Browsing by Author "Lawson, Nicholas J."
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Item Open Access Aerodynamic and performance characteristics of a passive leading edge Kruger flap at low Reynolds numbers(Royal Aeronautical Society, 2012-07-31T00:00:00Z) Moraris, Vassilis Michael; Lawson, Nicholas J.; Garry, Kevin P.An experimental and numerical study was performed on a Clark Y aerofoil with a 10% chord leading edge Kruger flap to examine its aerodynamic performance at Reynolds numbers of 0.6 × 106, 1 × 106, and 1.6 × 106, to help to identify the forces and moments acting on a basic configuration. A detailed comparison of the numerical and experimental data is presented in this paper. The leading edge flap was effective at high angles of attack with an increase in CL of up to 18% over a conventional no flap configuration and delayed separation by up to 3°. The moments around the Kruger flap rotation point were calculated from the numerical analysis as an initial stage in the design of a UAV passive flap system and they are also presented in the paItem Open Access The aircraft spin - a mathematical approach and comparison to flight test(American Institute of Aeronautics and Astronautics, 2017-06-09) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, Jim; Cooke, AlastairA Scottish Aviation Bulldog light aircraft operated by the National Flying Laboratory Centre (NFLC) at Cran eld University, modi ed with research equipment including bre optic sensors for wing strain and fuselage pressure measurements, is used to investigate the dynamics of a fully developed spin. A theoretical model is developed to compare with existing ight test data. In particular, the frequency of the aircraft spin is analysed as a function of the mass distribution of the aircraft to determine the e ect of the fuel load. It is found that the spin frequency is minimally a ected by the fuel load since the moments of inertia corresponding to the engine, for example, are far more signi cant. However, it is con rmed that the yawing e ect of the propeller causes the aircraft to spin faster to the right than to the left.Item Open Access Application of digital particle image velocimetry to insect aerodynamics: measurement of the leading-edge vortex and near wake of a Hawkmoth(Springer Verlag, 2007-02-13T16:45:48Z) Bomphrey, Richard J.; Lawson, Nicholas J.; Taylor, Graham K.; Thomas, Adrian L. R.Some insects use leading-edge vortices to generate high lift forces, as has been inferred from qualitative smoke visualisations of the flow around their wings. Here we present the first Digital Particle Image Velocimetry (DPIV) data and quantitative analysis of an insect’s leading-edge vortex and near wake at two flight speeds. This allows us to describe objectively 2D slices through the flow field of a tethered Tobacco Hawkmoth (Manduca sexta). The near-field vortex wake appears to braodly resemble elliptical vortex loops. The presence of a leading-edge vortex towards the end of the downstroke is found to coincide with peak upward force production measured by a six-component force–moment balance. The topology of Manduca’s leading-edge vortex differs from that previously described because late in the downstroke, the structure extends continuously from wingtip across the thorax to the other wingtip.Item Open Access CFD simulation of flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 - Part 1(Elsevier, 2017-03-16) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, James E.; Cooke, Alastair K.CFD modelling techniques are exploited to investigate the local velocity field around angle of attack and sideslip angle sensors fitted to the nose of a modified BAe Jetstream 3102 small airliner. Analysis of the flow angularity at the vane locations has allowed the vanes response to varying flight conditions to be predicted and errors in the readings to be quantified. Subsequently, a more accurate calibration of the system is applied to the current configuration on the Jetstream, and a better understanding of the position error with respect to the vane locations is obtained. The above aircraft was acquired by Cranfield University in 2003 with subsequent flow angle vane modifications taking place in 2005. The aircraft is currently in operation with the National Flying Laboratory Centre (NFLC) for research and demonstration purposes.Item Open Access CFD simulation of flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 - Part 2(Elsevier, 