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• MakaleAçık Erişim2026/r/gumushane/12309
  Refinement of field-measured velocity profiles via CFD comparison: A case study on single-phase flow in aeration tanks

  Yilmaz Çelik, Damla; Vaheddoost, Babak; Aras, Egemen; Şibil, Rahim

  The accuracy of field measurements obtained from aeration tanks is of critically important for the validation of Computational Fluid Dynamics (CFD) models. In many cases, the employed validation metrics serve as a fundamental keystone for evaluating both the credibility of experimental data and the accuracy of numerical simulations. In this study, a novel data refinement approach is developed to assess the physical plausibility of velocity measurements collected from a full-scale aeration tank. Unlike conventional validation approaches, the CFD model is utilized as a reference framework within a reverse-approach perspective to evaluate the reliability of field data. Measurement points affected by acoustic noise, surface sludge interference, and turbulence near static structures were identified and excluded through curve-fitting and statistical filtering techniques. Velocity data obtained with the help of an Acoustic Doppler Current Profiler (ADCP) across six lateral and 53 vertical layers were evaluated using the Coefficient of Determination (R2), Relative Error (RE), and Performance Index (PI) metrics. The maximum-elimination combined with polynomial fitting notably enhanced the model accuracy, reducing RE from −123 % to 20 %, increasing R2from 0.054 to 0.96, and improving PI from 2.6 to 1.16. As a result, the refined dataset provided a more consistent and realistic representation of the flow structure and established a robust observational basis for the future calibration.

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• MakaleAçık Erişim2025/r/gumushane/11761
  Hydrodynamic optimization of full-scale aeration tanks using field measurements and computational fluid dynamics modeling

  Yılmaz Çelik, Damla; Yılmaz, Naz; Şibil, Rahim; Aras, Egemen; Vaheddoost, Babak

  Improving energy efficiency and operational performance in wastewater treatment plants largely relies on precise hydrodynamic analysis. In this context, field-based studies are essential for understanding system behavior under real operational conditions. This study was conducted at a full-scale wastewater treatment plant, where flow dynamics in the aeration tank were evaluated through extensive field measurements and computational fluid dynamics modeling. Data were collected from 98 locations across 15 different depth levels using an Acoustic Doppler Current Profiler and a Hach FH950 velocity meter. The numerical model was initially validated with the help of experimental field data, enabling an accurate assessment of flow characteristics at varying depths. Results revealed that the low-velocity zones and non-uniform velocity distributions negatively affect system performance. It is also concluded that the inlet and outlet positions disturb the favorable circulation patterns and flow uniformity. Geometric optimization strategies were implemented to develop solutions, which led to a more uniform velocity distribution and improved hydraulic efficiency. By integrating detailed field measurements with numerical modeling, this study provides a comprehensive understanding of aeration tank hydrodynamics and offers practical design recommendations for improving overall system performance.

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• MakaleYalnız künye2024/r/gumushane/16537
  Analysis of open channel flow with various layered vegetation using CFD, considering different near-wall treatment methods

  Sibil, Rahim

  PurposeThe purpose of this paper is to investigate the impact of near-wall treatment approaches, which are crucial parameters in predicting the flow characteristics of open channels, and the influence of different vegetation covers in different layers.Design/methodology/approachAnsys Fluent, a computational fluid dynamics software, was used to calculate the flow and turbulence characteristics using a three-dimensional, turbulent (k-e realizable), incompressible and steady-flow assumption, along with various near-wall treatment approaches (standard, scalable, non-equilibrium and enhanced) in the vegetated channel. The numerical study was validated concerning an experimental study conducted in the existing literature.FindingsThe numerical model successfully predicted experimental results with relative error rates below 10%. It was determined that nonequilibrium wall functions exhibited the highest predictive success in experiment Run 1, standard wall functions in experiment Run 2 and enhanced wall treatments in experiment Run 3. This study has found that plant growth significantly alters open channel flow. In the contact zones, the velocities and the eddy viscosity are low, while in the free zones they are high. On the other hand, the turbulence kinetic energy and turbulence eddy dissipation are maximum at the solid-liquid interface, while they are minimum at free zones.Originality/valueThis is the first study, to the best of the author's knowledge, concerning the performance of different near-wall treatment approaches on the prediction of vegetation-covered open channel flow characteristics. And this study provides valuable insights to improve the hydraulic performance of open-channel systems.

