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To decrease the computational cost of genetic algorithm optimizations, surrogate models are used during optimization. Online update of surrogate models and repeated exchange of surrogate models with exact model during genetic optimization converts static optimization problems to dynamic ones. However, genetic algorithms fail to converge to the global optimum in dynamic optimization problems. To address these problems, a multiploid genetic algorithm optimization method is proposed. Multi-fidelity surrogate models are assigned to corresponding levels of fitness values to sustain the static optimization problem. Low fidelity fitness values are used to decrease the computational cost. The exact/highest-fidelity model fitness value is used for converging to the global optimum. The algorithm is applied to single and multi-objective turbine blade aerodynamic optimization problems. The design objectives are selected as maximizing the adiabatic efficiency and torque so as to reduce the weight, size and the cost of the gas turbine engine. A 3-D steady Reynolds-Averaged Navier-Stokes solver is coupled with an automated unstructured grid generation tool. The solver is validated by using two well known test cases. Blade geometry is modelled by 37 design variables. Fine and coarse grid solutions are respected as high and low fidelity surrogate models, respectively. One of the test cases is selected as the baseline and is modified in the design process. The effects of input parameters on the performance of the multiploid genetic algorithm are studied. It is demonstrated that the proposed algorithm accelerates the optimization cycle while providing convergence to the global optimum for single and multi-objective problems.

Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η πειραματική και η υπολογιστική διερεύνηση της επίδρασης της γωνίας εισόδου των πτερυγίων στη σπηλαίωση και την απόδοση μίας φυγοκεντρικής αντλίας. Στην εργασία αυτή πραγματοποιείται ο σχεδιασμός των πτερυγίων εφαρμόζοντας μία νέα μέθοδο, το σύνθετο διπλό κυκλικό τόξο(Double-Arc Synthetic Method - DASM), η οποία συνδυάζει δύο μεθόδους σχεδιασμού κατά Pfleiderer. Για την υλοποίηση της πειραματικής μελέτης, κατασκευάζονται τρία διαφορετικά στροφεία με γωνία εισόδου των πτερυγίων 9, 15 και 21 μοίρες, από κράμα αλουμινίου και από πλεξιγκλάς. Κατασκευάζεται πειραματική εγκατάσταση αντλίας και εξοπλίζεται με μεγάλης ακρίβειας όργανα μέτρησης. Διαφανή μέρη της πειραματικής εγκατάστασης επιτρέπουν την παρατήρηση της ροής και της σπηλαίωσης στο εξεταζόμενο στροφείο της αντλίας και με τη βοήθεια ενός στροβοσκόπιου φωτογραφίζεται η σπηλαίωση που αναπτύσσεται στα πτερύγια. Η πειραματική ανάλυση επικεντρώνεται στη μελέτη της μονοφασικής ροής και της σπηλαίωσης. Συγκεκριμένα, για την πειραματική μελέτη της μονοφασικής ροής, εξετάζεται η μεταβολή του μανομετρικού και του βαθμού απόδοσης της αντλίας συναρτήσει της παροχής της. Επιπλέον, μελετάται η μεταβολή του μανομετρικού και του βαθμού απόδοσης της αντλίας συναρτήσει της γωνίας εισόδου των πτερυγίων, για τρεις διαφορετικές εξεταζόμενες παροχές. Εξετάζεται η απόκλιση των πειραματικών αποτελεσμάτων του μανομετρικού από τα αντίστοιχα αποτελέσματα που προκύπτουν από το νόμο ομοιότητας. Τέλος, υπολογίζεται η αβεβαιότητα των μετρήσεων και συγκεκριμένα του μανομετρικού και του βαθμού απόδοσης της αντλίας. Μελετώντας πειραματικά τη σπηλαίωση, επικεντρωνόμαστε στη μεταβολή του μανομετρικού και του βαθμού απόδοσης της αντλίας συναρτήσει του διαθέσιμου καθαρού θετικού ύψους αναρρόφησης, για διάφορες παροχές της αντλίας. Μελετάται η μεταβολή του μανομετρικού