Publications
Preprints and the author copies of the published articles can be made available on request for academic purposes. Data can also be shared for select projects for the purpose of cross-validation and collaborations
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The possibility of jet-installation noise reduction has been experimentally demonstrated using a flat-plate fitted with flow permeable metal foam fitted at the trailing-edge. Tests were conducted for single-stream cold subsonic jets with a round nozzle adjacent to a flat-plate for a wide range of flow velocities (M= 0. 3− 0. 9) in an anechoic chamber. Thorough investigations of the far-field noise for various polar angles were carried out to demonstrate the regions with noise reduction. Four porous trailing-edges were tested with various increasing permeability and surface roughness. Far-field results showed substantial noise reduction for the installed configuration fitted with porous trailing-edges. Overall sound pressure level scaling with velocity demonstrates that trailing-edge scattering noise is reduced by the application of from porous trailing-edge. Detailed analysis using coherence and correlations of the far-field …
Jet installation with chevron nozzles beneath a wing significantly modifies jet noise at low frequencies, and its physical mechanism must be comprehended to develop efficient noise reduction solutions. A numerical investigation on the jet-installation noise with an SMC006 chevron nozzle is performed using Wall Modelled Large Eddy Simulation (WMLES) using the high-resolution CABARET method, accelerated on Graphics Processing Units. To simulate the jet installation, an SMC006 chevron nozzle with a penetration length of 20 degrees and length L is put at 2Dj vertically above the flat plate, resulting in a rise in noise levels at low frequency. The low frequency amplification is associated with the scattering of the near-field hydrodynamic pressure waves at the trailing edge. The numerical simulation for the baseline chevron is validated with the …
Imperfectly expanded jet flows are known to have additional noise sources known as Screech and broadband shock associated noise. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock cell structures. In this study, thorough experimental investigations were carried out on chevron nozzles to assess the importance of chevron parameters such as the chevron count and chevron penetration angle on the pressure field emitted by the jet. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as pressure spectra, directivity and overall sound pressure levels along with near-field measurements were acquired for jet Mach numbers ranging from M= 1.1-1.4. Fourier-based and Wavelet-based analyses were used to highlight the different features of the various tested nozzles. Wavelet decomposition results highlight that the presence of the chevrons reduce the acoustic noise especially at a higher axial distance with increased levels of noise reduction achieved by chevron nozzle with deep penetration angle.
A detailed investigation of the statistical properties of the near-field pressure fluctuations induced by an under-expanded jet, by varying the nozzle exit shapes has been presented. Experiments using different convergent Chevron nozzles were carried out in the anechoic chamber at the University of Bristol to assess the importance of the Chevron shape on the near pressure field emitted by a single stream under-expanded jet. Measurements were carried out through an axial microphone array traversed radially to various positions for jet in an under-expanded condition at Mach number M = 1.3. The intermittent behavior is investigated considering the standard statistical indicators and a wavelet-based conditional approach, including the phase angle. The intermittent degree of various features related to different scales, such as Screech tones and broadband shock associate noise were estimated. A series of recently developed wavelet-based tools were assessed as a viable approach to investigate the noise emitted by under-expanded jets.
