Υπολογιστική ανάλυση μεταβατικών και έντονα αποκολλημένων ροών με εφαρμογή σε ανεμογεννήτριες

Laminar to turbulent transition and higher fidelity turbulence modeling have been implemented in the parallelized, unstructured, compressible Navier-Stokes solver MaPFlow.In the case of laminar to turbulent transition, both boundary layer and transport equation approaches were assessed. These include the e N method and the transport equation models γ-Re θ , γ and AFT. All approaches were validated against a wide range of cases concerning airfoils, wings/blades and generic fuselage, stemming from both the wind energy and the aeronautics sectors. The focus was on integrated loads and transition locations. In the context of two-dimensional simulations, the boundary layer e N method and the AFT transport equation model exhibit better performance than the other alternatives. The γ-Re θ model is also a viable option if Reynolds numbers not higher than 6 x 10 6 are considered. For Reynolds numbers higher than this limit, the accuracy of the model was found to deteriorate. However, both the e N method and the AFT model cannot be used to predict crossflow transition in the context of three-dimensional simulations. In such scenarios, the γ-Re θ model can give accurate results, provided that Re numbers fall within the aforementioned limit.In the case of higher fidelity turbulence modeling, both Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) approaches were implemented. LES utilized the Smagorinsky subgrid model. Regarding DES, both Delayed DES (DDES) and Improved Delayed DES (IDDES) variants were considered. The focus was on flow cases with massive separation. Both LES and DES provided more accurate results than the baseline Unsteady Reynolds Averaged Navier Stokes (URANS) simulations when compared to experiments and reference results. Neither LES nor DES were pushed to their limits. DES is considered computationally less demanding, due to wall modeling inside the boundary layer region. Therefore, it is a more viable option than LES for industrial applications. However, due to wall modeling, DES is not expected to perform well in flows where the presence and development of small turbulent scales inside the boundary layer are important. In those cases, LES using fine meshes should be considered.Στην παρούσα διατριβή μελετήθηκε η μετάβαση της ροής από στρωτή σε τυρβώδη καθώς και η συμπεριφορά ροών μεγάλων αριθμών Reynolds στα πλαίσια προσομοίωσης τους με μεθόδους υψηλής πιστότητας.Για την προσομοίωση ροών με μετάβαση εξετάστηκαν μέθοδοι με υπολογισμό οριακού στρώματος και μέθοδοι με εξισώσεις μεταφοράς. Αυτές περιλαμβάνουν την μέθοδο e N καθώς και τα μοντέλα γ-Re θ , γ και AFT. Όλες οι μέθοδοι δοκιμάστηκαν σε αεροτομές, πτέρυγες και άτρακτο γενικής μορφής, σε εφαρμογές οι οποίες προέρχονταν από τους τομείς της αεροναυτικής και της αιολικής ενέργειας. Οι συγκρίσεις αφορούσαν κατά κύριο λόγο σε αεροδυναμικά φορτία και θέσεις μετάβασης. Στα πλαίσια διδιάστατων προσομοιώσεων, η μέθοδος e N με υπολογισμό οριακού στρώματος και το μοντέλο AFT έδωσαν πιο ακριβή αποτελέσματα από τις υπόλοιπες μεθόδους. Το μοντέλο γ-Re θ είναι μια καλή εναλλακτική, αρκεί ο αριθμός Reynolds να μην υπερβαίνει τα 6 εκατομμύρια. Πέραν αυτού του ορίου, η ακρίβεια των αποτελεσμάτων του μοντέλου μειώνεται σημαντικά. Ωστόσο, η μέθοδος e N και το μοντέλο AFT δεν δύνανται να χρησιμοποιηθούν για την μοντελοποίηση τρισδιάστατης μετάβασης στο πλαίσιο τρισδιάστατων προσομοιώσεων. Σε αυτές τις περιπτώσεις, το μοντέλο γ-Re θ εμπλουτισμένο με όρους εγκάρσιας ροής μπορεί να δώσει καλά αποτελέσματα, αρκεί ο αριθμός Reynolds να είναι στα αποδεκτά για το μοντέλο όρια. Όσον αφορά στις μεθόδους προσομοίωσης τύρβης υψηλής πιστότητας, εξετάστηκαν οι μέθοδοι Large Eddy Simulation (LES) και Detached Eddy Simulation (DES). Για τις προσομοιώσεις LES χρησιμοποιήθηκε το μοντέλο μικρών κλιμάκων του Smagorinsky. Η εφαρμογή του DES περιελάμβανε τις μεθόδους Delayed DES (DDES) και Improved Delayed DES (IDDES). Το ενδιαφέρον εστιάστηκε στην μοντελοποίηση ροών με μεγάλη αποκόλληση. Τόσο το LES όσο και το DES ήταν σε θέση να δώσουν πιο ακριβή αποτελέσματα από τους απλούς, μη-μόνιμους Reynolds Averaged Navier Stokes υπολογισμούς (Unsteady RANS) σε σύγκριση με πειράματα και υπολογιστικά αποτελέσματα από τη βιβλιογραφία. Το μοντέλο DES θεωρείται λιγότερο απαιτητικό σε υπολογιστικούς πόρους λόγω της μοντελοποίησης του οριακού στρώματος η οποία οδηγεί σε μικρότερες απαιτήσεις πλέγματος κοντά στην στερεή επιφάνεια. Ωστόσο, το DES δεν αναμένεται να μπορεί να δώσει αξιόπιστα αποτελέσματα σε ροές όπου η παρουσία και η εξέλιξη μικρών κλιμάκων τύρβης στο οριακό στρώμα είναι σημαντική, και που το μοντέλο LES πλεονεκτεί εκ κατασκευής. Σχετικά σημειώνεται ότι οι LES προσομοιώσεις δεν έφτασαν στα υπολογιστικά τους όρια όσον αφορά στο πλέγμα. Για να παραχθούν αξιόπιστα αποτελέσματα σε αυτές τις περιπτώσεις πρέπει να χρησιμοποιηθεί LES με πυκνό υπολογιστικό πλέγμα