και του βαθμού απόδοσης της αντλίας συναρτήσει της γωνίας εισόδου των πτερυγίων, για τρεις διαφορετικές τιμές του διαθέσιμου καθαρού θετικού ύψους αναρρόφησης. Στη συνέχεια εξετάζεται το ποσοστό πτώσης του μανομετρικού τη στιγμή που ξεκινάει η σπηλαίωση, αλλά και το μέγιστο ποσοστό πτώσης του, για τη μεγαλύτερη εξεταζόμενη παροχή. Εξετάζεται η μεταβολή του απαιτούμενου καθαρού θετικού ύψους αναρρόφησης και του κρίσιμου αριθμού σπηλαίωσης συναρτήσει της παροχής της αντλίας, για τις τρεις γωνίες εισόδου των πτερυγίων. Τέλος, υπολογίζεται η αβεβαιότητα των μετρήσεων και συγκεκριμένα του μανομετρικού, του διαθέσιμου καθαρού θετικού ύψους αναρρόφησης και του βαθμού απόδοσης της αντλίας. Επιπλέον, στην παρούσα διδακτορική διατριβή πραγματοποιείται υπολογιστική ανάλυση τρισδιάστατων μοντέλων φυγοκεντρικής αντλίας με δομημένο πλέγμα, χρησιμοποιώντας το υπολογιστικό πακέτο ANSYS CFD-Fluent, για τη μελέτη της μονοφασικής ροής και της σπηλαίωσης των εξεταζόμενων στροφείων της αντλίας. Η υπολογιστική μελέτη της μονοφασικής ροής για τα τρία διαφορετικά εξεταζόμενα στροφεία της φυγοκεντρικής αντλίας επικεντρώνεται στη μεταβολή του μανομετρικού της αντλίας συναρτήσει της παροχής της και εξετάζεται η απόκλιση των υπολογιστικών αποτελεσμάτων του μανομετρικού από τα αντίστοιχα αποτελέσματα που προκύπτουν από τα πειράματα. Μελετάται η κατανομή της απόλυτης πίεσης στο μέσο επίπεδο των εξεταζόμενων στροφείων της αντλίας και η αδιάστατη κατανομή της απόλυτης πίεσης γύρω από το μέσο επίπεδο των στροφείων, για τη μέγιστη εξεταζόμενη παροχή. Η υπολογιστική μελέτη της σπηλαίωσης επικεντρώνεται, κυρίως, στη μεταβολή του μανομετρικού της αντλίας συναρτήσει του διαθέσιμου καθαρού θετικού ύψους αναρρόφησης και εξετάζεται η απόκλιση των υπολογιστικών αποτελεσμάτων του μανομετρικού από τα αντίστοιχα αποτελέσματα που προκύπτουν από τα πειράματα. Εξετάζεται η κατανομή της απόλυτης πίεσης στο μέσο επίπεδο των εξεταζόμενων στροφείων της αντλίας και η αδιάστατη κατανομή της απόλυτης πίεσης γύρω από το μέσο επίπεδο των στροφείων, για τη μέγιστη εξεταζόμενη παροχή. Τέλος, παρουσιάζονται οι κατανομές της σπηλαίωσης, που προκύπτουν από τα υπολογιστικά αποτελέσματα και συγκρίνονται με τις αντίστοιχες φωτογραφίες με σπηλαίωση που ελήφθησαν με τη βοήθεια του στροβοσκόπιου κατά τη διάρκεια των πειραμάτων, για τις τρεις γωνίες εισόδου των πτερυγίων. Από τα αποτελέσματα της πειραματικής και της υπολογιστικής διερεύνησης παρατηρούμε ότι η απόκλιση των υπολογιστικών αποτελεσμάτων από τα αντίστοιχα πειραματικά είναι πολύ μικρή. Επομένως, η υπολογιστική ανάλυση που αναπτύσσεται στην παρούσα εργασία αποτελεί ένα αξιόπιστο εργαλείο διερεύνησης των ροϊκών μεγεθών και της σπηλαίωσης σε φυγοκεντρικές αντλίες και αποσκοπεί σε μελλοντικές μελέτες, όπως την παραμετρική διερεύνηση και τη βελτιστοποίηση του σχεδιασμού μίας αντλίας. / Object of the present doctoral thesis constitutes the experimental and computational study of the effect of the blade leading edge angle to the cavitation and performance of a centrifugal pump. In this study, the blade design is realized, applying a new blade design method (Double-Arc Synthetic Method - DASM), that combines two Pfleiderer' s design methods. For the realization of the experimental study, three different centrifugal pump impellers, with blade leading edge angle of 9, 15 and 21 deg, are constructed by aluminium alloy and plexiglas. A pump test rig is constructed and equipped with high accuracy instrumentation. Transparent parts of the pump test rig allow the observation of fluid flow inside the examined impeller and the photography of the cavitation that is developed in the blades, using a stroboscope. The