This thesis introduces the application of computer-aided engineering techniques to the dynamic analysis of reciprocating compressor designs. The analysis process is detailed in three steps. The first step, an interactive pre-processor, develops the shaking forces and torques acting on the machine. The second step is a batch processed program that performs a dynamic simulation of the compressor in operation. The compressor and mounting are simulated as a rigid body with six degrees-of-freedom (X, Y, and Z translations and roll, pitch, and yaw) mounted to the ground with up to 25 arbitrarily oriented springs and dampers. Additionally, an eigenanalysis is performed that returns the natural frequencies and modes for the machine. The final step is an interactive postprocessor where the user may examine the results of the eigenanalysis as well as the operating orbit of the machine. A series of programs that implement the analysis process was developed. The specialized formulations for the six coupled, non-linear equations of motion are presented. Color computer graphics and animation are used for visual output displays. The dynamic simulation program is designed to function on many computer systems, from low-cost personal computers to large mainframes, while the pre- and post-processing programs are designed for the personal computer. The programs were tested by comparing the predicted results with those of an Ingersoll-Rand model 242 two piston, two stage, 3 hp compressor. The correlation between the experimental and predicted results show that the programs can accurately simulate the dynamics of a reciprocating compressor operating at steady-state. Typically, the acceleration results agree for the six degrees-of-freedom in both the time and frequency domain to within 8%. / Master of Science

A three-color, three-component Laser Doppler Anemometer (LOA) capable of making simultaneous measurements of three components of velocity is described, and the use of this LOA to measure three non-orthogonal velocity components in the rotor blade passage of a single-stage axial-flow compressor is reported. Measurements were made at four radial locations from 50% span out to the blade tip, and at seven different axial locations from -0.55 axial chord 1.40 axial chord. Measurements were made at only one throttle setting. The measured velocities are used to determine the flow in the orthogonal axial - tangential - radial, x - t - r, coordinate system of the compressor. Although the mean velocities and entire Reynolds stress tensor are obtained with this system, only the mean velocities are reported. Results are presented in the form of a series of vector plots showing: 1.) the primary flow as projected on the x - t plane and 2.) the secondary flow in the t - r plane. The LOA measurements are shown to agree with pitot probe measurements in the stationary frame and basic secondary flow theory. A detailed error analysis is presented, taking into account both measurement uncertainties and statistical biasing. An analysis is also made of particle lag in the rotating flow of the compressor blade passage. A discussion of the difficulties encountered in making three dimensional velocity measurements in turbomachinery blade passages is presented. Suggestions are made for improving the present system for this task. / Master of Science

This thesis presents the results from measurements taken during the transient unstable operation of an axial-flow transonic core-compressor rotor. The measurements were taken to better understand the unstable flow physics of transonic rotors. The rotor, commonly referred to as Rotor 37, was designed by NASA Lewis to be the first stage of an advanced, eight-stage, core-compressor having a high pressure ratio (about 20:1), good efficiency and sufficient stall margin. The rotor was tested without the presence of a stator (or any of the following seven stages) at the NASA Lewis single-stage, high-speed, core-compressor test-rig. The measurements were obtained with a single circumferential, high-response, total pressure and total temperature probe. The measurements were taken immediately after the machine was ’tripped’ into unstable operation by slowly closing the downstream throttle valve. Measurements were obtained at several different span-wise locations and at two different operating speeds. The rotor was shown to exhibit many of the same characteristics typical of low-speed axial-flow machines. Both rotating stall cells and surge cycles were present during unstable operation. The surge cycles present immediately after the inception of unstable operation involved a large-extent single-cell type