bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow field and performance analysis of an integrated diverterless supersonic inlet
Authors: Masud J. 
Published: February 2016

AbstractIn this paper the computed flow and performance characteristics at low angle-of-attack (AOA) of an integrated diverterless supersonic inlet (DSI) are presented. The subsonic characteristics are evaluated at M∞ = 0·8 while the supersonic characteristics are evaluated at M∞= 1·7, which is near the design Mach number for the intake. In addition to the external flow features, the internal intake duct flow behaviour is also evaluated. The results of this study indicate effective boundary layer diversion due to the ‘bump’ compression surface in both subsonic and supersonic regimes. At M∞ = 1·7, the shockwave structure (oblique/normal shockwave) on the ‘bump’ compression surface and intake inlet is satisfactory at design (critical) mass flow rate. The intake duct flow behaviour at subsonic and supersonic conditions is generally consistent with ‘Y’ shaped intake duct of the present configuration. The secondary flow structure inside the duct has been effectively captured by present computations. The computed intake total pressure recovery at M∞ = 1·7 exhibits higher-than-conventional behaviour at low mass flow ratios, which is attributed to unique inlet design. Overall computed subsonic and supersonic total pressure recovery characteristics are satisfactory under the evaluated conditions and are also in agreement with wind tunnel test data.
Prediction of total pressure characteristics in the settling chamber of a supersonic blowdown wind tunnel
Authors: Suryanarayana G. K. , Bhoi S. R. 
Published: February 2016

AbstractOccurrence of transient starting and stopping loads during tests at high Mach numbers is one of the major problems in intermittent blowdown wind tunnels. It is believed that in order to overcome this problem, the wind tunnel could be started at a low Mach number and low stagnation pressure; the desired high Mach number condition could be reached by continuously changing the nozzle contour while synchronously increasing the stagnation pressure. After completing the tests, the nozzle could be brought back to the initial low Mach number accompanied by synchronous decrease in the stagnation pressure. In such a scenario, it is important to ensure that the pressure regulating valve (PRV) of the wind tunnel delivers and maintains a specified minimum stagnation pressure at any Mach number, so that supersonic breakdown of the test section flow does not occur. In this paper, the problem is formulated based on quasi-steady one-dimensional isentropic equations and numerically solved to predict the time histories of settling chamber pressure and storage tank pressure for a given trajectory of the opening of the PRV, as the Mach number is changed from Mach 1 to 4·0 continuously in four seconds and vice versa. The effects of rate of change of PRV open area and rate of change of Mach number on the stagnation pressure characteristics in the settling chamber and storage tank are predicted. The measured trajectories of the PRV in experiments in the NAL 0·6m transonic wind tunnel are used as input to the prediction program to validate the methodology. Predictions indicate that when the nozzle throat is changed from Mach 1 to 4 in four seconds, the settling chamber stagnation pressure rapidly builds up and approaches the pressure in the storage tank. Predictions show an alarming rise in free stream dynamic pressure during transition from Mach 1 to 4 and vice versa, which needs to be verified through measurements.
Parameter estimation using unsteady downwash model from real flight data of Hansa-3 aircraft
Authors: Kumar R. , Ghosh A. K. 
Published: February 2016

AbstractThe paper presents the estimation of longitudinal aerodynamic parameters from simulated as well as real flight data using an unsteady downwash model. The task of parameter estimation was accomplished using the Maximum Likelihood (ML) method in the frequency domain for the Hansa-3 aircraft. The presented work pertains to the aircraft having a semi-sweptback wing configuration, however, the work reported earlier considered a rectangular wing configuration. A simple vortex system was used to model downwash effects in the longitudinal equations of motion. First, it was established that the indicial lift function had a minor or negligible influence on aircraft motion and on the estimated aerodynamic parameters using simulated data for the configuration of Hansa-3 aircraft. Next, two parameter extraction algorithms were used for parameter estimation using simulated data (with unsteadiness only in downwash) and real flight data (Hansa-3 aircraft). The first algorithm included unsteadiness only in downwash while the second neglected all the unsteady effects. It was observed from the results obtained that if unsteady effects were omitted from the parameter estimation algorithm, the extracted parameters included the effects of unsteady aerodynamics. Therefore, application of the extraction algorithm in the two modes provides a convenient means of separating steady-state and acceleration derivatives.
Flexible flapping systems: computational investigations into fluid-structure interactions
Authors: Fitzgerald T. , Valdez M. , Vanella M. , Balaras E. , Balachandran B. 
Published: February 2016

