This study investigates the influence of wall roughness on large-scale structures within turbulent boundary layers, using wall-parallel stereoscopic Particle Image Velocimetry (PIV) at a Reynolds number of 1.3 × 106m−1. The data was collected at a distance of = 2.8 from the wall under adverse = 0.98, small = −0.04, and favorable = −0.60 pressure conditions. It was observed that coherent structures larger than the field of view (FOV) modify their length scales, streamwise orientation and spanwise distribution in response to changes in surface roughness and pressure gradients. The study also examines implications wall similarity hypothesis by comparing the development of these large-scale structures over smooth and rough wall flows under small pressure gradient and identical test conditions. Notably, the results reveal that existing models may not accurately capture the observed dynamics, as evidenced by discrepancies with previous studies, thereby enhancing our understanding of turbulent flow dynamics in non-equilibrium conditions. / Master of Science / Understanding the behavior of turbulent air and water flows around objects is crucial for improving engineering designs and various environmental applications. This study investigates how surface roughness, such as on ship hulls or aircraft wings, affects the movement of large-scale structures in turbulent flows. Advanced flow visualization techniques were employed to observe these turbulent structures in detail over homogeneous roughness and varying pressure gradients. The findings demonstrate that rough surfaces significantly alter the movement and interaction of these large-scale turbulent structures. Specifically, favorable pressure gradients result in organized flow structures, whereas adverse pressure gradients cause reorganization, altering the size and distribution of these structures within the flow. By comparing smooth and rough surfaces under identical conditions, the study aims to evaluate how well existing hypotheses predict these changes. The results highlight that rough surfaces and pressure variations critically impact turbulent flow characteristics, emphasizing the need for more sophisticated criteria to improve predictions and designs in real-world applications. This research provides valuable insights into the dynamics of turbulent flows over rough surfaces and stresses the importance of refining current models for better accuracy in practical engineering applications.

Doctoral thesis in detail and comprehensively deals with mechanic of incipient bedload motion for gravel-bed rivers. This study based on theoretical knowledge, experimental researches, numerical models and field survey extends present knowledge concerning with incipient bedload motion and sediment transport at small relative height and hydraulically rough surface bed for turbulent unaerated free surface flow. Incipient bedload motion and sediment transport have been determined for homogeneous and inhomogeneous bed materials. For homogeneous bed material the velocity profiles have been described by different methods in near the bed. Further, hydraulic flow resistance has been evaluated. In the case of inhomogeneous bed material, static armouring and influence of surface layer sorting on hydraulic roughness have been investigated. The correctness of obtained knowledge has been confirmed on the object of nature-inspired river widening. Results shown, among others, that incipient bedload motion does not depend on relative height or final armouring of surface layer to what extend hydraulic roughness is influenced.

Στην εργασία αυτή αξιολογούνται οι πετρογραφικές και φυσικομηχανικές ιδιότητες που καθορίζουν την καταλληλότητα των ανθρακικών σχηματισμών του Νομού Αιτωλοακαρνανίας Δυτικής Ελλάδας,που ανήκουν στη ζώνη Ωλονού-Πίνδου ηλικίας Άνω Κρητιδικού.Σκοπός είναι να συσχετισθούν οι ιδιότητες αυτές,να προσδιοριστεί η συμπεριφορά των αργιλικών προσμίξεων και να καθορισθεί η καταλληλότητας τους,για χρήση τους ως αδρανή σε έργα οδοποιϊας.Δυο από τις δοκιμές που προσδιορίζουν την καθαρότητα των αδρανών είναι η δοκιμή ισοδύναμου άμμου και η δοκιμή μπλε του μεθυλενίου,τα αποτελέσματα των οποίων συσχετίστηκαν με τις πετρογραφικές και φυσικομηχανικές παραμέτρους των πετρωμάτων. / In this paper we evaluate the petrographic and physicomechanical properties which determine the suitability of carbonate formations of Aitoloakarnania Western Greece , in Olonos - Pindos unit Cretaceous age.The objective is to relate these properties to determine the behavior of clay impurities and determine the suitability for use as aggregates in road construction.Two of the tests that used to determine the purity of the aggregates is the sand equivalent and methylene blue, the results of which were associated with the petrographic and physico-mechanical parameters of rocks .