rotating stall that was present only during the first half of the surge cycles (the second half of these surge cycles involved operation in the stable operating region). However, as the unstable operation progressed (approximately three to five surge cycles later), surge cycles were present that contained a multiple-cell smaller-extent type rotating stall that existed throughout the entire surge cycle with no partial operation in the stable operating region. Thus, compressor system recovery from single-cell large-extent rotating stall (partial operation in stable operating range during the surge cycle) is more probable than recovery from multiple-cell small-extent rotating stall (no operation in stable operating range during the surge cycle). Rotor wheel speed was shown to be an important variable in influencing the form of unstable operation. Surge and rotating stall were shown to be coupled during the unstable operation. Furthermore, the surge/stall coupling was shown to be related more by pressure interactions than by temperature or efficiency interactions. Also, this high hub-tip ratio transonic rotor was shown to exhibit instantaneous stalling across the entire blade span (typical of low-speed, high hub-tip ratio machines). Attempts to fit the data to Greitzer’s one-dimensional lumped-parameter model are presented and the reasons for poor agreement are discussed. / Master of Science

The rigid-body rotational vibration of a resiliently mounted air compressor about an axis parallel to the axis of the rotor is investigated. An analysis of the motion of the compressor base is conducted using empirical acceleration data. The effect on roll vibration of changing various compressor design parameters is studied using a computer simulation program, PABEWE. This digital simulation incorporating slider-crank linkage analysis employs the strict equations of motion. Control theory is used to control the roll vibration. The control theory is applied to simplified equations of motion and incorporates various feedbacks. Recommendations are offered for the reduction of roll vibration levels. / Master of Science

The study involves the development of a finite element model of a hermetic reciprocating compressor for noise prediction applications. Inherent difficulties in developing the finite element model of a complicated structure are discussed and appropriate modeling strategies are evolved. The development of the complete compressor finite element model is carried out in two stages - modeling of the compressor housing and the assembly of components into the compressor assembly. The compressor housing is isolated for detailed modeling. Geometry complexity, secondary masses, spring mounts, lap-joint and manufacturing variations pose challenges in developing a reliable model. Frequent comparisons are made with experimental mobility scans to obtain insights into the actual behavior of the modeled structure. When possible, weaknesses are located in the finite element model and corrected. After sufficient revisions, 23 natural frequencies (excluding the rigid body modes) are found for the compressor housing in the low frequency range (below 2000 Hz) of analysis. Forced response calculations are also used to correlate the analytical model and test data, with a maximum of 5% disagreement for the 14 natural frequencies that could be correlated. Compressor assembly modeling involves detailed solid modeling of internal components for inertia properties, developing reduced-degrees-of-freedom models of mounting springs and modeling of the shockloop. The dynamic behavior of the crankcase is investigated separate from the compressor assembly model. Finally, the components are assembled and the compressor assembly is solved for its natural frequencies by the component mode synthesis method. Eighty seven natural frequencies below 2000 Hz (excluding the rigid body modes) are found for the compressor assembly model. This model can be used to predict velocity responses on the surface of the housing, with the internally generated forces as excitations. Velocity response data are directly used in sound prediction. / Master of Science

