Özkol, Ünver
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Ozkol, U.
Oezkol, Ue
Ozkol, U
Ozkol, Unver
Özkol, Ü.
Özkol, Ü
Oezkol, Ue
Ozkol, U
Ozkol, Unver
Özkol, Ü.
Özkol, Ü
Job Title
Email Address
unverozkol@iyte.edu.tr
Main Affiliation
03.10. Department of Mechanical Engineering
Status
Current Staff
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WoS Researcher ID
Sustainable Development Goals
1NO POVERTY
0
Research Products
2ZERO HUNGER
1
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3GOOD HEALTH AND WELL-BEING
0
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4QUALITY EDUCATION
1
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5GENDER EQUALITY
0
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6CLEAN WATER AND SANITATION
2
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7AFFORDABLE AND CLEAN ENERGY
19
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8DECENT WORK AND ECONOMIC GROWTH
4
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9INDUSTRY, INNOVATION AND INFRASTRUCTURE
28
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10REDUCED INEQUALITIES
0
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11SUSTAINABLE CITIES AND COMMUNITIES
1
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12RESPONSIBLE CONSUMPTION AND PRODUCTION
5
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13CLIMATE ACTION
13
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14LIFE BELOW WATER
2
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15LIFE ON LAND
1
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16PEACE, JUSTICE AND STRONG INSTITUTIONS
0
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17PARTNERSHIPS FOR THE GOALS
0
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Documents
17
Citations
271
h-index
8
Documents
11
Citations
202
Scholarly Output
58
Articles
15
Views / Downloads
61730/31757
Supervised MSc Theses
35
Supervised PhD Theses
4
WoS Citation Count
252
Scopus Citation Count
279
Patents
0
Projects
7
WoS Citations per Publication
4.34
Scopus Citations per Publication
4.81
Open Access Source
48
Supervised Theses
39
| Journal | Count |
|---|---|
| Biomass Conversion and Biorefinery | 2 |
| Applied Mechanics Reviews | 1 |
| Architectural Science Review | 1 |
| Asme Turbo Expo: Turbine Technical Conference And Exposition, 2015 | 1 |
| Engineering Applications of Computational Fluid Mechanics | 1 |
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58 results
Scholarly Output Search Results
Now showing 1 - 10 of 58
Conference Object Citation - WoS: 1Citation - Scopus: 1Development of a New Universal Inverse Through-Flow Program and Method for Fully Coupled Split-Flow Turbomachinery Systems(The American Society of Mechanical Engineers(ASME), 2015) Acarer, Sercan; Özkol, ÜnverStreamline curvature technique for inverse through-flow modeling of turbomachinery is still one of the most prevalent alternatives in design. Even though the subject has been studied in numerous aspects over many years, open literature on fully coupled split-flow turbomachinery system design which is encountered in turbofan engines, is still limited. The principal method, viable for analysis mode, may easily give rise to undesired streamline distortion near the splitter leading edge whilst operating in design mode. Besides, spanwise discontinuity of flow properties along the stagnation streamline prior to final solution convergence may be another outcome. The present study is geared towards eliminating these potential drawbacks by developing an alternative generally applicable split-flow scheme incorporated in a recently developed streamline curvature software. This new scheme disposes the need to define a stagnation streamline, while preserving full coupling between the main and split ducts. This is achieved through removal of by-pass ratio restriction, which makes local velocity vector always perfectly aligned with the splitter leading edge without any limit on fan-splitter axial distance. A two-step validation strategy is followed: Firstly, 2D split-flow solutions of the developed method for representative duct geometries having design by-pass ratios ranging between 0.25 and 6.5, but without turbomachinery, are compared with a commercial CFD software; Secondly, the method is compared with 3D viscous CFD solution of NASA Rotor 37 geometry, whose flowpath is modified to include a downstream flowpath splitter. It is shown that the proposed scheme can be used as a practical alternative to the conventional treatment that promises minimal effort to implement to an existing compressor streamline curvature methodology.Master Thesis Spray Characteristics of Emulsified Biodiesel-Diesel Blends in a Constant Volume Combustion Chamber(01. Izmir Institute of Technology, 2020) Tezel, Yusufcan; Özkol, Ünver; Özkol, ÜnverOver the last decades, various studies have been carried out by the researchers to find out an alternative fuel that can overcome emission problems caused by diesel fuel which affect the environment and human health significantly. Due to emulsified biodiesel-diesel blend (EBB) fuels are being a possible alternative fuel for diesel, in this study, it was aimed to investigate the macroscopic spray parameters such as spray penetration length and cone angle of different EBB fuels, namely B20W15 and B20W5, containing 