Imperial College London

DrJeffreyGreen

Faculty of EngineeringDepartment of Mechanical Engineering

Visiting Professor
 
 
 
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Contact

 

+44 (0)20 7594 7070jeffrey.green

 
 
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Assistant

 

Mr Peter Higgs +44 (0)20 7594 7078

 
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Location

 

557City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

32 results found

Tuzzi G, Schwingshackl CW, Green JS, 2020, Study of coupling between shaft bending and disc zero nodal diameter modes in a flexible shaft-disc assembly, JOURNAL OF SOUND AND VIBRATION, Vol: 479, ISSN: 0022-460X

Journal article

Lu Y, Green J, Stapelfeldt SC, Vahdati Met al., 2019, Effect of Geometric Variability on Running Shape and Performance of a Transonic Fan, JOURNAL OF TURBOMACHINERY-TRANSACTIONS OF THE ASME, Vol: 141, ISSN: 0889-504X

Journal article

Lu Y, Lad B, Green J, Stapelfeldt S, Vahdati Met al., 2019, Effect of geometry variability on transonic fan blade untwist, International Journal of Turbomachinery, Propulsion and Power, Vol: 4

Due to manufacturing tolerance and deterioration during operation, fan blades in the same engine exhibit geometric variability. The absence of symmetry will inevitably exacerbate and contribute to the complexities of running geometry prediction as the blade variability is bound to be amplified by aerodynamic and centrifugal loading. In this study, we aim to address the fan blade untwist related phenomenon known as alternate passage divergence (APD). As the name suggests, APD manifests as alternating passage geometry (and hence alternating tip stagger pattern) when the fan stage is operating close to/at peak efficiency condition. APD can introduce adverse influence on fan performance, aeroacoustics behaviour, and high cycle fatigue characteristics of the blade. The main objective of the study is to identify the parameters contributing to the APD phenomenon. In this study, the APD behaviours of two transonic fan blade designs are compared.

Journal article

Lu Y, Vahdati M, Stapelfeldt SC, Lad B, Green Jet al., 2019, Effect of geometry variability on transonic fan blade untwist

Due to manufacturing tolerance and deterioration during operation, fan blades in the same engine exhibit geometric variability. The absence of symmetry will inevitably exacerbate and contribute to the complexities of running geometry prediction as the blade variability is bound to be amplified by aerodynamic and centrifugal loading. In this study, we aim to address the fan blade untwist related phenomenon known as Alternate Passage Divergence (APD). As the name suggests, APD manifests as alternating passage geometry (and hence alternating tip stagger pattern) when the fan stage is operating close to/at peak efficiency condition. APD can introduce adverse influence on fan performance, aeroa-coustics behaviour, and high cycle fatigue characteristics of the blade. The main objective of the study is to identify the parameters contributing to the APD phenomenon. In this study, the APD behaviours of two transonic fan blade designs are compared.

Conference paper

Lu Y, Vahdati M, Green J, Stapelfeldt Set al., 2018, Effect of Geometry Variability on Fan Performance and Aeromechanical Characteristics, 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines

Conference paper

Pesaresi L, Salles L, Jones A, Green JS, Schwingshackl CWet al., 2017, Modelling the nonlinear behaviour of an underplatform damper test rig for turbine applications, Mechanical Systems and Signal Processing, Vol: 85, Pages: 662-679, ISSN: 1096-1216

Underplatform dampers (UPD) are commonly used in aircraft engines to mitigate the risk of high-cycle fatiguefailure of turbine blades. The energy dissipated at the friction contact interface of the damper reduces the vibrationamplitude significantly, and the couplings of the blades can also lead to significant shifts of the resonance frequenciesof the bladed disk. The highly nonlinear behaviour of bladed disks constrained by UPDs requires an advancedmodelling approach to ensure that the correct damper geometry is selected during the design of the turbine, and thatno unexpected resonance frequencies and amplitudes will occur in operation. Approaches based on an explicit modelof the damper in combination with multi-harmonic balance solvers have emerged as a promising way to predict thenonlinear behaviour of UPDs correctly, however rigorous experimental validations are required before approaches ofthis type can be used with confidence.In this study, a nonlinear analysis based on an updated explicit damper model having different levels of detail isperformed, and the results are evaluated against a newly-developed UPD test rig. Detailed linear finite element modelsare used as input for the nonlinear analysis, allowing the inclusion of damper flexibility and inertia effects. The nonlinearfriction interface between the blades and the damper is described with a dense grid of 3D friction contact elementswhich allow accurate capturing of the underlying nonlinear mechanism that drives the global nonlinear behaviour. Theintroduced explicit damper model showed a great dependence on the correct contact pressure distribution. The use ofan accurate, measurement based, distribution, better matched the nonlinear dynamic behaviour of the test rig. Goodagreement with the measured frequency response data could only be reached when the zero harmonic term (constantterm) was included in the multi-harmonic expansion of the nonlinear problem, highlighting its importance when thecontact inter

