Sürdürülebilir Kalkınma Amaçları

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• MakaleAçık Erişim2026Scopus SJRQ3/r/munzur/1326
  CFD Simulation of Aerodynamic Forces on a Simplified Heavy Vehicle Model with Steady Base Blowing

  Firat, Erhan; Seydhan, Mehmet

  A numerical investigation was conducted to examine the flow around a European tractor-trailer combination model (GETS) using a steady RANS model k-ω SST at a Reynolds number of 100000. Experimental aerodynamic force measurements were also carried out for the purpose of validating the CFD simulations. The present paper focuses on the effect of steady blowing from the thin slots positioned on the rear surface (base) of the model on the aerodynamic characteristics of the GETS. The combination of three key parameters was tested: the jet-to-freestream velocity ratio (VR), the inclination angle of the jet (θ), and the jet’s location. More than 100 CFD simulations were performed over a range of key parameters. The findings indicate that the jet direction’s inclination towards the rear surface typically leads to a modest yet favorable effect on the drag reduction. It has been demonstrated that increasing the VR to 2 has the potential to reduce aerodynamic drag by up to 50%. However, it is also demonstrated that employing VR values greater than approximately 1.25 is not viable in terms of active flow control efficiency. At θ=0°, the active control efficiency of the both-jets configuration is approximately 6 for VR=0.5 and approximately 1.6 for VR=1. The total drag coefficient on the model is reduced by 8.3% and 17.7% for the VR=0.5 and 1 cases, respectively. It has been demonstrated that the viscous components of total drag and lift are independent of jet configuration, VR, and θ. In both upper and lower jet configurations, it is possible to increase or decrease the aerodynamic lift acting on the model by changing the inclination angle.

  İncele
• MakaleAçık Erişim2026Scopus SJRQ1/r/munzur/1239
  Large-eddy simulation of flow over a square prism with moving belts

  You, Rui; Fırat, Erhan

  This three-dimensional (3D) numerical study investigates the feasibility of controlling the intermittently reattaching flow (IRF) by using the moving-surface boundary-layer control (MSBC) method. To this end, a fixed square prism was preferred due to its geometric simplicity and was equipped with moving belts that placed side surfaces close to the trailing edges. The effects of three dimensionless key parameters including velocity ratio (i.e., VR, the ratio of the velocity of the moving belt to the freestream velocity), length ratio (i.e., LR, the ratio of the belt length to the edge length of the square prism), and gap ratio (i.e., GR, the ratio of the spanwise distance between the neighboring belts to the edge length of the square prism) mainly on the aerodynamic characteristics were investigated using large-eddy simulation (LES). The findings suggest that the rise in VR and LR parameters leads to a proportional decrease in the time-averaged drag, 〈CD〉, attributable to their contribution to the linear momentum transfer mechanism by the moving surfaces. This mechanism, firstly, provides an additional thrust to the prism in the opposite direction of the main flow. Secondly, this mechanism increases the base pressure by stretching the shear layers from the leading edges of the prism in the streamwise direction. For LR = 0.4 and VR = 4, a 17 % reduction in 〈CD〉 was observed. Additionally, the root-mean-square (RMS) values of fluctuating drag and lift coefficients, CD-RMS and CL-RMS, have decreased by 71 % and 55 %, respectively. Conversely, the increase in the GR parameter led to an increase in the spanwise distance between each individual moving belt and a reduction in the positive effect of the linear momentum transfer mechanism on the 〈CD〉 reduction. The segmentation of moving belts along the spanwise direction also triggered the vorticity redistribution mechanism concurrently. The study also elucidated the underlying mechanisms that led to the failure of the vorticity redistribution mechanism to adequately reduce the 〈CD〉.