experimental analysis is focused on the study of the one-phase flow and cavitation. Concretely, for the experimental study of the one-phase flow, the change of the total head and performance of the pump with respect to the flow rate is examined. Moreover, the change of the total head and performance of the pump with respect to the blade leading edge angle is studied, for three different flow rates. The deviation of the experimental results of the total head from the corresponding results of the affinity law is investigated. Lastly, the uncertainty of the measurements and concretely of the total head and performance of the pump is calculated. Studying experimentally the cavitation, we focus on the change of the total head and performance of the pump with respect to the net positive suction head available, for different flow rates. The change of the total head and performance of the pump with respect to the blade leading edge angle, for three different values of the net positive suction head available is tested. Afterwards, the percentage of the total head drop is examined, when cavitation begins. Moreover, the maximum percentage of the total head drop is studied for the greatest tested flow rate. The change of the net positive suction head required and the crucial cavitation number with respect to the flow rate is studied, for three different blade leading edge angles. Lastly, the uncertainty of the measurements and concretely of the total head, the net positive suction head available and the performance of the pump is calculated. Furthermore, in the present doctoral thesis the computational analysis of three-dimensional centrifugal pump with structured mesh is realized using the computational package ANSYS CFD-Fluent, for the study of both the one-phase flow and the cavitation, of the tested centrifugal pump impellers. The computational study of the one-phase flow for the three different examined centrifugal pump impellers, is focused on the change of the total head with respect to the flow rate. Furthermore, the deviation of the computational results of the total head from the corresponding results of the experimental study is investigated. The absolute pressure distribution inside the tested centrifugal pump impellers at the middle span and the dimensionless pressure distribution around the impellers, at the middle span, are investigated for the greatest flow rate. The computational study of the cavitation, is mainly focused on the change of the total head with respect to the net positive suction head available. Moreover, the deviation of the computational results of the total head from the corresponding results of the experimental study is investigated. The absolute pressure distribution inside the tested centrifugal pump impellers at the middle span and the dimensionless pressure distribution around the impellers, at the middle span, are investigated for the greatest flow rate. Lastly, the vapour distributions are resulted by the computational analysis and are compared with the corresponding photographs of cavitation that were snapped with the aid of the stroboscope, during the experiments, for the three blade leading edge angles. From the experimental and computational results, we observe that the deviation of the computational results from the corresponding experimental results is very small. Thus, the computational analysis that is developed in the present work constitutes a reliable tool of the investigation of the flowfield and cavitation in centrifugal pumps and it aims at future studies, such as parametric investigation and optimization of pump design.

No description available.

