CERES :: Browsing by Author "Saddington, Alistair J."

Browsing by Author "Saddington, Alistair J."

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Open Access
Aero-whisker for the measurement of aircraft flight speed and angle of attack in compressible flow conditions
(AIAA, 2023-06-08) Debiasi, Marco; Atkinson, Kevin; Saddington, Alistair J.; Finnis, Mark
A whisker-like device has been designed and tested that simultaneously measures the speed and the direction of a flow in which it protrudes. The device consists of a thin cylindrical probe longer than the thickness of the local boundary layer whose aerodynamic drag produces a moment at its base which is measured by a solid-state torque transducer. With proper calibration, the orthogonal components of the moment can be used to measure the speed and the direction of the flow. Measurements have been performed in a wind tunnel to validate the design at flow velocities ranging from Mach 0.15 to Mach 0.87 and for flow angles relative to the probe ranging from -88° to +88°. The results obtained indicate that the aero-whisker is capable to accurately measure the Mach number and direction of the flow with potential for further optimization for aircraft applications.
Open Access
Aerodynamic problems of urban UAV operations
(2011-09-09) Kittiyoungkun, S; Saddington, Alistair J.; Knowles, Kevin
Unmanned Air Vehicles, UAVs are designed to operate without any onboard controllers. Consequently, they are considered to operate in a wide range of applications. Missions in undesirable conditions such as bad weather and/or highly unsteady gustiness could cause an unsuccessful operation. In many ways, aerodynamics is a key feature in the performance of UAVs such as influencing deformation vehicle, guidance and control. Two aspects of this research are, therefore, to understand flying conditions of UAVs in an urban environment and how the flying performance is affected by such conditions. The first objective relies on understanding air flow behaviour in the lower part of the urban environment which has the most important role on the response of UAVs. The second objective will be to look at the characteristics of a three-dimensional airfoil when it encounters an unsteady sinusoidal gust at different oscillation frequencies and freestream velocities. As the first step of the studies on the aerodynamic problem of UAV operations in the lower part of an atmospheric boundary layer in an urban environment, the boundary layer thickness in a suitable wind tunnel facility were the first experimental results obtained. Experimental measurements of the mean velocity profile in a turbulent boundary layer were investigated for three different floor roughness conditions as well as a smooth wall condition. As a result, three different boundary layer thicknesses were then classified depending on the wall surface roughness and a combination with turbulence generators providing a maximum thickness of 280 mm at the centre of the tunnel test section. However,the experimental investigations into the turbulent boundary layer over a rough wall have shown that the boundary layer thickness is dependent on the surface roughness and is different from that obtained under the smooth wall condition. An experimental study into a simulated urban flow regime was then carried out after the measurement of the boundary layer. Wind tunnel experiments on the airflow around a single and twin buildings including an investigation of the airflow between the gap of the buildings were obtained. Wind in the lower part of the atmospheric boundary layer is more a micro-scale problem which increases or decreases the wind speed induced by buildings nearby. The studies have found some strong concentrated vortices caused by the flow separation essentially independent of the nature of the upstream flow and usually as a direct result of the building geometry and orientation. As the measurement location increased further downstream from the back of the buildings, the concentrated vortices were found to be weak and disappeared into the wake region. Finally, an experiment was conducted using a sinusoidal gust generator to describe the effects of wind oscillation parameters such as oscillation amplitude, oscillation frequency and reduced frequency under static and dynamic conditions. An evaluation was made of the onset of dynamic stall due to rapid changes in angle of attack during an unsteady pitch motion. The NACA 23012 wing profile was tested at a fixed angle of attack condition with varying oscillation flow parameters. Results demonstrate that those parameters influence the dynamic stall and hysteresis loop based on lift coefficient and angle of attack
Open Access
Aerodynamics and performance enhancement of a ground-effect diffuser
(2018-04) Ehirim, O H; Knowles, Kevin; Saddington, Alistair J.
