Browsing by Author "Proenca, Anderson"
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Item Open Access Aeroacoustic analysis of a closely installed chevron nozzle jet using the high-order discontinuous Galerkin method(AIAA, 2023-06-08) Lindblad, Daniel; Sherwin, Spencer J.; Cantwell, Chris D.; Lawrence, Jack; Proenca, Anderson; Moragues Ginard, MargaridaIn this paper, we use Large Eddy Simulations (LES) in combination with the Ffowcs Williams - Hawkings method to study the influence of chevrons on the flow field as well as the noise produced by a closely installed M = 0.6 jet. The LES simulations are performed with the spectral/hp element framework Nektar++. Nektar++ uses the high-order discontinuous Galerkin method and an implicit scheme based on the matrix-free Newton-GMRES method to discretize the unfiltered Navier-Stokes equations in space and time, respectively. The far-field noise is computed using Antares. Antares solves the Ffowcs Williams - Hawkings equation for a permeable integration surface in the time-domain using a source-time dominant algorithm. The aerodynamic results show good agreement with experimental data obtained in the Doak Laboratory Flight Jet Rig, located at the University of Southampton. Some discrepancies are observed in terms of the far-field noise levels, especially for higher polar observer angles relative to the downstream jet axis. In terms of noise reduction potential, the simulations predict that the chevrons reduce the OASPL by 1dB compared to an installed round nozzle for all observers located on the unshielded side of the wing. This should be compared to the experiments, which predict a 1.5dB noise reduction for the same chevron nozzle.Item Open Access Analysis of triangular cross-section slender bodies in supersonic regime using RANS simulations(AIAA, 2023-06-08) Bourny, Quentin; Proenca, Anderson; Di Pasquale, Davide Di; Prince, Simon A.This paper presents an investigation on the ability of RANS simulations to capture the aerodynamic forces and the flow topology of triangular cross-section slender bodies. At Cranfield University’s Transonic and Supersonic Wind Tunnel, force measurements and Schlieren images were obtained at zero incidence, Mach number equals to 2.5, and Reynolds number of 2.38 · 10^5 (based on section width). Tests were performed for three bodies of different nose geometries, but constant nose fineness ratio of 1.732. Tests were compared with RANS simulations for three turbulence models: Spalart-Allmaras, k− epsilon Realizable and k − omega SST using the ANSYS Computational Fluid Dynamics software Fluent. In addition, simulations for a configuration presented in the literature which investigated several angles of attack were also conducted. At Mach 2.5, the normal force was predicted accurately by all turbulence models. The axial force, however, was clearly predicted more accurately with the k − epsilon Realizable model. At the other hand, this turbulence model showed inferior ability to capture the flow features, particularly the leeside vortices. Spalart-Allmaras and k − omega SST gave similar results.Item Open Access Evaluation of turbulent jet characteristic scales using joint statistical moments and an adaptive time-frequency analysis(MDPI, 2022-03-25) Proenca, Anderson; Meloni, StefanoThis 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.Item Open Access Feasibility of a spinning cylinder on the leading and trailing edges of a flap for high lift(AIAA, 2023-01-19) Francannet, Antoine; Prince, Simon A.; Di Pasquale, Davide; Proenca, AndersonThis paper presents a numerical feasibility study of a spinning cylinder mounted on the leading edge and trailing edge of a flap to improve lift force generation. The baseline used in this study is a two-dimensional NLR 7301 airfoil with a single-slotted trailing-edge flap. For this configuration, experimental data is available in the literature. The Ansys computational fluid dynamics (CFD) simulation software has been used in this work to simulate the aerodynamic properties of several configurations. Firstly, a turbulence model dependency study over the existing geometry was conducted, providing lift, drag and pitching moment coefficients, as well as pressure distribution for three angles of attack. Data was then acquired using the Spalart-Allmaras turbulence model at Mach and (chord-based) Reynolds numbers 0.185 and 2.51×10^6, respectively. Three configurations with a leading-edge spinning cylinder and one with a trailing-edge spinning cylinder were investigated. Results suggest that the introduction of a cylinder in the baseline geometry decreased lift and drag performance by inducing flow separation. Nevertheless, for the leading edge configurations, the rotation of the cylinder allowed recovery of the original flapped airfoil performance by re-energizing the flow around the flap and reattaching the boundary layer. For the trailing edge configuration, the spinning cylinder generated additional lift due to Magnus and suction effects at high rotation speed of the cylinder, and by modifying the flow circulation around the flap’s trailing edge. Overall, no benefit over the lift-to-drag ratio could be derived from this preliminary study.