Journal article

Ruffini V, Green JS, Schwingshackl CW, 2017, THE INFLUENCE OF MISTUNING AND CORIOLIS EFFECTS ON THE MODAL PARAMETERS OF BLADED DISCS: AN EXPERIMENTAL STUDY, ASME Turbine Technical Conference and Exposition (Turbo Expo), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Carnevale M, Wang F, Parry AB, Green JS, di Mare Let al., 2017, FAN SIMILARITY MODEL FOR THE FAN-INTAKE INTERACTION PROBLEM, ASME Turbine Technical Conference and Exposition (Turbo Expo), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Barbarossa F, Rife ME, Carnevale M, Parry AB, Green JS, di Mare Let al., 2017, FAST OPTIMISATION OF A THREE-DIMENSIONAL BYPASS SYSTEM USING A NEW AERODYNAMIC DESIGN METHOD, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Barbarossa F, Parry AB, Green JS, di Mare Let al., 2016, An Aerodynamic Parameter for Low-Pressure Turbine Flutter, Journal of Turbomachinery-Transactions of the ASME, Vol: 138, ISSN: 1528-8900

Journal article

Rife ME, Barbarossa F, Parry AB, Green JS, di Mare Let al., 2016, MINIMISATION OF DUCTED FLOW NON-UNIFORMITY CAUSED BY DOWNSTREAM BLOCKAGES, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Carnevale M, Wang F, Green JS, Di Mare Let al., 2016, Lip Stall Suppression in Powered Intakes, JOURNAL OF PROPULSION AND POWER, Vol: 32, Pages: 161-170, ISSN: 0748-4658

Journal article

Ruffini V, Schwingshackl C, Green J, 2015, Experimental and Analytical Study of Coriolis Effects in Bladed Disk, ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, Publisher: American Society of Mechanical Engineers

Modern aero-engines have reached a high level of sophistication and only significant changes will lead to the improvements necessary to achieve the economic and environmental targets of the future. Open rotors constitute a major leap in this direction, both in terms of efficiency and of technological innovation. This calls for a revision of the accepted design practices, and a new focus on phenomena that have been little investigated in the past, such as the Coriolis effect, or the gyroscopic coupling of the blades with the shaft. Experimental results from modern fans, with large blades and strong stagger angles, are showing dependence on Coriolis gyroscopic effects already, an effect that is expected to be strongly enhanced with the proposed open rotor designs.For an accurate prediction of the Coriolis and gyroscopic effects in rotating assemblies a fully experimentally validated approach is needed. Today’s FE models can capture the basic physical phenomena, but experimental confirmation is still needed for the evolution of the mode shapes with angular speed, and the influence of damping and geometric nonlinearities when gyroscopic coupling is considered. To support this validation effort a new rotating test rig will be introduced, initial measurement data will be discussed, and a comparison with a finite element analysis presented.Different forcing patterns, including forward and backward travelling-wave engine order excitation could be experimentally excited in the new rig, Coriolis-induced frequency splits were found in the dynamic response, showing a significant change in the dynamic behaviour of the investigated dummy disk, and only a minor impact of the mistuning was observed on the frequency splits due to Coriolis effects. The experimental results have been compared to a finite element analysis, and after some updating a good agreement between the predicted and measured Campbell diagrams could be obtained, demonstrating the reliability of the modelling

Conference paper

Ruffini V, Schwingshackl CW, Green JS, 2015, Prediction capabilities of coriolis and gyroscopic effects in current finite element software, Pages: 1853-1862, ISSN: 2211-0984

The progress towards a whole-engine design philosophy and the development of new technologies like open rotors, where coupled behaviour due to Coriolis and gyroscopic effects could be more pronounced, calls for an assessment of the prediction capabilities currently available in commercial FE software packages. Finite element models including these rotational effects are rarely used in simulations of bladed disc-shaft assemblies, and the confidence in FE codes to provide reliable frequency and mode shape data can therefore be improved. Different models were used as benchmark test cases in the evaluation, including the classic Stodola-Green rotor, and a blade-disc-shaft assembly, and the resulting Campbell diagrams were compared to analytical solutions from the literature. The ability of the codes to exploit the cyclic symmetry of bladed discs for computational efficiency was also assessed. The results show that all investigated codes are able to capture the Coriolis-induced frequency splits, but discrepancies arise at high speeds and in the vicinity of instabilities.

