Browsing by Author "Meloni, Stefano"

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    Evaluation of turbulent jet characteristic scales using joint statistical moments and an adaptive time-frequency analysis
    (MDPI, 2022-03-25) Proenca, Anderson; Meloni, Stefano
    This paper presents an analysis of turbulence characteristic scales and eddy convection velocity of jet flows computed using joint statistical moments, digital filters, and a modified version of the empirical mode decomposition (EMD). The ongoing aim of this study is to develop semi-empirical space-time cross-correlation models based on stationary statistics and jet physical lengths. Multivariate statistics are used to correlate jet properties to one-dimensional time series. The data available to this study were recorded from single-point and two-point hot-wire anemometry experiments carried out for a range of jet Mach numbers (0.2≤M≤0.8). Firstly, the jet eddy convection velocity, turbulence length, and time scales are computed using space-time cross-correlation functions. Isotropic flow and frozen turbulence hypothesis are then used to estimate the joint moments from single-point statistics in the fully developed turbulence region. An EMD-based decomposition method is presented and assessed in both the Gaussian and non-Gaussian signal regions. It is demonstrated that the artificially filtered signal reconstructs the physical properties of single and multi-point jet statistics. The relationship between central moments and joint moments presented here focuses on the region of high turbulence levels, which generates the vast majority of jet mixing noise produced by turbofan engines. Further analysis is required to extend this investigation to intermittent zones and other jet noise sources, such as jet-surface installation noise.
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    An experimental investigation into the influence of installed chevron jet flows on wall-pressure fluctuations
    (InterNoise, 2022-08-24) Carbini, Eduardo; Meloni, Stefano; Camussi, Roberto; Lawrence, Jack; Proença, Anderson
    Jet-surface interaction represents a significant community noise problem for the installation of modern ultra-high bypass ratio turbofan engines. The use of chevron nozzles is known to reduce low-frequency jet mixing noise by increasing the mixing rate close to the nozzle. It is currently unknown, however, to what extent such a nozzle lip treatment affects the Kelvin-Helmholtz instability, generated in the vicinity of the wing, which will modify the source of jet-surface interaction noise. To clarify the physics of the jet-surface interaction noise source, an extensive experimental investigation was conducted using the Flight Jet Rig in the anechoic chamber of the Doak Laboratory, at the University of Southampton. Various measurements were carried out on a round and a chevron single stream, unheated subsonic jet, both in an isolated configuration and installed beneath a 2D NACA4415 airfoil "wing". The wall-pressure field on the wing surface was investigated using a pair of miniature wall-pressure transducers and a set of ultra-thin precision microphones. These sensors were flush-mounted in both the stream-wise and span-wise directions on the pressure side of the wing and the unsteady wall-pressure data were analysed in the time and frequency domains. The far-field noise results show significant broadband noise reduction by the chevron jet. This is further evidenced by a reduction in the span-wise correlation length along the wing trailing edge over a wide range of frequencies. Significant reduction of the tonal trapped wave energy is also observed.