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Turbomachinery plays an important role in the efficiency of power generation and combustion processes used in the automotive and aerospace industries. The potential for fulfilling future energy needs has been identified in both civilian and military applications, for example micro gas turbines (MGTs) used in unmanned aireial vehicles (UAVs). The goal of this thesis was to build a performance testing facility for small-scale centrifugal compressors, for use in MGTs. The objectives of this study were mainly achieved through experimental work. In addition to the experimental work, numerical simulations using computational fluid dynamics (CFD) software were performed to substantiate the experimental results. The project methodology followed the process whereby a compressor performance map is constructed from experimental data and compared to map obtained from theoretical data. The test facility consists of a turbocharger fitted with an experimental compressor section. The turbocharger turbine is driven by unheated compressed air. Sensors, data acquisition and ancillary equipment required to perform performance test measurements, were obtained and installed on the test facility. Performance curves at three different rotational speeds were successfully obtained for the experimental compressor. When compared to the CFD results there was good qualitative agreement, although deviations in the results increased with rotational speed. In addition a second impeller design was tested which correlated well with the theoretical data. / AFRIKAANSE OPSOMMING: Turbomasjinerie speel 'n belangrike rol in die doeltre endheid van kragop- wekking en verbrandingsprosesse wat in die motor- en lugvaartbedryf gebruik word. Die potensiaal om in toekomstige energiebehoeftes te voorsien is in beide burgerlike en militêre toepassings uitgewys, byvoorbeeld mikrogastur- bines (MGT's) wat in onbemande vliegtuie (OLV's) gebruik word. Die doel met hierdie tesis was om 'n prestasietoetsfasiliteit vir kleinskaalse sentrifu- gale kompressors te bou wat in MGT's gebruik kan word. Die doelstellings van hierdie studie is hoofsaaklik deur eksperimentele werk behaal. Daarbe- newens is numeriese simulasies met gebruikmaking van sagteware vir bereke- ningsvloeidinamika (BVD) gedoen om die eksperimentele resultate te staaf. Die projekmetodologie volg die proses om 'n kompressorprestasiekaart uit eks- perimentele data op te stel en dit te vergelyk met 'n kaart wat uit teoretiese data bekom is. Die toetsfasiliteit bestaan uit 'n turboaanjaer wat met 'n eksperimentele kompressordeel toegerus is. Die turboaanjaer se turbine word deur onverhitte druklug aangedryf. Sensors, dataverwerwing en bykomstige toerusting, wat benodig is om prestasietoetsmetings mee te doen, is bekom en op die toetsfasiliteit geïnstalleer. Prestasiekrommes is vervolgens by drie verskillende omwentelingsnelhede suksesvol met die eksperimentele kompres- sor bekom. In vergelyking met die BVD-resultate was daar goeie kwalitatiewe ooreenstemming, ofskoon afwykings in die resultate vergroot het namate die omwentelingspoed toegeneem het. Daarby is 'n tweede stuwerontwerp getoets wat goed met die teoretiese resultate korreleer.

This thesis constitutes detailed computational investigation on ow through the passages of a centrifugal compressor used for turbocharging applications. Given the dynamic nature of operation of the turbocharger, it becomes necessary to under- stand the ow that occurs within the blade passages and its e ect on performance. CFD is an established computational technique wherein the ow is dissected to fun- damental levels and a detailed picture is presented, application of this technique with limited and diverse sense towards understanding of ows through a turbocharger compressor has been successfully carried out by many before. This work presented attempts to address many of the lacuna reported and carries forward the work of several researchers to ll in the gaps. The complexity of the geometry of the blade shape poses many challenges in model- ing within the virtual space, an e ective way to overcome the obstacles is presented as a part of this work. Grid generation of the impeller and casing are discussed and adaptive approach is followed with generation of hexahedral grids for the impeller whereas tetrahedral for the casing. Since the grids of the impeller and its casing are di erent, ways of interfacing between the two domains in a CFD environment is discussed. An industry standard implicit 3D RANS solver was used to carry out the simula- tions. The importance of use of boundary conditions for the domain at unsteady operating points is presented in detail. On the choice made for turbulence model that governs the validity of the solution obtained, an extensive literature survey of the relevant topic as applicable for centrifugal compressors is presented and logic of the choice made for the present work is discussed. Menter's two equation SST-k! model emerges as the clear choice to be used even though the di erence in perfor- mance predictions by other turbulence models are insigni cant. Dynamics