Steady state, inter row measurements in multistage axial compressors are relevant to the current design process. The objective in obtaining such data is for evaluation of compressor blading as well as validation for the computer programmes used in compressor design. Multi-hole pressure probes are a reliable and economical method of collecting detailed flowfield data in compressors for these purposes. These probes are calibrated in a uniform flow in a wind tunnel prior to use, to determine their response to a range of flow angles and speeds. When the probe is subsequently used for measurements in the compressor, often the small inter row spacing means that the probe has to be close to the downstream stator passage and upstream rotor. The result is that the probe is no longer situated in the uniform flow in which it was calibrated, in terms of influences from both the upstream rotor and downstream stator. This project presents the investigation of these two effects on steady state pressure probe measurements. The effects of blockage on a probe positioned in front of a stator row in a high speed compressor were studied using CFD. This was also carried out on a large scale probe in a low speed compressor. It was found that the blockage effect caused a reduced mass flow in the downstream stator passage which in turn lead to an altered flow angle and a small reduction in measured total pressure. Experimental in rig calibrations showed that the change in flow angle was due to an angular offset of the pressure distribution about the probe. These calibrations also showed that the wind tunnel calibration was valid in the compressor within a small angular range. The influence of the upstream rotor passing was studied using an unsteady CFD model. Responses of the individual probe ports and the deduced flow angle and total pressure indicated that the steady state blockage effect is present throughout the wake passing. The wake passing was found to be a largely two dimensional effect in that the radial flow component changes in the low speed compressor wakes had little influence. The Total Technology thesis incorporates a management project on the relevant topic of project selection within companies. An existing project selection model was applied to a sample group of projects to determine the applicability of such models. The main findings were that these models can generate useful information for further selection decisions and that the applicability is towards lower budget projects where a structured approach is often not used.

During hot days, gas turbine power output deteriorates significantly. Among various means to augment gas turbine output, inlet air fog cooling is considered as the simplest and most costeffective method. During fog cooling, water is atomized to micro-scaled droplets and introduced into the inlet airflow. In addition to cooling the inlet air, overspray can further enhance output power by intercooling the compressor. However, there are concerns that the water droplets might damage the compressor blades and increased mass might cause potential compressor operation instability due to reduced safety margin. Furthermore, the two-phase flow thermodynamics during wet compression in a rotating system has not been fully established, so continued research and development in wet compression theory and prediction model are required. The objective of this research is to improve existing wet compression theory and associated models to accurately predict the compressor and the entire gas turbine system performance for the application of gas turbine inlet fog cooling. The following achievements have been accomplished: (a) At the system level, a global gas turbine inlet fog cooling theory and algorithm have been developed and a system performance code, FogGT, has been written according to the developed theory. (b) At the component level, a stage-stacking wet compression theory in the compressor has been developed with known airfoil configurations. (c) Both equilibrium and non-equilibrium water droplet thermal-fluid dynamic models have been developed including droplet drag forces, evaporation rate, breakup and coalescence. A liquid erosion model has also been developed and incorporated. (d) Model for using computational fluid dynamics (CFD) code has been developed to simulate multiphase wet compression in the rotating compressor stage. In addition, with the continued increase in volatility of natural gas prices as well as concerns regarding national energy security, this research has also investigated employing inlet fogging to gas turbine system fired with alternative fuels such as low calorific value synthetic gases. The key results include discovering that the saturated fogging can reduce compressor power consumption, but overspray, against conventional intuition, actually increases compressor power. Nevertheless, inlet fogging does increase overall net power output.

