Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2026Scopus SJRQ3CFD 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.
- MakaleAçık Erişim2025Scopus SJRQ4Pasif 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.
- MakaleYalnız künye2025Scopus SJRQ1Aerodynamic 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.
AtıfScopus2WoS2OpenAlex2
İncele - MakaleYalnız künye2024Scopus SJRQ1Aerodynamic 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.
AtıfScopus4OpenAlex4İncele - MakaleYalnız künye2024Scopus SJRQ1An 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.
AtıfScopus9WoS8OpenAlex9İncele - MakaleAçık Erişim2022Yan 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.
AtıfOpenAlex1TR Dizin1
İncele - MakaleYalnız künye2019Scopus SJRQ1Flow 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.].
AtıfScopus17WoS17OpenAlex16İncele - MakaleYalnız künye2018Tek Taraflı Isıtmaya Maruz Yüksek Şekil Oranlı Minikanallarda Pasif Akış Kontrol Yöntemi Kullanılarak Isı Transferinin İyileştirilmesi
Firat, Erhan
Pasif akış kontrol silindirinin olduğu ve olmadığı durumlarda, bir geniş yüzeyinden ısıtılan dar, dikdörtgen şeklindeki bir minikanal içerisindeki taşınımla ısı transferi durumunun hesaplamalı akışkanlar dinamiği (HAD) benzetiminin sonuçları rapor edilmiştir. Silindirin çapı (d), kanal yüksekliğinin (t) yaklaşık olarak onda biri kadardır. Bu çalışmanın amacı, ısıtılan kanal duvarı ve silindirin merkezi arasındaki üç farklı mesafeyi (s) çalışarak, pasif kontrol silindirinin sistemin ısıl performansı üzerindeki etkisini anlamaktır. Test edilen boyutsuz mesafelere (s/t) bakılmaksızın, pasif kontrol silindirinin mevcudiyetinde sistemin ısıl performansının iyileştiği bulunmuştur. Bu, üniform ısı akısına maruz kalan yüzey üzerindeki hidrodinamik sınır tabaka ile sırayla büyük-ölçekli çevrilere dökülen, silindirden olan serbest kayma tabakalarının şiddetli etkileşimlerine dayandırılmıştır.
- MakaleYalnız künye2018Scopus SJRQ1Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind
Tunay, Tural; Firat, Erhan; Sahin, Besir
Crosswinds which stem from on-road flow conditions can deteriorate a ground vehicle's driving performance. In spite of the numerous studies investigating aerodynamics of the ground vehicles in the previous literature, there is still a need for thorough understanding of the underlying flow phenomena related to crosswind sensitivity of the ground vehicles. Therefore, the present study is aimed to investigate characteristics of the flow features around the ground vehicles under steady crosswind conditions within a range of yaw angles 0° ≤ β ≤ 15° using the Ahmed vehicle model with rear slant angles of α = 25° and 35°. Throughout the investigations, flow visualizations using dye injection technique and velocity measurements using particle image velocimetry PIV technique are conducted. The Reynolds number of the flow which is based on the free stream flow velocity U = 200 mm/s and height of the model H = 72 mm is ReH= 1.4 × 104. Results are presented in terms of time-averaged vorticity <ω> contours and streamline <ψ> patterns together with velocity magnitude ((<u>2+<w>2)1/2/U) of the flow fields. Additionally, turbulence quantities such as Reynolds stresses <u'w'>/U2 and turbulent kinetic energy TKE are presented and discussed in details. Results of the present study show that characteristics of the flow features in the near wake region downstream of the Ahmed model are very sensitive to the effects of the crosswind.
AtıfScopus36WoS35OpenAlex39İncele - BildiriYayıncıda açık erişim2018An investigation of the near-wake flow structure of a cylinder with guiding plates
Ekinci, Firat; Firat, Erhan; Özkan, Göktürk M.; Akilli, Hüseyin; Dancova, P.
In this study, the flow behind a circular cylinder with a pair of outer identical guiding plates was investigated using particle image velocimetry (PIV) for various angular positions of the plates (i.e. α=±70°, ±100°, and ±130°). The gaps between these plates and cylinder are equal and are 0.3D. Experiments were carried out at a subcritical Reynolds (Re=ρ·U∞·D/μ) number of 7500, based on the cylinder diameter (D) and the flow velocity (U∞). The features of the near-wake with and without the guiding plates were interpreted in terms of patterns of time-averaged vorticity and streamlines, time-averaged and fluctuating velocity components. The spectral analysis was also carried out to determine the time-dependent variation of the transverse velocity at given locations in the near-wake. Two-dimensional computations of flow around circular cylinders with and without guiding plates have also been performed to predict the timeaveraged and root-mean-square of force coefficients of the various models. It was seen that the guiding plates at an appropriate angular position can lead to substantial attenuation, or retardation, of the process of large-scale vortex formation in the near-wake, thus can lead to vortex-induced vibration (VIV) suppression without any increase in drag.