of ow at optimum design point, surge and choke of the compressor are presented in detail. With the geometry modeled with a tip clearance and the casing included within the simulation environment, it can be seen that the performance predicted is closer to actual at all operating points. A study of behavior of the compressor at extreme o design points is carried out and it can be seen that it depicts the trends that are seen in experimental works available in open literature. The distortion of pressure within the vaneless di user and the inviscid nature of the ow within the volute space are e ectively captured and an in depth analysis is carried out to uncover new patterns. A parametric study involving important geometric features such as the tip clearance and wrap angles are conducted leading to discovery of anomalies. The work summarizes to point out that the investigation carried out with the CFD simulations comprehensively leads to uncovering of ow dynamics within a complex system such as the centrifugal compressor within the limits of numerical analysis.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Stellenbosch University participated in a project to re-design the compressor section of a diesel locomotive turbocharger. Tests conducted on the prototype compressor showed possible rotating stall in the diffuser section before the designed higher pressure ratio could be achieved. When approaching the higher pressure ratio, the compressor inlet trunk started to rhythmically collapse (due to suction), the engine shook and bellows of black smoke were exhausted by the engine. It was decided to simulate the prototype compressor's operation by using the 1-D theory of Aungier (2000) and to perform a 3-D CFD analysis of the compressor using FINE/Turbo of NUMECA International. A veri cation process was followed to show the accuracy of the 1-D and 3-D modelling methods using two well-known centrifugal compressor test cases found in the literature, namely the O-Rotor by Eckardt (1975, 1976, 1980) and the "Radiver" open CFD test case by Ziegler et al. (2003c). Results from the models were compared to available experimental results and the accuracy was found to be su cient to investigate the prototype compressor's impeller and diffuser. Both prediction methods con rmed separation in the vaned di user across the entire operating ow range of the prototype compressor at the design impeller speed. The 3-D method identi ed supersonic ow at the vaned diffuser inlet at the operating point and also predicted a smaller operating range than originally anticipated. Both the 1-D and 3-D methods also predicted impeller blade stall over the entire operating ow range at the design impeller speed. A recommendation was made to redesign the impeller and diffuser of the prototype compressor. / AFRIKAANSE OPSOMMING: Die Universiteit van Stellenbosch het deel geneem aan 'n projek om die kompressor gedeelte van 'n diesel lokomotief se turbo-aanjaer te herontwerp. Toetse uitgevoer op die prototipe kompressor het moontlike roterende wegbreking in die diffuser seksie uitgewys voordat die ontwerpte hoër drukverhouding bereik kon word. Toe die hoër drukverhouding genader is, het die kompressor inlaatpyp begin ritmies inmekaar vou (as gevolg van die suig aksie), die enjin het geskud en wolke swart rook is deur die enjin uitgeblaas. Die besluit is geneem om die prototipe kompressor se werking te simuleer met behulp van die 1-D teorie van Aungier (2000) en om ook 'n 3-D berekenings vloeimeganika (BVM) analise op die kompressor uit te voer met behulp van FINE/Turbo van NUMECA Internasionaal. 'n Veri kasieproses is gevolg om die akkuraatheid van die 1-D en 3-D modelle te illustreer met behulp van twee welbekende sentrifugaal kompressor toetsgevalle beskikbaar in die literatuur, naamlik die O-Rotor deur Eckardt (1975, 1976, 1980) en die "Radiver" oop BVM toetsgeval deur Ziegler et al. (2003c). Resultate van die modelle is vergelyk met beskikbare eksperimentele resultate en die bevinding is gemaak dat die akkuraatheid genoegsaam is om die prototipe kompressor se rotor en diffuser te ondersoek. Beide voorspellingsmetodes het wegbreking bevestig in die gelemde diffuser oor die hele werksbestek van die prototipe kompressor teen die ontwerp rotorspoed. Die 3-D metode het supersoniese vloei by die gelemde diffuser se inlaat by die bedryfspunt geïdenti seer en het ook 'n kleiner werksbestek voorspel as wat vroeër verwag is. Beide die 1-D en 3-D metodes het ook wegbreking in die rotor oor die hele werksbestek teen die ontwerp rotorspoed voorspel. 'n Voorstel is gemaak om die rotor en diffuser van die prototipe kompressor te herontwerp.