  İncele
• MakaleAçık Erişim2025Scopus SJRQ4/r/munzur/6198
  Pasif venturi aktüatörlü bir silindir etrafındaki akış: Reynolds sayısı ve hücum açısının etkileri

  Seyhan, Mehmet; Firat, Erhan

  Bu çalışmanın temel amacı, Reynolds sayısı (Re) ve hücum açısının (α) yeni geliştirilen bir akış kontrol yöntemi olan Pasif Venturi Aktüatör’ünü (PVA) içeren bir silindirin aerodinamik karakteristikleri üzerindeki etkilerini araştırmaktır. Bu amaçla hem aerodinamik kuvvet ölçümleri hem de hesaplamalı akışkanlar dinamiği (HAD) benzetimleri gerçekleştirilmiştir. Deneysel çalışmanın Reynolds sayıları Re=28000 ile 80000 arasında değişmektedir. Deneysel çalışmanın hücum açıları α=-30° ile +30° arasında değişmektedir. PVA içeren ve içermeyen silindir için HAD benzetimleri Re=36000 ve α=0°’de gerçekleştirilmiştir. Kuvvet ölçümleri kullanılarak elde edilen bulgular, zaman ortalamalı direnç katsayısı (C_D ) ̅ ile Re arasında oldukça doğrusal bir ilişki olduğunu göstermiştir. α=0° için Re değerinin 28000’den 80000’e arttırılması (C_D ) ̅ değerinde bir düşüşe neden olmuştur. Sonuçlar, test edilen hücum açısı ne olursa olsun, PVA’lı silindirin PVA’sız silindire kıyasla daha düşük bir (C_D ) ̅ sergilediğini göstermektedir. Ayrıca PVA’nın benzer Re aralığında test edilen pasif kontrol yöntemlerine kıyasla çok iyi bir direnç performansı sergilediği de karşılaştırmalı olarak gösterilmiştir.

  İncele
• MakaleYalnız künye2025Scopus SJRQ1/r/munzur/900
  Reduction of fluid forces on a circular cylinder in the laminar flow regime using a pair of airfoils

  Fırat, Erhan; Oruç, Vedat; You, Rui; Biçer, Uğur; Devecioğlu, Atilla G.

  Flow around the cylinder, with/without a pair of airfoils symmetrical to the cylinder's horizontal axis, was simulated for a diameter-based Reynolds number (Re) of 100. The objective of this numerical study is to simultaneously reduce the values of the time-averaged and fluctuating forces acting on a system consisting of a pair of airfoils and a cylinder below those of a single cylinder by using different combinations of the parameters chord (c), angle of rotation (β), angle of attack (α), and the shortest distance between the aerodynamic center of the airfoil and the surface of the cylinder (g). The values of these key parameters are determined primarily through two approaches. The first approach involves emulating the flow pattern surrounding the system to match the potential flow pattern. The second approach involves disrupting the interaction between the shear layers from the cylinder by stretching them in the mean flow direction. The second approach has been demonstrated to exhibit superior performance in terms of reducing both time-averaged and fluctuating forces concurrently. The second approach has been demonstrated to exhibit superior performance in terms of reducing both time-averaged and fluctuating forces concurrently. The optimal geometrical parameters that yield the desired end results are determined to be c = 0.5D, α = 0°, β = 60°, and g = 0.2D. Utilizing these parameters has been demonstrated to result in a substantial reduction in the time-averaged drag, fluctuating drag, and fluctuating lift coefficients of the system, with the respective percentage reductions reaching 14.4 %, 92.1 %, and 73 %, respectively, when compared to the values obtained for a single cylinder.

  AtıfScopus4·OpenAlex3

  İncele
• MakaleYalnız künye2025Scopus SJRQ1/r/munzur/791
  Aerodynamic characteristics of a symmetrical airfoil in the presence of segmentally distributed leading-edge tubercles

  Seyhan, Mehmet; Demirci, Veysel; Çolak, Aleyna; Kan, Furkan Erman; Firat, Erhan; Sarioglu, Mustafa

  In recent decades, experimental and numerical studies have demonstrated that wings with leading-edge (LE) tubercles exhibit advantageous aerodynamic performance at high attack angles compared to their unmodified counterparts. A substantial portion of these studies employed a single sinusoidal function to design the tubercles applied along the entire span. In this study, two functions were utilized to design tubercles. This experimental study was conducted to evaluate the effects of segmentally distributed (i.e., equally spaced) LE tubercles on the aerodynamic characteristics (ACs) of the National Advisory Committee for Aeronautics (NACA) 0018 airfoils and to associate them with the flow patterns observed on the suction surface. To this end, five different airfoil models have been produced and tested. The models consist of one plain airfoil, one fully tubercled airfoil, and three segmentally tubercled airfoils. The test results were obtained at Reynolds numbers (Re) of 0.6 × 10 5 to 1.2 × 10 5 . It has been determined that the distance between neighboring tubercled segments possesses a critical value with regard to performance enhancements in the post-stall regime. In the range below this critical distance, the tubercled segments lack the capacity to reattach the separated flow from the plain segments of the airfoil. Furthermore, the presence of a novel vortical structure (i.e., single rotating vortex cell, SRVC) under certain conditions was demonstrated qualitatively.