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• MakaleAçık Erişim2024/r/gumushane/20005
  Hesaplamalı akışkanlar dinamiği ile açık kanal akımında bitki örtüsünün akım özelliklerine etkisinin analizi

  Şibil, Rahim

  Bu çalışmada bitki örtüsünün, dikdörtgen bir açık kanal üzerindeki akım özelliklerine olan etkisi, Hesaplamalı Akışkanlar Dinamiği analizi kullanılarak incelenmiştir. Hesaplamalı Akışkanlar Dinamiği (HAD) için ANSYS Fluent yazılımı kullanılmıştır. Akımın üç boyutlu, sıkışmayan, türbülanslı ve kararlı olduğu kabul edilmiştir. Sayısal çalışma literatürde yapılan deneysel bir çalışma ile doğrulanmıştır. Sayısal çalışmanın deney sonuçlarını başarılı bir şekilde tahmin ettiği gözlemlenmiştir. Sayısal çalışma ve ölçüm sonuçları arasındaki bağıl hata %10’un altında bulunmuştur. Yapılan sayısal çalışmalar sonucunda, bitki örtüsünün kanalın akım ve türbülans özelliklerini önemli ölçüde değiştirdiği gözlemlenmiştir. Bitki örtüsü olan bölgelerde, su yüzeyinde hızların çok düşük olduğu, yaprak örtüsünün altında kökler arasında ise hızların yüksek olduğu ve maksimum hızın 0,1177 m/s ile bu bölgede gerçekleştiği tespit edilmiştir. Ayrıca türbülans viskozitesinin serbest alanlarda fazla olduğu gözlemlenirken türbülans enerji kırılımının katı-sıvı temas bölgelerinde fazla olduğu görülmüştür. Bu çalışma, açık kanal akışının bitki örtüsüyle etkileşimini anlamak ve açık kanal sistemlerinin hidrolik açıdan performansını geliştirmek için önemli bilgiler sağlamaktadır.

  İncele
• MakaleAçık Erişim2024/r/gumushane/14016
  Evaluation of turbulence models for the prediction of flow properties in vegetated channels

  Sibil (Şibil), Rahim

  The performance of turbulence models was investigated to predict the flow and turbulence features of the vegetated channel using computational fluid dynamics (CFD). The Ansys Fluent, CFD software was implemented for the numerical studies. The flow was three-dimensional, incompressible, steady, and turbulent. Ten turbulence models, provided by Ansys Fluent, were implemented for the comparative study. The numerical model was validated against an experimental study conducted in the literature. The numerical studies show that the Renormalization group k-ϵ model is the most successful model for predicting the flow characteristics of the vegetated channel with a Root Mean Square Error (RMSE) value of 0.2752. At the same time, the Reynolds Stress Model gives the least successful predictive performance, indicated by an RMSE value of 0.4302. Moreover, the Spalart-Allmaras (S-A) model offers the shortest computation time with a value of 6652.393 s, whereas the Shear Stress Transport k-ω model proves to be the most time-consuming with a value of 11 952.219 s. The velocity of water flow in a channel is not uniform as it is slower at the surface of leaves and faster in the free zones. The maximum velocity is observed in the middle section of the channel, below the leaf, and between the roots with the value of u = 0.1158 m/s. Furthermore, the characteristics of turbulence in a channel are influenced by several factors such as channel geometry, flow velocity, and vegetation distribution. As a result, the presence of vegetation in a channel affects the flow and turbulence characteristics of the water significantly.

