Gas turbine sub-idle performance modelling : groundstart altitude relight, and windmilling

Engine performance modelling is a major part of the engine design process, in which specialist solvers are employed to predict, understand and analyse the engine’s behaviour at various operating conditions. Sub-idle whole engine performance synthesis solvers are not as reliable and accurate as design point solvers. Lack of knowledge and data result in component characteristics being reverse-engineered or extrapolated from above-idle data. More stringent requirements on groundstart and relight capabilities, has prompted the need to advance the knowledge on low-speed engine performance, thereby requiring more robust sub-idle performance synthesis solvers. The objective of this study, was to improve the accuracy and reliability of a current aero gas turbine sub-idle performance solver by studying each component in isolation through numerical simulations. Areas researched were: low-speed and locked-rotor com- pressor characteristics, low-power combustion efficiency, air blast atomizer and combustor performance at sub-idle, torque-based whole engine sub-idle performance synthesis, and mixer performance at far off-design conditions. The observations and results from the numerical simulations form the contribution to knowledge of this research. Numerical simulations of compressor blades under highly negative incidence angles show the complex nature of the flow, with the results used to determine a suitable flow deviation model, a method to extract blade aerodynamic char- acteristics in highly separated flows, and measure the blockage caused by highly separated flow with operating condition and blade geometry. The study also concluded that the use of Blade Element Theory is not accurate enough to be used at such far off-design con- ditions. The linearised parameter-based whole engine performance solver was converted to used torque-based parameters, which validated against engine test data, shows that it is suitable for low-power simulations with the advantage of having the potential to start engine simulations from static conditions. A study of air-blast atomization at windmilling relight conditions has shown that current established correlations used to predict spray characteristics are not suitable for altitude relight studies, tending to overestimate the atomization quality. Also discovered is the highly influential interaction of compressor wakes with the combustor and atomizer under altitude relight conditions, resulting in more favourable lighting conditions than previous assumptions and models have shown. This is a completely new discovery which will result in a change in the way combustors are designed and sized for relight conditions, and the way combustion rig tests are conducted. The study also has valuable industrial contributions. The locked-rotor numerical data was used within a stage-stacking compressible flow code to estimate the compressor sub- idle map, of which results were used within a whole engine performance solver and results validated against actual engine test data. The atomization studies at relight were used to factor in the insensitivity of current spray correlations, which together with a newly de- veloped sub-idle combustion efficiency sub-routine, are used to determine the combustion efficiency at low-power settings. The interaction of compressor wakes with the atomizer showed that atomizer performance at relight is underestimated, resulting in oversized combustors. By using the knowledge gained within this research, combustor size can be reduced, resulting in lower NOx at take-off and a smaller and lighter core, with a com- bustor requiring less cooling air. The component research has advanced the knowledge and modelling capability of sub-idle performance solvers, increasing their reliability and encouraging their use for future aero gas turbine engines

Mental health and legal representation for asylum seekers in the ‘legacy caseload’

This article examines the legal challenges asylum seekers arriving by boat to Australia experience when seeking assistance with their claims and its impact on their mental health. The authors outline the experiences of asylum seekers in the “legacy caseload” group who have been waiting up to four years to have their protection claims assessed. The complex interplay between legal assistance to support refugee claims and the way those making claims inevitably struggle to understand, engage and participate in the process is analysed. It is argued that provision of legal assistance for this group will be essential to ensuring that the refugee status determination process is fair and allows asylum seekers to understand and participate more fully in the process. Recent changes to the assessment of claims combined with a reduction in funding for legal assistance create significant hurdles and combine to compound existing stress and emotional trauma leading to detrimental outcomes on the mental health of asylum seekers

Dynamic Ferromagnetic Hysteresis Modelling Using a Preisach-Recurrent Neural Network Model

In this work, a Preisach-recurrent neural network model is proposed to predict the dynamic hysteresis in ARMCO pure iron, an important soft magnetic material in particle accelerator magnets. A recurrent neural network coupled with Preisach play operators is proposed, along with a novel validation method for the identification of the model's parameters. The proposed model is found to predict the magnetic flux density of ARMCO pure iron with a Normalised Root Mean Square Error (NRMSE) better than 0.7%, when trained with just six different hysteresis loops. The model is evaluated using ramp-rates not used in the training procedure, which shows the ability of the model to predict data which has not been measured. The results demonstrate that the Preisach model based on a recurrent neural network can accurately describe ferromagnetic dynamic hysteresis when trained with a limited amount of data, showing the model's potential in the field of materials science

The effects of cold arm width and metal deposition on the performance of a U-Beam electrothermal MEMS microgripper for biomedical applications

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated 'hot and cold arm' microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14 μm, 30 μm, 55 μm, 70 μm and 100 μm. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)TM. This process results in an overhanging 25 μm thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2 μm. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare ®. The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs.peer-reviewe

Parametric design of non-axisymmetric separate-jet aero-engine exhaust systems

Future civil air vehicles are likely to feature propulsion systems which are more closely integrated with the airframe. For a podded underwing configuration, this close coupling is expected to require non-axisymmetric design capabilities for the aero-engine exhaust system. This work presents the development of a novel parametric representation of non-axisymmetric aero-engine exhaust system geometries based on Intuitive Class Shape Transformation (iCST) curves. An exhaust design method was established and aerodynamic analyses of a range of non-axisymmetric configurations was demonstrated. At typical flight conditions, the introduction of non-axisymmetric separate jet nozzles was shown to increase the engine net propulsive force by 0.12% relative to an axisymmetric nozzle