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 Installed jet noise reduction using a zigzag vortex generator(AIAA, 2022-06-13) Proenca, Anderson; Lawrence, JackIn this paper, an experimental investigation into a vortex generator ring is performed to establish its potential as a noise reduction technology for next generation of closely coupled engine-airframe aircraft. A zigzag ring was 3D-printed onto the internal surface of a round, single-stream nozzle upstream of the nozzle exit plane. Isolated and installed jet configurations were studied under static and in-flight ambient flow conditions. Unsteady pressure measurements were performed using both a linear far-field microphone array and an azimuthal near-field microphone array. Unsteady velocity data at the jet nozzle exit were acquired via hot-wire anemometry. Far-field acoustic data show that the lip treatment produces a 1 dB overall sound pressure level reduction on the jet mixing noise source. The maximum benefit for this particular noise source occurs at low jet polar angles. A greater noise reduction, in excess of 3 dB, is observed for the installed configuration, where the maximum benefit is seen at forward arc polar angles. The presence of forward flight slightly reduces the overall noise advantage provided by the vortex generator. The unsteady velocity data suggest that the zigzag ring does not alter the aerodynamic performance of the nozzle significantly, but further investigation into potential thrust penalties is necessary.Item Open Access Large eddy simulations of isolated and installed jet noise using the high-order discontinuous Galerkin method(AIAA, 2023-01-19) Lindblad, Daniel; Sherwin, Spencer J.; Cantwell, Chris; Lawrence, Jack; Proenca, Anderson; Moragues Ginard, MargaridaA recently developed computational framework for jet noise is used to compute the noise generated by an isolated and installed jet. The framework consists of two parts. In the first part, the spectral/hp element framework Nektar++ is used to compute the near-field flow. Nektar++ solves the unfiltered Navier-Stokes equations on unstructured grids using the high-order discontinuous Galerkin method. The discrete equations are integrated in time using an implicit scheme based on the matrix-free Newton-GMRES method. In the second part, the Antares library is used to compute the far-field noise. Antares solves the Ffowcs Williams - Hawkings equation for a permeable integration surface in the time domain using a source-time dominant algorithm. The simulations are validated against experimental data obtained in the Doak Laboratory Flight Jet Rig, located at the University of Southampton. For the isolated jet, good agreement is achieved, both in terms of the flow statistics and the far-field noise. The discrepancies observed for the isolated jet are believed to be caused by an under-resolved boundary layer in the simulations. For the installed jet, the flow statistics are also well predicted. In the far-field, very good agreement is achieved for downstream observers. For upstream observers, some discrepancies are observed for very high and very low frequencies.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 Measurement and modelling of noise-power-distance curves of a fixed-wing UAV(AIAA, 2022-06-13) Amargianitakis, Daniel C.; Self, Rod; Proenca, Anderson; Boyd, Cameron; Westcott, Oliver; Ferraro, Mario; Erbil, Mehmet Ali; Entwistle, RobertThis paper presents an investigation into the noise produced by an unmanned aerial vehicle (UAV). The platform used, `Spotter', is a fixed-wing, light UAV comprising a 4-meter wingspan. Spotter was originally designed to perform long-endurance, all-weather patrol missions in coastal and maritime environments. This vehicle has been continuously upgraded and is now used in a broader range of applications. Increasing demand by research and industrial partners, as well as the UK Civil Certification Authority (CAA) has led to a survey of the Spotter's in-flight noise footprint. The CAA Operating Safety Case of this platform is currently being updated and the major findings are presented in the paper. Preliminary results were obtained in flight tests performed at the Draycot Aerodrome over two expeditions in the summer of 2021, in the UK. A series of flyovers, takeoff and landing operations were measured. Flyovers were performed at constant altitude at series of power settings, incrementing from low to maximum power output. These measurements are then used to generate Noise-Power-Distance curves for the Spotter UAV. Static directivity characteristics of the dual propeller setup were also measured, with intent of feeding into future airport exposure studies.