2017-03-16) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, James E.; Cooke, Alastair K.A previous study analysing the local flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 turboprop is extended to study the additional effects of bank angle. A full matrix of CFD simulations is carried out to investigate how the introduction of a bank angle affects vane performance for a range of flight conditions. An updated calibration method to convert the raw vane readings into true values of angle of attack and sideslip, incorporating a correction factor as a function of the bank angle, is presented. The results are shown to be accurate for a wide range of flight configurations. Uncertainty analysis indicates that raw vanes reading errors should be below ±0.1°±0.1° to ensure that total calibration errors are restricted to less than 2%2% for angle of attack and 5%5% for sideslip angle.Item Open Access Characterizing instrumentation canister aerodynamics on the FAAM BAe-146-301 atmospheric research aircraft(ASCE, 2019-04-30) Bennett, Christopher J.; Wellpott, A.; Lawson, Nicholas J.; Delise, M.; Woodcock, B.; Gratton, Guy; Nott, G. J.A computational fluid dynamics (CFD) investigation was aimed at accurately predicting the air flow characteristics in the vicinity of underwing-mounted instruments on the Facility for Airborne Atmospheric Measurement’s (FAAM) BAe-146-301. Perturbation of the free stream airflow as it passes through the region of detection of the underwing instruments may lead to additional uncertainties in the measurement of clouds and cloud particles. The CFD model was validated with flight data from an Aircraft-Integrated Meteorological Measurement System (AIMMS-20) in a wing-mounted instrument canister. Flow predictions showed a consistent slowing from the true air speed of the aircraft in the longitudinal direction and the introduction of horizontal and vertical flows up to 10% of the air speed. The potential impact of these flow perturbations on sizing of particles with cloud imaging probes was modeled. Sizing errors were dependent on the methodology used and the shape of the particle; those due to transverse flows remained very small but mis-sizing due to unaccounted longitudinal flow perturbations were potentially more serious.Item Open Access Combined Stereoscopic Particle Image Velocimetry and Line Integral Convolution Methods: Application to a Sphere Sedimenting Near a Wall in a Non-Newtonian Fluid.(The Visualization Society of Japan, 2005) Lawson, Nicholas J.; Finnis, Mark V.; Tatum, J. A.; Harrison, G. M.The flow fields for a sphere sedimenting through a Newtonian and two non-Newtonian liquids near a wall in a square tank are investigated using 3-D stereoscopic particle image velocimetry (PIV) and line integral convolution (LIC) methods. The PIV data were taken using an angular stereoscopic configuration with tilt and shift arrangements for the Scheimpflug condition and a pair of liquid correction prisms. Data were recorded from planes perpendicular and parallel to the wall for each fluid case over a range of distances from the wall. The PIV and LIC results highlight significant differences in the wake structure for all three cases. Out of plane flow was also found to persist up to two sphere diameters downstream in the wake for all cases.Item Open Access Coupled piezoelectric fans with two degree of freedom motion for the application of flapping wing micro aerial vehicles(Elsevier Science B.V., Amsterdam., 2008-10-03T00:00:00Z) Chung, H. C.; Lal Kummari, K.; Croucher, S. J.; Lawson, Nicholas J.; Guo, Shijun J.; Huang, ZhaorongPiezoelectric fans consisting of a piezoelectric layer and an elastic metal layer were prepared by epoxy bonding and a coupled flexible wing was formed by a pair of carbon fibre reinforced plastic wing spars and polymer skin attached to two piezoelectric fans. Two sinusoidal voltages with phase differences were then used to drive the coupled piezoelectric fans. High speed digital cameras were used to characterize the two degree of freedom (DOF) motion of the wing and these results were compared to finite element model of the wing and the coupled piezoelectric fans. It has been observed that the phase delay between the driving voltages applied to the coupled piezoelectric fans plays an important role in the control of the flapping and twisting motions of the wing and this set-up has the potential for application to the control of flapping wings for micro aerial vehicles. (c) 2008 