15% and 5% water by volume, respectively. In order to examine the spray characteristics of B20W15 and B20W5, the experiments were carried out by means of constant volume combustion chamber and utilizing shadowgraph technique with a high-speed camera. Experiments were performed with 600 bar and 800 bar injection pressure while the ambient pressure was 0 bar, 5 bar and 10 bar, respectively. After experiments were fulfilled, the recorded images of test fuels were processed via ImageJ program. The results showed that stability of the emulsion can be obtained when HLB value was 8 and surfactant concentration was 5% by volume. It was understood that increment in water concentration in the emulsion caused deterioration in emulsion stability while it led higher viscosity, higher density, longer spray penetration lengths and narrower cone angles. It was observed that B20W5 resulted wider spray cone angles and shorter spray penetration lengths than B20W15 under 0,5 and 10 bar chamber pressure with injections pressures of 600 and 800 bar. Also, it was understood that both EBB lead longer spray penetration lengths and narrower spray cone angles compared to reference diesel while they lead vice versa compared to reference biodiesel. The reason of spray geometry difference between diesel and EBB fuels can be associated with the higher viscosity and density of EBB fuels compared to diesel. As a result, considering that B20W5 reduce the use of fossil fuels, and no significant difference compared to diesel in terms of spray geometry, it can be said that B20W5 may be a promising alternative fuel for the futurDoctoral Thesis Aerodynamic Optimization of a Transonic Aero-Engine Fan Module(Izmir Institute of Technology, 2016) Kor, Orçun; Özkol, ÜnverAerodynamic design of an aero-engine fan blade is a multi-step process with multi-variables. The general purpose in aerodynamic design is to obtain proper blade angles and flowpath geometry providing the necessary pressure ratio with maximum efficiency, while respecting the structural and aerodynamic constraints. The throughflow design in aerodynamic design procedure is a key step where one can obtain a basic aero-design which generally fixes 80% to 90% of the final fan geometry, by adjusting parameters like blade exit angle distribution, solidity, hub and shroud contour, meridional chord length, etc. Throughout this procedure, the aim of the designer is to obtain an optimum (i.e. light, reliable and robust) system with highest efficiency. Among optimization methods, zero order methods are reported to fit best for turbomachinery problems, due to their good performance in discrete and non-differentiable problems and their ability to find the global optimum. Genetic algorithm is the most widely used optimization method in turbomachinery optimization. Methods inspired by swarm intelligence are reported as promising global optimizers, whereas, to the author’s knowledge, there are no reported studies that employs such algorithms in turbomachinery throughflow optimization. These methods can find the neighborhood that provides the globally optimum design, rather than exactly finding the global design. This drawback is overcome by hybridizing genetic/swarm inspired algorithms by first order (gradient based) methods. Within this aspect, the present study focuses on developing genetic and swarm inspired algorithms hybridized with gradient based algorithms to find the optimum throughflow design of a transonic aero-engine fan module.Doctoral Thesis An Experimental and Numerical Study on Interfacial Convective Heat Transfer Coefficient and Thermal Dispersion Conductivity of a Periodic Porous Medium Under Mixed Convection Heat Transfer(Izmir Institute of Technology, 2017) Çelik, Hasan; Özkol, Ünver; Mobedi, MoghtadaThe need on effective heat transfer enhancement has been increasing day by day. Because of that, researchers/engineers who work on heat transfer are required to obtain new techniques to address raising accumulation of heat transfer. Heat transfer can be enhanced by active and passive methods and passive methods are mostly chosen, as no external power input is required. Porous media is one of the most popular passive heat transfer techniques. Porous media can be divided into periodic and stochastic structures. In this thesis, the analysis of heat and fluid flow in 2D periodic structure and 3D aluminum and ceramic foam structures under mixed and forced convection heat transfer are studied. The governing equations are solved at pore scale and volume-averaged transport parameters as permeability, inertia coefficient, interfacial heat transfer coefficient and thermal dispersion are obtained by using volume averaging of the obtained pore scale velocity, pressure and temperature. For the change of periodic structure, the interfacial heat transfer coefficient and thermal dispersion with respect to Reynolds, Richardson and porosity under mixed convection are studied probably for the first time in literature. For foam structure, the changes of permeability, inertia coefficient, interfacial heat transfer coefficient and thermal dispersion with respect to Re are discussed. The determination of thermal dispersion by using tomography method is probably reported for the first time. For 2D periodic structures, the interfacial convective heat transfer