Theses supervised by Prof. Dr. Hüseyin Akıllı
19 theses · Çukurova University
Flow control downstream of a circular cylinder by perforated semi circular cylinder in shallow water
In this study, it was aimed to control the unsteady flow occurred in the near wake of a circular cylinder in shallow water. Outer cylinders of six different porosities (ß=0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) and three different arc angles (?=120o, 150o and 180o) were used as control equipment. Nine different cylinder diameters (Di=25mm, 30mm, 40mm, 50mm, 60mm, 70mm, 75mm, 80mm and 90mm) were used in order to examine the effect of the diameter ratio. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to a Reynolds number of ReDo=10,000 based on the outer cylinder diameter. The data obtained from the experiments showed that the arc angle of perforated cylinders affect flow control significantly and that the optimum arc angle was ?=180o. It was observed that although the outer cylinders with ?=120o and ?=150o arc angle were effective on smaller diameter ratios, they lost their effectiveness on the flow structure at higher diameter ratios. The time averaged vorticity contours and Turbulence Kinetic Energy statistics show that porosity is highly effective on the flow structure. It was concluded for ?=180o outer cylinder arc angle that the ideal porosities in moving away the unsteady flow in the near wake of cylinder and reducing the peak magnitude of Reynolds stress were ß=0.5 and 0.6. It was determined that the most effective diameter ratio with which unsteady vorticity move the point where Turbulence Kinetic Energy contours occur further downstream was Di/Do=0.5. Di/Do=0.75 was determined the most ideal diameter ratio in reducing Turbulence Kinetic energy value and the peak magnitude of Reynolds stress compare with bare cylinder case.
Flow control downstream of a circular cylinder by a permeable circular cylinder in deep water
The aim of this study is to investigate the flow structure downstream of a circular cylinder surrounded by an outer permeable cylinder which is made from chrome-nickel wire mesh in deep water using Particle Image Velocimetry technique. All experiments were performed at Reynolds number 5000 based on the inner cylinder diameter. In order to understand the effects of diameter and porosity of the outer cylinder on the flow structures of the inner cylinder, seven different outer cylinder diameters (D=37.5, 45, 52.5, 60, 67.5, 75 and 90 mm) and eight different porosities (ß=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were considered. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The experimental results indicated that both the diameter ratio and the porosity are important parameters to control the flow structure behind the inner cylinder-outer permeable cylinder arrangement. The outer permeable cylinder significantly suppressed the vortex shedding downstream of the inner cylinder-outer permeable cylinder arrangement for the diameter ratio greater than D/d=1.5. The effect of D/d= 3.0 on the attenuation of vortex shedding downstream of the inner cylinder-outer permeable cylinder arrangement was much more pronounced compared to other diameter ratios. Furthermore, the effectiveness of the outer permeable cylinder increased as the value of porosity increased up to ß=0.7. In terms of the case of the permeable cylinder without the inner cylinder, the flow structure downstream of the permeable cylinder was independent of the diameter of the permeable cylinder
Passive flow control downstream a circular cylinder using perforated circular cylinder in deep water
The aim of the present study was to control the vortex shedding downstream of a circular cylinder (inner cylinder) by the existence of outer perforated cylinder concentrically located around the inner cylinder in deep water. The flow characteristics downstream of concentrically placed coupled (shrouded) cylinders were investigated quantitatively by the Particle Image Velocimetry (PIV) technique. Diameter of the outer perforated cylinder was kept constant as Do=100 mm while diameter of the inner cylinder was varied within the range of 25? Di ?90 mm. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to the Reynolds number of ReDo=10,000 based on the outer cylinder diameter. Experiments were conducted for seven porosities (ß=0.25, 0.30, 0.40, 0.50, 0.60, 0.70 and 0.80) and nine diameter ratios (Di/Do=0.25, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 0.90) in order to show the effect of these parameters on the flow control. Maximum values of both Reynolds shear stress and turbulence kinetic energy significantly decreased with the existence of outer perforated cylinder and also, the location of peak magnitudes of turbulence statistics occurred at locations further downstream compared to the bare cylinder cases. The most effective control was revealed for the porosity range of 0.50?ß?0.60 for all diameter ratios. It was concluded that the perforated cylinder could be used as a passive control element as indicated by the results presented in this study. Key Words: Cylinder, Passive control, PIV, Turbulence Kinetic Energy, Deep water
