Browsing by Author "Sibilli, Thierry"

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    Cryogenic fuel storage modelling and optimisation for aircraft applications
    (American Society of Mechanical Engineers, 2021-09-16) Rompokos, Pavlos; Rolt, Andrew Martin; Nalianda, Devaiah; Sibilli, Thierry; Benson, Claire
    Designing commercial aircraft to use liquid hydrogen (LH2) is one way to substantially reduce their life-cycle CO2 emissions. The merits of hydrogen as an aviation fuel have long been recognized, however, the handling of a cryogenic fuel adds complexity to aircraft and engine systems, operations, maintenance and storage. The fuel tanks could account for 8–10% of an aircraft’s operating empty weight, so designing them for the least added weight is of high significance. This paper describes the heat transfer model developed in the EU Horizon 2020 project that is used to predict heat ingress to a cylindrical tank with hemispherical end caps with external foam insulation. It accounts for heat transfer according to the state of the tank contents, the insulation material properties, the environment, and the dimensions of the tank. The model also estimates the rate of pressure change according to the state of the fuel and the rate at which fuel is withdrawn from the tank. In addition, a methodology is presented, that allows for tank sizing taking into consideration the requirements of a design flight mission, the maximum pressure developed, and the fuel evaporated. Finally, the study demonstrates how to select optimal insulation material and thickness to provide the lightest design for the cases where no gaseous hydrogen is extracted, and where some hydrogen gas is extracted during cruise, the latter giving gravimetric efficiencies as high as 74%.
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    Modelling the aerodynamics of propulsive system integration at cruise and high-lift conditions
    (Cranfield University, 2012-03) Sibilli, Thierry; Savill, Mark A.
    Due to a trend towards Ultra High Bypass Ratio engines the corresponding engine/airframe interference is becoming a key aspect in aircraft design. The present economic situation increases the pressure on commercial aviation companies to reduce the Direct Operating Cost, and the environmental situation requires a new generation of aircraft with a lower environmental impact. Therefore detailed aerodynamic investigations are required to evaluate the real benefits of new technologies. The presented research activity is part of a long-term project with the main objective of generating a reliable and accurate tool to predict the performance of an aircraft over the whole flight domain. In particular the aim of this research was to perform advanced CFD in order to establish a tool able to evaluate engine installation effects for different configurations and attitudes. The developed tool can be provided with correlations of the Net Propulsive Force (NPF), the force exerted by the power-plant to the aircraft, as a function of position. This can be done in principle at cruise, hold, climb, descent, take-off and landing, to model the different integration effects at different phases. Due to the complexity of the problem it was only possible at an initial stage to determine these correlations at cruise condition. Two parametric test cases were evaluated, showing that the engine horizontal positioning can influence the mission fuel burn by up to 6.4%. According to the extensive literature review that has been done, this study can be regarded as the first open literature engine position-NPF parametric study using CFD. Even though no correlations were extracted for other conditions; a deployed high-lift wing configuration was also studied in detail, defining the main aerodynamics effects of the engine integration at high angle of attack. A topological study of the high-lift installation vortices is presented in this work and it can be considered the first in the open literature. It should be pointed out that extensive research is currently underway to correctly evaluate the high-lift aerodynamic using CFD. The Propulsive System Integration (PSI) in high-lift conditions is adding flow features to an already demanding problem, making it a real challenge for the numerical methods. Nevertheless the additional effects of a nacelle chine on the maximum lift were also evaluated. The main outcomes of this PhD research were: a coupled performance modelling tool able to handle the effects of engine-airframe integration as a function of geometry and attitude, and a topological study of the high-lift installation vortices. During the course of the work, this research was successfully suggested as an extra activity for the European NEWAC project (New Aero Engine Core Concepts), and resulted in a new deliverable for that project.
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    Transient thermal modelling of ball bearing using finite element method
    (ASME, 2017-07-11) Sibilli, Thierry; Igie, Uyioghosa
    Gas turbines are fitted with rolling element bearings, which transfer loads and supports the shafts. The interaction between the rotating and stationary parts in the bearing causes a conversion of some of the power into heat, influencing the thermal behaviour of the entire bearing chamber. To improve thermal modelling of bearing chambers, this work focused on modelling of the heat generated and dissipated around the bearings, in terms of magnitude and location, and the interaction with the components/systems in the bearing chamber. A thermal network model and a finite element model of an experimental high-pressure shaft ball bearing and housing were generated and a comparison to test rig results have been conducted. Nevertheless, the purpose of the thermal matching process that focused on the finite element model and experimental data is to provide a template for predicting temperatures and heat transfers for other bearing models. The result of the analysis shows that predictions of the thermal network are considerate, despite the simplifications. However, lower relative errors were obtained in the finite element model compared to the thermal network model. For both methods, the highest relative error is seen to occur during transient (acceleration and deceleration). This observation highlights the importance of boundary conditions and definitions: surrounding temperatures, heat split and the oil flow, influencing both the heat transfer and heat generation. These aspects, incorporated in the modelling and benchmarked with experimental data, can help facilitate other related cases where there is limited or no experimental data for validation.