coefficient successfully found while for the thermal dispersion conductivity the Volume Averaging Technique fails for high Richardson numbers under mixed convection. Based on good agreement between the computational values of this study and reported correlation in literature, it is observed that the use of micro-tomography technique for determination of volume-averaged transport parameters yield satisfactory results if properly used. The comprehensive methods for inspection, verification and validation of the obtained computational results for 3D digitally generated foam are suggested.Article Citation - WoS: 11Citation - Scopus: 11A Numerical Study on Determination of Volume Averaged Thermal Transport Properties of Metal Foam Structures Using X-Ray Microtomography Technique(Taylor & Francis, 2018) Çelik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Özkol, ÜnverVolume averaged thermal transport properties of two metal foams with 10 and 20 PPI are obtained by using microtomography technique. The digital 3D structures of samples are generated in computer environment. The governing equations are solved for the entire domain and the volume averaged technique is used to determine interfacial heat transfer coefficient, longitudinal and transverse thermal dispersion conductivity. The study is performed for the pore scale Reynolds number from 100 to 600. The obtained results are within the ranges of the suggested correlations in literature. The present study supports the correlations suggested by Calmidi and Mahajan (2000) and Zhang et al. (2016).Master Thesis Model Design and Experimental Investigation of Floating Wind Turbine(01. Izmir Institute of Technology, 2022) Arıdıcı, Ali; Özkol, ÜnverFloating offshore wind energy has great potential (which constitutes almost 80% of total offshore wind energy) to meet electricity demand of the world at the same time to reach net-zero emission goal by 2050. Floating offshore wind turbines (FOWT) are able to achieve highest capacity factor since local effects of the offshore terrains are lesser. Thus, it receives stronger and more stable wind. On the other hand, combined hydrodynamic and aerodynamic forces with 6 degrees of freedom (DoF) bring unsteadiness and there- fore, challenges on FOWT design. Furthermore, significant rotational motions, particu- larly pitch motion, lead the turbine to transient state which can not be simulated through conventional numerical tools. Therefore, to understand the dynamics of the FOWT, it is necessary to conduct experimental studies to obtain results by considering all the param- eters. The main aim of the thesis is to investigate the dynamic response of the FOWT under the extreme wind and wave conditions. A 1/40 Froude-scaled version of the Northel POYRA P36/300 mounted on the spar-type floating platform was developed by colleagues as a part of TUBITAK (217M451) project. In this thesis, experimental studies were car- ried out in the wave flume with a wind nozzle in the hydraulic laboratory of IZTECH Civil Engineering Department. Atmospheric boundary layer (ABL) was scaled, and in- struments of the experiment were calibrated to characterize wind nozzle and wave maker, which are vital to obtaining reliable results. The wind nozzle was designed based on experimental data to reproduce correct Froude-scaled ABL.Master Thesis Experimental and Numerical Analysis of Heat Transfer Performance of Off-Set Strip Fins(Izmir Institute of Technology, 2009) Durmaz, Gürcan; Özkol, Ünver; Özkol, ÜnverThe aim of this study is to computationally and experimentally investigate the heat transfer and pressure drop characteristics of an offset-strip fin. In the present study, experiments are conducted at the range of Reynolds number from 150 to 3500 and a 3-D numerical domain, which is investigated as a conjugate problem, is created for finite volume computations. The computations are conducted by assuming that the flow in the offset-strip fin channels is steady and laminar at the range of Reynolds numbers from 200 to 5000. In this thesis, the effects of the flow behaviors in the offset strip fin channels on Colbourn j factor, which is the non-dimensional form of heat transfer coefficient, and fanning friction f factor, which is the non-dimensional form of pressure drop, are investigated. Also, the heat transfer boundary conditions and the Prandtl numbers of the fluids are kept different for these fins in order to see the effect of those.The effect of Prandtl number is investigated by using air, 0.707 < Pr < 0.71 and water, 2 < Pr < 4.35 and ethylene glycol, 94 < Pr < 138. The effect of the thermal boundary conditions is investigated by using constant heat flux and uniform temperature. Moreover, all results are compared with Kays and London.s experiments (1964) and also the results of Manglik and Bergles.s correlations (1995). The results show a very good agreement between the results of Kays and London (1964) and of Manglik and Bergles.s correlations (1995). It is also observed that results obtained from the two alternatives for the thermal boundary condition are very close to each other. According to obtained results, it is concluded that our computational results from laminar flow assumption and experiments are reliable at almost all the range of Reynolds numbers studied.Master Thesis Investigation