Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η πειραματική και υπολογιστική διερεύνηση αεροδυναμικής συμπεριφοράς πτερύγων σε διφασική ροή αέρα–νερού και η εφαρμογή σε πτερύγια ανεμοκινητήρων. Αρχικά, γίνεται πειραματική και υπολογιστική μελέτη μονοφασικής ροής αέρα γύρω από αεροτομές, πτέρυγες και πτερύγιο ανεμοκινητήρα και στη συνέχεια μελέτη διφασικής ροής αέρα-νερού γύρω από τα ίδια σώματα. Η σύγκριση μεταξύ των αποτελεσμάτων της μονοφασικής ροής με τα αντίστοιχα της διφασικής ροής αέρα-νερού είναι αναγκαία ώστε να μελετηθούν οι επιπτώσεις της διφασικής ροής αέρα–νερού στην αεροδυναμική απόδοση. Η πειραματική ανάλυση αφορά τη διεξαγωγή πειραμάτων για τη μελέτη της αεροδυναμικής συμπεριφοράς αεροτομών και πτερύγων σε συνθήκες μονοφασικής και διφασικής ροής. Για την προσομοίωση συνθηκών διφασικής ροής αέρα-νερού τροποποιείται η αεροσήραγγα που διαθέτει ήδη το Εργαστήριο με την προσαρμογή ειδικών ακροφυσίων ψεκασμού νερού (συνθήκες βροχής). Για τις ανάγκες των πειραμάτων χρησιμοποιούνται τα μοντέλα αεροτομών και πτερύγων NACA 0012 που συνοδεύουν την αεροσήραγγα και κατασκευάζονται αεροτομή και πτέρυγες S809. Τα πειράματα μονοφασικής και διφασικής ροής γίνονται για την ίδια ταχύτητα αέρα. Για τη διφασική ροή αέρα-νερού εξετάστηκαν τέσσερις διαφορετικές πυκνότητες περιεχόμενης βροχής. Η υπολογιστική ανάλυση γίνεται με το υπολογιστικό πακέτο ANSYS CFD-Fluent. Αρχικά, γίνονται προσομοιώσεις για μονοφασική ροή αέρα γύρω από την αεροτομή NACA 0012, για την οποία υπάρχει πλήθος δημοσιευμένων αποτελεσμάτων, με τρία διαφορετικά μοντέλα τύρβης ώστε να βρεθεί το καταλληλότερο. Ο συντελεστής άνωσης υπολογίζεται με μεγάλη ακρίβεια, σε αντίθεση με το συντελεστή αντίστασης. Το πρόβλημα αυτό οφείλεται στην αδυναμία του Fluent να υπολογίσει το σημείο μετάβασης του οριακού στρώματος από στρωτό σε τυρβώδες. Κρίνεται επομένως αναγκαίο να γίνει σύγκριση του συντελεστή αντίστασης με πειραματικά δεδομένα για πλήρως τυρβώδες οριακό στρώμα. Για ακόμα πιο ακριβή αποτελέσματα αναπτύσσεται αλγόριθμος για τον υπολογισμό του σημείου μετάβασης από στρωτό σε τυρβώδες οριακό στρώμα και γίνονται προσομοιώσεις ορίζοντας την περιοχή αριστερά από το σημείο μετάβασης ως στρωτή και δεξιά από αυτό ως τυρβώδη. Υπολογίζονται οι κατανομές πίεσης και ταχύτητας γύρω από την αεροτομή, καθώς επίσης και τα σημεία ανακοπής, μέγιστης ταχύτητας, αποκόλλησης και επανακόλλησης του οριακού στρώματος. Παρουσιάζονται επίσης οι ροϊκές γραμμές και τα διανύσματα της ταχύτητας γύρω από την αεροτομή. Αντίστοιχες προσομοιώσεις γίνονται και για την αεροτομή S809. Για τη μελέτη του τρισδιάστατου χαρακτήρα της ροής, γίνονται προσομοιώσεις γύρω από πτέρυγα S809. Υπολογίζονται οι συντελεστές άνωσης και αντίστασης, τα σημεία ανακοπής, μέγιστης ταχύτητας, αποκόλλησης και επανακόλλησης του οριακού στρώματος. Επίσης παρουσιάζονται κατανομές της έντασης της τύρβης στην άνω επιφάνεια της πτέρυγας και της συνισταμένης ταχύτητας, της ταχύτητας στη z-διεύθυνση, της έντασης της τύρβης και της επιτάχυνσης της ροής πίσω από την πτέρυγα. Για τη μελέτη της ροής γύρω από περιστρεφόμενο πτερύγιο γίνονται προσομοιώσεις γύρω από το πτερύγιο Phase IV της NREL. Γίνεται μελέτη της κατανομής της αξονικής ταχύτητας πίσω από το δρομέα, της κατανομής της στατικής πίεσης και της έντασης της τύρβης πάνω στην επιφάνεια του πτερυγίου και της κατανομής της στατικής πίεσης σε διάφορα σημεία πάνω στο πτερύγιο. Η υπολογιστική μελέτη της διφασικής ροής αέρα-νερού γίνεται αρχικά για την αεροτομή NACA 0012 με πυκνότητα περιεχόμενης βροχής LWC=30 g/m³, επειδή υπάρχουν αντίστοιχα έγκυρα πειραματικά αποτελέσματα ώστε να γίνει σύγκριση για την εγκυρότητα της διαδικασίας της προσομοίωσης. Στη συνέχεια γίνονται προσομοιώσεις για διφασική ροή αέρα-νερού γύρω από την αεροτομή S809, την πτέρυγα S809 και το περιστρεφόμενο πτερύγιο Phase IV της NREL. Προσομοιώσεις γίνονται επίσης για διαφορετικές πυκνότητες περιεχόμενης βροχής για τη ροή γύρω από τις αεροτομές σε χαμηλό αριθμό Reynolds. Τα αποτελέσματα της διφασικής ροής αέρα-νερού συγκρίνονται με τα αντίστοιχα της μονοφασικής ροής ώστε να προκύψουν