Muhammet Emin Emiroglu

The safety of hydraulic structures has social, economic, and environmental significance. To eliminate the damage induced by local scouring, either the scouring should be prevented entirely or the scouring depth should be minimized. This study numerically investigated the local scour that develops in the plunge pool downstream of high-head, classical contracted rectangular weirs operating under free overfall conditions. In the numerical analysis, a three-dimensional Reynolds-averaged Navier–Stokes (RANS) model with a standard k–ε turbulence closure was implemented in Flow-3D®. The analyses were conducted for three unit flow rates (q=0.15, 0.30, and 0.60 m3/s m) and three drop heights (H=0.25, 0.50, and 1.00 m) to determine the maximum scouring depth. Furthermore, the water jet velocity and impingement angle were analyzed. The experimental results were utilized to test the accuracy of the numerical model. For all cases, about 90 % of the equilibrium scour depth was reached within the first 15–20 min, consistent with previous studies. According to the results, the equilibrium scour depth increased from approximately 0.16 m to 0.23 m when the unit discharge was raised. However, after a specific value of the head height, the effect on the depth of scouring is slightly reduced due to the increased air entrainment entering the downstream pool. Computed jet impact velocities ranged from about 2.0 to 4.9 m/s, with impact angles increasing up to ~82° as the drop height increased. The results of the numerical model are generally compatible with experimental studies. This study is original in that it provides a three-dimensional CFD-based assessment of local scour downstream of high-head weirs under free overfall conditions and proposes a practical approach to estimate long-term equilibrium scour depth and jet impact characteristics.

Savaklar, hidrolik mühendisliğinde suyun akışını kontrol etmek, akımı düzenlemek ve debi ölçümleri yapmak amacıyla yaygın olarak kullanılan yapılardır. Bu çalışmada, deney kanalına yerleştirilen eğrisel savaklar üzerindeki akımın su yüzü profili, hassas ölçümler yapılarak deneysel olarak incelenmiştir. Bu amaçla, savak memba bölgesinde beş, savak kretinde on bir ve mansap bölgesinde yedi adet ölçüm noktası belirlenmiştir. Belirlenen okuma noktaları, akımın farklı bölgelerdeki davranışını daha hassas bir şekilde gözlemlemeye olanak tanımış ve su yüzü profilinin kapsamlı bir analizini sağlamıştır. Deneysel çalışmalar, farklı akım koşullarında, savak geometrisinin değişimi ile su yüzü profilindeki değişimi belirlemek amaçlanmıştır. Çalışmada elde edilen bulgulara göre, savak uzunluğundaki değişim su yüzü profilinde çok önemli bir değişikliğe neden olmamıştır. Ayrıca, savak yüksekliğindeki değişimin, su yüzü profilinde, savak yüksekliğinin artması ile birlikte artan eğrisel bir akım çizgisi oluşturduğu görülmüştür. Genel olarak, debinin artması ile birlikte nap yükündeki artışla su yüzünün eğriselliği daha belirgin hale gelmiştir.

Few studies have focused on abutments located on curved channels; previous studies have typically focused on straight channels. The present study experimentally examined the local scour that occurs around abutments of different lengths placed on inner and outer banks along a curved channel under clear-water scour flow conditions. The local scour around an abutment in a curved channel is a function of the upstream Froude number, flow intensity, the angle of the bend curvature and the ratios of abutment length to flow depth, abutment length to abutment width and abutment length to channel width. The maximum scour depth around the abutments placed on the outer bank was 1.45 times the scour depth on the inner bank. An empirical equation was developed containing all the dimensional parameters for equilibrium scour depth. The average percentage error of the proposed equation was 2%.

Aeration is a procedure carried out to enhance water quality. Various hydraulic structures and devices for water aeration have been utilized in the literature. The venturi nozzle plays a significant role in water jet aeration. The aeration efficiency achieved with the venturi nozzle is seven times higher than that of the classic circular nozzle. In this experimental study, various holes of different sizes were created in the throat portion of the venturi nozzle; thus, air was drawn into the flow by creating negative pressure. The study examined the impact of the venturi nozzle on aeration efficiency by varying the length of the throat portion. The findings revealed that making a hole in the throat portion significantly improved aeration efficiency in-creasing the size of the throat portion had a detrimental effect.

Check dam designs have attracted attention recently due to the clogging of classical check dam structures with sediment and wooden material carried during the flood quickly. These structures regulate flow characteristics and debris flow. However, until now, the impacts of these structures on flow characteristics have received little attention in the literature. Therefore, it is necessary to develop new models to increase these structures' trapping capacity or extend the clogging time. In this study, the flow characteristics of check dams with horizontal, vertical, and angled openings were numerically analyzed for two-phase (water and air) flow. The numerical model was validated using experimental results in the literature. For the study in which twelve analyses were performed, four different check dam models (i.e., check dam with the classical, the narrow horizontal opening, the vertical openings, and angled openings) and three different unit flows (0.04, 0.03, and 0.02 m3 s-1 m-1) were used in the analysis. The open-source software OpenFOAM and the k-ω SST turbulence model were used for the numerical analysis using the Computational Fluid Dynamics (CFD) method. The highest energy dissipation rate among slit check dam models was seen in Model-3 at maximum unit flow, whereas it was attained in Model-2 at minimum unit flow. There is no difference in the energy dissipation rate at low unit flows whether the openings are positioned vertically or angled; nevertheless, the vertical model (Model-3) is observed to be more efficient at maximum unit flow.

The purpose of aeration in water is to transfer or remove gases from the water. Dissolved oxygen is critical for living life. In water engineering, aeration and oxygen transfer using water jets are common. In this study, various venturi nozzles with air holes in the throat portion were manufactured and meaningful experiments were conducted to determine their oxygen transfer efficiency and aeration performance., the venturi nozzles with throat diameters 14, 17 and 20 mm were used in the experimental study. The ratio of the diameter of the air holes to the diameter of the throat portion is taken as 0.1, 0.2 and 0.3. Different experiments were carried out for nine different hole diameters. In addition, the ratio of the throat portion length to the throat portion diameter was taken as 1.00 and 0.50. In addition, comprehensive experiments were carried out by considering the ratio of outlet length to outlet diameter for all nozzles, 1 and 2, and for one venturi, 1, 2, 3, 4 and 5. The experiments were also conducted for the circular nozzle to make comparisons. In this study, venturi nozzles gave better results than circular nozzles, and higher aeration performance values were obtained for the ratios 0.2 and 0.3, 1, 0.50 and 0.50. It was found that the aeration performance of the venturi nozzle was approximately 6.5 times higher than the air entrainment rate performance of the circular nozzle and 2.5 times higher in terms of oxygen transfer.