Person: ERTUNÇ, Özgür
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Özgür
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ERTUNÇ
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ArticlePublication Metadata only A design and optimization method for matching the torque of the wind turbines(AIP Publishing, 2015) Al-Abadi, A.; Ertunç, Özgür; Weber, H.; Delgado, A.; Mechanical Engineering; ERTUNÇ, ÖzgürAn aerodynamic shape optimization method for a horizontal axis wind turbine is developed and verified through experimentation with a laboratory-scale wind turbine. Our method is based on matching the rotor's and the coupled generator's torque. Prior to shape optimization, an initial rotor design is established with a hybrid use of Schmitz and blade element momentum theories. The experimental verification of the developed method is conducted with a small-scale wind turbine; thus, the operating Reynolds number is one order of magnitude lower than large-scale wind turbines. Therefore, a high-lift low-Re airfoil, namely, SG6043, is selected for the blade along the whole span. The shape is optimized by determining the optimum chord and cumulative pitch angle distributions by manipulating the tapering and twisting of the blade. The objective of the optimization is to maximize the turbine's power coefficient Cp , while maintaining the torque equal to that of the generator. The generator's characteristics are found through experimentations which are conducted apart from the wind tunnel experiments. During the optimization process, the local aerodynamic forces on the blade are calculated by interfacing the optimization program with XFOIL; thus, the torque and power can be calculated for the rotor at each iteration step. The optimized turbine performance is evaluated under a design and off-design operating condition. The performance verification experiments are carried out in the wind tunnel with a specially designed setup. A comparison of the measured and computed performance shows good agreement.ArticlePublication Metadata only The penetration of acoustic cavitation bubbles into micrometer-scale cavities(Elsevier, 2016) Vaidya, H. A.; Ertunç, Özgür; Lichtenegger, T.; Delgado, A.; Skupin, A.; Mechanical Engineering; ERTUNÇ, ÖzgürThe penetration of acoustically induced cavitation bubbles in micrometer-scale cavities is investigated experimentally by means of high-speed photography and acoustic measurements. Micrometer-scale cavities of different dimensions (width = 40 μm, 80 μm, 10 mm and depth = 50 μm) are designed to replicate the cross section of microvias in a PCB. The aim here is to present a method for enhancing mass transfer due to the penetration of bubbles in such narrow geometries under the action of ultrasound. The micrometer-scale cavities are placed in a test-cell filled with water and subjected to an ultrasound excitation at 75 kHz. A cavitation bubble cluster is generated at the mouth of the cavity which acts as a continuous source of bubbles that penetrate into the cavity. The radial oscillation characteristics and translation of these bubbles are investigated in detail here. It is observed that the bubbles arrange themselves into streamer-like structures inside the cavity. Parameters such as bubble population and size distribution and their correlation with the phase of the incident ultrasound radiation are investigated in detail here. This provides a valuable insight into the dynamics of bubbles in narrow confined spaces. Mass transfer investigations show that fresh liquid can be continuously introduced in the cavities under the action of ultrasound. Our findings may have important consequences in optimizing the filling processes for microvias with high aspect ratios.ArticlePublication Metadata only Turbulence impact on wind turbines: experimental investigations on a wind turbine model(IOP Publishing, 2016) Al-Abadi, A.; Kim, Y. J.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, ÖzgürExperimental investigations have been conducted by exposing an efficient wind turbine model to different turbulence levels in a wind tunnel. Nearly isotropic turbulence is generated by using two static squared grids: fine and coarse one. In addition, the distance between the wind-turbine and the grid is adjusted. Hence, as the turbulence decays in the flow direction, the wind-turbine is exposed to turbulence with various energy and length scale content. The developments of turbulence scales in the flow direction at various Reynolds numbers and the grid mesh size are measured. Those measurements are conducted with hot-wire anemometry in the absence of the wind-turbine. Detailed measurements and analysis of the upstream and downstream velocities, turbulence intensity and spectrum distributions are done. Performance measurements are conducted with and without turbulence grids and the results are compared. Performance measurements are conducted with an experimental setup that allow measuring of torque, rotational speed from the electrical parameters. The study shows the higher the turbulence level, the higher the power coefficient. This is due to many reasons. First, is the interaction of turbulence scales with the blade surface boundary layer, which in turn delay the stall. Thus, suppressing the boundary layer and preventing it from separation and hence enhancing the aerodynamics characteristics of the blade. In addition, higher