συμπεράσματα για τις επιπτώσεις της βροχής στην αεροδυναμική απόδοση. Γίνεται επίσης υπολογισμός του συντελεστή ισχύος του ανεμοκινητήρα σε συνθήκες μονοφασικής ροής αέρα και διφασικής ροής αέρα-νερού. Σε συνθήκες διφασικής ροής αέρα-νερού παρατηρείται υποβάθμιση της αεροδυναμικής απόδοσης, συγκεκριμένα μείωση της άνωσης με παράλληλη αύξηση της αντίστασης. Δυο είναι οι βασικοί μηχανισμοί που επικρατούν και έχουν ως αποτέλεσμα την υποβάθμιση αυτή. Στην επιφάνεια της αεροτομής δημιουργείται ανομοιόμορφο φιλμ νερού που αυξάνει την τραχύτητα και το πάχος της αεροτομής. Τα σταγονίδια καθώς προσκρούουν πάνω στο φιλμ νερού δημιουργούν «κρατήρες» αυξάνοντας την τραχύτητα της αεροτομής. Επίσης, τα σωματίδια νερού διασπώνται κατά την πρόσκρουσή τους πάνω στην αεροτομή σε άλλα σταγονίδια μικρότερης διαμέτρου και μειωμένης ταχύτητας. Αυτό έχει ως αποτέλεσμα τα σταγονίδια αυτά, επαναεπιταχυνόμενα από τη ροή του αέρα να αποσπούν ποσό ενέργειας από το οριακό στρώμα καθιστώντας το πιο ευάλωτο σε αποκόλληση. Στόχος της μελέτης της αεροδυναμικής συμπεριφοράς των πτερυγίων σε διφασική ροή αέρα-νερού είναι η κατασκευή ανεμοκινητήρων υψηλού βαθμού απόδοσης και η παραγωγή φθηνής ενέργειας από την όσο το δυνατόν καλύτερη αξιοποίηση της αιολικής ενέργειας. / The aim of the present doctoral thesis is the experimental and computational study of the aerodynamic behavior of wings in two-phase flow and the application on wind turbine blades. First of all, experimental and computational study of one-phase flow over airfoils, wings and wind turbine blade and afterwards study of two-phase flow over the same bodies is conducted. The comparison of the results between dry and wet conditions is necessary in order to show the effects of two-phase flow at the aerodynamic performance. Wind tunnel tests were conducted to show the aerodynamic behavior of airfoils and wings in one-phase and two-phase flows. To simulate two-phase flow, the wind tunnel of the Fluid Mechanics Laboratory has to be configured with adding commercial rain simulated nozzles. For the experiments NACA 0012 airfoils and wings which come along the wind turbine are utilized and airfoil and wings S809 are constructed. The experiments of one-phase flow and two-phase flow are conducted for the same air velocity. For the two-phase flow four different Liquid Water Contents are examined. For the computational analysis the commercial CFD code ANSYS Fluent is used. In first place, simulations of one-phase flow over the NACA 0012 airfoil are done with three different turbulence models. The NACA0012 airfoil is chosen because it has been studied in depth and has a precise data base to compare the results of the simulation with. The lift coefficients are computed with accuracy in contrast to the drag coefficient. The overprediction of drag is expected since the actual airfoil has laminar flow over the forward half. The turbulence models cannot calculate the transition point from laminar to turbulent and consider that the boundary layer is turbulent throughout its length. Therefore, it is necessary to compare the computational results with experimental data of a fully turbulent boundary layer. In order to get more accurate results, the computational domain could be split into two different domains to run mixed laminar and turbulent flow. The contours of pressure and velocity over the airfoil are presented, as well as stagnation, maximum velocity, detachment and reattachment points of the boundary layer are computed. Streamlines and velocity vectors over the airfoil are also presented. Similar simulations are conducted for the S809 airfoil. In order to study the tree-dimensional effects of the flow, simulations over the S809 wing are made. Lift and drag coefficients, stagnation, maximum velocity, detachment and reattachment points of the boundary layer are computed. Moreover, contours of turbulent intensity on the upper surface of the wing and velocity, z-velocity, turbulence intensity and helicity behind the wing are presented. Simulations over the Phase IV blade of NREL are also conducted. The