Numerical investigation of the aerodynamic and aeroacoustic characteristics of a symmetrical NACA 0012 airfoil developed by National Advisory Committee for Aeronautics (NACA) with a conventional hinged flap and a morphed flap has been carried out. The unsteady flow characteristics over the airfoil surface and at the airfoil wake are captured using high-fidelity Large Eddy Simulations. The tests were carried out for a freestream velocity of U∞= 20 m/s, corresponding to a chord-based Reynolds number of R c= 2× 10 5, at angles of attack α= 0° and 4°. The results of the airfoil static pressure distribution show that the airfoil with morphed trailing edge produces higher values of lift coefficient than the airfoil with hinged trailing edge due to its higher suction peak resulting in larger pressure difference between the suction and pressure sides. Furthermore, from the wake-flow measurements, boundary-layer analysis …
An experimental study was performed on a 30P30N three-element high-lift airfoil fitted with different types of slat finlets and its noise reduction capabilities were assessed. To develop a better understanding of the noise reduction mechanism, simultaneous measurements of the unsteady surface pressure were taken at various locations at the vicinity of the slat cove and at far-field locations. While there was a small reduction in far-field noise for the fundamental peak, the use of slat finlets showed a substantial reduction in surface pressure fluctuations. The reduction of vortex shedding energy by the slat finlets also resulted in the reduction of nonpropagating hydrodynamic field between the slat and the main-element substantially reducing the near-field pressure spectra. Fourier and wavelet-based analysis along with high-order spectral analysis were provided for further confirmation of the observations and hypothesis …
Experimental measurements were carried out to assess the aeroacoustic characteristics of a 30P30N high-lift device, with particular attention to slat tonal noise. Three different types of slat modifications, namely slat cove filler, serrated slat cusp, and slat finlets have been experimentally examined. The results are presented for an angle of attack of α = 18 at a free-stream velocity of U = 30 m/s, which corresponds to a chord-based Reynolds number of Re = 7 x 10. The unsteady surface pressure near the slat region and far-field noise were made simultaneously to gain a deeper understanding of the slat noise generation mechanisms. The nature of the low-frequency broadband hump and the slat tones were investigated using higher-order statistical approaches for the baseline 30P30N and modified slat configurations. Continuous wavelet transform of the unsteady surface pressure fluctuations along with secondary …
An experimental study of a simple NACA 0012 airfoil fitted with two different flap profiles was carried out to characterize their aerodynamic and aeroacoustic performance. The airfoil with a flap deflection angle of β= 10° was tested for a wide range of angles of attack at a chord-based Reynolds number of Re c= 2.6× 10 5. The aerodynamic lift and drag measurements show improved lift-to-drag performance for the morphed flap airfoil compared to the hinged flap airfoil at low angles of attack. Surface flow visualization and boundary layer measurements on the suction surface of the flap show delayed separation for the morphed flap airfoil. Higher-order moments of the wall pressure fluctuations were also used to observe the flow separation over the flap. Additionally, Particle Image Velocimetry was also used to study the flow over the flap and at the airfoil wake. Flow measurements showed that the downstream wake …
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 …
Additional noise sources known as Screech and BBSAN are common in jet noise for imperfectly expanded jet flow. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock-cells shock cell structures. In this study, thorough experimental investigations have been carried out on chevron nozzles to assess the importance of chevron parameters such as the number of chevrons (chevron count) and chevron penetration. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as overall sound pressure level, spectra, and directivity along with near-field measurements have been made for jet Mach numbers ranging from M = 1.1 - 1.4. Fourier-based and Wavelet-based analyses have been used to highlight the different features of …
Experiments were conducted using three different approaches to investigate the possibility of jet-installation noise reduction. The experiments were carried out for cold jets with round nozzle for Mach numbers ranging from 0.3 to 0.9. The three approaches for jet-installation noise reduction trough surface treatments were investigated. It involved the application of various types of trailing-edge modifications such as porous, serrated, and finlet to the trailing-edge of the flat-plate placed at the proximity to the jet. The characteristics of the jet hydrodynamic pressure fluctuations were investigated in the axial direction using far-field measurements. The trailing edge treatments were investigated for five different flat-plate positions away from the jet axis for a wide range of Mach numbers. This experimental study on jet-installation noise will aid us to explore the …
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Jet screech is the result of a resonant aeroacoustic feedback loop sustained by the intrinsic instability waves of the jet flow. Experimental study has been carried out at the University of Bristol for jet Mach number ranging from M = 1.1 - 1.4 to characterize the non-linear instability wave development in the shear layer of a round supersonic cold screeching jet. Near-field pressure fluctuations using a linear array of microphones on a traverse was used to measure the instability wave development in the jet shear layers. Time-frequency analysis was carried out to determine resonant nonlinear interaction between multiple instability modes that occur in screeching jets. Wavelet analysis was carried out to track the time evolution of the various scales for the near-field pressure fluctuations. Furthermore, the coexistence of the multiple acoustic modes from jet …
Experimental and numerical investigations on the effects of chevron nozzles on the jet-installation noise has been conducted for subsonic cold jets. The experiments were carried out for four different types of chevron nozzles at five plate positions away from the jet for Mach numbers ranging from 0.3 to 0.9. The use of chevron nozzles has been known to reduce the jet noise at low frequencies. In this study the possibility of jet-installation noise reduction with the use of chevron nozzles have been explored. The characteristics of the jet hydrodynamic pressure fluctuations were investigated in the axial direction using far-field measurements. The near-field flow features were studied using Wall-Modelled Large Eddy Simulations based on the GPU CABARET method for both the isolated and installed configurations. For the installed configuration, , the simulations were carried out for a plate position of h = 2D at M = 0.5 and 0.9 for the SMC 000 and SMC006 nozzles. The far-field noise was predicted using the Ffowcs Williams–Hawkings method based on multiple penetrable control surfaces. To quantify the difference in noise generation mechanisms between the round and chevron, and also isolated and installed jets, the LES solutions are analysed using Spectral Proper Orthogonal Decomposition are discussed. Opportunities for low-rank reduced-order modelling are discussed.