turbulence helps in damping the tip vortices. Thus, reduces the tip losses. Adding winglets to the blade tip will reduce the tip vortex. Further investigations of the near and far wake-surrounding intersection are performed to understand the energy exchange and the free stream entrainment that help in retrieving the velocity.ArticlePublication Metadata only Benchmark study of 2D and 3D VOF simulations of a simplex nozzle using a hybrid RANS-LES approach(Elsevier, 2022-07-01) Bal, M.; Kayansalçik, Gökhan; Ertunç, Özgür; Erhan Böke, Y.; Mechanical Engineering; ERTUNÇ, Özgür; Kayansalçik, GökhanIn this study, a simplex nozzle is tested with water for the benchmarking of different flow simulation models. A large scale Plexi-glass transparent nozzle is used to reduce the influence of production tolerances on the performance. Experiments are conducted at different flow rates and CD, spray angle and film thickness parameters are evaluated. 2D and 3D hybrid RANS-LES multiphase flow simulations of simplex nozzle are validated against the experimental data. Multiphase nature of the flow is modelled by volume of fluid method. The main goal is to assess the capabilities and drawbacks of 2D axisymmetric and full sector 3D modeling approaches. It is observed that although full sector 3D simulations require HPC cluster systems, accuracies in validation parameters are quite satisfying. Conversely, 2D axisymmetric simulations which can be run on a single core and give a general outlook of the flow field, they show an overshoot of CD and film thickness over the selected range of flow rate. It is shown that this overshoot is mostly related with the inlet boundary condition, which can not take the flow contraction and/or separation at the inlet slots into account. After correcting the inlet velocity 2D simulations by using the 3D results, it is shown that the predictions can be quite close to the experimental data.ArticlePublication Metadata only A torque matched aerodynamic performance analysis method for the horizontal axis wind turbines(Wiley, 2013-11) Al-Abadi, A.; Ertunç, Özgür; Weber, H.; Delgado, A.; Mechanical Engineering; ERTUNÇ, ÖzgürAn analysis method is developed to test the operational performance of a horizontal axis wind turbines. The rotor is constrained to the torque–speed characteristic of the coupled generator. Therefore, the operational conditions are realized by matching the torque generated by the turbine over a selected range of incoming wind velocity to that needed to rotate the generator. The backbone of the analysis method is a combination of Schmitz' and blade element momentum (BEM) theories. The torque matching is achieved by gradient-based optimization method, which finds correct wind speed at a given rotational speed of the rotor. The combination of Schmitz and BEM serves to exclude the BEM iterations for the calculation of interference factors. Instead, the relative angle is found iteratively along the span. The profile and tip losses, which are empirical, are included in the analysis. Hence, the torque at a given wind speed and rotational speed can be calculated by integrating semi-analytical equations along the blade span. The torque calculation method is computationally cheap and therefore allows many iterations needed during torque matching. The developed analysis method is verified experimentally by testing the output power and rotational speed of an existing wind turbine model in the wind tunnel. The generator's torque rotational speed characteristic is found by a separate experimental set-up. Comparison of experiments with the results of the analysis method shows a good agreement.ArticlePublication Metadata only Model-based optimization of CMP process parameters for uniform material removal selectivity in cu/barrier planarization(IOP Publishing, 2022-02-01) Akbar, Wazir; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, ÖzgürChemical mechanical planarization is a process of achieving planar surfaces in the semiconductor manufacturing industry. The planarization of a surface is achieved by material removal from the wafer surface. The material removal depends on material properties and the process input parameters. Several studies have investigated the role of slurry chemistry to achieve a certain material removal selectivity of different materials on a patterned wafer. Here we propose a methodology of achieving planar patterned surface of Cu/Mn/MnN system using a model-based optimization for mechanical process parameters. The parameters include applied force, slurry solid concentration, and abrasive particle size. The methodology has been developed via optimization using a genetic algorithm. The proposed methodology suggests that a lower downforce is the key parameter to achieve the desired material removal selectivity and planarity. The first part of the study suggests a low material removal rate (MRR) to achieve a lower standard deviation in MRR. The second part investigates the standard deviation in the thickness removed in the average time needed to remove a known thickness of the materials under consideration. It has been found that the application of lower downforce can also minimize the standard deviation in the thickness removed and a planar patterned surface can be achieved.ArticlePublication Metadata only A coupled material removal model for chemical mechanical polishing processes(IOP