.
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