Investigation of flow characteristics around in-line horizontal cylinders in shallow water
The aim of this thesis is to investigate the flow characteristics around in-line horizontal cylinders using two dimensional Particle Image Velocimetry (PIV) technique in shallow water. Experiments were undertaken in a water channel in Fluid Mechanics Laboratory, Mechanical Engineering Department of Cukurova University. The effect of gap between two horizontal cylinders on flow characteristics was investigated. Moreover, the effect of submergence of the horizontal cylinders in shallow water was investigated. All experiments were carried out fully developed shallow flow conditions. The free stream velocity was U=167 mm/sec, which represented a value of Reynolds number based on cylinder diameter of ReD= 5000. The observation showed that the second cylinder attenuate size of the wake region for L/D=0 case. The wake region clearly occurs between cylinders beginning of L/D=1 case. As the gap between cylinders rises, size of the wake region increases. Keywords: Shallow water, Horizontal cylinders, Vorticity, In-line, In tandem arrangement
Numerical and expermental investigation of flow around yawed cylinders in tandem arrangement
The aim of present research is to investigate the flow structure around a single yawed cylinder and two yawed cylinders both numerically and experimentally. In this purpose, the main circular was 50 mm in diameter and 60 cm in length is set against the fluid flow for the single cylinder case at a Reynolds number = 5000.The paricle imaging velocimetry (PIV) technique is used to investigate the wake structure experimentally. Single yawed cylinder was investigated in the water tunnel under steady upstream cross-flow conditions with angle configurations from α = 0o to 60o with 5o increments. For the case of two yawed cylinders, in order to understand the effects of gap ratio and yaw angle on the flow structure around two yawed cylinders in tandem, nine different gap ratios from L/D = 1 to 5 with 0.5 increments and five different yaw angles of α = 0, 15, 20, 25 and 30 were considered. ANSYS CFX software was used for numerical studies. The results obtained from CFX were compared with PIV results. SST turbulence model that was based on k – ω was used for the turbulence modeling.
Suppression of vortex shedding in the wake of a circular cylinder by attached permeable plates in deep water
The aim of present study is to control the vortex shedding downstream of a circular cylinder by means of attached permeable plates. Experiments were performed in deep water using Particle image velocimetry (PIV) and flow visualization techniques. The permeable plate was made of a chrome-nickel screen which was attached on the cylinder surface along its midspan. The main parameters of the study are porosity, β of the permeable plate, the plate angle, θ and the plate length, L/d. Within this context, six porosity values, eighteen plate angles and two plate lengths were defined and studied in order to examine their effects on vortex shedding control. The results showed that the use of a permeable plate with various plate angles suppresses the vortex shedding downstream of the circular cylinder by reducing the fluctuations in the wake, elongating the vortex formation region and attenuating the vortex shedding frequency. The porosity values of β=0.4 and 0.5 with plate angles of 45o≤θ≤135o were found to be effective on suppressing the vortical flow structure around the cylinder. Within these effective intervals, this study brings out a new approach on controlling the unsteady flow structure around bluff bodies and could be suggested for engineering applications concerning the vortex shedding and consequent Vortex-Induced Vibrations for deep water flow conditions.
Improvment of a coach air-conditioning system by applying a distinct air channel
The aim of this study is to design an A/C air channel providing uniform air distribution along the coach, which has 12-m length and a capacity of 50 passengers. The air channel was designed by means of Computational Fluid Dynamics (CFD). In order to determine the most suitable turbulence model for the air channel properties, a turbulence model determination study was conducted with 5 different turbulence models, which are k-ε Standard, k-ε Realizable, k-ε RNG, k-Ω Standard, Spallart-Almaras, and the numerical results were compared with the experimental results measured from the experimental setup designed and produced. A grid independence study was also conducted to be sure that the solution is independent of grid. At the beginning of the study, cooling load of the coach calculated with a detailed study. After the cooling load calculations, a proper A/C unit selected, fitted to the vehicle and detail road tests, which includes measurements of underbody temperature distribution, A/C nozzle exit velocities, temperature distribution inside the passenger cabin and internal noise level, was performed to compare the current situation and final application. As a result of this study, passenger comfort was improved with the application of distinct air channel from uniform air and temperature distribution along the vehicle and internal noise level points of views.