axial velocity behind the rotor, the static pressure and the turbulence intensity contribution on the blade’s surface and the static pressure contours at several blade cross-sections are studied. First of all, the computational study of the two-phase flow over a NACA 0012 airfoil and Liquid Water Content LWC=30 g/m3 is conducted, because there are published experimental data for comparison, in order to validate the CFD developed model. After that, simulations of two-phase flow over the S809 airfoil, S809 wing and Phase IV blade are made. In addition, computational study of the effects of different Liquid Water Content on the aerodynamic performance of NACA 0012 and S809 airfoil at low Reynolds number is made. The results from two-phase flow are compared with the corresponding results from one-phase flow in order to show the effects of two-phase flow at the aerodynamic performance. The influence of two-phase flow on the power coefficient of a wind turbine is also investigated. The results show that the aerodynamic performance degrades when encountering rain, especially lift is degreased and drag is increased. The aerodynamic degradation is caused by the water film formation on the airfoil’s surface and the cratering effects from the raindrops impact. The presence of uneven water film on the airfoil surface roughens the airfoil surface and increases the airfoil thickness. The cratering effects from the water droplets impact on the water film layer increase also the airfoil thickness. Moreover, the droplets splash-back when they impact the airfoil and as a result droplets with smaller diameter and velocity are formed. The acceleration of the splashed-back droplets by the air flowfield acts as a momentum sink, deenergizing the boundary layer and leaving it more susceptible to separation. The aim of the study of the aerodynamic behavior of blades in two-phase flow is the construction of wind turbines with greater efficiency and the production of energy from wind with low cost.

Throughout the development of this report there will be a brief explanation of what the actual Aircraft Design Process is and in which stages the methodology that the authors are proposing will be implemented as well as the tools that will interact to produce this methodology. The proposed tool will be the first part of a methodology that, according to the authors, by integrating separate tools that are currently used in different stages of the aeronautical design, will promote a decrease in the time frame for the initial stages of the design process. The first part of the methodology above, that is proposed in this project, starts by creating a computer generated aircraft model and analyzing its basic aerodynamic characteristics “Lift Coefficient” and “Induced Drag Coefficient”, this step will be an alternative to statistical and empirical methods used in the industry, which require vast amount of data. This task will be done in several steps, which will transfer the parametric aircraft model to an input file for the aerodynamic analysis program. To transfer the data a “translation” program has been developed that arranges the geometry and prepares the input file for analysis. During the course of this report the reader will find references to existing aircrafts, such as the MD-11 or Airbus 310. However, these references are not intended to be an exact computer model of the mentioned airplanes. The authors are using this as reference so the reader can relate what he/she is seeing in this paper to existing aircrafts. By doing such comparison, the author intends to demonstrate that the Parametric Model that has been created possesses the capability to simulate to some extend the shape of existing aircrafts. Finally from the results of this project it is concluded that the methodology in question is promising. Linking the two programs is possible and the aerodynamic characteristics of the models tested fall in the appropriate range. None the less the research must continue following the line that has been discussed in this report.