  AtıfScopus2·WoS2·OpenAlex2

  İncele
• MakaleYalnız künye2024Scopus SJRQ1/r/munzur/2194
  Aerodynamic drag improvements on a circular cylinder using passive Venturi actuators

  Firat, Erhan; Seyhan, Mehmet; Ozkan, Gokturk M.

  Scale-adaptive simulations (SAS) of three-dimensional flow around a circular cylinder fitted with a passive version of a novel flow control method (passive Venturi actuator, PVA) are performed at a diameter-based Reynolds number of Re = 28 000. The PVA consists of one or more narrow slits located at the top and/or bottom sides of the cylinder that connected to the throat of the axial Venturi slit in this cylinder. The main purpose of the study is to investigate the influence of divergence angle and narrow slit location relative to the axial Venturi slit on the aerodynamic performance of the cylinder. To this end, four models were designed with various PVAs. Additional models, a plain cylinder (unmodified model) and a cylinder fitted with an axial Venturi slit (model without a narrow slit), were also used for quantitative comparison. SAS predicts that an additional 5% reduction in the time-averaged drag coefficient, ⟨ C D ⟩ , was observed when two narrow slits located on the surface at an angle of ±80° from the front stagnation line were fitted to the cylinder with an axial Venturi slit. Reducing the divergence angle of the PVA leads to improvements in ⟨ C D ⟩ and root mean square of fluctuating force coefficients, C D − rms and C L − rms . It is found that a cylinder with a PVA that has two narrow slits and a divergence angle of 6° can produce a 28.6% reduction in ⟨ C D ⟩ , a 58.5% reduction in C D − rms , and an 81.2% reduction in C L − rms , when compared to the plain cylinder.

  AtıfScopus4·OpenAlex4

  İncele
• MakaleYalnız künye2024Scopus SJRQ1/r/munzur/2109
  An experimental investigation of the flow control of a circular cylinder in near wake with parallel plates at Re = 7500

  Durhasan, Tahir; Ekinci, Fırat; Firat, Erhan; Akilli, Huseyin

  The vortex street suppression in the near wake region of the cylinder with parallel plates was investigated using particle image velocimetry (PIV) at Reynolds number of Re = 7500. The rigid plates are designed as flat, parallel with the free-stream direction, and located on both sides of the cylinder. Two different plate lengths (0.5D and 1D based on the cylinder diameter, D) were examined at gap ratios of g/D = 0.1, 0.3, 0.5, 0.7, and 0.9, respectively. Proper Orthogonal Decomposition (POD) analyses were also employed to reveal vortex mechanism in the near wake region. The gap ratio significantly influences the interaction of the vortices. At low gap ratios, the plates directly affect the development of shear layers on both side of the cylinder. The shear layers elongate downstream with a reduction of the vortex shedding frequency. Moreover, Reynolds shear stress, vortex shedding instabilities and vortex street are suppressed in the near wake region with the help of using parallel plates. On the other hand, vortex shedding reinforces instabilities at higher gap ratios. Besides, the most effective gap ratio is different for each the plate lengths to suppress instabilities.

  AtıfScopus9·WoS8·OpenAlex9

  İncele
• MakaleAçık Erişim2023Scopus SJRQ3/r/munzur/2941
  Aerodynamic Drag Improvements on a Simplified Heavy Vehicle using Three-sided Plain and Notched Base Flaps

  Fırat, E.