The effect of holes on drag reduction and the near-wake of a circular cylinder in cross-flow
The main aim of this research is to assess the effect of double rows of holes on time-averaged drag reduction and the near-wake flow structure of a circular cylinder in cross-flow. Experiments were carried out for various combinations of six hole diameters, d = 0.075D, 0.1D, 0.125D, 0.15D, 0.2D and 0.25D, six hole-to-hole distances, l = 2d, 3d, 4d, 5d, 6d and 7d, nineteen angles of incidence (α), from 0° to 90° in steps of 5°, and twenty nine Reynolds numbers (Re), from 4,000 to 32,000 in steps of 1,000 where d and D (40 mm) are the diameters of hole and cylinder, respectively. It was found that the double rows of hole have great importance in terms of drag reduction. The is minimum at α = 0° regardless of test models. The drag reduction mechanism is directly relevant to that the jet filled the near-wake region with fluid and stretched the separated shear layers from the cylinder to form further downstream. So that, time-averaged drag coefficient, , can be reduced by 37% when compared to single isolated cylinder (d/D = 0.25, l/d = 2). This reduction is generally independent of Re. However, it depends severely on d, l and α. There are no direct specific relations between the above-mentioned parameters and . At small α values, from 0° to 15°, the reduction in was increased as hole diameter increased regardless of l. The generally increased proportional to the angle of incidence up to 30° regardless of test models. However, the of the test models are still lower than that of the single isolated cylinder. At relatively higher α values, from 55° – 60° to 65° – 75°, the values increased regardless of d. The level of increase is directly related to the l. As l reduced, the level of increase in increased, that is, the test models with lower hole number are generally more effective in terms of drag reduction in this α range. This unexpected increase in was interpreted as a change in flow structure inside the test models. The is remarkably reduced once again at α = 85° – 90° due to the transformation of two-dimensional vortices into weakened three-dimensional vortices by aid of holes which behave like a passive vortex generator. The whole field velocity measurements via PIV also supported this idea. The decreased fluid entrainment into the test models also contributed this reduction in . In the thesis, the near-wake flow topology, wake characteristics, velocity distributions, vortex shedding frequencies, vorticity and turbulent kinetic energy contours obtained via PIV measurements were presented in order to explain the advantages and drawbacks in aerodynamic/hydrodynamic aspect of double rows of holes as a passive flow control method.
Passive control of vortex shedding around a circular cylinder by detached plate
The aim of present study is to control the vortex shedding around a cylinder by use of single and double detached plate arrangements at various plate angles. Experiments were performed in deep water using Particle image velocimetry (PIV) and flow visualization techniques. The main parameters of the study are the normalized plate length (L/D), the plate angle (α), and the gap ratio between plate and cylinder (G/D). The effects of these parameters for experiments will be explained by means of the Reynolds Shear Stress (RSS), Turbulent Kinetic Energy contours (TKE), and Vorticity contours (ω).
Flow control in the near wake of a circular cylinder by splitter plate and perforated cylinder combination
In this study, it is aimed to flow control in the near wake of a circular cylinder by splitter plate and perforated cylinder combination in deep water. The cylinder diameter was kept to constant during the experiments as D=50 mm and corresponding Reynolds number based on the cylinder diameter Re=5×103. Experiments were performed in three stages. In the first stage, the effect of perforated cylinder on the flow control was investigated using the PIV measurement technique and also force measurement was performed in the air tunnel in order to calculate the drag and the lift coefficients of the cylinder for β=0.3, 0.4, 0.5, 0.6 and 0.7 at D/Ds=0.4, 0.5 and 0.6. In the second stage, the flow structure in the further downstream of the perforated cylinder was investigated using dye visualization technique. Finally, the effect of the splitter plate and perforated cylinder combination in the near wake was investigated on the flow control with respect to total drag and lift coefficients. The results depicted that the porosity, β and the diameter ratio, D/Ds have substantial effects on the flow control and the drag reduction of the cylinder. The flow control was achieved in the near wake region for β=0.5 and 0.6 at D/Ds=0.4 and 0.5. Also, the drag coefficient of cylinder was reduced by 65% for β=0.5 at D/Ds=0.4. It was observed that using of the splitter plate remarkably affected the flow structure and increased the total lift coefficient.