This study involved experimental and equivalent computational investigations into the automobile-type 3―D flow physics of a diffuser bluff body in ground-effect and novel passive flow-control methods applied to the diffuser flow to enhance the diffuser’s aerodynamic performance. The bluff body used in this study is an Ahmed-like body employed in an inverted position with the slanted section together with the addition of side plates along both sides forming the ramped diffuser section. The first part of the study confirmed reported observations from previous studies that the downforce generated by the diffuser in proximity to a ground plane is influenced by the peak suction at the diffuser inlet and subsequent static pressure-recovery towards the diffuser exit. Also, when the bluff body ride height is gradually reduced from high to low, the diffuser flow as indicated by its force curve and surface flow features undergoes four distinct flow regimes (types A to D). The types A and B regimes are reasonably symmetrical, made up of two low-pressure core longitudinal vortices travelling along both sides of the diffuser length and they increase downforce and drag with reducing ride height. However, below the ride heights of the type B regime, types C and D regimes are asymmetrical because of the breakdown of one vortex; consequently a significant loss in downforce and drag occurs. The second part of the study involved the use ― near the diffuser exit ― of a convex bump on the diffuser ramp surface and an inverted wing between the diffuser side plates as passive flow control devices. The modification of the diffuser geometry with these devices employed individually or in combination, induced a second-stage pressure-drop and recovery near the diffuser exit. This behaviour was due to the radial pressure gradient induced on the diffuser flow by the suction surface ii curvature of the passive devices. As a result of this aerodynamic phenomenon, the diffuser generated across the flow regimes additional downforce, and a marginal increase in drag due to the profile drag induced by the devices.
Open Access
Aerodynamics of a convex bump on a ground-effect diffuser
(Journal of Fluids Engineering, 2018-04-19) Ehirim, Obinna; Knowles, Kevin; Saddington, Alistair J.; Finnis, Mark V.
A ground-effect diffuser is an upward-sloping section of the underbody of a racing car that enhances aerodynamic performance by increasing the downforce, thus improving tire grip. The downforce generated by a diffuser can be increased by geometric modifications that facilitate passive flow control. Here we modified a bluff body equipped with a 17° diffuser ramp surface (the baseline/plane diffuser) to introduce a convex bump near the end of the ramp surface. The flow features, force and surface pressure measurements determined in wind-tunnel experiments agreed with previous studies but the bump favorably altered the overall diffuser pressure recovery curve by increasing the flow velocity near the diffuser exit. This resulted in a static pressure drop near the diffuser exit followed by an increase to freestream static pressure, thus increasing the downforce across most of the ride heights we tested. We observed a maximum 4.9% increase in downforce when the modified diffuser was compared to the plane diffuser. The downforce increment declined as the ride height was gradually reduced to the low-downforce diffuser flow regime.
Open Access
Angle of attack effects on the induced structural loads of a weapons bay
(Springer, 2024) Bacci, David; Saddington, Alistair J.
Aero-acoustic analysis was conducted on a weapons bay numerical model with doors, incorporating radar cross section reduction features. The effect of the angle of attack on the aero-acoustic response of the cavity was analysed at Mach numbers of 0.85 and 1.20. It was found that incidence influenced both mean-flow features and acoustic response. Further, linear and angular accelerations induced by the flow on the bay doors revealed potential adverse fluid–structure coupling when the results were compared with modal analysis. Again, the angle of attack did influence the aeroacoustic effects on the cavity door structure.
Open Access
Autonomy is the answer, but what was the question?
(The Institute of Marine Engineering, Science and Technology, 2024-10-21) Spayne, Peter; Lacey, Laura; Cahillane, Marie; Saddington, Alistair J.
In recent years aspirations regarding the implementation of autonomous systems have rapidly matured. Consequently, establishing the assurance and certification processes necessary for ensuring their safe deployment, across various industries, is critical. In the United Kingdom Ministry of Defence distinctive duty holder structures - formed since the publication of the Haddon Cave report in 2009 - are central to risk management. The objective of this research is to evaluate the duty holder constructs suitability to cater for the unique merits of artificial intelligence-based technology that is the beating heart of highly autonomous systems. A comprehensive literature review examined the duty holder structure and underpinning processes that form two established concepts: i) confirming the safety of individual equipment and platforms (safe to operate); and ii)the safe operation of equipment by humans to complete the human-machine team (operate safely). Bothtraditional and emerging autonomous assurance methods from various domains were compared, includingwithin wider fields, such as space, medical technology, automotive, software, and controls engineering. Thesemethods were analysed, adapted, and amalgamated to formulate recommendations for a single militaryapplication. A knowledge gap was identified where autonomous systems were proposed but could not be adequately assured. Exploration of this knowledge gap revealed a notable intersection between the two operating concepts when autonomous systems were considered. This overlap formed the development of a third concept, safe to operate itself safely, envisioned as a novel means to certify the safe usage of autonomous systems within the UK's military operations. A hypothetical through-life assurance model is proposed to underpin the concept of safe to operate itself safely. At the time of writing the proposed model is undergoing validation through a series of qualitative interviews with key stakeholders; duty holders, commanding officers, industry leaders, technology accelerator organisation leaders, requirements managers, system designers, Artificial Intelligence developers and other specialist technical experts from within the Ministry of Defence, academia, and industry. Preliminary analysis queries whether a capability necessitates the use of autonomy at all. Recognising that some autonomous systems will never be certified as safe to operate themselves safely, voiding ambitious development aspirations. This highlights that autonomy is simply one of many tools available to a developer, to be used sparingly alongside traditional technology, and not a panacea to replace human resource as originally thought. This paper provides a comprehensive account of the convergence between safe to operate and operate safely, enabling the creation of the safe to operate itself safely concept for autonomous systems. Furthermore, it outlines the methodology employed to establish this concept and makes recommendations for its integration within the duty holder construct.