Numerical investigation of a near-field flow over a highly cambered NACA 65(12)-10 airfoil with and without sawtooth-serrated trailing-edge has been carried out. Large Eddy Simulations (LES) for the airfoil with an inflow velocity of 30 m/s corresponding to a chord-based Reynolds number of Rec = 3x10^5 at a high angle of attack of α=15 have been performed. For flow simulations, Wall Modelled Large Eddy Simulation (WMLES) approach based on the high-resolution CABARET method for compressible gas equations is considered. To accelerate the calculations, CABARET is implemented on Graphics Processing Units (GPU) and works with unstructured snappy hex meshes which include hanging nodes enabling the semi-automatic grid refinement. The wake development results from previous studies have shown that the use of serrations can …
Slat noise is well known as one of the dominant noise components of airframe noise. The slat cove has been demonstrated to be one of the primary sound sources responsible for narrowband and broadband noise from high-lift devices. In order to reduce slat noise, several slat modifications mostly aerodynamic have been carried out in the past. In the present study, Wall-Modeled Large Eddy Simulations using GPU CABARET flow solver have been used to assess the aerodynamic and aeroacoustic performance of a 30P30N high-lift airfoil with effective slat modifications such as slat cove filler. The numerical simulations were carried out at an angle of attack of α = 5:5 at an inlet velocity of U1 = 58 m/s, corresponding to a chord-based Reynolds number of Rec = 1.71x10^6 The surface pressure distribution and far-field noise spectra have been validated …
Noise reduction capabilities of slat cusp serration were experimentally assessed and demonstrated for a 30P30N three-element high-lift airfoil fitted with two different types of serrated slat cusps. Aerodynamic characteristics were evaluated with the aid of surface pressure distribution, and insignificant differences were found among all the tested configurations. The unsteady flow characteristics of the slat serrations were examined using near- and far-field measurements to gain a deeper understanding of the noise generation mechanism. Although increased surface pressure fluctuations were demonstrated by the slat serrations, a substantial reduction in the far-field noise was observed. The increase in the near-field energy levels was attributed to the non-propagating hydrodynamic energy field within the slat cove and the main element, whereas the far-field noise reduction was attributed to the elimination of vortex …
Experimental measurements were carried out to assess the aerodynamic and aeroacoustic performance of an MDA 30P30N airfoil fitted with two different types of slat cove fillers. The aerodynamic results are presented for lift and drag measurements and mean surface pressure measurements, while the aeroacoustic results are presented for the near-field surface pressure fluctuations and far-field noise measurement. The flow measurement results show that there is no significant difference in the aerodynamic lift and drag between the tested cases, however, the slat cove filler configurations exhibit a much better lift-to-drag performance. The pressure coefficient results show that the use of slat cove fillers lead to a slight decrease in the suction peak over the main-element of the airfoil. In order to better understand the flow-field and the noise generation mechanism of the airfoil with slat cove fillers, simultaneous near …
Abstract Experimental measurements using Particle Image Velocimetry were carried out to understand the flow characteristics of a 30P30N high-lift airfoil with and without slat cove fillers. The tests were carried out for the 30P30N airfoil with a retracted chord of c= 0.35, at angles of attack of α= 6∘ and 12∘, and for a chord-based Reynolds number of R e c= 7.0× 10 5. The wall pressure fluctuation results show that the use of slat cove fillers eliminates the slat tonal noise component. The results of the mean flow fields such as the normalized mean velocity, Reynolds stress components, and turbulent kinetic energy are presented for the baseline, half-slat cove filler, and slat cove filler configurations. The velocity contour results with streamlines showed a recirculation region within the slat cavity. The use of the half-slat cove filler reduced the size of the recirculation region and the use of the slat cove filler eliminated the …
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 Rec = 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 …
Experimental studies of a NACA 0012 airfoil fitted with six different spanwise morphed flap profiles were successfully carried out to characterize their aerodynamic and aeroacoustic performance. The airfoil was tested with six configurations with different spanwise flap camber with a maximum deflection angle of β = 10◦ on one side and a minimum deflection angle of β = 0 ◦ on the other side. The tests were carried out for a flow velocity of U∞ = 20 m/s, corresponding to a chord-based Rec = 2.6 × 105 . The aerodynamic lift and drag measurements showed that improved lift-to-drag performance is highly dependant on the spanwise flap camber. Flow measurements at the downstream wake locations were carried out using hot-wire anemometry. Flow measurements also showed that the downstream wake development could be significantly influenced by the spanwise flap profile. The turbulent kinetic energy results …