Elsevier B.V. All rights reserved.Item Open Access Development and application of optical fibre strain and pressure sensors for in-flight measurements(IOP Publishing, 2016-09-16) Lawson, Nicholas J.; Correia, Ricardo N.; James, Stephen W.; Partridge, Matthew; Staines, Stephen E.; Gautrey, James E.; Garry, Kevin; Holt, Jennifer C.; Tatam, Ralph P.Fibre optic based sensors are becoming increasingly viable as replacements for traditional flight test sensors. Here we present laboratory, wind tunnel and flight test results of fibre Bragg gratings (FBG) used to measure surface strain and an extrinsic fibre Fabry–Perot interferometric (EFFPI) sensor used to measure unsteady pressure. The calibrated full scale resolution and bandwidth of the FBG and EFFPI sensors were shown to be 0.29% at 2.5 kHz up to 600 με and 0.15% at up to 10 kHz respectively up to 400 Pa. The wind tunnel tests, completed on a 30% scale model, allowed the EFFPI sensor to be developed before incorporation with the FBG system into a Bulldog aerobatic light aircraft. The aircraft was modified and certified based on Certification Standards 23 (CS-23) and flight tested with steady and dynamic manoeuvres. Aerobatic dynamic manoeuvres were performed in flight including a spin over a g-range −1g to +4g and demonstrated both the FBG and the EFFPI instruments to have sufficient resolution to analyse the wing strain and fuselage unsteady pressure characteristics. The steady manoeuvres from the EFFPI sensor matched the wind tunnel data to within experimental error while comparisons of the flight test and wind tunnel EFFPI results with a Kulite pressure sensor showed significant discrepancies between the two sets of data, greater than experimental error. This issue is discussed further in the paper.Item Open Access Development of the Cranfield University Bulldog Flight Test Facility(Cambridge University Press, 2017) Lawson, Nicholas J.; Correia, Richardo N.; James, Stephen W.; Gautrey, James E.; Staines, Stephen E.; Partridge, Matthew; Tatam, Ralph P.Cranfield University’s National Flying Laboratory Centre (NFLC) has developed a Bulldog light aircraft into a flight test facility. The facility is being used to research advanced in-flight instrumentation including fibre optic pressure and strain sensors. During the development of the test bed, computational fluid dynamics (CFD) has been used to assist the flight test design process, including the sensor requirements. This paper describes the development of the Bulldog flight test facility, including an overview of the design and certification process, the in-flight data taken using the installed fibre optic sensor systems and lessons learned from the development programme, including potential further applications of the sensors.Item Open Access Digital particle image velocimetry measurements of the downwash distribution of a desert locust Schistocerca gregaria(The Royal Society, 2006-04-22) Bomphrey, Richard J.; Taylor, Graham K.; Lawson, Nicholas J.; Thomas, Adrian L. R.Actuator disc models of insect flight are concerned solely with the rate of momentum transfer to the air that passes through the disc. These simple models assume that an even pressure is applied across the disc, resulting in a uniform downwash distribution. However, a correction factor, k, is often included to correct for the difference in efficiency between the assumed even downwash distribution, and the real downwash distribution. In the absence of any empirical measurements of the downwash distribution behind a real insect, the values of k used in the literature have been necessarily speculative. Direct measurement of this efficiency factor is now possible, and could be used to compare the relative efficiencies of insect flight across the Class. Here, we use Digital Particle Image Velocimetry to measure the instantaneous downwash distribution, mid-downstroke, of a tethered desert locust (Schistocerca gregaria). By integrating the downwash distribution, we are thereby able to provide the first direct empirical measurement of k for an insect. The measured value of k=1.12 corresponds reasonably well with that predicted by previous theoretical studies.Item Open Access Experimental and computational investigation of an 'open' transonic cavity flow(Professional Engineering Publishing, 2009-06-30T00:00:00Z) Atvars, K.; Knowles, Kevin; Ritchie, S. A.; Lawson, Nicholas J.This paper presents an investigation of a transonic flow (M∞=0.85) over a rectangular