  An experimental investigation has been undertaken to determine the effects of plain and notched base flaps on the drag performance of simplified tractor-trailer combination without any intermediate gap, Generalized European Transport System (GETS). Both plain and notched base flaps are rigid, made up of three identical flaps whose length is equal to the width of the GETS model, and not angled inward or outward. The experiments examined three-sided flap configurations corresponding to various combinations of seven heights of the plain part (from 10 to 40 mm in steps of 5 mm), four notch amplitudes (from 2.5 to 10 mm in steps of 2.5 mm), and five notch wavelengths (from 10 to 50 mm in steps of 10 mm). It is shown that the drag performance of the plain flap at zero yaw highly depends on the height of the plain flap. The maximum drag reduction occurs for e/w=0.1 yielding a drag reduction of 1.9% when compared to the GETS model without flap (baseline GETS). It was shown that the time-averaged drag coefficient increased slightly until a maximum was reached at e/w=0.3 but then decreased slightly with increasing e/w. Under zero yaw angle conditions, GETS model with a notched base flap, e10-a05.0-λ20, gives the lowest drag. The addition of this base flap to the GETS model resulted in a 2.8% drag reduction. This notched base flap was shown to be more effective not only at reducing <CD> under yawed flow conditions tested but also at reducing time-averaged side coefficient under yawed flow conditions tested, compared to the e10-a00.0-λ00 flap

  AtıfScopus8·WoS6·OpenAlex4

  İncele
• MakaleAçık Erişim2022/r/munzur/5867
  Yan rüzgar koşullarında ön kısmı düz plakalı bir otobüs modeli üzerindeki aerodinamik direncin düşürülmesi

  Seyhan, Mehmet; Firat, Erhan

  Akaryakıt fiyatları ve insanların çevrenin mevcut durumu üzerinde meydana getirdiği değişimler ticari taşıtların yakıt ekonomisinin iyileştirilmesine olan ilgiyi arttırmıştır. Büyük olasılıkla, bir taşıtın yakıt ekonomisini iyileştirmenin en ekonomik yolu taşıtı aerodinamik açıdan daha verimli yapmaktır. Bu çalışmada, sıfır ve sıfırdan farklı sapma açılarında (β≤9°), 1:25 ölçekli otobüs modelinin ön alt yüzeyine paralel ve modele göre daha önde olacak şekilde yerleştirilen düz plakaların aerodinamik performansı deneysel olarak incelenmiştir. Kıyaslama çalışmaları, düz plakasız otobüs modelini de hesaba katarak, genişliğe-dayalı Reynolds sayısının Rew=104000±3000 değerinde gerçekleştirilmiştir. Kuvvet ölçümleri, zaman ortalamalı sürükleme katsayısında, , dik bir artışın gözlemlendiği kritik bir plaka genişliğinin varlığını ortaya koymaktadır. Sıfır sapma açısında, otobüs genişliğinin (w) onda yedisi kadar genişlikli bir plakanın otobüs modelinin 0,16w daha önüne yerleştirildiği bir geometrik kurulum, plakasız otobüs modeline etkiyeninkinin %92,9’u kadarlık bir zaman-ortalamalı direnç oluşturmaktadır. Bu kurulumun, yan akış şartları altında da düşürmede etkin olduğu görülmüştür.

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  AtıfOpenAlex1·TR Dizin1

  İncele
• MakaleYalnız künye2019Scopus SJRQ1/r/munzur/3618
  Flow past a hollow cylinder with two spanwise rows of holes

  Firat, Erhan; Ozkan, Gokturk M.; Akilli, Huseyin

  Abstract: The flow over fixed, hollow, rigid circular cylinders with and without two series of equally spaced holes of equal diameter (0.2 cylinder diameter) along the surface of the cylinder has been studied by means of dye injection flow visualization, particle image velocimetry (PIV), and force measurements. Holes are connecting the front and rear stagnation lines or the upper and lower sides (i.e., they are positioned at ± 90° from the stagnation line) of the cylinder. The center-to-center distance between holes was 7-hole diameter. The experimental data were obtained from water channel and wind tunnel measurements performed at Reynolds numbers of 6900 and 20000, respectively. It was found that cylinder with holes located on the surface at an angle ± 90° from the front stagnation line behaves like a double-chamber synthetic jet actuator when subjected to cross-flow. The interaction of synthetic jet arrays with external flow over the side surfaces instigates the three-dimensional instabilities in the near wake and produces a 14.4% drag reduction compared to the drag of a plain cylinder. It was shown that cylinder with holes located on the surface at angles of 0° and 180° from the front stagnation line also instigates the three-dimensional instabilities in the near wake, but the primary mechanism responsible for drag reduction is self-bleed through downstream holes. This system producing drag reduction was found to have a drag coefficient equal to about 78.9% of that for a plain cylinder. Important flow structures inside and behind the cylinders with holes were also identified. Graphic abstract: [Figure not available: see fulltext.].

  AtıfScopus17·WoS17·OpenAlex16

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