Roberto Camussi - Academia.edu (original) (raw)

Papers by Roberto Camussi

Physics of Fluids, 1996

The statistical properties of the velocity fluctuation components at moderate Reλ are studied in ... more The statistical properties of the velocity fluctuation components at moderate Reλ are studied in homogeneous and non-homogeneous turbulence by an experimental technique. Measurements are performed by means of a hot-wire anemometer with X-probe downstream of a screen for several positions, x/M=9 up to 109, where M is the screen mesh size, with Reλ ranging from 37 to 82. The homogeneity of the flow is analyzed by means of velocity measurements in different transverse positions and a direct evaluation of the local isotropy of the flow is performed by means of velocity spectra. The scaling properties of the statistical moments of the structure functions up to the order of six, are investigated in the extreme positions by means of the extended self-similarity (ESS) method and the intermittency exponents are detected for both homogeneous and non-homogeneous flow conditions. A comparison of the longitudinal and transverse intermittency exponents as functions of the position is then perform...

Aerotecnica Missili & Spazio

The prediction of pressure fluctuations generated over the external surface of aerospace launcher... more The prediction of pressure fluctuations generated over the external surface of aerospace launchers during the atmospheric flight remains a challenging task due to the complexity of the geometry and the effects of compressibility at high supersonic Mach numbers. An experimental database is here analysed to the scope of providing a procedure to model and predict the relevant statistics of the wall pressure fluctuations generated by a supersonic flow overflowing the VEGA-C Launcher Vehicle. Data have been obtained in an extensive Wind Tunnel test campaign carried out in the trisonic wind tunnel of the National Institute for Aerospace Research (INCAS) in Bucharest. Wall-mounted pressure transducers allowed for the computation of the pressure Auto- and Cross-spectra over the fourth (the payload region) and third stages of the launcher model. Coherence functions are modelled through exponential-like analytical functions following the approaches usually adopted in canonical boundary layer ...

This paper describes an experimental test campaign aimed at the study of the influence of surface... more This paper describes an experimental test campaign aimed at the study of the influence of surface irregularities on the turbulent boundary layer noise emission. The irregularities were represented by a two-steps large aspect-ratio cavity. The main task of the experiments was to characterize, from the aeroacoustic and fluid-dynamic viewpoint, the effects of the main non-dimensional parameters on the statistical quantities of interest correlated to the wall pressure fluctuations, accounting for the geometrical and dynamical similarity requirements with respect to real conditions. The experiments were performed in the low speed wind tunnel at ENEA-DIMI research centre. Results allowed us to individuate the significant, independent dimensionless groups governing the point wall pressure spectra in-between the double steps discontinuity. Proper scaling relations of local (pressure spectra) and global (Sound Pressure Level-SPL) quantities are proposed, and universal form functions modelling the properly normalized spectra and SPL are presented. The ability of the proposed model to predict the noise emission is finally validated and tested on experimental data. List of Symbols α i Power laws coefficients B Cavity span c Speed of sound δ Boundary layer thickness f Frequency G pp Pressure auto-spectrum H Steps height L Cavity length q Dynamic pressure Re Reynolds number St Strouhal Number U Free stream velocity x Streamwise coordinate ∆ Thickness ratio Γ pp Universal spectrum Ψ Universal form function γ Velocity ratio υ Cinematic viscosity ũ Mean Turbul. level within TBL σ Standard deviation ' Dimensionless quantity AR Aspect ratio Average on the tests Average on x position

Journal of Fluid Mechanics

This work deals with the investigation and modelling of wall pressure fluctuations induced by a s... more This work deals with the investigation and modelling of wall pressure fluctuations induced by a supersonic jet over a tangential flat plate. The analysis is performed at several nozzle pressure ratios around the nozzle design Mach number, including slightly over-expanded and under-expanded conditions, and for different radial positions of the rigid plate. Pitot measurements and flow visualizations through the background oriented schlieren technique provided a general overview of the aerodynamic interactions between the jet flow and the plate at the different regimes and configurations. Wall pressure fluctuations were measured using a couple of piezoelectric pressure transducers flush mounted over the plate surface. The spectral analysis has been carried out to clarify the effect of the plate position on the single and multivariate wall pressure statistics, including the screech tone amplitude. The experimental dataset is used to assess and validate a surrogate model based on artific...