- MakaleYalnız künye2017Scopus SJRQ1PIV measurements in the near wakes of hollow cylinders with holes
Firat, Erhan; Ozkan, Gokturk M.; Akilli, Huseyin
The wake flows behind fixed, hollow, rigid circular cylinders with two rows of holes connecting the front and rear stagnation lines were investigated using particle image velocimetry (PIV) for various combinations of three hole diameters, d = 0.1D, 0.15D, and 0.20D, six hole-to-hole distances, l = 2d, 3d, 4d, 5d, 6d, and 7d, and ten angles of incidence (α), from 0° to 45° in steps of 5°, at a Reynolds number of Re = 6,900. Time-averaged velocity distributions, instantaneous and time-averaged vorticity patterns, time-averaged streamline topology, and hot spots of turbulent kinetic energy occurred through the interaction of shear layers from the models were presented to show how the wake flow was modified by the presence of the self-issuing jets with various momentums emanating from the downstream holes. In general, as hole diameter which is directly related to jet momentum increased, the values of time-averaged wake characteristics (length of time-averaged recirculation region, vortex formation length, length of shear layers, and gap between the shear layers) increased. Irrespective to d and l tested, the values of the vortex formation length of the models are greater than that of the cylinder without hole (reference model). That is, vortex formation process was shifted downstream by aid of jets. It was found that time-averaged wake characteristics were very sensitive to α. As α increased, the variation of these characteristics can be modeled by exponential decay functions. The effect of l on the three-dimensional vortex shedding patterns in the near wake of the models was also discussed.
AtıfScopus26WoS25OpenAlex28İncele - MakaleYalnız künye2017Scopus SJRQ1Passive flow control in the near wake of a circular cylinder using attached permeable and inclined short plates
Ozkan, Gokturk M.; Firat, Erhan; Akilli, Huseyin
The main objective of this study is to assess the effectiveness of attached permeable plates in suppressing nominally two-dimensional vortex shedding from a fixed cylinder. The permeable plate along the entire span of the cylinder was made of a chrome-nickel screen and was attached normal to the cylinder surface. The main parameters of the study are porosity of the permeable plate, β, and the plate angle of the cylinder-plate arrangement, θ, with respect to the freestream. Experiments were performed using Particle Image Velocimetry (PIV) and Flow Visualization Techniques. Additionally, drag force measurements were carried out in a wind tunnel to analyze the effects of permeable plates on drag coefficient of the circular cylinder. The results revealed that the use of a permeable plate successfully suppresses the vortex shedding downstream of the circular cylinder by reducing the velocity fluctuations in the wake, elongating the vortex formation region further downstream and attenuating the vortex shedding frequency. The porosity values of β=0.4 and 0.5 with plate angles in the range of 35°≤θ≤90° were found to be effective on suppressing the vortex shedding. Furthermore, both the drag coefficients of the cylinder-plate arrangement and the <TKE>maxwere reduced almost for all porosity ratios for θ<30°.
AtıfScopus63WoS55OpenAlex59İncele - MakaleYalnız künye2017Scopus SJRQ1Control of vortex shedding using a screen attached on the separation point of a circular cylinder and its effect on drag
Ozkan, Gokturk Memduh; Firat, Erhan; Akilli, Huseyin
The control of flow in the wake of a circular cylinder by an attached permeable plate having various porosity ratios was analyzed experimentally using both particle image velocimetry (PIV) and dye visualization techniques. The force measurements were also done in order to interpret the effect of control method on drag coefficient. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as D=50mm and L/D=1.0, respectively. The porosity ratio, β, which can be defined as the ratio of open surface area to the whole body surface area, was taken as β=0.4, 0.5, 0.6, 0.7, and 0.8 (permeable plates). The study was performed considering deep water flow conditions with a constant Reynolds number of ReD=5000 based on the cylinder diameter. Each permeable plate was attached on the separation point and the results were compared with the results of cylinder without permeable plate (plain cylinder) in order to understand the control effect. Both qualitative and quantitative results revealed that the permeable plates of 0.4 ≤ β ≤ 0.6 are effective on controlling the unsteady flow structure downstream of the cylinder, i.e., the vortex formation length was increased, turbulent statistics was reduced and vortex shedding frequency was diminished when the permeable plate attached normal to the cylinder surface from the lower separation point. However, the drag force acting on the cylinder was found to be increased due to the increased cross-sectional area.