Experimental measurements to assess the aeroacoustic capabilities of 30P30N airfoil fitted with two different types of serrated slat cusps were carried out at the aeroacoustic wind tunnel at the University of Bristol. The results from the simultaneous surface pressure measurement within and close to the slat cove region and far-field noise measurements above the slat trailing edge are presented to gain a deeper understanding of the noise generation mechanism of the slat and other presented configurations. The far-field noise measurement results showed that significant noise reduction at the vortex shedding frequency can be achieved by the use of serration-2 and No-Cusp configuration. The coherence results for all the frequencies are almost zero for the No-Cusp configuration and the coherence was notably reduced for the Serration-2 configuration. Further higher-order statistical and spectral analysis showed that …
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This paper provides an overview of the design and performance of the new aeroacoustic wind tunnel facility at the University of Bristol. The purpose of the facility is to enable near- and far-field acoustic and aerodynamic studies on a variety of different aerodynamic components and to examine diverse noise control techniques. The facility comprises a large acoustic chamber, anechoic down to 160 Hz, and a temperature controlled closed-circuit wind tunnel with an open test section. The wind tunnel features two interchangeable rectangular nozzles with a partially shared contraction. Both nozzles are shown to possess a high flow quality with high flow uniformity and low turbulence intensity of 0.09% and 0.12% for the smaller and larger nozzle, respectively. The maximum attainable flow speeds are 40 m/s for the larger nozzle and 120 m/s for the smaller nozzle corresponding to Reynolds numbers of 2.7 million …
Trailing edge serrations are a widely used passive technique for the suppression of aerodynamic noise from wind turbines. Despite their popularity, no reliable engineering prediction tool has yet been developed to estimate the noise reduction for different serrations. This paper concerns the development of an engineering noise prediction tool, based on a recently developed mathematical model. Results show that the new model has several advantages over Howe's model, as it can take both destructive and constructive sound interference effects into account. Two surface pressure wavenumber-frequency models are implemented, namely Chase and TNO models, to demonstrate the sensitivity of the model to boundary layer characteristics. The boundary layer parameters needed in the wavenumber-frequency models are obtained using RANS CFD simulations. Far-field noise comparisons are provided between the …
THE introduction of high bypass-ratio turbofans engines into civil aircraft have drastically reduced engine noise over the last several decades, making the airframe noise the same magnitude as that of the engine noise, especially during the landing phase. In order to reduce these prominent airframe noise sources several fundamental passive and active flow control methods have been investigated over the recent years, such as, morphing structures [1–7], porous materials [8–11], surface treatments [12], serrations [13–15] and transverse jets [16]. One of the prominent sources of airframe noises are the high-lift devices namely the slats and flaps. Studies on conventional slat and wing configurations have shown that it mainly comprises of broadband and tonal noise components. Several studies on slat noise have shown several discrete tones at mid-frequency range [17–29]. However, their aeroacoustic mechanism is …
The aerodynamic performance of a NACA 0012 airfoil fitted with different flaps were studied experimentally and numerically. Comprehensive aerodynamic measurements including pressure distribution, lift and drag forces and wake flow for airfoils with different mean flap camber profiles were carried out over a wide range of angles of attack and chord-based Reynolds numbers. The results show that the mean flap camber profiles significantly affect the aerodynamic performance and the downstream wake development of the airfoil. It was found that the highly cambered flap profiles provide higher lift coefficients compared to the moderately cambered flap profiles, with an insignificant reduction in the overall lift-to-drag ratio. Furthermore, the Q-criterion iso-surface results show that the separation near the trailing-edge is further delayed at high angles of attack for airfoils with high mean flap camber. This study shows that …
The purpose of this paper is to investigate airfoil self-noise generation and propagation by using a hybrid method based on the large-eddy simulation (LES) approach and Curle’s acoustic analogy as implemented in OpenFOAM.
