Person: ERTUNÇ, Özgür
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Özgür
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ERTUNÇ
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Conference paperPublication Metadata only Flow visualization and LES simulations inside a chevron type plate heat exchanger(Begell House Inc., 2018) Peçenek, Erdem; Ertunç, Özgür; Senkal, C.; Mechanical Engineering; ERTUNÇ, ÖzgürAn up-scaled model of a single channel of CPHE was used under dynamically similar conditions for the experiments. In experiments, pressure drop measurements and flow visualizations were conducted with aluminum flitter and dye. For the numerical study, large eddy simulations are preferred in the turbulent regime which has the best fit with experiments. Also mixing inside the channel is analyzed and reported through numerical simulations. Results of this study exhibit flow structures differ from previous visualization studies with corrugated channels. The numerical results exhibit that LES estimates friction factor at high Reynolds numbers with maximum 5% error. Numerical visualizations are close the experimental visualizations in the study. Lastly mixing study exhibits that there is asymmetric mixing inside the channel.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.Conference paperPublication Open Access Validation and comparison of 2D and 3D numerical simulations of flow in simplex nozzles(Europe, Institute for Liquid Atomization and Spray Systems, ILASS, 2021-08-31) Bal, M.; Kayansalçik, Gökhan; Ertunç, Özgür; Böke, Y. E.; Mechanical Engineering; ERTUNÇ, Özgür; Kayansalçik, GökhanNumerical simulations of pressure swirl atomizers are computationally expensive due to transient and multiphase flow behavior. In this study, 2D and 3D VOF simulations are performed for a geomerty which has high swirl chamber length-to-diameter ratio of 1.33. discharge coefficient (CD) and spray angle values are compared to the experimental data. Moreover, a benchmark study is conducted between 2D and 3D methods in terms of accuracy, computational cost and flow variables such as orifice exit axial and tangential velocity. The simulations are performed using a hybrid RANS-LES approach, IDDES model. It is observed that 2D simulation has lower accuracy in the validation parameters such as discharge coefficient and spray angle as compared to the 3D simulation. The main reason for 2D simulation inaccuracy might be the tangential port inlet effects and wrong estimation of the loss of swirl inside the swirl chamber. On the other hand, 2D simulations have approximately 1000 times lower computational cost than 3D simulations.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 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 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 Influence of turbulent flow characteristics on flame behaviour in diffuser combustors(Elsevier, 2019-03-01) Nazzal, Ibrahim Thamer; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür; Nazzal, Ibrahim ThamerThe influence of turbulence on flame location in a diffuser-type combustor is the focus of this study. Two types of diffuser combustors were selected to study the influence of turbulence intensity and length scale on flame location. The first combustor was a cylindrical diffuser, and the second combustor had a conical insert As turbulence intensity and length scale determine Taylor-scale Reynolds numbers, this parametric study also explored the effects of the latter. Flame moved towards the inlet of the diffuser with the increase in turbulence intensity and length scale in cases with and without a conical insert. At a high turbulent length scale, the flame rapidly dropped at the inlet of the diffuser with a conical insert as the turbulence intensity increased. By contrast, the flame dropped to an intermediate level for the diffuser without a conical insert. Results showed that the Taylor-scale Reynolds number is a parameter that influences flame location, as well as turbulence intensity and length scale. An increase in the Taylor-scale Reynolds number leads to the movement of flame location towards the combustor inlet. Flame drops to the inlet of the combustor at a high turbulent Taylor-scale Reynolds number.ArticlePublication Open Access Effects of turbulence intensity and length scale on the flame location of premixed turbulent combustion in a diffuser combustor(J-STAGE, 2017) Nazzal, Ibrahim Thamer; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür; Nazzal, Ibrahim ThamerThis study focused on the dependency of the flame location of a premixed propane-air flame on turbulence intensity and length scale. The flame location was investigated using a diffuser-type combustor to show the response of the flame location to varying turbulence intensities and length scales without changing the mixture velocity, i.e., the thermal power. Combustion simulations were conducted using a coherent flame model within the framework of Reynolds-averaged Navier-Stokes equations under unsteady state conditions. The flame generally moved toward the combustor inlet with increases in turbulence intensity and length scale. The combustion and inlet turbulence caused a flow separation mainly downstream of the flame front. Consequently, the secondary flow structures influenced the flame topology and location.Book ChapterPublication Metadata only Effect of the motion pattern on the turbulence generated by an active grid(Springer, 2021) Herbert, M.; Skeledzic, T.; Lienhart, H.; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, ÖzgürIn the field of turbulence research, many experiments are performed using turbulence generated under reproducible conditions. In the past mostly static grids having a fixed blockage were adopted, but in order to generate turbulence with high intensity and high turbulence Reynolds numbers, so called active grids can be used. Therefore, an experimental study has been carried out to investigate the effect of the motion pattern on the turbulence generated by an active grid with individually controllable paddles in the wind tunnel. Measurements were performed using the hot-wire technique. In comparison to former experiments, modifications of the active grid had been made concerning the arrangement of the paddles. The results show that the homogeneity of the turbulence could be improved using the modified grid. Turbulence Reynolds numbers could reach values up to 540. In order to produce even higher integral time scales or higher turbulence Reynolds numbers, synchronous movement of adjacent paddles was tested but did not show the intended improvements. In this paper, the results of the experimental study are presented in more detail.