AtıfScopus16WoS15OpenAlex16İncele - MakaleYalnız künye2011Scopus SJRQ2Akış kontrol çubuğu ile kare kesitli bir küt cisim etrafındaki akış kontrolünde hücum açısının girdap kopma olayına etkisi
Firat, Erhan; Özmert, Mehmet; Akansu, Yahya Erkan
Bu çalışmada, pasif akış kontrol elemanı olarak kullanılan dairesel kesitli bir çubuk ile kare kesitli bir küt cisimetrafındaki akış durumunda hücum açısının girdap kopma olayına etkisi deneysel olarak incelenmiştir. Hücumaçısının değeri 0°’ye eşit iken öndeki kontrol çubuğu ile kare model serbest akışa göre ardışık olarak durmaktadırlar.Deneyler Reynolds sayısının 1.0 x 10⁴değerinde, d/D=0.25 çap oranında, hücum açısının 0°leq alpha leq⁹⁰ aralığında, ikicisim arasındaki boyutsuz mesafe olan L/D’nin 1, 2, 3 ve 4 değerlerinde gerçekleştirilmiştir. Hız ölçümleri sabitsıcaklık anemometresi (CTA) ile yapılmış olup, girdap kopma frekansları hız-zaman değişiminin spektral analizindenelde edilmiştir. Duman tel yöntemi ile akış görünür hale getirilerek akış ayrılması, yeniden tutunması ve girdapoluşum bölgesinin özellikleri ortaya konulmuştur. L/D=2 ve 3 konumlarındaki alpha=0° hücum açısında, sürüklemekuvvetinde dikkate değer azalmalara ve ısı transferinde önemli artışlara neden olan yüksek girdap kopma frekansınasahip akış yapısı elde edilmiştir. Bu akış yapısının alpha=0^o, ye kadar artan hücum açısı ile azalarak devam ettiğigörülmüştür. Hücum açısının daha da arttırılması ile akış kontrol çubuğunun girdap oluşum yapısı üzerindeki etkisitamamen ortadan kalkmaktadır.
AtıfTR Dizin9İncele - MakaleYalnız künye2011Scopus SJRQ2THE EFFECT OF ATTACK ANGLE TO VORTEX SHEDDING PHENOMENON OF FLOW AROUND A SQUARE PRISM WITH A FLOW CONTROL ROD
Akansu, Yahya Erkan; Özmert, Mehmet; Firat, Erhan
In this study, the effect of attack angle on vortex shedding phenomena in the case of flow around the square prism as a bluff body and the circular rod which used as flow control component was experimentally investigated. While the value of attack angle equal to 0 degrees, the upstream control rod and square prism are in tandem arrangement to free stream. Experiments were conducted at Reynolds number of 1.0 x 10(4), for the diameter ratio of d/D=0.25, the attack angle between 0 degrees <= alpha <= 90 degrees, and the value of normalized distance between two prism LID is 1, 2, 3, and 4. The velocity measurements were conducted by means of constant temperature anemometer (CTA) as well as vortex shedding frequencies obtained by the spectral analysis of velocity-time history. Characteristics of the vortex formation region and location of flow attachments, reattachments, and separations were observed by means of the smoke-wire flow visualizations. At the angle of attack 0 degrees of the location L/D=2 and 3, the flow structure that possess high vorex shedding frequency which causes remarkable reductions on the drag force and significant increase in the heat transfer was obtained. This flow structure continous to decrease with increasing attack angle up to around 10 degrees. By further increasing of attack angle, the effect of flow control rod on vortex shedding frequency disappears completely.
AtıfWoS6İncele - BildiriYalnız künye2010CONTROL OF FLOW AROUND A SQUARE PRISM BY USING SYNTHETIC JET
Akansu, Yahya Erkan; Firat, Erhan; Vit, T; Dancova, P
Control of the flow around a square prism by means of synthetic jet through a single slot located on middle of upper surface of the model has been investigated experimentally for Reynolds number of 8000. Synthetic jet was implemented by using a pneumatic piston-cylinder which was driven by means of an electrical motor. The frequency and stroke of the piston were changed to obtain various values of the flow control parameters. For various excitation frequency and momentum coefficients of the synthetic jet, the mean and fluctuating pressure distributions on the square prism were measured. The velocity measurements at the slot exit and at a specific coordinate were conducted by means of constant temperature anemometer (CTA). Vortex shedding frequencies obtained by the spectral analysis of both pressure-time and velocity-time history. At a value of synthetic jet excitation frequency, vortex pairs generated at slot were perturbed the shear layer that separated from the upper leading edge of square model and disturbs it. When the synthetic jet excitation frequency closes enough to the vortex shedding frequency, the lock-in of vortex shedding frequency onto the exciting frequency was occurred. On the other hand, increasing excitation frequency of the synthetic jet causes a pressure recovery on the surface of the prism within the wake region. The efficiency of the synthetic jet is classified depending on change of the drag coefficient and vortex shedding frequency.
AtıfWoS1İncele