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Abstract

The beneficial application of vortex generators to control boundary layers in the sub- and supersonic flow regime has been shown in the past. In this thesis the use of vortex generators is extended beyond boundary layer control by using them within an ejector-diffuser type augmentor. During the course of the research work it was established that the vortex generators could be used as effective 'mixers' between the primary air stream and the secondary entrained air stream.

A previously developed mathematical model of ejector-diffuser flow, incorporating parameters such as pressure ratio, nozzle to duct area ratio and diffuser area ratio, was extended and refined. With the help of that model the above mentioned parameters were defined and according to these parameters a test rig was designed and manufactured. The primary ejector was driven by either a peripheral slit jet or eight individual air jets or the combination of both. The major task of the project was to design a rig which was short but produced a good thrust augmentation based on the bare nozzle thrust. A good thrust augmentation ratio was obtainable by ensuring rapid mixing between the primary and secondary air streams.

The test programme was split into two major parts, namely the use of vane vortex generators in conjunction with the peripheral jet and then the application of air jet vortex generators again with the peripheral jet. The vanes and also the air jets were configured either as eight co-rotating vortices or as four contra-rotating vortex pairs. A special case which was also considered involved the air jet vortex generators on their own without peripheral blowing. This test was possible because the eight air jets could be used as primary air injectors and vortex generators at the same time. It emerged that this configuration was particularly revealing because it highlighted the essential difference between co- and contra-rotating vortices. Near the design primary pressure ratio of 5.0 the bare nozzle thrust was augmented by a maximum of 30 per cent with the vanes installed. This was a considerable advance on the augmentation for the bare augmentor, i.e. the same configuration as above but without vortex generators installed, which came to 1.15 at the same pressure ratio of 5.0. The results of augmentation for the air jets were more complex due to the way in which the air was injected. Elevation and skew angle were responsible for the enlarged complexity. As a general trend it can be stated that the augmentation ratios were high for low pressure ratios, as high as 1.7 at a pressure ratio of 2.0, but fell off as the pressure was increased. Dynamic pressure contour plots in the exit plane gave good indications of the vortex movements produced by the co- and contra-rotating vortex generators.

This project showed that considerable thrust augmentations could be achieved by using vortex generators.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering > Mechanical Engineering & Aeronautics School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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