cavity having a length-to-depth ratio of 5. Velocities were measured inside the cavity on the central plane and two off-centre planes using a two-component particle image velocimetry system. These measurements were supported by surface flow visualization, and mean and time-varying surface pressure measurements. The flow was also simulated using an unsteady Reynolds-averaged Navier-Stokes code, with a realizable k - ε turbulence model. It is shown that this CFD model does not capture all the characteristics of the flowfield correctly. However, by using this integrated experimental and computational approach we have been able to identify three-dimensional flowfield structures within the cavity. The influence of the thickness of the approaching boundary layer is discussed.Item Open Access Experimental and Computational Investigation of an “Open” Transonic Cavity Flow(2009-11-10T18:31:10Z) Atvars, K.; Knowles, Kevin; Ritchie, S. A.; Lawson, Nicholas J.This paper presents an investigation of a transonic flow (M∞ = 0.85) over a rectangular cavity having a length-to-depth ratio of 5. Velocities were measured inside the cavity on the central plane and two off-centre planes using a two-component particle image velocimetry system. These measurements were supported by surface flow visualisation, and mean and time-varying surface pressure measurements. The flow was also simulated using an unsteady Reynolds-averaged Navier Stokes code, with a realizable κ− ε turbulence model. It is shown that this CFD model does not capture all the characteristics of the flow field correctly. However, by using this integrated experimental and computational approach we have been able to identify three-dimensional flow field structures within the cavity. The influence of the thickness of the approaching boundary layer is discussed.Item Open Access Experimental and numerical investigation of leading edge Krueger flaps at low Reynolds numbers(Cranfield University, 2012) Moraris, Vassilis Michael; Lawson, Nicholas J.Recent publications examining the flight of Eagles have shown that leading edge feather deflections occur on the lower surface of the wings in free flight to create a leading edge flap analogous to a Krueger flap system. Such passive high lift devices may be adaptable to the lifting surfaces of unmanned air vehicles (UAVs). This work is aimed to an application of a passive leading edge Krueger device which will deploy during the landing and takeoff stages of a UAV flight. Cont/d.Item Open Access Fibre-optic measurement of strain and shape on a helicopter rotor blade during a ground run: 2. Measurement of shape(IOP Publishing, 2022-06-08) Kissinger, Thomas; James, Stephen W.; Weber, Simone; Mullaney, Kevin; Chehura, Edmond; Pekmezci, Huseyin H.; Barrington, James; Staines, Stephen E.; Charrett, Thomas O. H.; Lawson, Nicholas J.; Lone, Mudassir; Atack, Richard; Tatam, Ralph P.Optical fibre strain and shape measurement sensors were deployed on a rotor blade during a full-speed helicopter ground run, with real-time data wirelessly streamed from rotor hub-mounted sensor interrogators. In part 2 of a 2-part paper series, two-dimensional direct fibre-optic shape sensing (DFOSS), using fibre segment interferometry-based interrogation is investigated. The concept of blade shape change visualisation over one rotation period using rotation displacement surfaces is introduced and the usefulness of DFOSS data to gain additional insights by determining operational modal frequencies independently for both horizontal and vertical vibration directions of the blade is demonstrated.Item Open Access Flow visualization and particle dispersion measurements inside an ambulance rear saloon while stationary and in motion(SAE International, 2022-04-07) Lawson, Nicholas J.; Blackburn, Kim; Sherwood, Glenn; Brighton, James; Atkinson, Helen V.The following paper presents flow field and particle dispersion data from a UK National Health Service (NHS) ambulance, under static and dynamic driving conditions and when using different ventilation modes. Data was recorded using laser sheet flow visualisation, particle image velocimetry and hot wire anemometry, from a common plane positioned about the patient centreline. Results indicated a significant influence of the ceiling fan ventilation system on gross flow field behaviour, with the ventilation fan on extract or intake mode. With either ventilation mode, flow velocities in the patient region were found to double from a quiescent condition, to around 50mm/s – 100mm/s. Particle dispersion data also showed dispersion decay rates over five times faster when using the ceiling fan extraction system. All these results were consistent when the vehicle was stationary or driving at a constant speed of 60mph. However, with the vehicle under dynamic driving conditions, such as acceleration or braking, the regular flow patterns were substantially disrupted, with bulk movement of the flow in the direction of the acceleration or braking action. Under these dynamic conditions, the magnitude of the net velocity change on the fluid exceeded any flow generated from the ceiling ventilation system.