Υπολογιστική ανάλυση μεταβατικών και αποκολλημένων ροών με εφαρμογή σε ανεμογεννήτριες

Laminar to turbulent transition and higher delity turbulence modeling have been implemented in the parallelized, unstructured mesh, compressible Navier-Stokes solver MaPFlow. In the case of laminar to turbulent transition, both boundary layer and transport equation approaches were assessed. These include the eN method and the transport equation models -Re , and AFT. All approaches were validated against a wide range of cases concerning airfoils, wings/blades and generic fuselage, stemming from both the wind energy and the aeronautics sectors. The focus was on integrated loads and transition locations. In the context of two-dimensional simulations, the boundary layer eN method and the AFT transport equation model exhibit better performance than the other alternatives. The -Re model is also a viable option if Reynolds numbers not higher than 6 x 106 are considered. For Reynolds numbers higher than this limit, the accuracy of the model was found to deteriorate. However, both the eN method and the AFT model cannot be used to predict cross ow transition in three-dimensional simulations. In such scenarios, the -Re model can give accurate results, provided that the Reynolds numbers fall within the aforementioned limit. In the case of higher delity turbulence modeling, both Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) approaches were implemented. LES utilized the Smagorinsky subgrid model. Regarding DES, both Delayed DES (DDES) and Improved Delayed DES (IDDES) variants were considered. The focus was on ow cases with massive separation. Both LES and DES provided more accurate results than the baseline Unsteady Reynolds Averaged Navier Stokes (URANS) simulations when compared to experiments and reference results. Neither LES nor DES were pushed to their limits. DES is considered computationally less demanding, due to wall modeling inside the boundary layer region. Therefore, it is a more viable option than LES for industrial applications. However, due to wall modeling, DES is not expected to perform well in ows where the presence and development of small turbulent scales inside the boundary layer are important. In those cases, LES using ne meshes should be considered

Aerodynamic analysis of non-conventional airfoils for use in wind turbine blades

85 σ.Στην παρούσα διπλωματική μελετήθηκε διδιάστατα η αεροδυναμική συμπεριφορά διάφορων μη-συμβατικών αεροτομών, ώστε να διαπιστωθεί αν δύνανται να αποτελέσουν βιώσιμη και περισσότερο παραγωγική λύση έναντι των αντίστοιχων συμβατικών για χρήση σε πτερύγια ανεμογεννητριών.In the current thesis, various non-conventional airfoils were analyzed in two dimensional airflow in order to ascertain whether they are more suitable for use in wind turbine blades than the corresponding conventional ones.Κωνσταντίνος Π. Διακάκη

Summary of the Blind Test Campaign to predict the High Reynolds number performance of DU00-W-210 airfoil

This paper summarizes the results of a blind test campaign organized in the AVATAR project to predict the high Reynolds number performance of a wind turbine airfoil for wind turbine applications. The DU00-W-210 airfoil was tested in the DNW-HDG pressurized wind tunnel in order to investigate the flow at high Reynolds number range from 3 to 15 million which is the operating condition of the future large 10MW+ offshore wind turbine rotors. The results of the experiment was used in a blind test campaign to test the prediction capability of the CFD tools used in the wind turbine rotor simulations. As a result of the blind test campaign it was found that although the codes are in general capable of predicting increased max lift and decreased minimum drag with Re number, the Re trend predictions in particular the glide ratio (lift over drag) need further improvement. In addition to that, the significant effect of the inflow turbulence on glide ratio especially at high Re numb ers is found as the most important parameter where the prediction as well as the selection of the correct inflow turbulence levels is the key for correct airfoil designs for the future generation 10MW+ wind turbine blades

Open City Museum: unveiling the cultural heritage of Athens through an -augmented reality based- time leap

Summarization: A nation’s cultural heritage is of great importance both for indigenous people as well as for foreigners as it is a nation’s contribution to humanity and global civilization. As the spark to discover that treasure has ignited and travelling around the world has become much easier, it is necessary to enhance the way that monuments are exhibited and communicated. Current technology offers the capability to alter the way that information is provided and represented. Augmented reality (AR) is the most characteristic example as it surpasses the limits that exist in other media offering a unique experience to the user. A great challenge for AR is to shed a new light on monuments, especially in cities like Athens, filled with historical monuments. In this paper we describe the methodology that was followed in order to create an AR application that will provide users with a virtual time leap experience in the past depicting the monument’s history in its social context. Thus, the issues emerging during the development of an AR app is discussed, as well as solutions to common problems regarding its utilization in outdoors space. Aiming to shed light on its importance throughout the centuries, an interdisciplinary research has been conducted combining fields like architecture and psychology in order to inform and in parallel, arouse emotions to visitors and thus, intensify the experience. Supporting that, user experience has been enhanced following a UI/UX approach, which provides the appropriate tools between easy-to-use and following a narrative.Παρουσιάστηκε στο: International Conference on Human-Computer Interactio