Applied Sciences

This paper presents a numerical investigation of noise radiated by two side-by-side propellers, s... more This paper presents a numerical investigation of noise radiated by two side-by-side propellers, suitable for Distributed-Electric-Propulsion concepts. The focus is on the assessment of the variation of the effects of blade tip Mach number on the radiated noise for variations of the direction of rotation, hub relative position, and the relative phase angle between the propeller blades. The aerodynamic analysis is performed through a potential-flow-based boundary integral formulation, which is able to model severe body–wake interactions.The noise field is evaluated through a boundary-integral formulation for the solution of the Ffowcs Williams and Hawkings equation. The numerical investigation shows that: the blade tip Mach number strongly affects the magnitude and directivity of the radiated noise; the increase of the tip-clearance increases the spatial frequency of the noise directivity at the two analyzed tip Mach numbers for both co-rotating and counter-rotating configurations; fo...

28th AIAA/CEAS Aeroacoustics 2022 Conference

Under-expanded jet noise prediction using surrogate models based on artificial neural networks.

Fluids, 2021

Wavelet transform has become a common tool for processing non-stationary signals in many differen... more Wavelet transform has become a common tool for processing non-stationary signals in many different fields. The present paper reports a review of some applications of wavelet in aeroacoustics with a special emphasis on the analysis of experimental data taken in compressible jets. The focus is on three classes of wavelet-based signal processing procedures: (i) conditional statistics; (ii) acoustic and hydrodynamic pressure separation; (iii) stochastic modeling. The three approaches are applied to an experimental database consisting of pressure time series measured in the near field of a turbulent jet. Future developments and possible generalization to other applications, e.g., airframe or propeller noise, are also discussed.

The effect of varying the nozzle exhaust diameter on the wall pressure fluctuations generated by ... more The effect of varying the nozzle exhaust diameter on the wall pressure fluctuations generated by the tangential flow of a compressible jet over a flat plate is experimentally investigated. Measurements were carried out in geometric similarity scaling the setup according to the nozzle diameters, thus varying the Reynolds number at a fixed Ma. The Mach number of the turbulent jet, exhausting from a convergent nozzle, was about 0.5. The nozzle diameters used for the experiments were of about 1/2’’ and 1’’. An instrumented flat plate was installed tangentially to the jet flow; this is equipped with a traversing system able to set the distance of the flat plate surface in radial direction with millimetre-precision. Different inclinations are also allowed by the system. Two high dynamic and frequency range pressure transducers were used to acquire the signals. Pressure transducers were screwed into a predrilled matrix of 200 pressure taps where the tangential and radial spacing distances ...

This paper is devoted to the experimental study of a circular converging nozzle in under-expanded... more This paper is devoted to the experimental study of a circular converging nozzle in under-expanded conditions interacting with a tangential flat plate. Measurements were carried out in the semi-anechoic chamber of the Fluid Dynamic laboratory at the University Roma Tre. Wall pressure fluctuations are acquired by means of flush mounted Kulite sensors displaced at several streamwise positions. Qualitative flow visualizations are obtained as well, through the Background Oriented Schlieren technique that provides density gradient fields integrated along the optical path. A parametric study is carried out in terms of jet/plate distance and nozzle pressure ratio. The investigation provides, for the first time, a detailed characterization of the wall pressure statistics also correlating the achieved statistics with the shock cell structure.

Training the next generation of aeroacoustic researchers is vital for addressing some difficult y... more Training the next generation of aeroacoustic researchers is vital for addressing some difficult yet very important societal challenges, such as the provision of environmentally sustainable air transport operations, both for what concerns airport noise pollution and cabin noise. Sustained demand for more fuel efficient, environmentally friendly, and quieter aircraft power plants is promoting the development of ultra-high bypass engines for large transport aircraft. These turbofan engines require trained aero-acousticians and improved industrial design tools, to tackle some of the difficult design challenges posed by the larger diameter and by the larger fraction of the thrust delivered through the secondary (annular) nozzle. Whilst aeroacoustics is a well-established discipline in its own right, it tends not to be offered as an undergraduate course. This creates a recruitment challenge in doctoral training, with new post-graduate students being recruited across a range of qualificati...

Journal of Fluid Mechanics, 2021

A model-scale experimental investigation of an installed jet–pylon–wing configuration was conduct... more A model-scale experimental investigation of an installed jet–pylon–wing configuration was conducted at the University of Southampton, with the scope to study the effect a pylon has on noise generation and to clarify its impact on the fluctuating wall-pressure load. The set-up consisted of two single-stream nozzles, a baseline axisymmetric annular nozzle and a partially blocked annular pylon nozzle. The nozzles were tested first isolated and then installed next to a NACA4415 aerofoil ‘wing’ at a single nozzle–wing position. The jet Mach number was varied between 0.5leqMjleq0.80.5 \leq M_{{j}} \leq 0.80.5leqMjleq0.8 and measurements were performed both under static and in-flight ambient flow conditions up to Mf=0.2{M_{{f}} = 0.2}Mf=0.2 . The jet flow-field qualification was carried out using a single-velocity-component hot-wire anemometer probe. The pressure field on the wing surface was investigated using two miniature wall-pressure transducers that were flush-mounted in the streamwise and spanwise directions within th...