Vehicle electrification plays a significant role in the effort to reduce the environmental impact of the automotive industry. Scania is one of the leading manufacturers ofheavy vehicles which is currently moving towards a sustainable transport system by manufacturing a new generation of heavy vehicles powered by batteries. Oneof the major concerns with these vehicles is related to the noise generated by the electric axial fans used in the cooling system. This project was conducted with thepurpose of investigating the factors that positively affect both noise and performance in the electric fans. Based on two different blade design methods and several noisecontrol techniques, 11 fan models were developed. The fan models created with design method 1 are equipped with cambered-plate blades, while the models madewith design method 2 consist of airfoil-shaped blades. Moreover, the performance of these models was analyzed by using theoretical methods and Computational FluidDynamics (CFD). In addition, two empirical approaches were used to estimate the acoustic energy emitted by the fan models. Furthermore, the developed modelswere compared with two commercially available fans. It was found that both design methods provide similar performance in low pressure differences. On the other hand,the efficiency and acoustic energy are influenced by the choice of the noise control methods. / Fordonselektrifiering har en väsentlig roll i arbetet med att minska bilindustrins miljöpåverkan. Scania är en av de ledande tillverkarna av tunga fordon som för närvarandegår mot ett hållbart transportsystem, genom att tillverka en ny generation tunga fordon drivna med batterier. Ett stort bekymmer med dessa fordon är relaterattill det ljud som genereras av de elektriska axialfläktarna som används i kylsystemet. Detta projekt genomfördes i syfte till att undersöka de faktorer som positivtpåverkar både buller och prestanda hos de elektriska fläktarna. Baserat på två olika bladdesignmetoder och flera brusstyrningstekniker, utvecklades 11 fläktmodeller.Fläktmodellerna som är utformade med konstruktionsmetod 1 är utrustade med krökformade plattor, medan modellerna som skapades med designmetod 2 bestårav vingprofil blad. Dessutom analyserades prestandan för dessa modeller med användning av teoretiska metoder och strömningsmekaniska beräkningar. Ytterligaretvå empiriska tillvägagångssätt användes för att uppskatta den akustiska energin som släppts ut av fläktmodellerna. Utöver det jämfördes de utvecklade modellernamed två kommersiellt tillgängliga fläktar. Detta visade att båda konstruktionsmetoderna resulterar i liknande prestanda vid lågtrycksskillnader, däremot påverkasverkningsgraden och den akustiska energin av valet av brusstyrningsmetoder.

The research in this thesis focuses on the investigation of tidal turbines using a small scale horizontal axis tidal turbine and a 2D hydrofoil testing rig, combining experiments with simulations to provide comprehensive results and to better understand some of the variables that affect their performance. The experimental campaigns were carried out at the University of Victoria fluids research lab and the Sustainable Systems Design Lab (SSDL). The experimental testing rigs were re-designed by the author and are now fully automated, including a friendly graphical user interface for easy implementation. Particle image velocimetry (PIV) technique was used as the quantitative flow visualization method to obtain the time-averaged flow fields. This thesis presents three investigations. The first study aims to quantify the impacts of channel blockage, free surface effects and foundations on hydrokinetic turbine performance, using porous discs and an axial flow rotor. The results were used to cross-validate computational fluid dynamics (CFD) simulations. It was found that as wall blockage increases, thrust and power are incremented with and without the inclusion of free surface deformation. Discrepancies between simulations and experimental results on free surface effects compared to a slip wall were obtained and hence further research is recommended and the author gives some advice on how to proceed in this investigation. The second study determines the performance of four hydrofoil candidates over a range of low Reynolds number (Re), delivering useful information that can be applied to low Re energy conversion systems and, specifically in this case, to improve the performance of the small scale tidal turbine at the SSDL lab. The study combines the 2D hydrofoil test rig along with PIV measurements in order to experimentally obtain lift and drag coefficients. The experiments were carried out in the recirculating flume tank over the range of low Re expected for the small scale rotor rig, in order to provide more accurate results to improve rotor blade design. In addition, numerical simulations using XFOIL, a viscid-inviscid coupled method, were introduced to the study. These results were analysed against experiments to find the most suitable parameters for reliable performance prediction. The final results suggested that adding a numerical trip at a certain chordwise distance produced more reliable results. Finally, an experimental study on turbine rotor performance and tip vortex behavior was performed using again the rotor rig and PIV. Blade design and rotor performance were assessed, showing good agreement with Blade Element Momentum (BEM) simulations, particularly at predicting the tip speed ratio corresponding to the maximum power coefficient point. Regarding the wake structure, tip vortex locations (shed from the blade tips) were captured using PIV in the near wake region, showing evidence of wake expansion. The velocity and vorticity fields are also provided to contribute to the development and validation of CFD and potential flow codes. / Graduate / 0548 / 0547 / 0538 / iafranch@uvic.ca

Three-dimensional design and three-dimensional CFD analysis of a compressor rotor stage are performed. The design methodology followed is based on a mean line analysis and a radial equilibrium phase. The radial equilibrium is established at a selected number of radii. NACA 65 series airfoils are selected and stacked according to the experimental data available. The CFD methodology applied is based on a three-dimensional, finite difference, compressible flow Euler solver that includes the source terms belonging to rotational motion. The accuracy of the solver is shown by making use of two different test cases. The CFD solution of the designed geometry predicts the static pressure rises and flow turning angles to a good degree of accuracy.