An axial compressor for a domestic appliance can be designed to be smaller than an equivalent centrifugal compressor. However, the performance of such a compact axial compression system is limited by increased viscous losses and reduced flow turning at low Reynolds numbers ($Re$). In domestic appliance compressors, $Re$ is typically in the range $10^4$ - $10^5$. Although the aerodynamics of isolated aerofoils operating at these $Re$ have been studied extensively, the flow fields within low $Re$ axial compressors have not been investigated in detail. This dissertation aims to develop an improved understanding of loss variation at low $Re$ and to explore how the losses can be reduced through design changes. Experiments on a 5 times scaled-up single stage axial compressor have been conducted across a range of $Re$ of $10^4$ - $10^5$. The flow field has been characterised using detailed area traverses with a miniaturised five-hole probe at the rotor inlet, rotor exit and stator exit and a miniature hot-wire at the rotor exit. The probe was specifically designed and calibrated for the scale of the experiments and methods to improve the accuracy of the measurements have been applied including a probe geometry correction. The traverse experiments were performed at the design operating condition ($\phi=0.55$ and $Re= 6\times10^4$) and at a condition close to stall for a datum stage design, a stage with an improved stator design and two stators with compound lean. It was found that losses in the rotor were greater than the stator losses across the whole range of $Re$. As expected, the loss decreased with increasing $Re$ for both the stator and rotor. The losses were also increased by three-dimensional flow, with typical loss coefficients at the hub and tip of the blade rows in the range of $20-30\%$. A major contributor to the rotor loss was an unexpected hub separation that increased in size as $Re$ was reduced. At higher $Re$, the major loss sources were the rotor tip leakage, the stator wake and the stator hub separation. The results indicate that an improved stator design that accounts for the actual, measured, rotor exit flow field at low $Re$ could reduce the $Re$ at which blade row losses start to rise dramatically as well as reduce the loss across all $Re$. The improved stator design was better matched to the radial distribution of rotor exit flow angle, which led to a decrease in stator loss across all $Re$. For all stator designs, however, the measured stage stall margin was identical at all $Re$. This, along with the increase in velocity deficit in the rotor tip region at off-design indicates that stall occurred in the rotor and was neither $Re$ nor stator design dependent. The introduction of compound lean to the the stator design had the expected result of decreasing the endwall corner separation loss and increasing midspan losses. The experiments have shown that there was a loss increase in both the midspan and casing region much greater than the corresponding decrease in the stator hub. Also the mass flow redistribution in the experiments was larger that the redistribution predicted by the CFD. Three-dimensional RANS computations at low $Re$ of the same designs as experimentally studied were also conducted in order to investigate the predictive accuracy of industry standard CFD. The simulation results predicted the overall loss distribution but overestimated the end-wall losses and failed to capture the drop in stage performance at low $Re$. The differences with the experiments were caused by the inherent limitations of a fully turbulent solver that cannot reproduce transitional flow-features. Similarly to the experiments, there was no stall margin dependency on $Re$ in the simulations. This thesis has shown that with axial compressors designed specifically for low $Re$, the $Re$ at which the losses start increasing exponentially can be shifted from $10\times10^4$ to $ 4\times10^4$. The loss increase is predominantly caused by the rotor hub corner separation.

In todays highly maneuverable jet aircraft designs, aircraft are required to have a propulsion system that can operate during sudden accelerations and rapid changes in angle-of-attack. Consequently, the compressor of the jet engine occasionally must operate at low-flow rates and rapid changes in inlet conditions. The high angle-of-attack and low-flow regime of compressor operation is often plagued by rotating stall and surge. Rotating stall and surge can result in loss of engine performance, rapid heating of the blades, and severe mechanical stresses. Traditional methods for suppressing rotating stall and surge only partially protect against rotating stall or reduce compressor efficiency. The objective of this research is to design a stall suppression system that will introduce oscillatory blowing into one of the rotor blade (stall suppression blade). This oscillatory blowing method has been tested on a wing section in a wind tunnel and has shown to increase the stall angle-of-attack by several degrees.\cite{gilarranzetal02} This increase in stall angle-of-attack will eliminate stall cells as they form in the compressor. The goal of this research is to design a single stage axial compressor that will incorporate the new oscillatory blowing stall suppression system; moreover, this research will design, build, and test a scaled down version of this suppression system.