Baigiamajame magistro darbe nagrinėjamos būsimo eksperimentinio akrobatinio lėktuvo aerodinaminės savybės. Pristatomos tokio pobūdžio sritys (temos), kaip tinkamo sparno profilio parinkimas orlaiviui, reikalingo sparno formos apibrėžimas, sparno būsimos charakteristikos ir parametrų apskaičiavimas, kitų orlaivio dalių ir jų įtakos visai lėktuvo dinamikai analizavimas. Kadangi analizuojamas dvivietis eksperimentinis akrobatinis lėktuvas, tikintis geresnių rodiklių, pasirinktas palyginimo objektas  dvivietis akrobatinis mokomasis lėktuvas SU 29. Remiantis šio lėktuvo esamomis charakteristikomis ir parametrais, pateikiamos išvados ir siūlymai. / The thesis examines the aerodynamics of future experimental aerobatic aircraft. Featured in such areas (topics): proper selection of an aircraft wing profile, the required form of the wing, the wing's future performance and parameter estimation, other aircraft parts and their impact on the entire plane dynamics analysis. As analyzed double seated, experimental aerobatic plane in the hope of better indicators selected comparison object  double seated acrobatic training plane SU 29. Based on the existing aircraft characteristics and parameters, the conclusions and recommendations will be made.

There is significant uncertainty in our knowledge of the Martian atmosphere and the aerodynamics of the Mars entry, descent, and landing (EDL) systems. These uncertainties result in conservatism in the design of the EDL vehicles leading to higher system masses and a broad range of performance predictions. Data from flight instrumentation onboard Mars EDL systems can be used to quantify these uncertainties, but the existing dataset is sparse and many parameters of interest have not been previously observable. Many past EDL reconstructions neither utilize statistical information about the uncertainty of the measured data nor quantify the uncertainty of the estimated parameters. Statistical estimation methods can blend together disparate data types to improve the reconstruction of parameters of interest for the vehicle. For example, integrating data obtained from aeroshell-mounted pressure transducers, inertial measurement unit, and radar altimeter can improve the estimates of the trajectory, atmospheric profile, and aerodynamic coefficients, while also quantifying the uncertainty in these estimates. These same statistical methods can be leveraged to improve current engineering models in order to reduce conservatism in future EDL vehicle design. The work in this thesis presents a comprehensive methodology for parameter reconstruction and uncertainty quantification while blending dissimilar Mars EDL datasets. Statistical estimation methods applied include the Extended Kalman Filter, Unscented Kalman Filter, and Adaptive Filter. The estimators are applied in a manner in which the observability of the parameters of interest is maximized while using the sparse, disparate EDL dataset. The methodology is validated with simulated data and then applied to estimate the EDL performance of the 2012 Mars Science Laboratory. The reconstruction methodology is also utilized as a tool for improving vehicle design and reducing design conservatism. A novel method of optimizing the design of future EDL atmospheric data systems is presented by leveraging the reconstruction methodology. The methodology identifies important design trends and the point of diminishing returns of atmospheric data sensors that are critical in improving the reconstruction performance for future EDL vehicles. The impact of the estimation methodology on aerodynamic and atmospheric engineering models is also studied and suggestions are made for future EDL instrumentation.

In this study, acoustic noise radiation through a duct in frequency domain is analyzed. Frequency domain linearized Euler equations are solved for turbofan exhaust noise propagation and radiation. The geometry in studied cases is assumed as axisymmetric. The acoustic waves are decomposed into periodic azimuthal modes. Characteristic boundary conditions, and buffer zone boundary conditions are employed. Iterative type pseudo time integration is employed. Nonuniform background flow effect on the radiation pattern is experienced. All computations are performed in parallel using MPI library routines in computer cluster. Results proved that the one with the buffer zone has a better radiation characteristic than the characteristic one because of absorbtion of spurious waves. It is seen that the efficiency of the buffer zone is frequency dependent.