Open Access
Autonomy is the answer; what was the question?
(Cranfield University Defence and Security, 2024-11-13) Spayne, Peter; Lacey, Laura J.; Cahillane, Marie; Saddington, Alistair J.
Open Access
Comparison of passive flow control methods for a cavity in transonic flow
(AIAA, 2016-03-21) Saddington, Alistair J.; Thangamani, Varun; Knowles, Kevin
Acomparative study of different passive control techniques was conducted on a cavity with a length of 320mmwith length-to-depth and length-to-width ratios of five and two, respectively. The tests were conducted at a freestream Mach number of 0.71. Both leading-edge and trailing-edge modifications were included in the studies. Results from surface pressure measurements showed that leading-edge control techniques were more effective at suppressing cavity tone amplitudes than trailing-edge modifications.Asquare-tooth spoiler showed the greatest reduction in tonal amplitude (8.8 dB); however, a sawtooth spoiler showed the greatest reduction in overall sound pressure level (8.13 dB). Velocity measurements inside the cavity were made using particle image velocimetry for the clean cavity and the cavity with sawtooth spoilers. The results showed a reduction in momentum exchange between the freestream flow and the cavity when spoilers were used. This is proposed to be the main reason for the reduced tonal amplitudes.
Open Access
Computational aeroacoustic study of a landing gear
(2009-11-10T00:00:00Z) Khanal, Bidur; Knowles, Kevin; Saddington, Alistair J.; Obayashi, S.
Computational study of a single wheel landing gear con guration was completed to understand the noise source and it's nature. The ow eld visualisation showed the present of large structural shedding in the wake side of the the landing gear wheel. These large structures were responsible for the low frequency noise. Spectral peaks at frequencies lower than 200 Hz were found to exist from the analysis of the frequency content of the pressure signals at far eld. These low frequency peaks were due to the large structural shedding.
Open Access
Computational investigation of cavity flow control using a passive device
(Royal Aeronautical Society, 2012-12-31T00:00:00Z) Khanal, Bidur; Knowles, Kevin; Saddington, Alistair J.
In this paper, the results of computational studies on the unsteady flow features in threedimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer and as a Large-Eddy Simulation LES Sub-Grid Scale model in the rest of the flow (commonly known as Detached-Eddy Simulation [DES]) are used in this study. The time-mean flow study showed the presence of three-dimensional effects inside the cavities. The mean flowfield visualisation also clearly showed the presence of a pair of 'tornado-like' vortices in the upstream half of the cavity which merge to a single, large recirculation further downstream. Visualisation for the cavity-with-store case revealed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. In the unsteady flow study, near-field acoustic spectra were computed for the empty cavity and cavity-with-store cases. Study of unsteady pressure spectra for the cavitywith- store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling, between the Rossiter modes. This may be the reason for the co-existence of multiple modes without the coupling among them.
Open Access
Computational study of cavity flowfield at transonic speeds
(2009-12-31T00:00:00Z) Khanal, Bidur; Knowles, Kevin; Saddington, Alistair J.
In this paper, the results of a computational study on the unsteady flow features in three-dimensional empty cavities and a cavity with a store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard RANS model within the attached boundary layer and as a LES Sub-Grid Scale model in the rest of the flow, including the separated regions, are used in this study. The time-mean flow study showed the existence of spanwise flow in the 3D cavity. In the unsteady flow study, computed near- field acoustic spectra were for empty cavity as well as cavity-withstore cases. Unsteady results from an empty cavity case are compared with experimental data and the frequency of the dominant mode is in good agreement with the experiment. Study of unsteady pressure spectra for the cavity-with-store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The mean flowfield visualisation for the cavity-with-store case clearly showed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. This blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling between, the Rossiter modes. This may be the reason for the coexistence of multiple modes without the coupling among them.