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(American Institute of Aeronautics and Astronautics Inc, 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 Hypersonic interference aerothermodynamics(2009-10) Estruch-Samper, David; Lawson, Nicholas J.; Garry, Kevin P.When a vehicle travels at hypersonic speeds during launch, cruise or atmospheric re-entry it is subject to extremely high surface flow temperatures. As well as on the vehicle forebody, extreme heating can take place close to surface protuberances which are almost impossible to avoid in a real flight vehicle. These disturbances interfere with the freestream flow and result in complex viscous interactions which induce a local heat flux augmentation that can become detrimental to the integrity of the vehicle. A greater understanding of these flow phenomena is required. This thesis develops the understanding of the behaviour of the flow around surface protuberances in hypersonic vehicles and presents an engineering approach to predict the location and magnitude of the highest heat transfer rates in their vicinity. To this end, an experimental investigation was performed in a gun tunnel at freestream Mach numbers of 8.2 and 12.3 and Reynolds numbers ranging from Reoo/m=3.35xl0 ⁶ to Reꚙ /m=9.35xl0 ⁶. The effects of protuberance geometry, boundary layer state, freestream Reynolds number and freestream Mach number were assessed. Further understanding of the flowfield was obtained through oil-dot visualisations and highspeed schlieren videos taken at frame rates of up to 50 kHz. Results show the local interference interaction is strongly three-dimensional and is dominated by the incipient separation angle induced by the protuberance. In subcritical interactions - in which the incoming boundary layer remains unseparated upstream of the protuberance - the highest heating occurs adjacent to the device. In supercritical interactions - in which the incoming boundary layer is fully separated ahead of the protuberance - the highest heating generally occurs on the surface just upstream of it. An exception is for low-deflection protuberances under low-Reynolds freestream flow conditions in which case the heat flux to the side is greater.Item Open Access Hypersonic interference heating in the vicinity of surface protuberances(Springer Science Business Media, 2010-09-30T00:00:00Z) Estruch-Samper, David; MacManus, David G.; Stollery, J. L.; Lawson, Nicholas J.; Garry, Kevin P.The understanding of the behaviour of the flow around surface protuberances in hypersonic vehicles is developed and an engineering approach to predict the location and magnitude of the highest heat transfer rates in their vicinity is presented. To this end, an experimental investigation was performed in a hypersonic facility at freestream Mach numbers of 8.2 and 12.3 and Reynolds numbers ranging from Re (a)/m = 3.35 x 10(6) to Re (a)/m = 9.35 x 10(6). The effects of protuberance geometry, boundary layer state, freestream Reynolds number and freestream Mach numbers were assessed based on thin-film heat transfer measurements. Further understanding of the flowfield was obtained through oil-dot visualizations and high-speed schlieren videos. The local interference interaction was shown to be strongly 3-D and to be dominated by the incipient separation angle induced by the protuberance. In interactions in which the incoming boundary layer remains unseparated upstream of the protuberance, the highest heating occurs adjacent to the device. In interactions in which the incoming boundary layer is fully separated ahead of the protuberance, the highest heating generally occurs on the surface just upstream of it except for low-deflection protuberances under low Reynolds freestream flow conditions in which case the heat flux to the side is greater.