<p>This dissertation investigates the optimal aerodynamic performance and design of conventional and coaxial helicopters in hover and forward flight using conventional and higher harmonic blade pitch control. First, we describe a method for determining the blade geometry, azimuthal blade pitch inputs, optimal shaft angle (rotor angle of attack), and division of propulsive and lifting forces among the components that minimize the total power for a given forward flight condition. The optimal design problem is cast as a variational statement that is discretized using a vortex lattice wake to model inviscid forces, combined with two-dimensional drag polars to model profile losses. The resulting nonlinear constrained optimization problem is solved via Newton iteration. We investigate the optimal design of a compound vehicle in forward flight comprised of a coaxial rotor system, a propeller, and optionally, a fixed wing. We show that higher harmonic control substantially reduces required power, and that both rotor and propeller efficiencies play an important role in determining the optimal shaft angle, which in turn affects the optimal design of each component. Second, we present a variational approach for determining the optimal (minimum power) torque-balanced coaxial hovering rotor using Blade Element Momentum Theory including swirl. We show that the optimal hovering coaxial rotor generates only a small percentage of its total thrust on the portion of the lower rotor operating in the upper rotor's contracted wake, resulting in an optimal design with very different upper and lower rotor twist and chord distributions. We also show that the swirl component of induced velocity has a relatively small effect on rotor performance at the disk loadings typical of helicopter rotors. Third, we describe a more refined model of the wake of a hovering conventional or coaxial rotor. We approximate the rotor or coaxial rotors as actuator disks (though not necessarily uniformly loaded) and the wake as contracting cylindrical vortex sheets that we represent as discrete vortex rings. We assume the system is axisymmetric and steady in time, and solve for the wake position that results in all vortex sheets being aligned with the streamlines of the flow field via Newton iteration. We show that the singularity that occurs where the vortex sheet terminates at the edge of the actuator disk is resolved through the formation of a 45 degree logarithmic spiral in hover, which results in a non-uniform inflow, particularly near the edge of the disk where the flow is entirely reversed, as originally hypothesized by previous authors. We also quantify the mutual interference of coaxial actuator disks of various axial spacing. Finally, we combine our forward flight optimization procedure and the Blade Element Momentum Theory hover optimization to form a variational approach to the multipoint aerodynamic design optimization of conventional and coaxial helicopter rotors. The resulting nonlinear constrained optimization problem may be used to map the Pareto frontier, i.e., the set of rotor designs for which it is not possible to improve upon the performance in one flight condition without degrading performance in the other. We show that for both conventional and coaxial rotors analyzed in hover and high speed flight, a substantial tradeoff in performance must be made between the two flight conditions. Finally, computational results demonstrate that higher harmonic control is able to improve the Pareto efficiency for both conventional and coaxial rotors.</p> / Dissertation

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Computational Aeroelasticity is a complex research field which combines structural and aerodynamic analyses to describe a vehicle in flight. This thesis investigates the feasibility of including such an analysis in the development of control systems for unmanned aerial vehicles within the Electronic Systems Laboratory at the Department of Electrical and Electronic Engineering at Stellenbosch University. This is done through the development of a structural analysis algorithm using the Finite Element Method, an aerodynamic algorithm for Prandtl’s Lifting Line Theory and experimental work. The experimental work was conducted at the Low-Speed Wind Tunnel at the Department of Mechanical and Mechatronic Engineering. The structural algorithm was applied to 20-noded hexahedral elements in a winglike structure. The wing was modelled as a cantilever beam, with a fixed and a free end. Natural frequencies and deflections were verified with the experimental model and commercial software. The aerodynamic algorithm was applied to a Clark-Y airfoil with a chord of 0:1m and a half-span of 0:5m. This profile was also used on the experimental model. Experimental data was captured using single axis accelerometers. All postprocessing of data is also discussed in this thesis. Results show good correlation between the structural algorithm and experimental data. / AFRIKAANSE OPSOMMING: Numeriese Aeroelastisiteit is ’n komplekse navorsingsveld waar ’n vlieënde voertuig deur ’n strukturele en ’n aerodinamiese analise beskryf word. Hierdie tesis ondersoek die toepaslikheid van hierdie tipe analise in die ontwerp van beheerstelsels vir onbemande voertuie binne die ESL groep van die Departement Elektriese en Elektroniese Ingenieurswese by Stellenbosch Universiteit. Die ondersoek bevat die ontwikkeling van ’n strukturele algoritme met die gebruik van die Eindige Element Methode, ’n aerodinamiese algoritme vir Prandtl se Heflynteorie en eksperimentele werk. Die eksperimentele werk is by die Department Meganiese en Megatroniese Ingensierswese toegepas in die Lae-Spoed Windtonnel. Die strukturele algoritme maak gebruik van ’n 20-nodus heksahedrale element om ’n vlerk-tipe struktuur op te bou. Die vlerk is vereenvouding na ’n kantelbalk met ’n vasgeklemde en ’n vrye ent. Natuurlike frekwensies en defleksies is met die eksperimentele werk en kommersiële sagteware geverifieer. Die aerodinamiese algoritme is op ’n Clark-Y profiel met 0:1m koord lengte en ’n halwe vlerk length van 0:5m geïmplementeer. Die profiel is ook in die eksperimentele model gebruik. Die eksperimentele data is met eendimensionele versnellingsmeters opgeneem. Al die verdere berekeninge wat op ekperimentele data gedoen is, word in die tesis beskryf. Resultate toon goeie korrelasie tussen die strukturele algoritme en die eksperimentele data.