Türkiye'nin biyokütle enerji potansiyeli
Genel olarak, ülkemiz fosil yakıtlardan enerji ihtiyaçlarını karşılamaktadır. Bu yakıtların ana dezavantajları çevreyi kirletmeleri ve ülkemizin yabancı ülkelere bağımlı olmasıdır. Biyokütle çok çeşitli yerlerde yetiştirilebilir, kolayca depolanabilir, sosyo-ekonomik gelişmelere yardımcı olur ve çevresel etkileri daha olumludur, günümüzde farklı endüstrilerde elektrik, kimyasal hammadde ve sıvı yakıt kullanılmaktadır. Bu özellikler nedeniyle biyokütle enerjisi Türkiye için önem kazanmıştır ve bu önem giderek artmaktadır. Bu çalışmada Türkiye'nin tarımsal ve hayvansal bazlı biyokütle enerji potansiyeli araştırılmıştır. Tarımsal ve hayvansal istatistiksel verileri Türkiye İstatistik Kurumu 2017 verilerinden elde edilmiştir. Çalışmaya göre, toplam ekilen alan 15.856.351 hektar ve bu alandan elde edilebilecek ortalama kuru biyokütle miktarı 436.049.652, 5 tondur. Bu alanın ortalama kuru biyokütle enerji değeri 176.600.109, 3 TEO. Bu kuru biyokütle 2.053.859 MW enerjisine eşdeğerdir. Biyokütle kaynağı için kullanılan toplam hayvan sayısı 408.561.087 sayıdır. Türkiye'de bulunan hayvan atıkları miktarı 96.655.868, 19 tondur. Bu atıklardan 4.309.771.357 m3 /yıl biyogaz elde edilebilir. Bu biyogaz, 2.03 x 1010 kWh/yıl elektrik enerjisine eşdeğerdir. Anahtar Kelimeler: Tarımsal Biyokütle, Hayvan Bazlı Biyokütle, Biyogaz, Türkiye, Yenilenebilir Enerji
Flow control in the wake of a circular cylinder by means of perforated semi circular cylinder and splitter plate
The main purpose of the present experimental study was to control unsteady flow behaviors in the wake region of a circular cylinder (inner cylinder) by means of permeable semi circular cylinder (outer cylinder) and splitter plate. Inner and outer cylinder diameters and Reynolds number with respect to inner cylinder diameter were kept constant as 50 mm, 125 mm and Re=5000 respectively throughout the experiments. Two different porosity ratios were designated as cylinder porosity ratio (βC) and plate porosity ratio (βP). Three different cylinder porosity ratio and four different plate porosity ratio were determined as βC=0.3, 0.5, 0.7 and βP=0, 0.3, 0.5, 0.7 respectively. Also, plate angle (α) relative to the flow direction was defined to investigate the effect of splitter plate location to the flow behavior. And these plate angles were chosen as α=90°, 120°, 150°, 180°. For all configurations, dye visualization method was utilized initially, and then to have quantitative results PIV technique was applied. Results indicated that as the plate porosity ascends the TKEmax values has diminishing trend. Also cylinder porosity has remarkable influence on TKEmax values, TKEmax reduction was obtained for lower porous cylinders. And plate angles of 150° and 180° were found to be the most effective angles regardless of the plate porosity ratio. The highest TKEmax decrease was attained as 34% for the βC=0.3, βP=0.5 at 180°. On the other hand, βC=0.7 has insignificant control over flow by reason of its high permeability. Consequently, βC=0.3 and 0.5, βP=0.5 and 0.7, and plate angles of 150° and 180° were found as the most effective parameters in order to control the flow.