Axial compressors are widely used in many aerodynamic applications. The design of an axial compressor configuration presents many challenges. Until recently, compressor design was done using 2-D viscous flow analyses that solve the flow field around cascades or in meridional planes or 3-D inviscid analyses. With the advent of modern computational methods it is now possible to analyze the 3-D viscous flow and accurately predict the performance of 3-D multistage compressors. It is necessary to retool the design methodologies to take advantage of the improved accuracy and physical fidelity of these advanced methods. In this study, a first-principles based multi-objective technique for designing single stage compressors is described. The study accounts for stage aerodynamic characteristics, rotor-stator interactions and blade elastic deformations. A parametric representation of compressor blades that include leading and trailing edge camber line angles, thickness and camber distributions was used in this study A design of experiment approach is used to reduce the large combinations of design variables into a smaller subset. A response surface method is used to approximately map the output variables as a function of design variables. An optimized configuration is determined as the extremum of all extrema. This method has been applied to a rotor-stator stage similar to NASA Stage 35. The study has two parts: a preliminary study where a limited number of design variables were used to give an understanding of the important design variables for subsequent use, and a comprehensive application of the methodology where a larger, more complete set of design variables are used. The extended methodology also attempts to minimize the acoustic fluctuations at the rotor-stator interface by considering a rotor-wake influence coefficient (RWIC). Results presented include performance map calculations at design and off-design speed along with a detailed visualization of the flow field at design and off-design conditions. The present methodology provides a way to systematically screening through the plethora of design variables. By selecting the most influential design parameters and by optimizing the blade leading edge and trailing edge mean camber line angles, phenomenon s such as tip blockages, blade-to-blade shock structures and other loss mechanisms can be weakened or alleviated. It is found that these changes to the configuration can have a beneficial effect on total pressure ratio and stage adiabatic efficiency, thereby improving the performance of the axial compression system. Aeroacoustic benefits were found by minimizing the noise generating mechanisms associated with rotor wake-stator interactions. The new method presented is reliable, low time cost, and easily applicable to industry daily design optimization of turbomachinery blades.

The stable operating range of axial compressors is limited by the onset of rotating stall and surge. Mass injection upstream of the tip of an axial compressor rotor is a stability enhancement approach which can be effective in suppressing stall in tip-critical rotors, and thus increasing the operating range of compressors. In this article, investigations on active flow control related to the rotor tip gap sensitivity are discussed. The experiments were performed in a 1.5-stage low-speed research compressor. Measurements at part speed (80 per cent) and full speed (100 per cent) with varying injection rates are discussed. These tests were performed for two rotor tip clearances of 1.3 per cent and 4.3 per cent of rotor blade tip chord. Results on the compressor map, the flow field as well as transient measurements to identify the stall inception are discussed. Supplementary, the numerical results are compared to the experiments based on the configuration with the greatest benefit in operating range enhancement.

No description available.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this investigation is to determine the performance of an axial ow compressor operating in a closed loop helium cycle under high through- ow conditions. The GTHTR300 four-stage helium test compressor was chosen for this investigation. Limited information on the helium test compressor's blade pro les are available, therefore a mathematical model was developed to calculate the blade geometries based on the theory of Lieblein and Aungier. A locally available three-stage compressor was used to con rm whether the mathematical model calculated the blade pro le geometries correctly. The Stellenbosch University Compressor Code (SUCC), an axisymmetric inviscid through- ow code, was used to compare the performance of the calculated three-stage compressor blade geometries with available experimental data. Excellent correlation was obtained, thus it was concluded that the mathematical model as well as the SUCC could be used to predict the performance of an axial ow compressor. The blade geometries of the helium test compressor were calculated and the pressure ratio and e ciency predictions of the SUCC correlated well with the experimental data. The helium test compressor was simulated to verify the calculated blade geometries further using the Computational Fluid Dynamics (CFD) package NUMECA FINE /Turbo. The FINE /Turbo pressure ratio and e ciency predictions compared adequately with the SUCC and available experimental data, especially in the design region. At high mass ow rates the stator blade row experiences negative incidence stall which results in a large recirculation zone in the stator blade wake. / AFRIKAANSE OPSOMMING: Die doel van hierdie ondersoek is om vas te stel wat die werkverrigting is van 'n aksiale kompressor in 'n geslote lus helium siklus onderhewig aan hoë deurvloei kondisies. Die GTHTR300 vier-stadium helium toets kompressor is gekies vir die ondersoek. Daar is egter beperkte inligting oor die helium kompressor se lem geometrie, dus is 'n wiskundige model ontwikkel om dit te bereken gebaseer op die werk van Lieblein en Aungier. Om te bevestig dat die lem geometrie akkuraat was, was die lem geometrie van die 'n plaaslike beskikbare drie-stadium kompressor bereken. Die Stellenbosch University Compressor Code (SUCC), 'n aksisimmetriese nie-viskeuse deurvloei kode, is gebruik om die prestasie van die berekende lem geometrie met beskikbare eksperimentele data te vergelyk. Uitstekende korrelasie is verkry vir die drukverhouding en benuttingsgraad resultate, dus is die gevolgtrekking gemaak dat die wiskundige model sowel as die SUCC gebruik kon word om die lem geometrie en werkverrigting van aksiale kompressors te bereken en voorspel. Die helium toets kompressor is gesimuleer met behulp van die numeriese vloei-dinamika pakket NUMECA FINE /Turbo om die berkende lem geometrie verder te veri eer. Die FINE /Turbo drukverhouding en benuttingsgraad resultate het goed gekorreleer met beide die SUCC resultate en eksperimentele data, veral in die ontwerpsgebied. Teen hoë massa vloei tempo's vind daar groot wegbreking teen negatiewe invalshoek plaas in die stator lemry en dit veroorsaak 'n hersirkulasie sone in die naloop van die stator lem.