Publishing, 2021-10-01) Akbar, Wazir; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür; Akbar, WazirChemical mechanical polishing (CMP) is a process used to obtain planarized surfaces in microelectronic device manufacturing. The planarization is achieved by material removal from the wafer surface by synergistic effect of chemical and mechanical actions. The material removal rate (MRR) in chemical mechanical processes have a linear dependency on applied down pressure. However, some experimental studies have reported nonlinear relationship between MRR and applied pressure. The nonlinearity can be attributed to complex interactions among the wafer, pad, abrasive particles, and chemical agents in the slurry. Therefore, in modelling CMP processes, coupling of both the chemical and mechanical actions is imperative to provide insight into the nonlinear behavior of MRR, because treating the chemical effects only as a mere means of softening the wafer surface fails to explain the nonlinear behavior of MRR in silicon dioxide CMP. Here, we present a model that couples micro-contact mechanics with diffusion of slurry into the wafer and predict MRR in CMP of silicon dioxide. The model is validated with experimental results available in the literature. Moreover, the developed model may be used to explain the nonlinear increase in MRR of silicon dioxide with increasing applied pressure.ArticlePublication Metadata only Experimental and numerical study of rubber flow in the extrusion die of a weather strip(Society of Chemical Engineers, 2019) Talib, Nayyef Ahmed; Ertunç, Özgür; Türkistanli, T.; Aydın, E.; Mechanical Engineering; ERTUNÇ, Özgür; Talib, Nayyef AhmedExtrusion is the main method used to produce rubber weather strips in automotive industries, and the quality of the final product largely depends on the thermal properties of the process output. Therefore, precise thermal control of the process is the key to product quality control. This study establishes a three-dimensional model of the nonisothermal viscous flow of ethylene propylene diene monomer (EPDM) rubber melts through a power law rheological model and a mixed finite element method. The rheological properties of the filled rubber compound were characterized using a capillary rheometer (Rosand) at different temperatures to evaluate the required material parameters for numerical simulation. Curing characteristics were investigated using a rubber process analyzer (RPA-2000) to construct a curing curve at different temperatures. The pressure-stabilized Petrov-Galerkin (PSPG) method and streamline upwind/ Petrov-Galerkin numerical scheme were employed to solve the flow equations and increase numerical stability. The power law rheological model was combined with field equations such as continuity, momentum, and energy equations to determine the complex flow behavior in an extrusion die of real geometry. Extrusion experiments were performed in an industrial extrusion line, and temperature and pressure were measured at different extruder speeds by using special sensors mounted on the extrusion die. The results confirmed that for EPDM rubber compound, the extruder speed exerted a remarkable effect on the temperature rise and pressure drop in the extrusion die. The impact of viscous dissipation on the thermal behavior and pressure drop prediction of the rubber compound flow is also discussed. The obtained scorch time was compared with the estimated residence time in the flow domain to elucidate the influence of extruder speed on the processing characteristic. The results suggested the lack of premature vulcanization or the start of scorching inside the flow domain within the studied extruder speed range. The validity of model prediction was verified by comparison between simulation and experimental results. The predicted results of the model showed good agreement with the experimental data.ArticlePublication Metadata only Application of giesekus model for capillary extrusion of rubber compound(The Society of Chemical Engineers, 2019-02) Talib, Nayyef Ahmed; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür; Talib, Nayyef AhmedExtrudate swell is an important phenomenon occurring when high viscoelastic materials, such as rubber and rubber compounds, are extruded. In this work, the effects of relaxation time and relaxation mode on swell predictions using a nonlinear differential viscoelastic model, that is, the Giesekus model, are studied systematically for rubber extrusion in a capillary die. The corresponding 3D, steady-state finite element simulation for predictions of swelling is presented and compared with experimental data for validation. Velocity distribution, pressure drop and circulation flow in the die are analyzed and discussed through the simulation. The results of swell prediction reveal that three-relaxation mode of the Giesekus model with a wide range of relaxation times reproduce experimental data. In addition, the number of relaxation mode and relaxation time have remarkable effects on circulation flow at the die corner and some effect on other field variables.ArticlePublication Metadata only Numerical and experimental analysis of impinging synthetic jets for cooling a point-like heat source(ASME, 2018-05-01) Glowienko, G.; Derlien, H.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, ÖzgürHigh power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.