New helicopter rotor designs are desired that offer increased efficiency, reduced vibration, and reduced noise. This problem is multidisciplinary, requiring knowledge of structural dynamics, aerodynamics, and aeroacoustics. Rotor optimization requires achieving multiple, often conflicting objectives. There is no longer a single optimum but rather an optimal trade-off space, the Pareto Frontier. Rotor Designers in industry need methods that allow the most accurate simulation tools available to search for Pareto designs. Computer simulation and optimization of rotors have been advanced by the development of "comprehensive" rotorcraft analysis tools. These tools perform aeroelastic analysis using Computational Structural Dynamics (CSD). Though useful in optimization, these tools lack built-in high fidelity aerodynamic models. The most accurate rotor simulations utilize Computational Fluid Dynamics (CFD) coupled to the CSD of a comprehensive code, but are generally considered too time consuming where numerous simulations are required like rotor optimization. An approach is needed where high fidelity CFD/CSD simulation can be routinely used in design optimization. This thesis documents the development of physics based rotor simulation frameworks. A low fidelity model uses a comprehensive code with simplified aerodynamics. A high fidelity model uses a parallel processor capable CFD/CSD methodology. Both frameworks include an aeroacoustic simulation for prediction of noise. A synergistic process is developed that uses both frameworks together to build approximate models of important high fidelity metrics as functions of certain design variables. To test this process, a 4-bladed hingeless rotor model is used as a baseline. The design variables investigated include tip geometry and spanwise twist. Approximation models are built for high fidelity metrics related to rotor efficiency and vibration. Optimization using the approximation models found the designs having maximum rotor efficiency and minimum vibration. Various Pareto generation methods are used to find frontier designs between these two anchor designs. The Pareto anchors are tested in the high fidelity simulation and shown to be good designs, providing evidence that the process has merit. Ultimately, this process can be utilized by industry rotor designers with their existing tools to bring high fidelity analysis into the preliminary design stage of rotors.

Vortex generator jets (VGJs) have been found to be an effective method of active separation control on the suction side of a low pressure turbine (LPT) blade at low Reynolds numbers. The flow mechanisms responsible for this control were studied and documented in order to provide a basis for future improvements in LPT design. Data were collected using a stereo PIV system that enabled all three components of velocity to be measured. Steady VGJs were injected into a laminar boundary layer on a flat plate (non-separating boundary layer) in order to more fully understand the characteristics and behavior of the produced vortices. Both normal (injected normal to the wall) and angled (injected at 30° pitch and 90° skew angles to the freestream) jets were studied. The steady jets were found to create vortices that swept the low momentum fluid up from the boundary layer while transporting high momentum freestream fluid towards the wall, a phenomenon that provides the ingredients for flow control. Pulsed VGJs were then injected on a flat plate with an applied adverse pressure gradient equivalent to that experienced by a commonly tested LPT blade. This configuration was used to study the effectiveness of the flow control exhibited by both normal and angled jets on a separating boundary layer. Time averaged results showed similar boundary layer separation reduction for both normal and angled jets; however, individual characteristics suggested that the control mechanism of the two injection angles is distinct. Steady and pulsed VGJs were then applied to a new aggressive LPT blade design to explore the effect of the jets on a separating boundary layer along the curved blade surface. Steady injection provided flow control through freestream entrainment, while pulsed jets created a two-dimensional, spanwise disturbance that reduced the separated area as it traveled downstream. A detailed fluid analysis of the uncontrolled flow around the blade was performed in order to identify the separation and reattachment points and the area of transition. This information was used as a basis for comparison with the VGJ cases to determine flow control effectiveness.

No description available.