La réduction de l’impact environnemental est aujourd’hui l’un des défis cruciaux de l’industrie aéronautique. La poursuite d’une moindre consommation des aéronefs a conduit à concevoir des systèmes propulsifs en géneral, et des étages de compression en particulier, toujours plus compacts et chargés. Cette tendance dans la conception des moteurs est directement responsable de l’accentuation du caractère instationnaire des écoulements internes ainsi que de la favorisation dans l’émergence de phénomènes entrainant la perte de stabilité. L’étude expérimentale, conduite pendant ce projet de thèse, porte sur la caractérisation des écoulements dans un étage de compresseur axial en phase émergente et stabilisée du décrochage tournant, grâce à des mesures instationnaires de pression pariétale et de vitesse. L’étude doit son originalité à l’utilisation et au développement de techniques de post-traitement non-standard. La transformée par ondelettes se révèle être un outil particulièrement intéressant à la détection de structures cohérentes de brève durée, telles que le précurseur de type « spike » ainsi que les caractéristiques instantanées d’une cellule de décrochage tournant. A côté de cette approche d’analyse d’un signal localisé, différentes procédures de calcul de champs en moyenne de phase ont été mises au point, chacune adaptée aux spécificités du phénomène étudié et de la procédure expérimentale suivie. Il a été ainsi possible de suivre l’évolution des caractéristiques du champ de pression du régime nominal jusqu’à l’installation du décrochage tournant. L’alignement de la trajectoire du tourbillon de jeu avec la section d’entrée du rotor est associé au déclenchement du décrochage par précurseur de type « spike ». La comparaison entre les champs en phase transitoire et en décrochage établi, amène à affirmer que le précurseur n’est que le stade embryonnaire d’évolution du phénomène du décrochage. L’approche a, en outre, permis d’apprécier la complexité de la structure « interne » de la cellule qui apparait comme la succession d’une phase de propagation de décollement, une zone fortement débitante à charge presque nulle et une phase de ré-attachement de l’écoulement. / The reduction of the environmental impact is nowadays one of the crucial challenges of the aeronautic industry. The quest to lower the consumption of aircrafts has led to more compact and higher loaded engines in general, and especially compressor stages. This leads an increase of the internal flow unsteadiness and to the occurrence of unstable phenomena. The experimental study, performed during this work, concerns the characterization of flows in an axial compressor stage during both the emergence of rotating stall and its stabilized phase, by means of unsteady pressure and velocity measurements. The originality of the work proposed resides in the use and the development of non-standard data processing methods. The wavelets transform reveals to be an interesting tool for the detection of short coherent structures, like the spike-type precursor as well as the instantaneous features of a rotating stall cell. Beside this local approach, different procedures for phase-locked field measurements were developed, according to the specification of each studied phenomenon and the experimental proceedings. Thanks to these methods, it was possible to highlight the pressure field evolution until the development of the rotating stall regime. The alignment of the tip leakage vortex with the rotor inlet section forecasts a spike type stall onset. The comparison between transitional phase and fully developed stall fields conducts to assert that the precursor represent only the embryonic stage of the rotating stall evolution. This approach led to appreciate the complexity of the internal structure of the cell that appears to be the succession of stall propagation phase, zero-loaded high flow rate region and reattachment phase