Design/methodology/approach
Large-eddy simulation of near-field flow over a NACA6512-63 airfoil at zero angle of attack with a boundary layer trip at Rec = 1.9 × 105 has been carried out using the OpenFOAM® computational fluid dynamics (CFD) code. Calculated flow results are compared with published experimental data. The LES includes the wind tunnel installation effects by using appropriate inflow boundary conditions obtained from a RANS κ – ω SST model computation of the whole wind tunnel domain. Far-field noise prediction was achieved by an integral method based on Curle’s acoustic analogy. The predicted sound pressure levels are validated against the …
AIRFRAME noise is well known to be one of the major components of overall aircraft noise, especially during the landing phase. One of the prominent sources of airframe noises are the high-lift devices namely the slats and flaps. In order to reduce these prominent noise sources several passive and active flow control methods were investigated in the past; morphing structures [1–4], porous materials [5, 6], surface treatments [7] and serrations [8, 9]. The increasingly stringent regulations set by the International Civil Aviation Organisation has made the noise reduction of aircrafts a priority amongst the aerospace community around the world. Slat noise is of great interest to researchers due to the high levels of noise generated by it and its complex flow structures. Previous studies [10–14] on slat noise carried out by other researchers have shown that the broadband and tonal noise from conventional slat and wing …
SHAPE-ADAPTIVE structures are enabling wind turbine blades and aeroplane wings of improved performance with reduced weight and complexity penalty. Containing smooth geometric changes and continuous structural surfaces, these compliant light-weight control surfaces, which are increasingly known as morphing structures, remain conformal to the flow. As such, significant noise and drag reduction are envisaged through morphing structures. It is of fundamental importance in the concept synthesis of morphing structures to thoroughly investigate the flow behaviours and mechanisms of performance improvement.
Studies have shown that noise generated by kinetic energy scattering of turbulent eddies in the boundary layer as they cross the wing’s trailing edge becomes dominant for aeroplanes in clean configuration with projected reduction of the high-lift system noise [1]. As such, airfoil self-noise has been …
This paper provides an overview of the design and performance of the new aeroacoustic wind tunnel facility at the University of Bristol. The purpose of the facility is to perform near-and far-field acoustic and aerodynamic studies on a variety of different bodies and to examine diverse noise control techniques. The facility comprises a large anechoic chamber with a cutoff frequency of 160 Hz and a temperature controlled closed-circuit wind tunnel with an open test section. The wind tunnel features two interchangeable nozzles, 600mm× 200 mm and 500 mm× 775mm, for different applications, with both nozzles possessing a high flow quality with low turbulence intensity and high flow uniformity. The maximum attainable flow speeds are 40m/s for the larger nozzle and 120m/s for the smaller nozzle corresponding to Reynolds numbers of 2.7 million and 8.1 million per meter, respectively. The larger nozzle allows flow and …
The rapid expansion of air transport and the rising prevalence of wind turbines have resulted in negative, noise associated, health effects for a large number of people living in the vicinity of airports or large wind farms. 1 The European Union, amongst other governmental bodies worldwide, has introduced more stringent regulations to limit these adverse effects. Hence, it is now a key requirement and a critical design driver to reduce the aerodynamic noise from aircraft and wind turbines in order to comply with the existing...
