Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Turbomachines are exposed to several environmental factors which may
cause failure of components. One of these factors, high cycle fatigue, is often
caused by blade utter. This thesis forms part of a project of the European
Seventh Framework Programme (FP7), called project Future. Project Future
is doing theoretical and experimental investigation into the occurrence
of utter in turbomachinery. The objective of this thesis was to evaluate the
effectiveness of a gas injection system as a means of exciting vibrations on the
rst stage rotor blades of a compressor. Unsteady simulations of the excitation
velocity perturbations were performed in the Computational Fluid Dynamics
(CFD) software, Numeca FINE/Turbo. Experimental testing on the in-house
Rofanco compressor test bench, using one prototype of the 15 injector system,
provided data that was used to implement boundary conditions and to verify
certain aspects of the unsteady simulation results. The simulation results revealed
the following: the injector bypass frequency was so dominant that the
excitation frequency was hardly detectable in the majority of cases. Furthermore,
several secondary frequencies were consistently present. The injector
bypass frequency, as well as the secondary frequencies, occurred as a result
of the convolution of Fast Fourier Transforms. While the injector bypass frequencies
can theoretically be eliminated, it will not be possible to eliminate
the secondary frequencies from the blade response. In conclusion, according to
the CFD results, it will not be possible to excite a single excitation frequency
by making use of a nite number of gas injector vibration exciters. / AFRIKAANSE OPSOMMING: Turbomasjiene word onderwerp aan verskeie omgewingsfaktore wat falings
van komponente kan veroorsaak. Een van hierdie faktore, naamlik hoëfrekwensie vermoeidheid, word onder andere veroorsaak deur lem adder. Hierdie
tesis is deel van 'n projek in die Sewende Europese Raamwerk Program
(European Seventh Framework Programme - FP7), projek Future. Projek
Future doen teoretiese en eksperimentele ondersoek na die voorkoms van lemfl adder in turbomasjienerie. Die doelwit van hierdie tesis was om die effektiwiteit
van 'n gasinspuiter vibrasie-opwekkingstelsel te evalueer, deur gebruik te
maak van onbestendige simulasie in die berekenings vloei-meganika sagtewarepakket,
Numeca FINE/Turbo. Eksperimentele toetswerk op die plaaslike
Rofanco kompressortoetsbank, met 'n prototipe van die 15 inspuiter stelsel,
het inligting verskaf wat gebruik is om die inlaattoestande te spesi seer en
simulasieresultate te korreleer. Die simulasieresultate het getoon dat die frekwensie
waarteen 'n lem by die inspuiters verbybeweeg, so prominent is, dat
dit in die meerderheid van gevalle baie meer prominent is as die opwekkingsfrekwensie.
Verder was daar ook deurgaans 'n aantal sekondêre frekwensies
teenwoordig. Die teenwoordigheid van die inspuiter verbybeweeg frekwensie
en die sekondêre frekwensies is die resultaat van die konvolusie van Vinnige
Fourier Transforme. Alhoewel dit in teorie moontlik sal wees om die inspuiter
verbybeweeg frekwensie te elimineer, is dit onmoontlik om die sekondêre
frekwensies uit die lem vibrasie te elimineer. Ter opsomming, volgens die berekenings
vloei-meganika resultate, is dit nie moontlik om met 'n stelsel van
'n eindige aantal inspuiters, 'n enkele vibrasie frekwensie op te wek nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17987 |
| Date | 12 1900 |
| Creators | Raubenheimer, Gert |
| Contributors | Van der Spuy, S. J., Von Backstrom, T. W., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 151 p. : ill. |
| Rights | Stellenbosch University |
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