Este trabalho apresenta a simulação numérica do escoamento turbulento em torno de uma turbina eólica de eixo vertical de pequeno porte, Savonius tipo helicoidal com torção de 180° nas pás. Com o intuito de avaliar a metodologia computacional empregada os resultados numéricos obtidos são comparados com os resultados experimental e numérico contidos no estado da arte. Também, compara-se o coeficiente de toque da turbina Savonius helicoidal com a turbina Savonius convencional. As simulações numéricas são baseadas no Método de Volumes Finitos, e para tal emprega-se o programa Fluent /Ansys versão 13.0 que resolve as equações da continuidade e as equações de Navier-Stokes com médias de Reynolds, juntamente com o modelo de turbulência . As simulações são desenvolvidas empregando diferentes malhas computacionais em estudos transientes, tridimensionais, com a turbina estacionária. A avaliação da qualidade da malha é realizada através do método de Índice de Convergência de Malha (GCI) o qual analisa o quão longe os resultados estão da solução assintótica para a malha utilizada. Após a análise da qualidade de malha, realizam-se simulações com a turbina em rotação as quais fazem uso da malha contendo uma região móvel possibilitando a imposição de uma velocidade angular ao rotor. O coeficiente de torque é obtido nas simulações e a partir dele calcula-se o coeficiente de potência. Além da análise do desempenho do rotor realiza-se uma análise qualitativa das características do escoamento sobre a turbina. A turbina Savonius helicoidal apresenta um valor de coeficiente de potência de 0,175 para a razão de velocidade de ponta de 0,58 considerando correção do efeito de bloqueio. Os resultados obtidos apresentam boa concordância com os resultados publicados por outros autores. / This dissertation presents the numerical simulation of the turbulent flow around of a small sized vertical axis wind turbine, consisting in a helical Savonius type with a 180° degree of blade twist. In order to evaluate the used methodology the obtained results are compared with the state of the art numerical and experimental data. It will be also presented the comparison between the torque coefficient of the conventional Savonius turbine and the helical Savonius turbine. The numerical simulations are based on the Finite Volume Method (FVM), using the commercial code Fluent/ANSYS version 13.0, which solves the continuity and Navier-Stokes through the Reynolds time-averaged methodology, including the turbulence model. The simulations are developed using different computational meshes for transient and three-dimensional studies with the stationary turbine. The evaluating the quality of the mesh is performed by of Grid Convergence Index (GCI) method which analyzes how far the results are the asymptotic solution to the mesh used. After the evaluation of the mesh quality, it was simulated a case considering the rotor motion using the moving mesh configuration, allowing the imposition of an angular velocity to the turbine. In the post-processing stage, it is possible to obtain the torque coefficient on the rotor shaft, allowing the calculation of the power coefficient for the turbine. In addition to the performance analysis, it is also made a qualitative analysis of the flow characteristics over the turbine rotor and in both cases presenting a good correspondence with the results in the literature. The helical Savonius turbine presents a value of power coefficient of 0.175 to a tip speed ratio of 0.58 whereas blocking effect correction.

