Browsing by Author "Gallar, Luis"

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    Gas turbine shaft over-speed/failure performance modelling
    (Cranfield University, 2010-10) Gallar, Luis; Pachidis, Vassilios; Singh, R.; Rowe, Arthur; Brown, Steve
    A gas turbine engine can over-speed due to various reasons, including shaft failure, variable geometry mal-schedule or fuel system malfunction. In any case, engine manufacturers are required to demonstrate that a shaft over-speed event will not result in an uncontained failure with high energy debris being released from the engine. Although the certification authority can be satisfied that the engine is shaft failure safe by conducting large scale tests, a purely experimental approach would be very complex and expensive. Moreover, today’s poor understanding of the event leads to conservative designs that exert unavoidable penalties on the engine performance and weight. It is in this context that the need for an analytical approach and small scale testing arises to model the progression of the event. This work is part of a wider long term research collaboration between Cranfield University and Rolls-Royce that attempts to enhance today’s modelling capability of gas turbine shaft overspeed/ failure events. The final aim of the project is the development of a generic advanced performance prediction tool able to account for all the complex and heavily interrelated phenomena to ascertain the terminal speed of the over-speeding turbine. This multidisciplinary “all in one” tool will allow to include the shaft failure scenario early into the design process and eliminate current conservative design approaches while maintaining the high standard of airworthiness required for certification. This thesis focuses on the aerothermal performance modelling of turbomachinery components at the extreme off-design conditions experienced during a shaft over-speed event. In particular, novel modelling techniques and methodologies at the forefront of knowledge have been developed to simulate the performance of turbine vanes at high negative incidence angles, derive the extended compressor characteristics in reverse flow and calculate the response of the air system during rapid transient among others. These component models are ready to be integrated into a generic single computational tool that, once validated against engine data available from the sponsor, can be applied to different engines and scenarios. The collaboration with Rolls-Royce provided the opportunity to conduct research on other areas related to performance engineering apart from the shaft failure modelling. The present study makes several noteworthy contributions on compressor variable geometry loss, deviation and stall modelling, compressor variable geometry schedule optimisation and on the effect of using real gas models instead of the perfect gas assumption in engine performance simulation codes.
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    An investigation into the fertilizer particle dynamics off-the-disc
    (American Society of Agricultural and Biological Engineers, 2015) Antille, Diogenes Luis; Gallar, Luis; Miller, P. C. H.; Godwin, R. J.
    The particle size range specifications for two biosolids-derived organomineral fertilizers (OMF) known as OMF10 (10:4:4) and OMF15 (15:4:4) were established. Such specifications will enable field application of OMF with spinning disc systems using conventional tramlines spacing. A theoretical model was developed, which predicts the trajectory of individual fertilizer particles off-the-disc. The drag coefficient (Cd) was estimated for small time steps (10-6 s) in the trajectory of the particle as a function of the Reynolds number. For the range of initial velocities (20 to 40 m s-1), release angles (0° to 10°) and particle densities (1000 to 2000 kg m-3) investigated, the analysis showed that OMF10 and OMF15 need to have particle diameters between 1.10 and 5.80 mm, and between 1.05 and 5.50 mm, respectively, to provide similar spreading performance to urea with particle size range of 1.00 to 5.25 mm in diameter. OMF10 and OMF15 should have 80% (by weight) of particles between 2.65 and 4.30 mm, and between 2.55 and 4.10 mm, respectively. Due to the physical properties of the material, disc designs and settings that enable working at a specified bout width by providing a small upward particle trajectory angle (e.g., 10°) are preferred to high rotational velocities. However, field application of OMF with spinning discs applicators may be restricted to tramlines spaced at a maximum of 24 m; particularly, when some degree of overlapping is required between two adjacent bouts. The performance of granular fertilizers can be predicted based on properties of the material, such as particle density and size range, using the contour plots developed in this study.