<p>The fundamental design of axial compressors has matured to an exceptional level of performance due to a century of research. With the improvements in efficiency becoming increasingly difficult, attention continues to be channeled towards understanding and reducing secondary losses such as hub or tip clearance leakages, seal leakages, etc. Studies detailing the impact of seal leakages are relatively scarce due to difficulties of obtaining data in the complex rotating geometries of a high-speed compressor cavity. While the impact of seal leakages on primary passage is readily available, details inside the cavity geometry is scarce in open literature because majority of the investigations have been performed on linear cascades with slots machined as cavities or standalone labyrinth seals that fail to provide a wholesome understanding of the leakage flow and windage heating in the rotating geometries.<br></p> <p> Therefore, the principal objective of this work is to investigate flow physics in the stator cavity wells for understanding the flow path of the leakage fluid and windage heating within the cavity. A parametric model of the Purdue 3-Stage Compressor (P3S) is used to allow for rapid geometric modifications to the seal clearances in a coupled stator-cavity system. The investigations presented here consist of a series of numerical simulations using ANSYS CFX as the primary Computational Fluid Dynamics (CFD) tool. Measurements performed by previous investigators are utilized to define the boundary conditions of this model. This study’s goal is to characterize the interdependence of parameters such as cavity leakage flow rate, circumferential velocity, and windage heating for understanding the flow structure inside the cavity wells and their impact on cavity temperatures. Data acquired is intended to reveal mechanisms through which cavity leakage flows affect the stator passage aerodynamics and the windage heating, both regarding their effect on the compressor performance and the details of the flow path within the cavity. Consequently, this will provide insight into how the complex cavity leakage flow influences the design considerations for optimizing stator passage aerodynamics and minimizing stator cavity heating.</p> <p>The compressor operating conditions of Nominal Loading (NL) is the focus of this CFD work since the flow field at High Loading (HL) has significant boundary layer separation. NL is closest to both the design and peak efficiency conditions where the compressor would spend the majority of its time in operation, understanding cavity flow physics at this operating condition would have a direct impact on enhancing the overall compressor performance. A CFD model of the standalone primary passage is developed first using the dataset available from experiments performed by previous investigators for establishing confidence in the primary passage flow physics. Therefore, detailed total pressure, total temperature, velocity, and flow angle data collected behind each blade row is utilized for validating the primary passage flow in the CFD model. After validating the primary passage model, measurements in the coupled cavity model are acquired to understand the flow variations as well as temperature development in the cavity due to the varying labyrinth seal clearance.</p> <p>The investigations in this work are divided into two distinct branches. First, to aid the aerodynamic research community, the flow structure inside the cavity wells is investigated to understand the impact cavity leakage flow has on the compressor efficiency and on its interactions with the primary flow path. Secondly, for understanding the development and rise of temperature in the cavity wells, i.e., the windage effect, are performed to aid the thermo-mechanical research community so that the material choices and stress analysis of the cavity components can be optimized. Hence, the trends in the data acquired provide the aerodynamic, mechanical, and secondary flow system designers an indication of the complexities of the flow within shrouded stator cavities and provide insight into designing and optimizing more complex geometries.</p><p>Results from this investigation describe how increasing seal clearance deteriorates the stator performance and enables the cross-passage migration of low momentum fluid to worsen hub corner separation. The simulations also state the case for re-ingestion at tight seal clearances as the 3D streamlines show heated efflux emerges from the upstream cavity interface, dwells near the hub, and gets recirculated back into the cavity inlet well. Radial variations inside the cavity wells show high cavity temperatures with excessive cavity due to re-ingestion, while the cases that avoid re-ingestion are observed at the lowest temperatures. These radial variations also identify the cavity leakage flow path and the development of circumferential velocity. Lastly, the total pressure loss, total temperature rise and windage heating, all show a strong dependence on circumferential velocity development, which is inherently dependent on the labyrinth seal clearances.<br></p>