AbstractIn the present work, the authors examine two computational approaches that can be used to study flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a vortex kinematics problem, whereas with the DNS model, one is able to form a more detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous effects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or used as a predictive tool. In most of the cases studied, the UVLM based approach produces a good approximation. Apart from aerodynamic load comparisons, features of the system dynamics generated by using the two computational approaches are also compared. The authors also discuss limitations of both approaches.
Design of morphing winglets with the inclusion of nonlinear aeroelastic effects
Authors: De Breuker R. , Abdalla M. , Gürdal Z. 
Published: February 2016

AbstractA nonlinear aeroelastic model capable of assessing arbitrary morphing manoeuvres and calculating the associated morphing energy requirement is presented in this paper. The aeroelastic model consists of a close coupling between a corotational beam element, accounting for geometric nonlinearities, and a Weissinger method aerodynamic model, containing the Prandtl-Glauert correction for high-subsonic Mach numbers. The morphing deformations are discretised into three distinct morphing modes; fold morphing, twist morphing, and shear morphing, because of which virtually any morphed shape can be achieved, given a proper distribution of the three modes over the wing. The proposed aeroelastic morphing framework is used to design morphing winglets, and it has been shown that morphing winglets can improve the performance of fixed winglets significantly for regional airliners.
Gradient-based multifidelity optimisation for aircraft design using Bayesian model calibration
Authors: March A. , Willcox K. , Wang Q. 
Published: February 2016

AbstractOptimisation of complex systems frequently requires evaluating a computationally expensive high-fidelity function to estimate a system metric of interest. Although design sensitivities may be available through either direct or adjoint methods, the use of formal optimisation methods may remain too costly. Incorporating low-fidelity performance estimates can substantially reduce the cost of the high-fidelity optimisation. In this paper we present a provably convergent multifidelity optimisation method that uses Cokriging Bayesian model calibration and first-order consistent trust regions. The technique is compared with a single-fidelity sequential quadratic programming method and a conventional first-order trust-region method on both a two-dimensional structural optimisation and an aerofoil design problem. In both problems adjoint formulations are used to provide inexpensive sensitivity information.
Evolving fuselage designs by incorporating SHM technologies
Authors: Mistry S. , Mofakhami M. R. , Pinsonnault J. 
Published: February 2016

AbstractResearch efforts at Bombardier Aerospace have investigated design constraints that need to be addressed when considering the design of a future unconventional fuselage concept. Using a composite design platform integrated with structural health monitoring (SHM) technologies, the design space is broadened and there are many more unknowns to investigate from our current knowledge of the subject to date. The principal idea is to identify structural zones and quantify stress levels in areas of concern, referred to as ‘hot-spots’, by integrating an SHM system at a conceptual design level. This new concept would require an assessment of benefits and detriments in order to evaluate the certification processes, impact on maintenance, operation, and ownership costs.The integration of an SHM system using onboard sensors introduces many challenges, such as the requirement for multiple sensors in the structure and additional systems weight. The investigation shows how the aircraft structural design would be impacted and how design, stress, supply-chain, manufacturing, and the systems departments need to be harmonised in order to design a feasible and integrated SHM-structural fuselage concept.
Aeroelastic behaviour of a wing including geometric nonlinearities
Authors: Harmin M. Y. , Cooper J. E. 
Published: February 2016

AbstractA procedure for developing efficient aeroelastic reduced order models (ROMs) for aerospace structures containing geometric nonlinearities is described. The structural modelling is based upon a combined modal/FE approach that describes the non-linear stiffening effects from results of non-linear static analyses for a range of prescribed inputs. Once the structural ROM has been defined, it is coupled to the rational fraction approximation of the doublet lattice aerodynamic model corresponding to the wing planform. The aeroelastic model can then be used to predict the dynamic aeroelastic behaviour of the defined structure. The methodology is demonstrated on the aeroelastic model of a flexible high aspect ratio wing with the static deflections, LCO behaviour and gust response being predicted.
Predictive inverse simulation of helicopters in aggressive manoeuvring flight
Authors: Bagiev M. , Thomson D. G. , Anderson D. , Murray-Smith D. 
Published: February 2016