Applied Sciences, 2021

This paper investigates the aeroacoustic interactions of small hovering rotors, using both experi... more This paper investigates the aeroacoustic interactions of small hovering rotors, using both experiments and computations. The experiments were conducted in an anechoic chamber with arrays of microphones setup to evaluate the azimuthal and polar directivity. The computational methodology consists of high fidelity detached eddy simulations coupled to the Ffowcs-Williams and Hawkings equation, supplemented by a trailing edge broadband noise code. The aerodynamics and aeroacoustics of a single rotor are investigated first. The simulations capture a Reynolds number effect seen in the performance parameters that results in the coefficient of thrust changing with the RPM. The acoustic analysis enables the identification of self-induced noise sources. Next, dual side-by-side rotors are studied in both counter-rotating and co-rotating configurations to quantify the impact of their interactions. Higher harmonics appear due to the interactions and it is verified that the counter-rotating case l...

Physics of Fluids, 2021

Experiments were conducted to assess the aeroacoustic characteristics of a 30P30N three-element h... more Experiments were conducted to assess the aeroacoustic characteristics of a 30P30N three-element high-lift airfoil fitted with two different types of slat cove fillers in the Aeroacoustic Facility at the University of Bristol. The results are presented for the angle of attack α = 18° at a free-stream velocity of U∞ = 30 m/s, which corresponds to a chord-based Reynolds number of Rec = 7 × 105. Simultaneous measurements of the unsteady surface pressure were carried out at several locations in the vicinity of the slat cove and at the far-field location to gain a deeper understanding of the slat noise generation mechanism. The results were analyzed using a higher-order statistical approach to determine the nature of the broadband hump seen at low frequencies for the 30P30N high-lift airfoil observed in recent studies and also to further understand the tone generation mechanism within the slat cavity. Intermittent events induced by the resonant mechanism between the slat and its trailing ...

Theoretical and Computational Fluid Dynamics, 2021

The present paper reports an investigation of the statistical properties of pressure fluctuations... more The present paper reports an investigation of the statistical properties of pressure fluctuations in the near field of subsonic compressible jets. The database analyzed has been obtained numerically by DNS and LES of two single-stream circular jets, having diameter-based Reynolds numbers of 3125 and 100,000 and Mach number 0.9, respectively, initially laminar and highly disturbed. Pressure fluctuations are extracted from several virtual probes positioned in the near field of the jets and covering a region from 0 to 20 diameters in the axial direction and from 0.5 to 3 diameters in the radial. An azimuthal decomposition of the pressure fluctuations is performed, and the statistical analysis is applied to the axisymmetric 0-mode component and compared to the results obtained from the full original signals. The intermittent behavior is investigated by the estimation of standard statistical indicators, such as probability distribution functions and flatness factor, as well as through conditional statistics based on the application of the wavelet transform. It is shown that downstream of the potential core, intermittency estimated through the traditional indicators is relevant even at the lowest Re for the full signals, whereas it is apparently not significant for the 0-mode component. The wavelet analysis provides an estimation of intermittency scale-by-scale and allows for the calculation of a frequencydependent FF. This approach reveals that the 0-mode component has a relevant degree of intermittency around the frequencies associated with the Kelvin-Helmholtz instability. The statistics of the intermittent events, in terms of their temporal appearance and energy content, are shown to be weakly sensitive to the jet Reynolds number and the universal behavior can be reproduced by simple stochastic models.

AIAA AVIATION 2020 FORUM, 2020

Experimental measurements were carried out to assess the aeroacoustic characteristics of 30P30N a... more Experimental measurements were carried out to assess the aeroacoustic characteristics of 30P30N airfoil fitted with two different types of slat cove fillers at the aeroacoustic facility at the University of Bristol. The results are presented for the angle of attack α = 18 • at a free-stream velocity of U ∞ = 30 m/s which corresponds to a chord-based Reynolds number of Re c = 7 × 10 •. Simultaneous measurements of the unsteady surface pressure were made at several locations in the vicinity of slat cove and at the far-field location to gain a deeper understanding of the slat noise generation mechanism. The results are analyzed using a higher-order statistical approach to determine the nature of the broadband hump seen at low-frequency for the 30P30N high-lift airfoil observed in recent studies and also to further understand the tone generation mechanism within the slat cavity. A series of cross-correlation and coherence of the unsteady pressure measurements are carried out to identify and isolate the low-frequency hump. Wavelet analysis is performed to investigate the nature of the slat-wing resonant intermittent events in both time and frequency domains. The far-field noise measurement results showed that significant noise reduction can be achieved by the use of slat cove fillers. A series of far-field and near-field correlation are also presented to show the propagated noise from the slat.