Les études conduites au cours de ce travail de thèse ont montré que l’optimisation de la position du cycliste sur son vélo était un élément déterminant de la performance. Nos recherches ont porté sur quatre axes principaux : la conception et la validation d’outils de mesure, l’étude de la position aérodynamique, l’étude de la position assise et enfin l’étude de la position danseuse.L’ensemble des résultats obtenus montrent que la capacité de performance du cycliste peut être améliorée en position aérodynamique en augmentant le ratio entre la puissance mécanique (Pméca) et la surface frontale effective (SCx). Le confort représente également un des principaux facteurs de la performance en contre‑la‑montre (CLM) puisqu’il détermine l’aptitude du cycliste à maintenir sa position au cours du temps. Nos travaux montrent une amélioration du confort avec des semelles orthopédiques, chez les cyclistes affectés par une inégalité de longueur des membres inférieurs (ILMI), liée à une réduction des mouvements du bassin. Une correction orthopédique induit également une augmentation du rendement énergétique (+5,7 %). Ainsi, les cyclistes affectés par une ILMI sont recommandés de la compenser avec des semelles orthopédiques individualisées de façon à améliorer leur performance en CLM. Lors d’une étude préliminaire, nous avons également montré la relation entre les mouvements de la tête et le SCx, c’est pourquoi les cyclistes doivent réduire au maximum ces mouvements afin de minimiser leur SCx et ainsi maximiser leur performance. L’évaluation de la position aérodynamique doit être réalisée en conditions réelles de locomotion, que ce soit pour l’évaluation de S ou de SCx. Le développement de nos deux applications est donc un réel atout pour l’évaluation de la traînée aérodynamique (Ra) de manière individualisée dans les prochaines années puisqu’elles rendent le traitement plus accessible aux entraîneurs. Enfin, bien que nous ayons initié une nouvelle méthodologie d’évaluation de la position aérodynamique en associant numérisation 3D et modélisation numérique de la mécanique des fluides, cette méthode serait plutôt recommandée pour l’individualisation de l’équipement.La position assise peut également être optimisée en augmentant l’indice d’efficacité mécanique (IEM) du cycliste, quel que soit le niveau et le sexe. Cette augmentation de l’IEM passe principalement par une diminution de la force résistante (Fres) dans la phase de montée de la pédale. Malgré tout, le cycliste ne doit pas tirer sur la pédale pour générer un couple propulsif car cette stratégie est contre-productive d’un point de vue énergétique. Il serait intéressant d’étendre notre première étude, établie en laboratoire, sur le terrain pour analyser les adaptations biomécaniques du pédalage des cyclistes aux conditions rencontrées sur le terrain. Les différences observées en laboratoire, sur terrain plat et en montée laissent penser que les cyclistes adaptent leur pédalage selon les conditions dans lesquelles ils évoluent.Enfin, les travaux menés sur la position danseuse montrent que les cyclistes augmentent leur coût mécanique (CM) (+4,3 % en laboratoire vs. +19 % sur le terrain) par rapport à la position assise alors que la consommation d’oxygène reste stable entre les deux positions. Ces pertes mécaniques en position danseuse sont principalement dues à l’augmentation du coefficient de roulement (Cr) due aux oscillations latérales du vélo et donc à la torsion des pneus. Puisque les pertes mécaniques sont plus élevées sur le terrain que sur tapis roulant, d’autres facteurs semblent contribuer à cette différence comme la Ra (~10 W), le matériel utilisé par les cyclistes, le Cr de la route et la technique adoptée. Aussi, la position danseuse induit une augmentation du CM pour maintenir la vitesse de déplacement face aux variations de pente en montée. Les cyclistes sont donc fortement recommandés de réduire l’augmentation du CM en position danseuse comparée à la position assise. / The studies conducted during this PhD research showed that optimizing the position of the cyclist on the bicycle is a key factor influencing cycling performance. Our research focused on four main axes: the design and validation of measurement tools, the study of the aerodynamic position, the study of the seated position and the study of the standing position.All the results showed that the performance capacity of cyclists can be improved in aerodynamic position by increasing the ratio between the mechanical power (PO) and the drag area (ACd). Comfort is also a significant factor in time trial (TT) performance as it determines the ability of the cyclist to maintain position over time. Our works show that comfort can be improved via orthopaedic correction in cyclists affected by lower limb length inequality (LLLI) in the TT position, related to a reduction in pelvis movements. The orthopaedic correction also induces an increase in gross efficiency (+5.7%). Thus, this improvement in comfort could increase the PO and/or the amount of time the aerodynamic position can be maintained during a TT. Therefore, cyclists affected by LLLI should compensate LLLI with individualised