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.Item Open Access Upstream disturbance effects on self-similarity in the wake of a DrivAer model(Society of Automotive Engineers, 2023-04-11) Rallapalli, Anurag; Proenca, Anderson; Garry, KevinThis study aims to provide an understanding of self-similarity in the turbulent wake generated by a Fastback DrivAer automotive model and assess the impact of upstream disturbances on the wake. The disturbances are generated using a circular cylinder placed five cylinder diameters upstream. Multiple ‘cylinder-model’ positions were tested by offsetting the lateral positioning of the cylinder with respect to the centreline of the model. Data was obtained at cross-planes in the wake going from 25% to 100% car length. Wind tunnel data has been obtained using a total pressure probe rake and a four-hole cobra probe. Data has also been obtained using RANS based simulations with k – ε realisable turbulence model. Mean axial-component velocity profiles were analysed with momentum thickness (θ) and vorticity thickness (δω) used as the scaling parameters. It was seen that self-similarity marginally exists in the wake depending on the upstream conditions and the scaling parameter. Overall, vorticity thickness was seen to be better. Downstream, the mean profiles show a simpler collapse compared to the near wake. Understanding how deficit decay takes effect in the wake is useful to improve the aerodynamic performance of an automobile/motor car/ground vehicle. Therefore, establishing the similarity parameters presented in the work is an early step towards an analytical description of a turbulent wake model.Item Open Access Upstream turbulence effects on the self-similarity of wakes: vortex pair dynamics(AIAA, 2023-01-19) Murari, Prasanth K.; Proenca, Anderson; Garry, Kevin P.A pair of counter-rotating vortices is a very common flow feature associated with aircraft and ground vehicles. This paper details the research conducted by the authors to understand the effect of upstream turbulence on a pair of counter-rotating vortices generated using a slender delta wing model with a 76° leading-edge sweep. The level of upstream turbulence is predicted to have an effect on the spatial development and decay of such vortices, which is crucial to determine safe or optimal separation distances in aerospace, automotive and motorsport applications. CFD simulations were performed for four different angles of attack (10°, 15°, 20° and 25°) by employing RANS as well as DDES turbulence modeling approaches. Wind Tunnel testing was performed by utilising passive turbulence-generating grids. Unsteady, three-dimensional velocity data is recorded for three wake locations using a 4-hole cobra probe. Self-similarity analysis of mean velocity profiles has been performed for the near-wake region to quantify the effect of turbulence on vortex characteristics. The vortices were observed to retain their functional profile even in high turbulence conditions until the three-dimensional instabilities came into play. However, increasing turbulence reduced the strength (circulation) of the vortices and amplified the three-dimensional instabilities that led to the eventual decay of the pair. The findings of this research can be further evaluated to see if a viable flow control technique can be devised to accelerate the decay of undesirable trailing vortices.Item Open Access Use of an aerodynamic wake emulator to assess the impact on a high-performance ground vehicle in close proximity(AIAA, 2023-01-19) Cardona, Jordi; Proenca, Anderson; Garry, Kevin P.The interaction between ground vehicles in close proximity is currently of interest as it is known that the aerodynamic characteristics of the trailing vehicle may change significantly under the effect of a disturbed flow. The aim of this work is to map a wide range of situations where a trailing car, under racing conditions, is affected by another vehicle ahead. A sub-scale wind tunnel test in which the aerodynamic characteristics of a high-performance ground vehicle is affected by a simplified ‘wake emulator’ has been conducted. The trailing vehicle is a 35% scale model of the generic DrivAer geometry. These experiments were carried out at Cranfield University’s 8x6 Wind Tunnel facility, at a speed of 40 m/s. Several relative positions, such as longitudinal and lateral distances, together with different yaw angles have been investigated. The behavior of the trailing car is monitored with an internal balance that gathers the variations of all aerodynamic forces. Thus, a well detailed map displays the effect of close slipstreaming in high-performance cars alongside the variations due to yaw conditions. Results have shown similar trends on axial and vertical force as previous works regarding high performance vehicles. The variation on aerodynamic forces and moments are highly dependent on the relative position with the main vortices from the leading car’s wake.