AbstractA conventional inverse simulation does not accommodate control constraints; hence for aggressive manoeuvring flight conditions, where control inputs are close to the limits, these algorithms lose some of their applicability. A modification of the conventional inverse simulation technique that accommodates the onset of physical limits or constraints is proposed in this paper. In this way a process of constraints handling is incorporated into the inverse simulation algorithm. Therefore, the aim of this paper is to demonstrate that conventional inverse simulation can be improved in terms of the realism of the results by applying a predictive capability for applications involving manoeuvring flight. The paper gives details of the development of the predictive inverse simulation algorithm and helicopter model used and, by presenting examples of results calculated for pop-up and lateral realignment manoeuvres demonstrates that a ‘receding horizon’ predictive approach offers improvements in the realism of inverse simulation results.
Comprehensive multibody dynamics analysis for rotor aeromechanics predictions in descending flight
Authors: Park J.-S. , Jung S. N. 
Published: February 2016

AbstractThis paper studies the rotor aeromechanics in descending flight using a nonlinear flexible multibody dynamic analysis code, DYMORE. A freewake model is included in DYMORE to improve the rotor wake modelling. The wind-tunnel test data of the Higher-harmonic Aeroacoustics Rotor Test (HART) II rotor, with and without higher harmonic pitch control (HHC), and the flight test data of the full-scale utility helicopter rotor in descent are used for the aeromechanics correlation at an advance ratio of 0·15. The blade-vortex interaction (BVI) airloads are reasonably predicted for both the HART II and utility helicopter rotors, although some BVI peaks are missed on the advancing sides for both the rotors. The flap deflections and elastic torsion deformations at the blade tip are fairly correlated against the measured data of the HART II rotor. The correlation of blade structural moments for both HART II and utility helicopter rotors are not as good as the lift predictions; however, a reasonable prediction is obtained for the utility helicopter rotor.
Numerical simulations of the flow through the inlet and isolator of a Mach 4 dual mode scramjet
Authors: Janarthanam S. , Babu V. 
Published: February 2016

AbstractResults from numerical simulations of the three dimensional flow in the intake-isolator of a dual mode scramjet are presented. The FANS calculations have utilised the SST k -ω turbulence model. The effect of cowl length and cowl convergence angle on the inlet mass capture ratio, flow distortion, shock strength and pressure rise are studied in detail. Three cowl lengths and four or five cowl convergence angles for each cowl length are considered. The predicted values of the dimensionless wall static pressure and inlet mass capture ratio are compared with experimental data reported in the literature. The numerical predictions are shown to agree well with the experimental data. In addition, details of the flow field such as shocks, expansion fans and shock boundary interaction are also captured accurately. Inlet unstart is also demonstrated for one case.
A case study on the aerodynamic heating of a hypersonic vehicle
Authors: Mifsud M. , Estruch-Samper D. , MacManus D. , Chaplin R. , Stollery J. 
Published: February 2016

AbstractA Parabolised Navier-Stokes (PNS) flow solver is used to predict the aerodynamic heating on the surface of a hypersonic vehicle. This case study highlights some of the main heat flux sensitivies to various conditions for a full-scale vehicle and illustrates the use of different complimentary methods in assessing the heat load for a realistic application. Different flight phases of the vehicle are considered, with freestream conditions from Mach 4 to Mach 8 across a range of altitudes. Both laminar and turbulent flows are studied, together with the effect of the isothermal wall temperature, boundary-layer transition location and body incidence. The effect of the Spalart-Allmaras and Baldwin-Lomax turbulent models on the heat transfer distributions is assessed. A rigorous assessment of the computations is conducted through both iterative and grid convergence studies and a supporting experimental investigation is performed on a 1/20th scale model of the vehicle’s forebody for the validation of the numerical results. Good agreement is found between the PNS predictions, measurements and empirical methods for the vehicle forebody. The present PNS approach is shown to provide useful predictions of the heat transfer over the axisymmetric vehicle body. A highly complex flow field is predicted in the fin-body-fin region at the rear of the vehicle characterised by strong interference effects which limit the predictions over this region to a predominately qualitative level.
Aviation renewable fuels: technical status and challenges for commercialisation
Authors: Anderson S. , Cooper J. , Gudde N. , Howes J. 
Published: February 2016

AbstractAn overview of the major issues to be addressed for widespread commercial introduction and use of aviation biofuels is presented in this paper. These include the progress toward standards and approvals, bio-feedstock supply and sustainability, conversion routes to suitable fuel molecules, and policy and regulation considerations to create the necessary market and investment environment. It has been shown that while technical standards are now largely in place, biojet faces competition from biodiesel markets for feedstock, and existing sources of vegetable oil face sustainability challenges for greater supply. Other conversion routes exist that can use more sustainable feedstock, but they are capital intensive and will require a high fuel price to support investment. Policy approaches to cover the expected price premium above fossil fuel may also face political difficulties.
The estimation of aerodynamic forces on flat plate aerofoils at hypersonic and supersonic speed
Authors: Punniyakotti S. , Stollery J. L. 
Published: February 2016