AIRFOIL trailing edge noise has been a long-standing problem when it comes to airfoil self-noise. Among all the airfoil self-noise mechanism listed: vortex shedding noise, separation stall noise, tip vortex formation noise and trailing edge noise on turbulent boundary layer [1], the trailing edge noise has been a major concern since the turbulent boundary layers are more likely to develop on the vast majority of aircrafts and wind turbine applications. Several studies on airfoil trailing edge treatments have been carried out in the past in order to attenuate the noise generated by them. The predominantly used methods can be classified into passive and active flow control methods. For Passive flow control approach, no external energy is added to alter the boundary layer. The changes to the flow characteristics are introduced by adding devices like serrations [2–5], types of riblets, morphing [6–10] or by applying porous [11 …
A comprehensive experimental study has been performed for symmetric NACA 0012 and cambered NACA 65(12)-10 airfoils with a variety of trailing-edge serrations over a wide range of angles of attack. Results are presented for the aerodynamic force measurements, wake development, and energy content of the wake turbulent structure at moderate chord-based Reynolds numbers . The aerodynamic force measurements have shown that the use of trailing-edge serrations for cambered airfoils can lead to significant reductions in the lift coefficient at low angles of attack but does not particularly change the stall characteristics of the airfoils. The wake flow results have shown that the use of serrations can lead to considerable reduction of the wake turbulence intensity, which is shown to be due to a complex interaction between the flowfield over the tip and root planes of the serration in the near …
MORPHING structures have received significant interest from engineering community including the aviation and automobile industries, owing to their potential of high performance, low mechanism complexity and lightweight. Current high-lift systems used on aeroplane wings for example slats, aileron and trailing-edge flaps, mainly consist of discrete rigid structure components which are articulated around hinges and linkages to achieve wing shape change for flow control purposes. As such, the overall system complexity and structure weight are considerably increased. Unlike conventional wing control surfaces, morphing structures for example morphing leading-edge and trailing-edge usually use the conformal structural deformation achieved through bending and twisting of structures to adaptively change wing shape, leading to simplified systems and reduced weight. Furthermore, the intrinsic continuous …
THE impact on aircraft noise on the communities near the airport has been an issue since the entry of turbofan and turbojet engines into civil aviation from the 1960s and 1970s. The widespread global expansion of air travel has made the environmental impact of aircraft noise much more prominent in the recent times. This has forced the International Civil Aviation Organisation (ICAO) to set technical standards for civil air transport aircraft and 180 countries have adapted this. With such upcoming regulations to reduce noise impact on communities near airport further understanding into aircraft noise has to be achieved. The introduction of high bypass-ratio turbofans engines into civil aircrafts have drastically reduced engine noise over the last several decades, making the airframe noise the same magnitude as that of the engine noise especially during the landing phase. One of the prominent sources of airframe …
Aviation has grown rapidly over the past decades and attention has been attracted to the adverse environmental impact including the noise and green gas emissions. Future expansion of aviation puts more pressure on the aerospace industries to address these issues. In the Flightpath 2050 goals of protecting environment and the energy supply by Advisory Council for Aviation Research and Innovation in Europe [1], the CO2 emissions per passenger kilometre is expected to be reduced by 75%, NOx emissions by 90% and perceived noise by 65%. Technological efforts and improvements are necessary to meet the emission reduction goals, including utilization of light-weight materials, new aircraft configurations, innovative propulsion system design and novel high-lift systems. One particular topic is the morphing structure, which is considered as a promising candidate for the next generation of aircraft high-lift …
THE increasing popularity of air travel and rapid growth in the number of airports close to the city limits have increased noise pollution leading to negative physiological and psychological effects on the surrounding residents.