Investigation of wake flow characteristics of a splitter plate with different porosity behind a vertical cylinder
Researcher studies on flow over bluff bodies for understanding wake flow physic and the cylinders are widely used for experiments due to their basic geometry and large number of technical applications like heat exchanger tubes, cooling systems for nuclear power plants, power transmission lines, chimney stacks, bridges, buildings, radio telescopes, power lines, offshore drilling rigs, underwater pipelines, marine cables etc. Submerged hydrodynamics is a general term used to describe the hydrodynamics of floating or stationary structures that cause flow separation. A continuous flow causes periodic vortex fluctuations around the sinking object. When the vortex fluctuates behind the object, the drag force on the object increases and periodic forces are generated perpendicular to the flow direction on the object. These periodic forces cause structural vibrations and acoustic noise or resonance. At the same time vortexes increases the mixing behind the flow and in this way, the heat transfer also increases. Learning to control the vortex fluctuations can reduce the noise level by increasing energy efficiency. In this study, it is aimed to examine passive flow behind the cylinder passively with different permeability separator plates, using particle imaged velocity measurement (PIV) technique. Experiments have been carried out at Cukurova University, Mechanical Engineering Department, Fluid Mechanics Laboratories. According to the results obtained, the effects of the permeability ratio β, the separator plate length, the distance between the plate cylinder and the separator plate cylinder axis, the effects on the vortex formation behind the cylinder and the turbulence statistics of the flow (Turbulence Kinetic Energy) have been revealed.
Determination of drag coefficient from PIV data
In this thesis, the drag coefficient of circular and square section cylinders was estimated from Particle Image Velocimetry (PIV) data and compared to the one in the literature. PIV measurements were obtained up to 2.5D distance from the cylinder at Reynolds number 5x103, 10x103, 15x103 for the circular cylinder. For the square cylinder, PIV measurements were obtained up to 7D distance from the cylinder at Reynolds number 3x103, 3.5x103. The average velocities and Reynolds stress terms of flow around the circular and square section cylinders were measured to determine the drag coefficient. The equation for drag coefficient determination was solved by finite difference methods and Fortran code was written for calculations.
Fuel characterization and supercritical water gasification of dewatered poultry sludge for hydrogen production
In this study, to explore supercritical water gasification (SCWG) of dewatered poultry sludge (DPS), the essential fuel characterizations were carried out, and then the new model to estimate the high heating value from its ultimate analysis was developed. The reaction temperature (400ᴼC, 450ᴼC, and 500ᴼC), feed concentration (2%, 6%, and 10%), residence time (10min, 20min, and 30min) as well as different catalysts additives (K2CO3, Na2CO3, KOH, and NaOH) were selected as vital operating parameters. Furthermore, the response surface method (RSM) was employed to design the experimental and investigate the interaction between the selected operating parameters. The responses from SCWG of DPS were terms as produced gas yield compositions, carbon conversion, hydrogen efficiency, and gasification efficiency. The DPS has a high potential of using it as an energy source with acceptable fuel characterizations. From non-catalytic process results, the increase in the reaction temperature plays the main role in H2 production. Regarding the catalytic process, NaOH showed the best results, and loading of it increases the process responses, while low temperature increased the molar fraction of H2.
Fuel characterization and gasification of sunflower waste in sub and supercritical water with influence of catalysts on optimum state.
In this work to investigate sub and supercritical water gasification (SASCWG) of Sunflower waste (SFW). The basic fuel characterizations were carried out, as well as the ultimate analysis, As operational parameters, the reaction temperature (350°C, 400°C, and 450°C), feed concentration (2, 6, and 10%), residence time (10, 20, and 30 minutes), and various catalyst additives (K2CO3, Na2CO3, and NaOH) were used. The response surface method (RSM) was also used to construct the experiment and explore the interactions between the operational parameters. The response from SCWG of SFW was termed as produced gas yield compositions. The SFW has an acceptable fuel characterization using it as an energy source. According to the results of non-catalytic processes, subcritical water gasification has small influence on H2 generation counter to supercritical gasification, the rise in reaction temperature is the most important factor in H2 generation. Regarding the catalytic process on supercritical gasification, NaOH exhibited the greatest outcomes and loading it enhances the process responses. Keywords: Sunflower waste, Hydrogen, Fuel characterizations, Sub and Supercritical water gasification, Response surface method.