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, Alistair J.; Newby, B.; Taylor, N. J.
We 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.
Open Access
Determining the extent to which simulation can be used to train RAF pilots to fly and fight the Eurofighter Typhoon
(2017-06-19) Allsop, A J; Knowles, Kevin; Saddington, Alistair J.
This research examines the extent to which simulation can be used to train pilots of the Royal Air Force to fly and fight the Eurofighter Typhoon, and is the culmination of a series of trials over a period of 4 years. The approach was threefold, firstly examining the performance of students trained entirely on the Operational Conversion Unit’s full syllabus in the simulator and then tested against their peers on each of the four phases in live flight, secondly investigating the cultural acceptance levels of the present Typhoon pilots and lastly using lessons learnt to generate and test a syllabus to train Typhoon pilots to Mult Role Combat Ready in 40% of the present time. It was found that increasing the proportion of synthetics from the lowest Live Synthetic Balance (LSB) of 75:25 used on the front-line meets a cultural and resource barrier at 50:50. This did not represent the maximum LSB achievable however with the heavily synthetic Multi-Role Syllabus reaching an LSB of 21:79 with successful completion of the end of course test. Cultural acceptance of the simulator had correlations with the squadron a pilot was assigned to, the manner in which the simulators were programmed for use and the experience level of the pilot. No evidence was found within the sample to suggest age had an effect. Recommendations on minimum proportions of live and synthetic training was mapped for each of the required tasks and comparisons of these were made across complexity levels. Resource savings found by the generating and testing a Multi Role Combat Ready syllabus that recognised and incorporated all the strengths, weaknesses and lessons identified in the previous trials generated a saving of approximately 9 months and 100 Typhoon live flying hours per student, equivalent to approximately 1300 man maintenance hours that could be reinvested into personnel in the form of leave, adventurous training or development.
Open Access
The effect of angle of attack on the aeroacoustic environment within the weapons bay of a generic UCAV
(Elsevier, 2019-07-24) Bacci, David; Saddington, Alistair J.; Bray, Derek
Cavity flow studies are generally concerned with observing the effect of geometry changes whilst maintaining a fixed zero angle of attack. Cavities employed as weapons bays will, however, experience a range of angles of attack. This paper presents the first known results showing the effect of flight angle of attack on the aeroacoustic characteristics of an internal weapons bay installed in an uninhabited combat air vehicle (UCAV). The UCAV geometry consisted of a Boeing M219-type cavity in a Boeing UCAV1303 airframe. Numerical simulation was conducted using a full-scale detached eddy simulation model and representative transonic flight conditions. As well as the reference case of zero degrees, data for angles of attack of 3.0, 4.5 and 6.0 degrees were analysed. Experimental data was used to validate the reference computational model, which agreed with the overall fluctuating sound pressure level (OAFPL) to within the experimental uncertainty of 4 dB. Data from the computational model was post-processed with frequency-domain and time-frequency-domain techniques showing that the flow structure within the weapons bay was altered significantly by the angle of attack changes, affecting the mean pressure distribution, frequency spectra and resonant modes. Overall, increasing the angle of attack from 0.0 to 3.0 degrees produced an increment in the acoustic load whilst a further increase tended to affect the resonance mechanism and thereby reduce the coherence and the temporal footprints of the resonant modes.
Open Access
The effects of scaling and high subsonic cavity flow and control
(2014-08-15) Thangamani, Varun; Saddington, Alistair J.; Knowles, Kevin
The effects of scaling a cavity with respect to a fixed incoming boundary layer thickness on its flow dynamics and control was studied experimentally. Three cavity models with constant length-to-depth ratio of 5 and length-to-width ratio of 2 and with corresponding linear dimensions in the ratio 0.5 : 1 : 2 were tested at freestream Mach number 0.71. Additionally, the 0.5 and 1 scale models were tested at freestream Mach number of 0.85. The experiments involved timeaveraged pressure measurements, unsteady pressure measurements, and PIV measurements. Time-averaged pressure measurements made at the floor were used to study the ’flow-type’ of the cavities. Unsteady pressure measurements were used to study the acoustic characteristics of the cavity. The cavity length-to-boundary layer thickness ratios tested were 10, 20 and 40. The Cp distribution on the clean cavities indicated a change in the cavity flowtype with change in the cavity scale. Varying the L/δ from 10 to 40 changed the cavity flow-type from open to transitional. Analysis of the frequency spectra of the cavity revealed an increase in tonal amplitudes and OASPL with increasing L/δ . The PIV measurements indicated that this could be caused by an increase in energy exchange between the freestream and the cavity. The velocity magnitudes inside the cavities were found to increase with increase in L/δ . A comparative study of different passive control methods on the largest cavity showed that leading-edge spoilers were superior in cavity tone suppression. Of these, the effectiveness of a sawtooth spoiler on the three cavities of different scales was tested. The results showed that while the spoiler was effective in eliminating tones and suppression of noise for the smaller cavities, it was unable to eliminate the tones completely for the largest cavity. To find the correct method for scaling the spoilers with the cavity dimensions, different spoiler heights were tested on the three cavities. The results showed that the cavity noise suppression for a given cavity attains saturation level at a particular spoiler height, called the critical spoiler height. An increase in spoiler height beyond the critical spoiler height was found to have no effect on the noise suppression. It is also found that this critical spoiler height can be scaled with the length of the cavity (for given L/D, M and spoiler profile) irrespective of the boundary layer thickness.