Applied Sciences, 2020

Motivated by the problem of the installation effects of modern turbofan engines, we experimentall... more Motivated by the problem of the installation effects of modern turbofan engines, we experimentally investigated the interaction between a compressible subsonic jet and a tangential flat plate. Measurements of wall pressure fluctuations were performed in a semi-anechoic environment addressing the effect of several governing parameters, such as the stream-wise and span-wise location, the jet Mach number and the radial distance of the plate surface from the jet axis. The statistical properties of the wall pressure signals were analyzed in terms of both power spectra and cross-correlations, with the latter providing the estimation of the phase speed. The analysis is also carried out in the time-frequency domain through the application of the wavelet transform to further characterize the dynamics of the wall pressure signatures.

International Journal of Aeroacoustics, 2020

This work provides an experimental investigation into the interaction between a jet flow and a se... more This work provides an experimental investigation into the interaction between a jet flow and a semi-finite plate parallel to the jet. Wall pressure fluctuations have been measured in a high compressible subsonic regime and for different distances between the jet and the plate trailing edge. The experiment has been carried out in the ISVR anechoic Doak Laboratory at the University of Southampton, using wall pressure transducers flush mounted on the plate surface. Signals were acquired in the stream-wise direction along the jet centreline and in the span-wise direction in a region close to the trailing edge. The radial position of the flat plate was fixed very close to the jet axis to simulate a realistic jet–wing configuration. The plate was moved axially in order to investigate four different jet-trailing edge distances and to include measurements upstream of the nozzle exhaust. The acquired database was analyzed in both the frequency and the time domains providing an extensive stat...

CEAS Aeronautical Journal, 2020

An extensive aeroacoustic and aerodynamic investigation of an innovative regional turboprop aircr... more An extensive aeroacoustic and aerodynamic investigation of an innovative regional turboprop aircraft has been carried out experimentally and numerically under the framework of two research projects funded by the European Union through the CleanSky Research Programme. Experimental tests have been performed in the RUAG Large Subsonic Wind Tunnel in Switzerland and CFD results have been validated against the experimental data. The A/C high-lift performance, stability and control derivatives, aerodynamic noise sources, and low-noise solutions for high-lift devices, have been investigated under representative conditions in cruise, takeoff , and landing configurations. The aerodynamic and aeroacoustic investigation has been carried out parametrically, in terms of several reference quantities, including the propellers' thrust and rpm, the speed of the air-flow, the incidence angle of the aircraft and the position of the microphone array used for the acoustic investigation. The present paper gives an overview of relevant results obtained for selected aircraft configurations which have been tested in the wind tunnel and analyzed through CFD simulations. The focus lies on the overall aerodynamic characterization and on the noise sources identification carried out using standard beamforming techniques. Keywords Wind tunnel • CFD • Propeller • Beamforming Abbreviations c T Thrust coefficient (-) D Propeller diameter (m) f Frequency (Hz) h Height (m) J Advance ratio (-) n Rotational speed (1/s) V tip Blade tip velocity (m/s) U Air velocity (m/s) α Angle of attack (°) θ Propagation angle (°)

Journal of Physics: Conference Series, 2019

The interaction between a jet close to the sonic condition and a tangential flat plate was invest... more The interaction between a jet close to the sonic condition and a tangential flat plate was investigated. Measurements have been carried out in the semi-anechoic chamber of the Fluid Dynamic laboratory at the University Roma Tre. The converging nozzle has a conical shape and an outlet diameter of about D=12 mm. Wall pressure fluctuations are acquired at axial distances ranging between 1 < x/D < 6. Measurements are repeated for two different radial positions of the flat plate(H/D = 2 and H/D = 0.75) and they are performed at Mj = 0.9 and Mj = 1 in slightly under-expanded conditions until NPR = 1.94. Fluctuating pressure data are analyzed in time and frequency domain and compared with the flow visualization images obtained through a Background Oriented Schlieren technique. The investigation leaded to deepen the phenomena underlying the interaction between the planar surface and the high-speed jet, clarifying the influence on the shock cell structure.