Electricity generation by using micro wind turbine in metro lines
Due to the increasing human population, the consumption rate of exhaustible resources has also increased. Especially in energy production, methods for the use of renewable energy sources as an alternative to exhaustible sources are becoming more common day by day. The use of wind turbines in electricity generation can be given as an example of this situation. By using wind turbines, it is possible to generate energy with turbines at different locations and with different power capacities. The generation of electrical energy by using micro wind turbines in public transportation vehicles can be given as an example of what has become widespread in city life. The subject of generating electrical energy by the movement of the outside air, which is accelerated by the movement of public transportation vehicles, by using a wind turbine, has been studied by different researchers in recent years. Micro wind turbines are turbines that have many benefits such as do not cost towers, are easy to transport and install due to their size and, can be used almost everywhere in daily life. It has been studied in this thesis to generate energy from the kinetic energy of the air, which is moved by the train movement in the subway stations. Kızılay metro station, which is the most frequent station in Ankara, the capital and second-most crowded city is taken as an example station. The behaviour of the air moving inside, and the velocity profile was obtained by performing flow field analysis in the ANSYS Fluent package program by using the real station dimensions and the gauge dimensions of the wagons. According to the btained velocity data, a suitable micro wind turbine was selected and the daily, weekly, monthly and, annual electrical energy amount that could be obtained with this turbine system was calculated. The results were compared with similar studies in the literature, and it was seen that the amount of electricity produced varies depending on the selected turbine, train speed, and the speed of the air moving accordingly, the number of turbines. Keywords: Electricity Generation, Micro-wind Turbines, Energy Saving, CFD
Numerical and expermental investigation of flow downstream of perforated cylinder at low reynolds number
The aim of present study is to investigate the effects of deployment of perforated cylinder on vortex street suppression and flow structure on downstream of a circular cylinder in deep water and at low Reynolds numbers by using numerical simulations along with the technique of high-image-density Particle Image Velocimetry (PIV), in this purpose, during the sudies, porosity of perforated cylinder and diameters of cylinders were kept constant. This study carried out with the related to six diffrent of Reynolds numbers between750 to 2000 for PIV study and ten various value of Reynolds number is considered from range of 150 to 2000 for CFD analysis.For validation purposes, numerical investigations were run for solid cylinder cases to achieve agreement between the simulations and the experimental results as a case study. Furthermore, numerical simulations were performed to see the effect of placing the perforated cylinder around the solid cylinder, concentrically. In this regards, Velocity and vorticity contours, turbulent kinetic energy, and streamline topologies were investigated in the wake region in order to reveal the differences in flow structuers of circular cylinder among various distance rates at different Reynolds numbers. As a conclusion, According to the results, suppression of Karman vortex street is receivable with utilize of perforated cylinder around single cylinder. At all Re numbers according to the both numerical and expermental results, after perforated cylinder was concentrically placed with respect to the circular cylinder was obvioused a reduction approximately 20% to 45% in Drag coefficient.
Investigating the performance of a PV-driven VRF system using cold thermal storage in Mediterranean climate
The demand for cooling has surged due to rising global temperatures, prompting interest in solar cooling systems categorized as electrically driven and thermally driven. Thermally driven systems employ solar thermal collectors and absorption chillers for cooling, constrained to a 20-ton minimum capacity and requiring backup heating or electric cooling without solar energy. Electrically driven systems, powered by photovoltaic panels, suit existing air conditioning and smaller cooling setups. This study examines a photovoltaic solar electrical-driven variable refrigerant flow system paired with cold phase change material thermal storage, targeting nearly zero-energy cooling in a 300m² Adana villa. Using the "Design Builder" program, baseline and optimized energy models were built, adhering to Turkish Thermal Insulation Requirements. Models were compared for year-round cooling energy rates. The challenge of storage led to investigating cost-effective cold thermal storage, countering short-lived costly batteries with reduced initial expenses and load-shifting. The research aims to optimize PV panel area and electrical/thermal storage using the "Hooke and Jeeves" technique.