Browsing by Author "Bacci, David"
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Item Open Access Controlling unsteady cavity flows using internal structures(La Societe Savante de L'Aeronautique et de L'Espace, 2017-03-29) Knowles, Kevin; Bacci, David; Saddington, A. J.; Newby, B; Taylor, N JWe report experimental measurements and preliminary analysis on a series of geometric modifications to a rectangular cavity, aimed at alleviating the severity of the aeroacoustic environment. The cavity had a length-to-depth ratio of 5 and a width-to-depth ratio of 1, and featured a simplified representation of a generic missile on the centre line. The modifications consisted of full width and depth ribs or “collars” with a cutout for the missile. Collars could be fitted at various combinations of locations in the cavity and were either straight (i.e. perpendicular to the cavity centre line), leaned or yawed. The cavity flowfield was characterised by surface pressure measurements along the ceiling. Judging from the available measurements the presence of collars modified the mean pressure distribution, and appeared to reduce the acoustic tones and generally lower the broadband noise.Item Open Access Exploring angle-of-attack effects in the aero-acoustic response of a weapons bay at transonic and supersonic Mach number(AIAA, 2022-06-13) Bacci, David; Saddington, Alistair J.Numerical aero-acoustic analysis was conducted on a weapon bay model with doors, incorporating radar cross section reduction features. The effect of angle of attack on the aero-acoustic response of the cavity was analysed at a transonic Mach number of 0.85, and at a supersonic Mach number of 1.20. It was found that incidence had influence on both mean-flow features and acoustic response. Further, linear and angular accelerations induced by the flow on doors revealed potential adverse fluid-structure coupling when results were compared with modal analysis. Again, angle of attack did influence the aeroacoustic effects on the cavity door structure.Item Open Access Hilbert–Huang spectral analysis of cavity flows incorporating fluidic spoilers(AIAA, 2022-10-07) Bacci, David; Saddington, Alistair J.Numerical aeroacoustic analysis was conducted on an M219 cavity geometry, incorporating signature suppression features and leading-edge fluidic spoilers. The numerical model was validated against existing experimental data. The palliative properties of fluidic spoilers were investigated at Mach numbers of 0.85, 1.20, and 1.80 with blowing coefficients of 0.03 and 0.06. The results are presented for the acoustic spectrum, and further analysis was conducted using the Hilbert–Huang methodology. The fluidic spoilers were able to considerably reduce the overall level of acoustic noise and to reduce and/or suppress the resonant modes typical of cavity flows. The effectiveness of the spoilers was a direct consequence of their effect on the detached shear layer, of which the trajectory and coherence were altered. The Hilbert–Huang spectral analysis provided an enhanced understanding of the complex nature of the aeroacoustic behavior of the cavity. Acoustic modes were identified that, together with the Rossiter–Heller tones, governed the behavior of the spectrum. This demonstrated how the generated tones, appearing inside the cavity, were a result of complex nonlinear interactions between shear-layer acoustic instabilities and centrifugal instabilities originating in the flow recirculating in the internal part of the cavity. This also demonstrated that the fundamental frequencies had frequency and amplitude modulation characteristics that spread the energy in a wide bandwidth. This is not captured by classical Fourier analysis.Item Open Access A trade-off analysis between lateral/directional stability and radar cross section requirements of an air-to-air combat airframe(Elsevier, 2023-05-09) Bacci, David; Vagias, IoannisNumerical aerodynamic and radar analyses were conducted on 3 low-radar cross-section airframes, derived from the AVT-183 diamond wing. The geometries were developed by adding different configurations of vertical stabilators, to improve lateral and directional characteristics at high angles of attack whilst minimising the deterioration of radar signature characteristics. The analyses were conducted at a Mach number of 0.30, with angle of attack varying between 0 deg to 30 deg and angle of sideslip varying from 0 deg to 6 deg. Monostatic radar cross-section analysis was conducted in L and X bands. The study explored the trade-off between radar signature control (RCS) and the spin/departure requirements typical of a modern combat aircraft designed for air-superiority. Several of the proposed configuration were shown to improve both lateral and directional stability, whilst maintaining acceptable RCS.Item Open Access Wavelet analysis of complex geometry transonic cavity flows(2016-09-09) Bacci, David; Saddington, A. J.; Bray, DerekThe aero-acoustic analysis of a weapon bay of an Unmanned Combat Air Vehicle (UCAV) was predicted using Computational Fluid Dynamics (CFD) methods. Along the reference geometry, consisting in the installation of the Boeing M219 modified type cavity in the Boeing UCAV1303 airframe, two additional configurations, developed modifying the leading and trailing edge geometries of the bay, were tested. Pressure signals inside the cavity were post-processed using Joint Time Frequency Analysis (JTFA) techniques, consisting in a combination of frequency domain and time-frequency domain techniques based respectively on the Fourier and wavelet transform. Results showed an intermittency nature of the modes present in the spectra as well as a continuous change, during the temporal evolution of the signal, of the dominant mode. Also were recorded, using second order wavelet spectral moments, non-linear phenomena between the main modes like phase coupling.