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.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This dissertation is basically a summary, with some interpretation, of published research by the author. The scope is limited to the fields of turbo-machinery, computational fluid dynamics and solar chimney power plants. The main contribution in the field of turbo-machinery in general is in the development of a through-flow method that automatically satisfies mass conservation. Concerning fan design, the contributions are the realization of the importance of the exit kinetic energy in the determination of the efficiency of rotor-only axial flow fans, and the quantification of the effect of off-axis inflow into cooling system fans on their performance. In the field of centrifugal fans and compressors an original, unifying model for the prediction of slip factor was developed. To investigate accident scenarios in closed cycle gas turbine nuclear reactors, all possible operational modes of multi-stage axial compressor operation caused by flow and rotation direction were investigated experimentally and computationally. Spanning the fields of turbo-machinery and solar chimneys, the basic theory of solar chimney turbines was developed, showing that high turbine efficiency was possible. In the field of solar chimneys, an original thermodynamic approach was developed to predict the main relationships that govern solar chimney performance, and to solve the through-flow equations for non-ideal systems with losses. Equations for the accurate determination of all the thermodynamic variables in a solar chimney as dependent on chimney height, wall friction, additional losses, internal drag and area change were derived and solved. Coefficients of wall friction, bracing wheel loss and exit kinetic energy were determined experimentally, and empirical equations were developed to predict the loss coefficient of the collector to turbine transition section and and the turbine inlet flow angle. A simple power law approach allowed the calculation of the optimal turbine pressure drop in solar chimney power plants. A comparison of two sets of equations used to calculate the heat fluxes into, inside and leaving the solar collector, resulted in similar air temperature rises in the collector, and similar produced power. It turned out however that the optimal flow for minimal turbine pressure drop was dependent on the heat transfer models. Investigation of the performance of various solar chimney turbo-generator layouts using analytical models and optimisation techniques showed that the optimal number of turbines varies with plant size, but the individual turbine size, the number of blades and even the efficiency remains close to constant. It was found that the cost of a turbogenerator system, however, varies significantly with size. A joint paper with several German universities and institutions did a comparative cost analysis of solar chimney power plants / AFRIKAANSE OPSOMMING: Hierdie verhandeling is basies ’n opsomming, met interpretasie, van gepubliseerde navorsing deur die outeur. Die omvang is beperk tot die gebiede van turbomasjinerie, berekeningsvloeidinamika en sonskoorsteenkragstasies. Die hoof bydrae op die gebied van turbomasjinerie in die algemeen is in die ontwikkeling van ’n deurvloeimetode wat outomaties massabehoud bevredig. Wat waaierontwerp betref is die bydrae die besef van die belangrikheid van die uitlaat kinetiese energie in die bepaling van waaierbenuttingsgraad, en die kwantifisering van die effek van af-as invloei in verkoelingswaaiers op hulle gedrag. Op die gebied van sentrifugaalwaaiers en -kompressors is ’n oorspronklike, samevattende model vir die voorspelling van glipfaktor ontwikkel. Om ongeluk-scenario’s in geslote kringloop gasturbine kenreaktors te ondersoek is al die moontlike werksmodusse veroorsaak deur vloei en rotasie rigting van ’n multistadium aksiaalkompressor eksperimenteel en numeries ondersoek. As brug tussen turbomasjinerie en sonskoorstene is die basiese teorie van sonskoorsteenturbines ontwikkel met die aanduiding dat hoë turbine benuttingsgraad moontlik is. Op die gebied van sonskoorstene is ’n oorspronklike termodinamies benadering ontwikkel om die hoofverwantskappe te voorspel wat sonskoorsteen gedrag bepaal, en om die deurvloei vergelykings op te los vir nie-ideale stelsels met verliese. Vergelykings vir die akkurate bepaling van al die termodinamiese veranderlikes in ’n sonskoorsteen soos afhanklik van skoorsteenhoogte, wandwrywing, bykomstige verliese, interne sleur en oppervlakte verandering is afgelei en opgelos. Koëffisiënte vir wandwrywing, verstywingswiel-verlies en uitlaat kinetiese energie is eksperimenteel bepaal, en empiriese vergelykings is ontwikkel om die verlieskoëffisiënt van die kollektor-tot-skoorsteen oorgang en die turbine inlaatvloeihoek te bepaal. ’n Eenvoudige magswet benadering het dit mootlik gemaak om die optimum turbine-drukval in sonskoorsteen aanlegte te bepaal. ’n Verglyking van twee stelle vergelykings om warmtevloede in, binne en uit die sonkollektor te bereken het gelei na soortgelyke temperatuurstygings en gelewerde drywing. Die optimale vloei vir maksimum drywing was egter afhanklik van die warmteoordrag modelle. Ondersoek van die gedrag van verskeie turbo-generator uitlegte, deur gebruik van analitiese modelle en optimeringstegnieke het getoon dat die optimale aantal turbines wissel met aanleg grootte, maar die individuele turbine grootte, die aantal lemme en selfs die benuttingsgraad bly feitlik konstant. Daar is egter gevind dat die koste van ’n turbogenerator stelsel beduidend wissel met grootte. ’n Gesamentlike artikel met verskeie Duitse universiteite en instansies het ’n vergelykende koste analise van sonskoorstene gedoen.