Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 1Citation - Scopus: 1Numerical and Experimental Investigation of Aspect Ratio Effect on Aerodynamic Performance of Naca 4415 Airfoil Section at Low Reynolds Number(Assoc Mechanical Engineers Technicians Slovenia, 2025) Uemuetlue, Hatice Cansu Ayaz; Kiral, Zeki; Karadeniz, Ziya HaktanIn this study, the effect of aspect ratio on the aerodynamic coefficients is investigated for a NACA 4415 airfoil profile. Four different aspect ratios which are 3, 5, 7, and 9 are evaluated with the computational fluid dynamics (CFD) simulations and the experiments. The CFD studies are performed using a threedimensional (3D) computational domain and by using the k-omega shear stress transport (SST) turbulence model for turbulence calculations. The measurements of the aerodynamic forces are carried out in open jet type wind tunnel using a three-component balance. CFD and experimental studies are performed at angles of attack from 0 degrees to 25 degrees and Reynolds number 85<middle dot>103. The results show that as the aspect ratio increases, separation points move towards the leading edge of the airfoil and the stall angle reduces. Furthermore, it is observed that the lift coefficients increase with the increasing aspect ratio. The results obtained indicate that there is a harmony between the experimental data and the CFD solutions.Article Citation - WoS: 1Citation - Scopus: 1Investigation of Flow and Heat Transfer Performance of Gyroid Structure as Porous Media(Turkish Soc Thermal Sciences Technology, 2024) Genc, Alper Mete; Karadeniz, Ziya HaktanThere are active and passive methods used to improve heat transfer. One of the passive methods is utilising porous media with high heat transfer surface area. Porous media are divided into two groups: regular and irregular structures. One of the regular structures is triply periodic minimal surfaces (TPMS), which have been studied quite frequently recently. In this study, heat transfer and flow analysis of a Gyroid geometry, one of the most used TPMS in the literature, is investigated numerically considering the conjugate heat transfer conditions. A single porosity is considered (epsilon = 0.6), and aluminium, ceramic and PLA are selected for the heat exchanger material to examine the temperature change in the heat exchanger. To understand the different flow characteristics, Reynolds numbers are assumed to be 19.12, 95.61 and 172.09. The fluid inlet temperature is assumed to be constant at 298.15 K, and the initial temperature of the heat exchanger is assumed to be constant at 278.15 K to be consistent with the regenerative heat recovery temperature difference in ventilation standards. Nusselt numbers under different operating conditions are compared, and it is the ceramic material with low thermal diffusivity is at the highest level despite its low thermal conductivity. At the highest Reynolds number, it provided approximately 6% better heat transfer than the aluminium heat exchanger.Article Citation - WoS: 2Citation - Scopus: 2Sleep Quality: Design of Bedroom Ventilation and Evaluation Within the Scope of Current Standards(Elsevier Science Sa, 2025) Cobanoglu, Nur; Karadeniz, Ziya Haktan; Sofuoglu, Sait Cemil; Toksoy, MacitIndoor air pollution is one of the leading environmental risks to public health considering people now spending nearly 90 % of their day in indoor environments. A significant portion of this time indoors is devoted to sleeping, making it crucial to address the impact of indoor environmental conditions on sleep quality. International ventilation standards such as ASHRAE and CEN, as well as country-specific guidelines, offer valuable recommendations for ventilation design in residential buildings, including bedrooms. This study aims to evaluate the importance of determining ventilation rates in sleeping spaces using Indoor Air Quality Procedure (IAQP) compared to Ventilation Rate Procedure (VRP) in accordance with current standards. Here, the IAQP approach for determining air flow rate is based on the CO2 balance by maintaining CO2 levels in any sleeping environment below specified upper limits of 750 ppm and 1000 ppm. This study focused on the adult population, which forms the majority of society, with analyses conducted for both single and double occupancy sleeping conditions. The volume of environment where ventilation is not required during sleep (Vf) is inaccessible in conventional sleeping environments (10-21.6 m3 per person). Therefore, proper ventilation is of great importance for any sleeping space that is smaller than the Vf. The results of the analyses show that for the conventional sleeping volumes, CO2 levels reach 750 ppm (upper limit for comfortable sleep) in the first hour and increase to the disturbed sleep zone in about 2 h. Additionally, a chart outlining the necessary ventilation flow rates is suggested for maintaining maximum CO2 concentrations of 750 and 1000 ppm during different sleep durations and in various sleeping environments with varying volumes. Finally, the ventilation rates determined based on unit area and/or occupancy levels in standards (referred to as VRP) may not always be adequate or may be excessive in order to maintain CO2 concentrations below the recommended limits of 750 and 1000 ppm. It is advised to utilize demand-controlled ventilation by considering the system design as recommended by IAQP.Article Citation - WoS: 1Citation - Scopus: 1Experimental Investigation of Naca 4415 Airfoil Using Vibration Data for Stall Detection(Emerald Group Publishing, 2023) Ayaz Ümütlü, Hatice Cansu; Kıral, Zeki; Karadeniz, Ziya HaktanPurposeThe