Ayşe Yüksel Ozan

This research employs computational fluid dynamics to examine the velocity field and bed shear stress produced by a propeller jet. A steady-state MRF approach was utilized to approximate the propeller’s swirling. 10 inflation layers were applied at both the propeller and the seabed to better enhance the resolution of the near-wall gradients. Model sensitivity to turbulence-model selection was evaluated by testing the SST and the realizable k-ε models. The findings indicated that both models effectively simulated the overall jet structure and shear footprint, yet they exhibited differences in detail: the k-ε model estimated a higher shear stress value of ~0,11 Pa with a broader scour pattern, whereas the SST model maintained a narrower jet core and a more concentrated vortex with shear stress maxima of ~0,078 Pa. The results indicate the importance of selecting appropriate mesh configurations and turbulence models for accurately predicting propeller jet scours.

This study investigated twin-propeller-induced scour on sandy seabeds with varying grain sizes (d₅₀ = 0.11, 0.5, and 0.95 mm) through a series of laboratory experiments. The effects of propeller rotation speed (rpm), offset height (y₀), propeller diameter (D_p), and sediment grain size (d₅₀) on scour development were examined. Results indicated that sediment grain size significantly influences scour patterns. A key objective was to develop predictive expressions for primary scour characteristics at equilibrium: maximum scour depth (S_max), scour hole length (L_max), and maximum scour width (B_max). Using a nonlinear regression approach, the proposed expressions demonstrated strong predictive performance. Findings show that equilibrium scour depth increases with higher Froude numbers (F₀) but decreases with larger sediment size (d₅₀) and higher propeller offset (y₀). Additionally, empirical equations were formulated to predict the temporal evolution of scour depth, achieving high correlations with experimental data (R² > 0.97). These results enhance understanding of scour induced by unconfined twin-propeller jets in harbors or navigation channels and provide valuable data for the design and protection of harbor basins.

This study presents an experimental investigation of seabed scour in front of a quay wall due to the interaction between propeller jet flow and the wall effect. For this purpose, two propellers (D_p = 6 and 9 cm in diameter) were used, and four different wall clearances (X_w = 2, 4, 6 and 8D_p) were selected. The experiments were carried out for propeller rotational speeds ranging from 300 rpm to 1000 rpm. The effect of clay content was also investigated using three different clay contents of 0, 5 and 10% by weight (i.e., p = 0, 0.05 and 0.1). The results of the study reveal that at low propeller rotational speeds, scour in the cohesive seabed is decreased compared to that in the cohesionless bed. The scour profiles obtained at high propeller rotational speeds for the seabed with a clay content of 5% were found to have the same characteristics as those obtained for the cohesionless seabed. However, as the clay content increases to 10%, significant changes occur in the scour profiles, and the cohesion effect begins to dominate.

Bu çalışmada, deneysel olarak yapılan tam batmış bitkilerin açık kanal akımlarına olan etkisinin incelendiği bir çalışma, FLOW-3D ile modellenmiştir. Deney sonuçları ve sayısal model sonuçları karşılaştırılmıştır. Modellemede Yılmazer ve ark. [10] tarafından gerçekleştirilen deneye ait veriler kullanılmıştır.

Urban stormwater is an important environmental problem, especially for metropolitans worldwide. The most important issue behind this problem is the need to find green infrastructure solutions, which provide water treatment and retention. Floating treatment wetlands, which are porous patches that continue down from the free-surface with a gap between the patch and bed, are innovative instruments for nutrient management in lakes, ponds, and slow-flowing waters. Suspended cylindrical vegetation patches in open channels affect the flow dramatically, which causes a deviation from the logarithmic law. This study considered the velocity measurements along the flow depth, at the axis of the patch, and at the near-wake region of the canopy, for different submerged ratios with different patch porosities. The results of this experimental study provide a comprehensive picture of the effects of different submergence ratios and different porosities on the flow field at the near-wake region of the suspended vegetation patch. The flow field was described with velocity and turbulence distributions along the axis of the patch, both upstream and downstream of the vegetation patch. Mainly, it was found that suspended porous canopy patches with a certain range of densities (SVF20 and SVF36 corresponded to a high density of patches in this study) have considerable impacts on the flow structure, and to a lesser extent, individual patch elements also have a crucial role.

Aquatic vegetation in rivers and coastal regions controls the flow structure in terms of mean velocity and turbulence. The vegetation in the flow affects the transportation of nutrients, microbes, dissolved oxygen, sediment, and contaminants; therefore, the flow characteristics of different types of vegetation layers should be examined in order to understand the effects of vegetation on the flow structure. In this paper, the effect of the submergence ratio and SVF (Solid Volume of Fraction) of a vegetation patch, which was present across half of the channel in a spanwise direction, on the flow structure at the wake region was examined. For this purpose, different submergence ratios with different SVFs were considered in the experiments, and velocity measurements were performed in the wake region of the vegetation layer with an Acoustic Doppler Velocimeter (ADV). According to the results, the effect of different vegetation heights and SVFs on the velocity distribution was obtained. Moreover, inflectional velocity distribution over the cross-section in the wake region of the vegetation layer was obtained, and it was concluded that jet flow occurred in the non-vegetated half of the channel due to the vegetation layer.