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• MakaleAçık Erişim2023/r/gumushane/20263
  Bitki Örtülü Kanalların Akım Özelliklerinin Hesaplamalı Akışkanlar Dinamiği ile Belirlenmesinde Yakın Duvar Davranışının Etkisi

  Şibil, Rahim

  Bu çalışmada bitki örtülü kanalların akım özelliklerinin sayısal olarak tahmin edilmesinde önemli parametrelerden biri olan yakın duvar davranışı yaklaşımlarının sonuçlara etkisi incelenmiştir. Bu amaçla sayısal çalışmalar, Hesaplamalı Akışkanlar Dinamiği (HAD) metodu ile analiz yapabilen Ansys Fluent yazılımı kullanılarak üç boyutlu, türbülanslı, sıkıştırılamayan ve kararlı akım koşullarında bitki örtülü dikdörtgen kesitli bir kanal için gerçekleştirilmiştir. Türbülans modeli olarak gerçekleşebilir k-ε (realizable k-ε) türbülans modeli kullanılmıştır. Sayısal çalışmalarda yakın duvar davranışı için farklı yaklaşımlar kullanılarak (standart duvar fonksiyonları, ölçeklenebilir duvar fonksiyonları, denge dışı duvar fonksiyonları ve geliştirilmiş duvar davranışı) kanaldaki hız dağılımları tahmin edilmeye çalışılmış ve sayısal çalışmalardan elde edilen sonuçlar literatürde yapılmış deneysel bir çalışmayla karşılaştırılarak en başarılı metot ortaya konulmuştur. Yapılan karşılaştırma sonucunda “geliştirilmiş duvar fonksiyonu” yaklaşımıyla kurulan sayısal çalışma en başarılı tahmin sonucu veren yaklaşım olmuştur. Ayrıca HAD analizi sonucunda elde edilen kanaldaki hız dağılımları verilerek, bitki örtülü açık kanal akımında hidrolik özellikler incelenmiştir. Kanal içerisinde bitkisiz bölgede minimum hızlar sadece kanal tabanında oluşurken maksimum hız ise y=14.1 cm yükseklikte su yüzeyinde V=0.051 m/s olarak hesaplanmıştır. Bitkili bölgede ise hızların kanal tabanı ve yüzeydeki yaprak yüzeylerinde sürtünmeden dolayı sıfır olduğu görülmektedir. Maksimum hız tabandan y=7.8 cm yükseklikte V= 0.041 m/s olarak gözlemlenmiştir. Bu çalışma, açık kanal akışının bitki örtüsüyle etkileşimini anlamak ve açık kanal sistemlerinin hidrolik performansını geliştirmek için önemli bilgiler sağlamaktadır.

  İncele
• MakaleYalnız künye2023/r/gumushane/12707
  Hydrodynamic performance evaluation of screening on the physical unit operations in wastewater treatment based on experimentally validated CFD computations

  Şahin, Nagehan; Şibil, Rahim

  This paper introduces an evaluation of the hydrodynamic performance of the flow in the screens used on the physical unit operations in a selected full-scale wastewater treatment plant (WWTP) based on Computational Fluid Dynamics (CFD) simulations. The numerical study was carried out with the ANSYS Fluent, CFD software by using the three-dimensional (3 D), steady, incompressible flow based on the Reynolds-Average Navier-Stokes equations with three different turbulence modeling. The hydrodynamic behavior of the screening facility, combined with head pond-upstream channel-bar screens was evaluated under different conditions of the mass flow rate and velocity fields. Also, the numerical study was validated against the experimental study, which implemented in-situ measurements by Acoustic Doppler Velocimeter (ADV), and consistent results were obtained between the numerical and experimental study. Interestingly, while the Realizable (real) k-ε turbulence model with the relative error of 9.31% gave the best predicting results in the head pond, the renormalization group (RNG) k-ɛ turbulence model with the relative error of 9.05% gave the best predicting results in the upstream channel and through bar screens. As a result of the experimental measurements and CFD analyses carried out in the full-scale WWTP, the function of the screening facility was found to be incomplete. Moreover, a hydraulically improved new geometry was presented to operate the existing WWTP efficiently.

