Cranfield Defence and Security
Permanent URI for this community
Browse
Browsing Cranfield Defence and Security by Publisher "AIAA"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item 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, MarkA 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.Item Open Access Comparison of passive flow control methods for a cavity in transonic flow(AIAA, 2016-03-21) Saddington, Alistair J.; Thangamani, Varun; Knowles, KevinAcomparative 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.Item 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.Item 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.Item Open Access Forcing boundary-layer transition on an inverted airfoil in ground effect(AIAA, 2017-07-21) Roberts, L. S.; Finnis, Mark V.; Knowles, Kevin; Lawson, Nicholas J.The influence of the laminar boundary-layer state on a wing operating in ground effect has been investigated using experiments with a model that provides two-dimensional flow. The effect of a boundary-layer trip placed at varying distances from the leading edge was observed at various incidences in terms of on-surface characteristics, including pressure measurements, flow visualization, and hot-film anemometry, and off-surface characteristics with velocity surveys below and behind the wing. The act of forcing transition led to downforce being reduced and drag increased, moreover, it altered almost all aspects of the wing’s aerodynamic characteristics, with the effect becoming greater as the trip was placed closer to the leading edge. These aspects include the replacement of a laminar separation bubble with trailing-edge separation, a thicker boundary layer, and a thicker wake with greater velocity deficit. The importance of considering laminar phenomena for wings operating in ground effect has been shown.Item Open Access Forcing boundary-layer transition on an inverted airfoil in ground effect and at varying incidence(AIAA, 2016-06-17) Roberts, L.; Finnis, Mark V.; Knowles, Kevin; Lawson, Nicholas J.The influence of the laminar boundary-layer state on a wing operating in ground effect at Re = 6 × 10 has been investigated using experiments with a model that provides two-dimensional flow and computations with a panel-method code. The effect of a boundary-layer trip placed at varying distances from the leading edge was observed at various incidences in terms of on-surface characteristics, including pressure measurements, flow visualisation and hot-film anemometry, and off-surface characteristics with LDA surveys below and behind the wing. The act of forcing transition led to downforce being reduced and drag increased, moreover, it altered almost all aspects of the wing’s aerodynamic characteristics, with the effect becoming greater as the trip was placed closer to the leading edge. These aspects include the replacement of a laminar separation bubble with trailing-edge separation, a thicker boundary layer, and a thicker wake with greater velocity deficit. The importance of considering laminar phenomena for wings operating in ground effect has been shownItem Open Access Further development of feedback control of cavity flow using experimental based reduced order model(AIAA, 2006-01-31) Caraballo, Edgar; Yuan, Xin; Little, Jesse; Debaisi, M.; Serrani, Andrea; Myatt, James; Samimy, MoIn our recent work we presented preliminary results for subsonic cavity flow control using a reduced-order model based feedback control derived from experimental measurements. The model was developed using the Proper Orthogonal Decomposition of PIV images in conjunction with the Galerkin projection of the Navier-Stokes equations onto the resulting spatial eigenfunctions. A linear-quadratic optimal controller was designed to reduce cavity flow resonance by controlling the time coefficient and tested in the experiments. The stochastic estimation method was used for real-time estimation of the corresponding time coefficients from 4 dynamic surface pressure measurements. The results obtained showed that the controller was capable of reducing the cavity flow resonance at the design Mach 0.3 flow, as well as at other flows with slightly different Mach number. In the present work we present several improvements made to the method. The reduced order model was derived from a larger set of PIV measurements and we used 6 sensors for the stochastic estimation of the instantaneous time coefficients. The reduced order model so obtained shows a better convergence of the time coefficients. This combined with the 6-sensor estimation improves the control performance while using a scaling factor closer to the theoretically expected value. The controller also performed better in off design flow conditions.Item 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.Item Open Access Influence of door gap on aeroacoustics and structural response of a cavity(AIAA, 2023-11-20) Bacci, David; Saddington, Alistair J.Numerical aeroacoustic analysis using the Shear Stress Transport–Scale Adaptive Simulation turbulence model was conducted on a weapon bay model based on the M219 geometry with doors incorporating radar cross-section reduction features. The effect of the introduction of a gap between the doors and the cavity edge on the aeroacoustic and structural response of the cavity was analyzed at Mach 0.85. The effect of introducing 3 deg of sideslip was also investigated. Both mean and unsteady flow analyses were conducted. The results showed a strong palliative effect of the door gap with and without sideslips. The overall analysis of the spectral signature on the forces and moments acting on the doors indicated the possibility of fluid–acoustic coupling, as all acoustic spectra showed a predominant tone located at the same frequency of the first structural mode.Item Open Access Influence of stochastic estimation on the control of subsonic cavity flow – A preliminary