AbstractExisting theories are reviewed and compared. From the Tangent Wedge formula a simple expression for the normal force on thin wings is derived and compared with some existing experimental data, which cover the whole supersonic-hypersonic range of Mach numbers.
Modelling progressive failure of fibre reinforced laminated composites: mesh objective calculations
Authors: Pineda E. J. , Waas A. M. 
Published: February 2016

AbstractA thermodynamically-based work potential theory for modelling progressive damage and failure in fibre-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, enhanced Schapery theory, utilises separate ISVs for modelling the effects of damage and failure. Damage is considered to be the effect of any structural changes in a material that manifest as pre-peak non-linearity in the stress versus strain response. Conversely, failure is taken to be the effect of the evolution of any mechanisms that results in post-peak strain softening. It is assumed, matrix microdamage is the dominant damage mechanism in continuous, fibre-reinforced, polymer matrix laminates, and its evolution is captured with a single ISV. Three additional ISVs are introduced to account for failure due to mode I transverse cracking, mode II transverse cracking, and mode I axial failure. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs is derived. Typically, failure evolution (i.e. post-peak strain softening) results in pathologically mesh dependent solutions within a finite element method numerical setting. Therefore, consistent characteristic element lengths are introduced into the formulation of of the three failure potentials. The theory is implemented into commercial FEM software. The model is verified against experimental results from a laminated, quasi-isotropic, T800/3900-2 panel containing a central notch. Global load versus displacement, global load versus local strain gauge data, and macroscopic failure paths obtained from the models are compared to the experiments. Finally, a sensitivity study is performed on the failure parameters used in the model.
Modelling of impact damage zones in composite laminates for strength after impact
Authors: Olsson R. 
Published: February 2016

AbstractThis paper reviews findings on the type, morphology and constitutive behaviour of impact damage zones during loading after impact and their effect on the laminate strength and stability. The paper is limited to tape prepreg based monolithic laminates, although some similarities exist with impact damage in textile based laminates. Damage zones have a complex geometry with several damage types, which results in an interaction and competition between different failure mechanisms, e.g. local and global buckling, compressive failure, and delamination growth. Hence, simplified damage models may provide incorrect predictions of the failure load and failure mechanisms after impact. The constitutive behaviour of damage zones has been studied experimentally in tension and compression using an inverse method, and the results have been compared with detailed FE models of a generic impact damage. The paper is concluded with a discussion on analytical and computational models to predict the resulting strength of impacted laminates.
Vision guidance of a fixed wing UAV using a single camera configuration
Authors: Iong P.-T. , Chen S.-H. , Yang Y. 
Published: February 2016

AbstractIn this paper a single camera vision guidance system for fixed wing UAV is developed. This system searches for and identifies a target object with known colour and shape from images captured by an onboard camera. HSV colour space and moment invariants are utilised to describe the colour and shape features of the target object. Position, area and rotation angle of the target object in the image plane are collected. This information is then processed by the Extended Kalman Filter to estimate the relative positions and attitudes of the UAV. The vision guidance system guides the UAV towards the target object automatically based on these estimated states by using a proportional controller. A Senior Telemaster aircraft model kit installed with an onboard camera and computer is used for flight test. The target object for the flight test is a white flag with a red cross. Flight simulations and flight tests results are presented in this paper, showing that the vision guidance system can recognise the target object and guide the UAV effectively.
Rotorcraft simulation fidelity: new methods for quantification and assessment
Authors: Perfect P. , White M. D. , Padfield G. D. , Gubbels A. W. 
Published: February 2016

AbstractFlight simulators are integral to the design/development, testing/qualification, training and research communities and their utilisation is ever expanding. The use of flight simulation to provide a safe environment for pilot training, and in research and development, must be underpinned by quantification of simulator fidelity. While regulatory simulator standards exist for flight training simulators and new standards are in development, previous research has shown that current standards do not provide a fully quantitative approach for assessing simulation fidelity, especially in a research environment. This paper reports on progress made in a research project at the University of Liverpool (Lifting Standards), in which new predicted and perceptual measures of simulator fidelity have been developed. The new metrics have been derived from handling qualities engineering practice. Results from flight tests on the National Research Council (Canada) Bell 412 ASRA research aircraft and piloted simulation trials using the HELIFLIGHT-R simulator at Liverpool are presented to show the efficacy of adopting a handling qualities approach for fidelity assessment. Analysis of the new metrics has shown an appropriate degree of sensitivity to differences between flight and simulation.