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• MakaleYalnız künye2023/r/gumushane/12622
  A Numerical Study to Evaluate the Changes in Dynamic Properties of Various Steel Truss Types Under Fire Conditions

  Sibil, R.; Ozyurt, E.

  This study numerically examines the changes in dynamic properties of fire-damaged steel trusses made of square hollow sections subjected to uniform and non-uniform heating scenarios. After verifying the numerical models at both ambient and elevated temperatures, a vast number of the simulations were analysed using non-linear finite element software to evaluate the effects of fire scenarios, truss types, and fire-damaged levels on the fire dynamic characteristics of square hollow section Warren, Howe, and Pratt trusses. The results indicated that the natural frequency of steel trusses significantly decreased as the fire-damaged level increased. In the case of local fire, the natural frequencies of the trusses began to drop suddenly at temperatures above 550 °C. Whereas the drop in the natural frequency of the uniformly heated trusses started at even much lower temperature levels. Moreover, the decrease in the natural fundamental frequencies of the uniformly heated trusses was lower than the reduction rate of the modulus of elasticity at high temperatures due to the large non-linear deformations. Since the modification of the stiffness of the truss by simply the reduction factor of the elastic modulus of the steel may be inappropriate to calculate the fundamental frequency of the trusses in the local and global fires, a new method was introduced to calculate the fundamental frequency value of the steel trusses in the fire.

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• MakaleYalnız künye2021/r/gumushane/12848
  Comparison of various turbulence model performance in computational fluid dynamics analyses of the oxidation ditches with experimental validation

  Şibil, Rahim; Aras, Egemen; Kankal, Murat

  Experimental and numerical studies were carried out to determine the full-scale Oxidation Ditch (OD) hydrodynamics considering various turbulence models. Firstly, the experimental work was carried out in a full-scale plant by Acoustic Doppler Velocimeter (ADV) for field-measurements. Secondly, the experimental data was used to validate numerical models by using Computational Fluid Dynamics (CFD) software Ansys Fluent. Eight different turbulence models were compared in the numerical study to predict full-scale hydrodynamics. Results showed that standard k-ε, renormalization group k-ε, realizable k-ε turbulence models gave more accurate prediction results with relative errors of 13 %, 17 %, and 18 % respectively, whereas the standard k-ω turbulence model gave the worst prediction results with 39 % relative error. This study also shows that the velocities in the ODs are very low without external force such as air diffusers, rotors, and mixer and there is no homogeneous flow field distribution in the ODs. Moreover, the maximum wastewater velocities occurred at the inlet and outlet.

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• MakaleAçık Erişim2021/r/gumushane/11309
  Experimental and numerical studies on predicting and improving the full-scale wastewater treatment plant hydrodynamics

  Şibil, Rahim; Aras, Egemen; Kankal, Murat

  This paper presents the results of both experimental and numerical studies on biological wastewater treatment plant (WWTP), oxidation ditches (OD) hydrodynamics to design and develop the desired flow conditions of the WWTP. Computational fluid dynamics (CFD) models were developed using CFD software, ANSYS Fluent (V13) with the three-dimensional, steady, incompressible flow based on the Reynolds-Averaged Navier-Stokes equations for flow field calculations in the combined ODs. Also, three different turbulence models [standard k–ε (ske), renormalization group k–ε (RNG), and realizable k–ε (real)] were performed for a comparative study. The numerical model was verified based on the experimental data in the relative errors for ske, RNG, and real 13%, 17%, and 18%, respec-tively. According to the parametric studies, the hydrodynamic characteristics of the existing WWTP were investigated. The maximum wastewater velocity occurred at the inlet and outlet, affecting the flow field in ODs. Moreover, the water velocity decreased as it moved away from the inlet and outlet locations at vertical and horizontal. It can also be noted that there was no homogeneous flow field distribution in ODs. Because the current OD model needs improvement hydrodynamically, a new original OD geometry was presented to eliminate the hydraulic weakness of existing WWTP by CFD analysis. The new original geometry provides a more homogeneous flow field in ODs that mean it will also help treatment efficiency and energy saving according to the operating principles of this facility.

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