Design and analysis of a MEMS-based electrothermal microgripper

Microelectromechanical systems (MEMS) have established themselves in various science and engineering domains. MEMS-based microgrippers provide several advantages in terms of compact size and low cost, and they play vital roles in microassembly and micromanipulation fields within both micromanufacturing and biological sectors. Microactuators based on different actuation principles have been devised to drive MEMS microgrippers. This paper presents a finite element model of a MEMS-based electrothermally actuated microgripper performed using CoventorWare ®. The microgripper design follows standard micromachining processes that make use of reactive ion etching where polysilicon acts as the main structural material while a chromium and gold layer is deposited on the structure for thermal actuation. The simulations are used to assess the performance of the microgripper and to optimise its operating parameters.peer-reviewe

Design optimisation of separate-jet exhausts for the next generation of civil aero-engines

This paper presents the development and application of a computational framework for the aerodynamic design of separate-jet exhaust systems for Very-High-Bypass-Ratio (VHBR) gas-turbine aero-engines. An analytical approach is synthesised comprising a series of fundamental modelling methods. These address the aspects of engine performance simulation, parametric geometry definition, viscous/compressible flow solution, design space exploration, and genetic optimisation. Parametric design is carried out based on minimal user-input combined with the cycle data established using a zero-dimensional (0D) engine analysis method. A mathematical approach is developed based on Class-Shape Transformation (CST) functions for the parametric geometry definition of gas-turbine exhaust components such as annular ducts, nozzles, after-bodies, and plugs. This proposed geometry formulation is coupled with an automated mesh generation approach and a Reynolds Averaged Navier–Stokes (RANS) flow-field solution method, thus forming an integrated aerodynamic design tool. A cost-e ective Design Space Exploration (DSE) and optimisation strategy has been structured comprising methods for Design of Experiment (DOE), Response Surface Modelling (RSM), as well as genetic optimisation. The integrated framework has been deployed to optimise the aerodynamic performance of a separate-jet exhaust system for a large civil turbofan engine representative of future architectures. The optimisations carried out suggest the potential to increase the engine’s net propulsive force compared to a baseline architecture, through optimum re-design of the exhaust system. Furthermore, the developed approach is shown to be able to identify and alleviate adverse flow-features that may deteriorate the aerodynamic behaviour of the exhaust system

Performance comparison of nuclear magnetic resonance and FerriMagnetic resonance field markers for the control of low-energy synchrotrons

A field marker is a magnetic field sensor used in synchrotrons, which provides a digital trigger when the magnetic field reaches a pre-set threshold. This paper describes the results of an in-situ measurement performed on the Extra Low ENergy Antiproton (ELENA) decelerator's main bending dipoles at the European Organization for Nuclear Research (CERN). It compares the dynamic behavior of Nuclear Magnetic Resonance (NMR) markers and FerriMagnetic Resonance (FMR) markers in different magnetic fields for the operation of these sensors in low-energy synchrotrons.peer-reviewe

Analytical, numerical and experimental study of a horizontal electrothermal MEMS microgripper for the deformability characterisation of human red blood cells

Microgrippers are typical microelectromechanical systems (MEMS) that are widely used for micromanipulation and microassembly in both biological and micromanufacturing fields. This paper presents the design, modelling, fabrication and experimental testing of an electrothermal microgripper based on a ‘hot and cold arm’ actuator design that is suitable for the deformability characterisation of human red blood cells (RBCs). The analysis of the mechanical properties of human RBCs is of great interest in the field of medicine as pathological alterations in the deformability characteristics of RBCs have been linked to a number of diseases. The study of the microgripper’s steady-state performance is initially carried out by the development of a lumped analytical model, followed by a numerical model established in CoventorWare® (Coventor, Inc., Cary, NC, USA) using multiphysics finite element analysis. Both analytical and numerical models are based on an electothermomechanical analysis, and take into account the internal heat generation due to the applied potential, as well as conduction heat losses through both the anchor pads and the air gap to the substrate. The models are used to investigate key factors of the actuator’s performance including temperature distribution, deflection and stresses based on an elastic analysis of structures. Results show that analytical and numerical values for temperature and deflection are in good agreement. The analytical and computational models are then validated experimentally using a polysilicon microgripper fabricated by the standard surface micromachining process, PolyMUMPs™ (Durham, NC, USA). The microgripper’s actuation is characterised at atmospheric pressure by optical microscopy studies. Experimental results for the deflection of the microgripper arm tips are found to be in good agreement with the analytical and numerical results, with process-induced variations and the non-linear temperature dependence of the material properties accounting for the slight discrepancies observed. The microgripper is shown to actuate to a maximum opening displacement of 9 μ m at an applied voltage of 3 V, thus being in line with the design requirement of an approximate opening of 8 μ m for securing and characterising a RBC.peer-reviewe

Error characterization and calibration of real-time magnetic field measurement systems

In synchrotrons at the European Organization for Nuclear Research (CERN), magnetic measurement systems known as B-trains measure the magnetic field in the main bending magnets in real-time, and transmit this signal for the control of the synchrotron’s RF accelerating cavities, magnet power converter and beam monitoring systems. This work presents an assessment of the capabilities and performance of the new FIRESTORM (Field In REal-time STreaming from Online Reference Magnets) system as part of the first phase of commissioning. A short summary of the architecture of the measurement system is provided first, followed by the definition of an error model which can be used to characterize random and systematic errors separately. We present a procedure for the metrological calibration and qualification of the B-trains, including an experimental evaluation of the different error sources for the four new systems being commissioned in the Proton Synchrotron Booster (PSB), Low Energy Ion Ring (LEIR), Proton Synchrotron (PS) and the Extra Low ENergy Antiproton (ELENA) ring. In particular, we discuss a method to calibrate systematic gain and offset errors based on the RF cavity frequency offset needed to center the beam on its theoretical orbit