Therefore, stringent standards have been set by ICAO for aircraft noise control, attracting researchers interest to aeroacoustics. Noise generated from aircraft can be broadly classified in the airframe noise and engine noise. The engine noise has been reduced considerably over the last half century by the introduction of high bypass ratio turbofan engines and introduction of chevrons in the back of the nacelle and the engine exhaust nozzle. However, the reduction of broadband noise component from the compressor, due to the interaction of laminar and turbulent flows with blades, has remained a challenging task. It is also believed to play a significant role in the overall engine noise [1] and also …
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Jet installation beneath a wing significantly enhances jet noise at low frequencies, and its physical mechanism must be comprehended to develop efficient noise reduction solutions. A numerical investigation on the jet-installation noise is performed using Wall Modelled Large Eddy Simulation (WMLES) based on the high-resolution CABARET method accelerated on Graphics Processing Units. To simulate jet installation, a flat plate is put outside of the jet’s plume, causing a rise in noise levels due to the scattering of near-field hydrodynamic waves at the trailing edge of the plate. The configuration adopted in this work replicates a series of experiments performed at the University of Bristol, against which the numerical results are validated. The numerical simulation is performed for Mach numbers of 0.5 and 0.9, and the influence of the selected noise reduction technique, ie, the usage of chevron nozzles in comparison with the baseline round nozzle, on the jet-installation is studied by modelling SMC006 chevron nozzle. The properties of jet-hydrodynamic pressure variations and their effect on nozzle type and Mach number are investigated. Far-field noise spectra from the isolated and installed jet cases, obtained through the Ffowcs-Williams Hawkings method, are compared at different polar angles. In addition, a hybrid semi-analytical hydrodynamic-edge scattering prediction model is implemented following the model of Lyu and Dowling [1] to analyse jet-installation noise, using inputs obtained directly from the LES calculation. The implemented model is found to capture the correct physics at peak jet installation frequencies and can be used as a …
OVER the past decade, the boost in the commercial air travel has stipulated the aircraft industry to produce efficient and quieter aircraft than the ones already in use. With the use of high bypass engines, the noise generated by the engine has significantly been lowered, yet, the airframe noise remains unaltered. This airframe noise is extensively caused by landing gears and high-lift devices like the slats and flaps. Various passive and active flow control methods have shown to reduce these noise levels by the use morphing structures [1–6], porous materials [7–11], and serrations [12–18]. Nonetheless, conventional slat and wing configurations prove that slat noise majorly comprises of broadband and tonal noise components and in addition to this, studies have also shown several discrete tones at mid-frequency range [19–31]. The aeroacoustic mechanism used in these configurations is yet to be completely understood and interpreted. Slat noise reduction mechanisms that have proven successful are slat cove cover, slat hook extensions, slat cove filler, slat gap reduction, slat acoustic liners, slat hook tripping, slat hook serrations and slat trailing with porous or brush extensions [32].
One of the most definite ways of reducing the broadband noise generated from the slat cove region is by filling the recirculation area within the slat cove gap [33–43]. These tonal peaks in the slat are a result of vortex shedding at the slat cusp and impingement on the lower surface of the slat along with a feedback loop present in between them. Filling the slat cavity has shown to have eliminated this tonal noise and the broadband noise from the shear layer impingement …
Experimental and numerical studies to characterize aerodynamic and aeroacoustic performance of simple and multi-element aerofoils using morphing structures are conducted and some preliminary results are presented here. For the simple aerofoil, a NACA 0012 aerofoil with morphing trailing-edge with deflection angle β= 10◦ for a chord-based Reynolds number of Rec= 2.6× 105 has been reported for two different morphing trailing-edge designs. Comprehensive flow field investigations including lift and drag forces measurements, wake profiles using hot-wire, pressure distribution along the chord and aerofoil noise emission are carried out. LES studies have been performed to further investigate the flow behaviours around aerofoils and good agreement between the experimental results and that from LES is found. For multi-element aerofoil, a parametric experimental study of MDA 30P30N multi-element aerofoil has been carried out to investigate the aerodynamic and aeroacoustic effects and efficiency of morphing structures. The study involved the use of slat cove fillers, flap cove fillers, Droopnose configuration and slat cusp serrations. Static surface pressure measurements, unsteady surface pressure measurements using microphones and flow visualisation using particle image velocimetry (PIV) has been carried out. Results confirmed the great potential of the morphing structures, which is one of the highly sought candidate for the next generation aircraft control surfaces.