study(AIAA, 2006-06-30) Debiasi, Marco; Little, J.; Serrani, A.; Yuan, X.; Myatt, James; Samimy, MoThis work aims at understanding how the different elements involved in the feedback loop influence the overall control performance of a subsonic cavity flow based on reducedorder modeling. To this aim we compare preliminary and limited sets of experimental results obtained by modifying some relevant characteristics of the loop. Our results support the findings in the literature that use of quadratic stochastic estimation is preferable to the linear one for real-time update of the model parameters. They also seem to indicate the merit of using more than one time sample of the pressure for performing the real-time update of the model through stochastic estimation. The effect of using two different sets of pressure signals for the stochastic estimation also corroborates previous findings indicating the need for optimizing the number and the placement of the sensors used in the feedback control loop. Finally we observed that the characteristics of the actuator can alter significantly the overall control effect by introducing in the feedback loop additional, undesirable frequency components that are not modeled and hence controlled. A compensator for the actuator is currently being designed that will alleviate this problem thus enabling a clearer understanding of the overall control technique.Item Open Access Low-noise flapping wings with tensed membrane(AIAA, 2020-04-15) Debiasi, Marco; Lu, Zhenbo; Nguyen, Quoc Viet; Chan, Woei LeongMicro air vehicles with flapping wings have the potential to be both more efficient and maneuverable than similar-sized fixed- or rotary-wing aircraft. Reducing the perceived noise produced by flapping wings without compromising or possibly enhancing their aerodynamic performance would be crucial in surveillance and military applications. To this aim, flapping wings have been designed and fabricated for which the supporting stiffeners tense the Mylar membrane to which they are bonded. The sound produced by these wings at different flapping frequencies has been recorded in an anechoic chamber simultaneously to the upward thrust they create. Comparing their characteristics and performance with those of flapping wings of conventional design suggests that tensing the wing’s membrane can increase the thrust while decreasing the typical rustling noise of the flapping wingsItem Open Access Multi-view monocular pose estimation for spacecraft relative navigation(AIAA, 2018-01-07) Rondao, Duarte; Aouf, NabilThis paper presents a method of estimating the pose of a non-cooperative target for spacecraft rendezvous applications employing exclusively a monocular camera and a threedimensional model of the target. This model is used to build an offline database of prerendered keyframes with known poses. An online stage solves the model-to-image registration problem by matching two-dimensional point and edge features from the camera to the database. We apply our method to retrieve the motion of the now inoperational satellite ENVISAT. The combination of both feature types is shown to produce a robust pose solution even for large displacements respective to the keyframes which does not rely on real-time rendering, making it attractive for autonomous systems applications.Item Open Access Robust on-manifold optimization for uncooperative space relative navigation with a single camera(AIAA, 2021-03-31) Rondao, Duarte; Aouf, Nabil; Richardson, Mark A.; Dubanchet, VincentOptical cameras are gaining popularity as the suitable sensor for relative navigation in space due to their attractive sizing, power, and cost properties when compared with conventional flight hardware or costly laser-based systems. However, a camera cannot infer depth information on its own, which is often solved by introducing complementary sensors or a second camera. In this paper, an innovative model-based approach is demonstrated to estimate the six-dimensional pose of a target relative to the chaser spacecraft using solely a monocular setup. The observed facet of the target is tackled as a classification problem, where the three-dimensional shape is learned offline using Gaussian mixture modeling. The estimate is refined by minimizing two different robust loss functions based on local feature correspondences. The resulting pseudomeasurements are processed and fused with an extended Kalman filter. The entire optimization framework is designed to operate directly on the SE(3) manifold, uncoupling the process and measurement models from the global attitude state representation. It is validated on realistic synthetic and laboratory datasets of a rendezvous trajectory with the complex spacecraft Envisat, demonstrating estimation of the relative pose with high accuracy over full tumbling motion. Further evaluation is performed on the open-source SPEED dataset.Item Open Access Undercarriage drag prediction for a fixed undercarriage light aircraft(AIAA, 2017-06-09) Bennett, Christopher J.; Gautrey, Jim; Lawson, Nicholas J.The following paper presents undercarriage drag predictions for a light aircraft with fixed landing gear. A Scottish Aviation Bulldog 120, operated by the National Flying Laboratory Centre (NFLC) at Cranfield University, is considered as the test case for this study. Taking advantage of a recently developed laser scanned model, computational fluid dynamics (CFD) techniques are exploited to investigate the undercarriage drag. Results via standard theoretical and empirical methods are compared to the CFD results. It is found that the established empirical methods matched the CFD predictions to within the stated error bands for moderate angles of attack. However, due to the aircraft flow field at higher angles of attack, some discrepancies in the level of drag predicted are observed. Further flight test data is recommended to confirm these findings