purpose of this study is to identify the possible relation between the vibration and the stall by using the vibration response of the airfoil. For this purpose, the root mean square values of the acceleration signals are evaluated to demonstrate the compatibility between the stall angles and the vibration levels. Design/methodology/approachAn experimental study is conducted on NACA 4415 airfoil at Reynolds numbers 69e3, 77e3 and 85e3. Experiments are performed from 0 & DEG; to 25 & DEG; of the angles of attack (AoA) for each Reynolds number condition. To observe the change of the vibration values at the stall region clearly, experiments are performed with the AoA ranging from 10 & DEG; to 25 & DEG; in 1 & DEG; increments. Three acceleration sensors are used to obtain the vibration data. FindingsThe results show that the increase in the amplitude of the vibration is directly related to the decrease in lift. These findings indicate that this approach could be beneficial in detecting stall on airfoil-type structures. Originality/valueThis study proposes a new approach for detecting stall over the airfoil using the vibration data.Article Citation - WoS: 3Citation - Scopus: 3Investigation of External Magnetic Field Effect on the Performance of Ferrofluid-Based Single-Phase Natural Circulation Loops(Elsevier, 2023) Bozkır, Selim Can; Çobanoğlu, Nur; Doğanay, Serkan; Karadeniz, Ziya Haktan; Elçioğlu, Elif Begüm; Turgut, AlpaslanThe goal of this study is to investigate the performance of a Single-Phase Natural Circulation mini Loop (SPNCmL) operating under the influence of an external magnetic field (EMF). For this purpose, a numerical SPNCmL model working with Fe3O4 ferrofluids (1-3 vol%.) under the influence of an EMF is developed to reflect the effect of a NdFeB permanent magnet with a remanence of 1.22 T located at the outlet of the cooler-end for the magnetic field generation. System characteristics such as temperature difference at heater-end (& UDelta;Theater) and maximum temperature (Tmax) and performance in terms of effectiveness (& epsilon;) are investigated. In addition, the effect of EMF on boundary layer energy transport along the cooler-end is evaluated in terms of the change in the local Nusselt number. Applying an EMF dramatically affects the system performance in terms of an increase in & UDelta;Theater and & epsilon;, respectively up to 34% and 25% compared to those with water. Tmax values are obtained by up to 9% higher for Fe3O4 ferrofluids compared to water, while applying EMF results in an increment in Tmax by up to 5%. Improved heat transfer performance by employing EMF at the cooler-end outlet of the SPNCmLs emphasizes their potential in cooling applications.Article Citation - Scopus: 21The Developing Flow Characteristics of Water - Ethylene Glycol Mixture Based Fe3o4 Nanofluids in Eccentric Annular Ducts in Low Temperature Applications(Elsevier, 2022) Çobanoğlu, Nur; Banisharif, Alireza; Estelle, Patrice; Karadeniz, Ziya HaktanNatural circulation loops with double pipe heat exchangers at heating and cooling ends have a potential to be used in the refrigeration systems as an alternative to suction line heat exchangers. The heat transfer capability of such natural circulation loops depends on the geometrical parameters as well as thermophysical properties of the working fluid. This study aims to investigate the effect of water-ethylene glycol mixture based Fe3O4 nanofluids (0.01, 0.05 and 0.1 vol.%) on the annular flow propagation and heat transfer in the annuli of double pipe heat exchanger at low pressure side of the refrigeration cycle. In addition to increased non-dimensional velocity values due to the lower viscosity and higher non-dimensional temperature values with expanded temperature gradient, improved heat transfer by nanofluids shows that they can be used as secondary heat transfer fluids at low-pressure side in refrigeration systems. Although the maximum transferred (13.6% improvement compared to base fluid) heat observed for the highest concentration, the nanofluids with smallest concentration has the minimum pressure drop value (25% reduction compared to base fluid) and the highest performance evaluation criteria (PEC) value (PEC = 1.08) with tiny increase in exergy destruction (1.45% compared to base fluid)Article Citation - WoS: 12Citation - Scopus: 15Assessment and Improvement of Indoor Environmental Quality in a Primary School(Taylor and Francis Ltd., 2017) Ekren, Orhan; Karadeniz, Ziya Haktan; Atmaca, İbrahim; Ugranlı Çiçek, Tuğba; Sofuoğlu, Sait Cemil; Toksoy, MacitThis study reports levels of indoor environmental quality variables before and after installation of heat recovery ventilation in a primary school located in an urban area in Izmir, Turkey. A CO2-based modeling was performed to determine the required flow rates that would comply with an international ventilation standard, followed by computational fluid dynamics modeling for best airflow distribution in a classroom. Temperature, CO2, PM2.5, and total volatile organic compounds were found at undesired levels, among which relative humidity, CO2, and PM2.5 were improved after the intervention. Reductions in the mean and maximum concentrations were 29% and 68% for CO2 and 29% and 46% for PM2.5. This intervention study was a part of the city-wide main project that aimed to increase awareness of the students and their families, teachers, and staff regarding importance of indoor environmental quality in both at school and home due to its possible effects on children's health and academic performance, one of the major challenges of today's societies all around the globe.