Open Access
Effects of scaling on high subsonic cavity flow oscillations and control
(AIAA, 2014-02-28) Thangamani, Varun; Knowles, Kevin; Saddington, Alistair J.
The effects of scaling on cavity oscillations and control have been studied by measuring the unsteady pressure on the floor of three cavities of different scales. The cavities have a length-to-depth ratio of 5 and a length-to-width ratio of 2, and the corresponding linear dimensions are in the ratio0.5∶1∶2. The experiments were conducted with clean cavities and cavities fitted with leading-edge sawtooth spoilers so as to study the influence of scaling on clean cavities as well as the effectiveness of the passive control method on different sized cavities. The results showed significant variation of certain spectral characteristics of the clean cavities. The control effectiveness of the spoilers also showed variations with a change in scale of the model. It is recommended that, before implementing a passive control device for practical applications, the device should be tested in the possible range of cavity length-to-boundary-layer-thickness ratio (L/δ) that can be experienced in actual flight.
Open Access
An efficiently parallelized high-order aeroacoustics solver using a characteristic-based multi-block interface treatment and optimized compact finite differencing
(MDPI, 2017-05-28) Khanal, Bidur; Saddington, Alistair J.; Knowles, Kevin
This paper presents the development of a fourth-order finite difference computational aeroacoustics solver. The solver works with a structured multi-block grid domain strategy, and it has been parallelized efficiently by using an interface treatment based on the method of characteristics. More importantly, it extends the characteristic boundary condition developments of previous researchers by introducing a characteristic-based treatment at the multi-block interfaces. In addition, most characteristic methods do not satisfy Pfaff’s condition, which is a requirement for any mathematical relation to be valid. A mathematically-consistent and valid method is used in this work to derive the characteristic interface conditions. Furthermore, a robust and efficient approach for the matching of turbulence quantities at the multi-block interfaces is developed. Finally, the implementation of grid metric relations to minimise grid-induced errors has been adopted. The code was validated against a number of benchmark cases, which demonstrated its accuracy and robustness across a range of problem types
Open Access
Engineering maintenance decision-making with unsupported judgement under operational constraints
(Elsevier, 2022-05-10) Green, Richard N.; McNaught, Ken R.; Saddington, Alistair J.
In operational engineering maintenance situations, limitations on time, resource or the information available often inhibit rigorous analysis on complex decision problems. Decision-makers who are compelled to act in such circumstances, may be informed by some level of analysis if available, or else may have to rely on their unsupported judgement. This paper presents three engineering risk decision-making case studies across a 20 year span from the rail, aerospace, and military aviation contexts, highlighting the fallibilities of using unsupported judgements in an unstructured manner. To help situate this type of decision situation, we provide a descriptive model of the decision space which extends an existing description from the discipline of decision analysis. Furthermore, to help make and describe the distinction between unsupported and supported thinking, we provide another descriptive model, this time drawing parallels with the distinction made between Type 1 and Type 2 reasoning. This model is an extension of the default-interventionist model from cognitive psychology. The paper concludes that there is a pressing need to provide some form of support to engineering decision-makers facing operational decisions under severe time pressure. While the ultimate aim must be to improve the quality of decision-making, improved transparency is an important additional benefit. Increased emphasis on decision justification and self-awareness are suggested as potential ways of improving this situation. A further contribution of this paper is to identify and strengthen linkages between safety science and two other relevant disciplines, decision analysis and psychology. Such linkages make it easier to communicate across traditional disciplinary boundaries and may provide opportunities for interdisciplinary learning or suggest future directions for collaborative research.
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.
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.