foot orthotics to improve their TT performance. In a preliminary study, we also showed that there is a relationship between head movements and ACd. Therefore, cyclists should minimise these movements to minimise their ACd and maximise their performance. Aerodynamic position must be evaluated in real cycling locomotion, whether for the evaluation of A or ACd. We have developed two applications that are a real asset for the dynamic evaluation of aerodynamic drag (Ra) as they make the data analysis more accessible to coaches. Finally, although we have initiated a new method to assess ACd in the aerodynamic position by combining 3D scanning and computational fluid dynamics simulation, this method is also recommended for individualisation of cycling equipment.The seated cycling position can also be optimised by increasing the cyclists’ force effectiveness (FE), regardless of practice level or gender. This increase in FE is mainly due to a decrease in resistive force (Fres) during the upstroke phase of pedalling. Nevertheless, the cyclist should not pull on the pedal to generate propulsive torque because this strategy is counterproductive from an energy point of view. It would be interesting to extend our first study, which was set up in a laboratory, to the field to analyse the biomechanical adaptations of cyclists to the real conditions of locomotion. The differences observed in the laboratory, on level ground and over an uphill grade suggest that cyclists adjust their pedalling technique according to the conditions under which they are performing.Finally, studies of the standing cycling position show that cyclists increase their mechanical cost (MC) (+4.3% in the laboratory vs. +19% in the field) compared to the seated position; however, oxygen consumption was similar between the two positions. These mechanical losses (13 W in the laboratory vs. 49 W in the field) in the standing position are mainly due to increased rolling resistance coefficient (Crr), induced by the lateral sways of the bicycle and therefore torsion of the tyres. Because the observed mechanical losses are higher in the field than on the treadmill, other factors could contribute to this difference, such as Ra (~10 W), the equipment used by cyclists, the Crr of the road surface and the technique adopted. Also, the standing position induces an increase in MC to maintain constant speed when faced with uphill slope variations. Cyclists are therefore strongly recommended to reduce the increase of the MC in standing position compared to the seated position. This reduction in mechanical losses can be achieved by decreasing lateral sways and Ra.

Atmospheric icing presents serious challenges to the development of wind power of the wind energy industry in cold regions. The potential detrimental impact on the safe operation of wind turbines and the energy harvest hasn't been fully understood and requires further investigation. This thesis presents the research on icing profiles under different weather conditions and their impact on natural frequency, fatigue life, and lift and drag of the wind turbine blade. The research aims to develop a further understanding of the effect of atmospheric ice accretion on the structural integrity and aerodynamic performance of wind turbine blades through numerical and aerodynamic investigations to address the challenges facing the industry. A 5-MW NREL (National Renewable Energy Laboratory) wind turbine blade was selected for this study, due to availability of required geometric design parameters and experimental data for verification. The turbine rotor and its three blades were modelled and numerically simulated with commercial finite element software ANSYS. Three icing scenarios were chosen according to the ISO Standard and the corresponding icing profiles were developed to investigate their influence on vibrational behaviours of the wind turbine blade and rotor under different weather conditions. Icing loads were applied on the leading edge of the blade and natural frequency results were compared between clean and iced blades. It was found that harsh icing weather drove the natural frequency down to the near resonance limit, which could lead to significant issue on structural integrity of the wind turbine. The effect of atmospheric ice accretion with additional load due to varying wind speeds on the fatigue life of the wind turbine blade has been investigated. Significant reduction of fatigue life was found due to the increase of the von Mises stresses. Finally, computational fluid dynamics (CFD) analysis was carried out to investigate the effect of atmospheric ice accretion on the aerodynamic performance of typical 1-MW and 5-MW wind turbine blades. Results of the drag and lift coefficients and power production under different icing scenarios were obtained for five angles of attack. Compared with the results of the clean aerofoil profile, remarkable reduction in the power generation was observed due to the accreted ice at various aerofoil sections in the spanwise direction of the blade, demonstrating the detrimental impact of atmospheric icing on energy harvest for the wind energy industry.