Browsing by Author "Lawrence, Jack"
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Item Open Access 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, AndersonJet-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.Item Open Access Flow and noise predictions of the isolated subsonic jets from the Doak Laboratory experiment(AIAA, 2022-06-13) Gryazev, Vasily; Markesteijn, Annabel P.; Karabasov, Sergey A.; Lawrence, Jack; Proenca, AndersonFlow and noise solutions using Large Eddy Simulation (LES) are evaluated for two jets at acoustic Mach numbers 0.6 and 0.8. The jets correspond to Doak Laboratory Experiment performed at the University of Southampton. LES method is based on the Compact Accurately Boundary-Adjusting High-Resolution Technique (CABARET) scheme and is implemented on Graphics Processing Units. In comparison with many other jet noise benchmarks, the Doak jet cases include well-defined boundary conditions corresponding to the meanflow velocity and turbulent intensity profiles measured just downstream of the nozzle exit. The far-field noise predictions are obtained using two approaches. First, the LES solutions are coupled with the penetrable surface formation of the Ffowcs Williams–Hawkings method. The second approach is based on the reduced-order implementation of the Generalised Acoustic Analogy model for which time averaged quantities are obtained from the LES solutions. All numerical solutions are compared with the flow and acoustic microphone measurements from the Doak experiment. The results are cross-validated using the sJet code, which corresponds to an empirical model obtained from interpolations over a large set of NASA jet noise data.Item Open Access LES study of noise and its sources of closely installed jets(AIAA, 2022-06-13) Wang, Zhong-Nan; Proenca, Anderson; Lawrence, Jack; Tucker, Paul; Self, RodWhen a jet is closely installed under a solid surface, turbulent jet plume is modified. Two levels of jet-plate interactions are present. In addition to linear evanescent instability wave scattered by the plate trailing edge, nonlinear jet turbulence strongly interacts with the plate underneath surface. Both of the interactions could lead to far-field noise change but with different mechanisms. Large-Eddy Simulation (LES) has been performed on two installed jets and one baseline isolated jet to investigate the noise generation mechanisms for this closely installed jet. The distance between jet and plate surface is adjusted for the two installed jets so that strong hydrodynamic interaction is only present in one of the configurations. Far-field noise, computed using Ffowcs Williams-Hawkings (FW-H) equations, is compared for the two installed jets to show the effect of close installation. The near-field sound sources are exmined by analysing quadrupole souces of turbulent mixing and dipole sources of unsteady plate surface loading.Item Open Access Prediction of far-field noise from installed corrugated nozzles(AIAA, 2024-05-30) de Souza, Francisco J.; Lawrence, Jack; Cruz, Ricardo H.; Proenca, AndersonIn this study, a reduced order model, devised by Lyu and Dowling, is used to predict the farfield installation noise of corrugated nozzles installed beneath a NACA aerofoil. A complementary investigation, detailed in another paper, reveals that employing square corrugations near the nozzle lip diminishes jet-surface interaction (JSI) noise compared to a round 40-mm diameter nozzle. This reduction is particularly notable for Strouhal numbers ranging from 0.3 to 0.9 and at high polar angles. The near-field pressure data, required for Lyu and Dowling’s model, is gathered using a circular array consisting of eight 1/8-inch microphones in the Doak Laboratory, at the University of Southampton, UK. Generally, the predictions align well with the experimental trends for Mach numbers ranging from 0.4 to 1 under static ambient flow conditions. Furthermore, it is observed that a minimum of four azimuthal modes must be available to accurately predict the noise generated by the corrugated nozzles. The effects of free-stream Mach number, particularly focusing on the predictive capacity of Lyu and Dowling’s model, are also investigated. Quantitative agreement at Strouhal numbers between 0.1 and 0.5 in evidenced.Item Open Access Reduced-order model prediction of far-field mixing noise from internally-notched nozzles(AIAA, 2024-05-30) de Souza, Francisco J.; Lawrence, Jack; Proenca, AndersonThis work presents a numerical investigation of the effect of internal notches on the reduction of jet mixing noise from round nozzles. The baseline jet is produced by the University of Southampton’s Doak Laboratory 40mm-diameter convergent, round nozzle. Numerical predictions of mixing noise for both round and internally-notched nozzles are conducted using a Generalized Acoustic Analogy that relies on Reynolds-Averaged Navier-Stokes (RANS) solutions of the nozzle flows, particularly the one proposed by Leib and Bridges. In this method, the RANS variables of interest, including mean axial velocity, Mach number, density, turbulence kinetic energy, and its dissipation rate, are interpolated onto a cylindrical structured grid suitable for aeroacoustic calculations. Subsequently, the respective Green’s function and a hybrid spectral-time source model are computed, and power spectral densities at various polar and azimuthal angles are predicted. Comparison between predictions and experiments demonstrates good qualitative agreement for both nozzles, although the inversion in trends at certain Strouhal numbers is not captured by the numerical model. Additionally, the significance of the numerical scheme’s order employed to solve the adjoint Green’s function is evaluated. To elucidate the noise reduction attributed to internal notches, distributions of turbulent kinetic energy are analyzed at different azimuthal cross-sections.