Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO / Includes bibliographical references. / by Saeed Farokhi. / Ph.D.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Council for Scientific and Industrial Research has developed a vibration excitation system. The system is designed to excite the rotor blades of an axial compressor in the specified vibration mode and at the specified frequency. The vibration excitation system was tested on Stellenbosch University’s Rofanco compressor test bench. A two-way staggered fluid-structure interaction (FSI) model was created that was capable of simulating the vibration of the rotor blades excited by the system. The results of the FSI model were verified using available experimental data. It was concluded that the FSI model is able to recreate the vibration excited by the system to within the desired level of accuracy. In addition, the results of the FSI model showed that the vibration excitation system should be able to excite the blades in the selected vibration mode and at the selected frequency provided that the excitation frequency is close the natural frequency of the first bending mode. The results also suggested that a transient computational fluid dynamics model should be sufficient for the prediction of the aerodynamic forces acting on the rotor blades. Furthermore, a one-way staggered FSI model should be adequate for calculating the motions of the blades. / AFRIKAANSE OPSOMMING: Die Wetenskaplike en Nywerheidnavorsingsraad het ’n vibrasie-opwekkingstelsel ontwerp om die rotorlemme van ’n aksiaalvloei kompressor in die gespesifiseerde vibrasiemodus en teen die gespesifiseerde frekwensie op te wek. Die vibrasieopwekkingstelsel is met behulp van die Universiteit Stellenbosch se Rofanco kompressortoetsbank getoets. Daarna is ’n tweerigting vloeistof-struktuur-interaksie model geskep om die vibrasie van die rotorlemme, wat deur die stelsel opgewek is, te simuleer. Beskikbare eksperimentele data is gebruik om die resultate van die vloeistof-struktuur-interaksie model te bevestig. Die gevolgtrekking is gemaak dat die model wél die vibrasie van die lemme met die nodige akkuraatheid kan simuleer. Die resultate van die vloeistof-struktuur-interaksie model toon ook dat die stelsel die lemme in die gekose vibrasiemodus en teen die gekose frekwensie behoort te kan opwek, solank die opwekkingsfrekwensie na aan die natuurlike frekwensie van die eerste buigmodus is. Voorts dui die resultate daarop dat ’n berekeningsvloeimeganika model die aërodinamiese laste van die lemme sal kan voorspel. ’n Eenrigting vloeistof-struktuur-interaksie model behoort voldoende te wees om die beweging van die rotorlemme te bereken.

Methods of determining natural frequencies of the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs for various environmental conditions were investigated by application of Finite Element Analysis and beam theory. Modelling and simulation methods were developed ; the first method composed of 15 finite element simulations ; the second composed of 15 finite element simulations and a set of experimental frequency survey results; the third composed of 5 simulations , an incorporated mathematical model and a set of experimental frequency survey results. Each of these methods was designed to allow prediction of resonant frequency changes across a range of exhaust gas temperature and shaft rotational speed. For the new modelling and simulation methods, an analysis template and a plotting tool were developed using Microsoft Excel and MATLAB software. A graph showing a frequency-temperature-speed variations and a Campbell Diagram that incorporates material stiffening and softening effects across a range of rotational speeds was designed, and applied to the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs. New design methodologies for turbine wheels were formulated and validated, showing a good agreement with a range of data points from frequency survey, strain-gauge telemetry and laser tip-timing test results. The results from the new design method were compared with existing single compensation factor methodology, and showed a great improvement in accuracy of prediction of modal vibration. A new nomenclature for the mode shapes of a turbocharger’s blade was proposed, designed and demonstrated to allow direct identification of associated mode shape. It is concluded that Finite Element Analysis combined with the frequency survey is capable of predicting changes in turbine natural frequencies and, when incorporated into the existing turbine design methodology, resulted in a major improvement in the accuracy of the predictions of vibration frequency.

Methods of determining natural frequencies of the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs for various environmental conditions were investigated by application of Finite Element Analysis and beam theory. Modelling and simulation methods were developed ; the first method composed of 15 finite element simulations ; the second composed of 15 finite element simulations and a set of experimental frequency survey results; the third composed of 5 simulations , an incorporated mathematical model and a set of experimental frequency survey results. Each of these methods was designed to allow prediction of resonant frequency changes across a range of exhaust gas temperature and shaft rotational speed. For the new modelling and simulation methods, an analysis template and a plotting tool were developed using Microsoft Excel and MATLAB software. A graph showing a frequency-temperature-speed variations and a Campbell Diagram that incorporates material stiffening and softening effects across a range of rotational speeds was designed, and applied to the D76D88, B76D88, A86E93, C86G90, C86L90 and C125L89 turbine wheel designs. New design methodologies for turbine wheels were formulated and validated, showing a good agreement with a range of data points from frequency survey, strain-gauge telemetry and laser tip-timing test results. The results from the new design method were compared with existing single compensation factor methodology, and showed a great improvement in accuracy of prediction of modal vibration. A new nomenclature for the mode shapes of a turbocharger’s blade was proposed, designed and demonstrated to allow direct identification of associated mode shape. It is concluded that Finite Element Analysis combined with the frequency survey is capable of predicting changes in turbine natural frequencies and, when incorporated into the existing turbine design methodology, resulted in a major improvement in the accuracy of the predictions of vibration frequency. / Additional data files have been restricted by request.