of the Effect of Pase-Change Metarials on the Performance of Household Refrigerators(Izmir Institute of Technology, 2014) Coşkun, Çağlar; Özkol, Ünver; Özkol, ÜnverThe main problem that this study deals with is the issues of thermal effectiveness of phase change materials (or PCM) application to household refrigerators and investigating the performance improvement with numerical methods. PCMs are materials that store thermal energy in latent heat form between its solidus and liquidus points. By this way, these materials can store large amount of heat in a narrow temperature range, which made them to gain popularity in recent years. By exploiting this feature of PCMs, it is thought that using these materials in household refrigerators could increase the energy efficiency, thus energy class of a refrigerator. Because, keeping the cold energy inside the refrigerated space as latent heat will decrease the number of stop and start cycles of the compressor. Decreasing the number of stop and start cycles is beneficial since the distribution of refrigerant fluid in the refrigeration cycle breaks down every time compressor is stopped and established again on the next start, which is the main inefficiency source. In this study, at first, the steady temperature contours are extracted by steady state numerical simulations to see the possible locations for the application of PCMs. Then, transient simulations are conducted to understand the transient thermal behavior of the refrigerated space and these transient results are validated with experimental data. In the light of these steady and transient thermal pictures, PCMs having proper phase change temperatures are placed in appropriate places on the walls of the refrigerator and transient simulations are conducted to see the effects of PCMs. Since radiative heat transfer cannot be ignored in household refrigerators, all simulations are conducted with and without radiation and effects of radiation are also presented. The well – known commercial computational fluid dynamics (CFD) code, FLUENT is employed for the numerical simulations.Master Thesis Numerical Investigation of Pumping Power Minimization for Coolant Circulation in Sinusoidal Channels(Izmir Institute of Technology, 2013) Akça, Ali; Özkol, Ünver; Özkol, ÜnverThe electronic devices consume more energy with the increasing their process capacity. Therefore, their temperature increase and unless they are cooled down sufficiently, electronic devices exceed the safety operating temperature and break down. Improvements in electronic technology are obtained as this heat transfer bottleneck is overcome. Moreover, this cooling system consumes electric power as well and this should be minimized. In this thesis, minimization study of the consumed energy to cool down an electronic device is carried out. In this study, the heat transfer in the rectangular cross-sectional sinusoidal wavy channels is investigated numerically and heat transfer augmentation is considered with reference to a straight channel geometry. Minimization of the surface temperature and the pump power are elaborated for the different wave amplitudes and wavelengths in the channel. The flow in the channel is conducted at the range of Re numbers from 7 to 368 and it assumed laminar and steady state condition. Dissipating heat flux from the electronic module is assumed to be constant. Thermal performance is calculated with observing of the temperature of the critic device on the electronic module and the pump power is evaluated by utilizing pressure drop calculations in the channel. To investigate how the sinusoidal wavy channel affects the cold plate compared to the straight channel, some dimensionless numbers are defined and the assessments are done in accordance with these numbers. Generally, it was observed that, sinusoidal wavy channel contributes the heat transfer enhancement. While wave amplitude affects heat transfer positively, pump power is affected adversely. Wavelength effect is not important comparing with wave amplitude for the augmentation of heat transfer performance. Nevertheless, it was observed that the increasing the wavelength causes to decrease pump power.Master Thesis Experimental Investigation of Heat and Fluid Flow in an Actuated Impinging Jet Flow(Izmir Institute of Technology, 2009) Bilgin, Necati; Özkol, ÜnverThe objective of this work is to how the surface heat transfer and flow characteristics can be affected by jet flow by excitation of which changes the turbulence characteristics of the flow. Main body of this work is experimental analysis; nevertheless some simple numerical analysis is also presented in order to make some comparisons. The hot-wire measurements and flow visualizations are performed. As a flow actuator a loudspeaker is used once the piezo-electric benders were found to be unsuccessful. Acoustic (pressure) wave generated by the loudspeaker travels along the flow system and reaches the jet nozzle where it generates an oscillating component on the mean nozzle velocity. Parameters used on this study are shortly Re.10000, dimensionless jet to plate distance is equal to 6, as a non-dimensional excitation frequency Strouhal number is changed in the range of 0.St.1, and as for the excitation amplitude, voltages sent to the 20X amplifier are 0.5V, 1.0V and 1.5V.