Conference paper

Schwingshackl CW, Joannin C, Pesaresi L, Green JS, Hoffmann Net al., 2014, Test method development for nonlinear damping extraction of dovetail joints, ISSN: 2191-5644

The traditional measurement techniques to acquire the linear dynamic response of a single component are well established and have been in use for many decades to provide reliable input data for model updating. The measurement of assembled structures normally follows a very similar approach, although the presence of joints can introduce a nonlinear dynamic behaviour, which impacts the measurement results. Applying traditional linear test methods to a highly nonlinear structure, such as a dovetail joint in an aircraft engine blade-disk connection, does not necessarily take the special features of the nonlinear response into account and may lead to unreliable data. This is particularly true, if modal information such as damping are required. The influence of the measurement setup and the test procedures must be well understood for an accurate measurement. In this paper the influence of the different measurement components on a simple clamped beam and a compressor blade dove tail test rig will be investigated. A particular focus will be on the support of the test rig, the location and control of the excitation and the influence of the accelerometer on the response. Based on the findings an approach will be recommended that allows a reliable measurement of the dynamic behaviour of this heavily nonlinear structure.

Conference paper

Di Mare L, Thirumurthy D, Green JS, Myers Jet al., 2014, UNSTEADY AERODYNAMICS AND FORCED RESPONSE STUDIES ON AERODERIVATIVE GAS TURBINE EXHAUST SYSTEM, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Carnevale M, Green JS, Di Mare L, 2014, NUMERICAL STUDIES INTO INTAKE FLOW FOR FAN FORCING ASSESSMENT, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Schwingshackl CW, Di Maio D, Sever I, Green JSet al., 2013, Modeling and Validation of the Nonlinear Dynamic Behavior of Bolted Flange Joints, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 135, ISSN: 0742-4795

Journal article

Ruffini V, Schwingshackl CW, Green JS, 2013, LDV measurement of local nonlinear contact conditions of flange joint, Pages: 159-168, ISSN: 2191-5644

The traditional approach to evaluating the linear dynamic behavior of structures for modal validation is based on the acquisition of frequency response functions and their modal analysis. With small modifications, a similar technique can be used to validate nonlinear response predictions. The use of nonlinear dynamic analysis of flange joints for sealing and wear predictions makes it necessary to also provide validation information for the localised nonlinear mechanisms at the contact surface. For this purpose, a technique based on two Laser Doppler Vibrometers has been developed. The experimental set-up can provide data of the relative out-of-plane displacement of the bolted flange joint during a vibration cycle, which indicates contact separation and permanent gap locations. The observed influence of different excitation levels and bolt torques on the global and local dynamic response led to an understanding of the nonlinear behaviour of the flange and of the local contact conditions. © The Society for Experimental Mechanics, Inc. 2013.

Conference paper

Salles L, Schwingshackl C, Green J, 2013, Modelling friction contacts in nonlinear vibration of bladed disks

Conference paper

Schwingshackl CW, Di Maio D, Green JS, 2013, MODELLING AND VALIDATION OF THE NONLINEAR DYNAMIC BEHAVIOUR OF BOLTED FLANGE JOINTS, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

di Mare L, Imregun M, Green JS, Sayma AIet al., 2010, A Numerical Study of Labyrinth Seal Flutter, JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, Vol: 132, ISSN: 0742-4787

Journal article

Coghlan RP, Green JS, Baron AK, 2010, MECHANICAL DAMPING ANALYSIS OF A VIBRATING LABYRINTH SEAL STRUCTURE WITH FRICTIONAL CONTACT, ASME Turbo Expo 2010, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 949-957

Conference paper

di Mare L, Imregun M, Green JS, 2009, EFFECT OF REAL GEOMETRY ON COMPRESSOR PERFORMANCE PREDICTIONS, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 263-271

Conference paper

Mata S, Di Mare L, Mehmet I, Green Jet al., 2009, GENERALISED SINGLE-PASSAGE MULTI-BLADEROW METHOD FOR TURBOMACHINERY FORCED RESPONSE, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1685-1692

Conference paper

Phibel R, di Mare L, Green JS, Imregun Met al., 2009, NUMERICAL INVESTIGATION OF LABYRINTH SEAL AEROELASTIC STABILITY, 54th ASME Turbo Expo 2009, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 573-583

Conference paper

Green JS, 2008, FORCED RESPONSE OF A LARGE CIVIL FAN ASSEMBLY, 53rd ASME Turbo Expo 2008, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 685-692

Conference paper

Green JS, Fransson TH, 2006, Scaling of turbine blade unsteady pressures for rapid forced response assessment, 51st ASME Turbo Expo 2006, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1081-1089

Conference paper

Breard C, Green JS, Imregun M, 2003, Low-engine-order excitation mechanisms in axial-flow turbomachinery, JOURNAL OF PROPULSION AND POWER, Vol: 19, Pages: 704-712, ISSN: 0748-4658

Journal article

Breard C, Green JS, Vahdati M, Imregun Met al., 2001, A non-linear integrated aeroelasticity method for the prediction of turbine forced response with friction dampers, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 43, Pages: 2715-2736, ISSN: 0020-7403

Journal article

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