Demir, Fatih; Ekiciler, Recep

This study investigates the effects of individual nanoparticle concentrations at a ternary nanofluid on flow and heat transfer characteristics under confined impingement jet conditions. The results shed light on the development of high-performance thermal management applications. The total nanoparticle concentration of the ternary nanofluid in the impingement jet formed by the circular nozzle was kept constant at 3%. Four cases were considered by varying the concentration of Al2O3, CuO, and SiO2 nanoparticles in the total nanoparticle concentration between 0.5 and 2%. The study was carried out for dimensionless nozzle-to-plate distances of 1.1, 2.2, and 3.3, and Reynolds numbers of 9000, 15,000, 21,000, and 27,000. The results show that 0.5% Al2O3- 0.5% CuO-2% SiO2/water ternary nanofluid increases the heat transfer than water and other ternary nanofluids, and it provides a 16.53% enhancement in heat transfer compared to water. It is also noticed that the concentration of nanoparticles and Reynolds numbers are generally more effective on average Nusselt numbers and pumping power than at nozzle-to-plate distances. Nevertheless, the stagnation Nusselt number change depends much more on the dimensionless nozzle-to-plate distance. A 15.24% rise in the stagnation point Nusselt number is noted as the H/D is increased from 1.1 to 3.3 at Re = 27,000. Furthermore, it is seen that after a certain Reynolds number, the entropy production due to friction becomes more dominant than the entropy production due to heat in the total entropy production.

Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter

In this study, effects of number of consecutive laser ignition pulses on combustion and particle emission characteristics of CH4/Air mixtures were investigated in a rapid compression machine (RCM) by using a passively Q-switched Nd:YAG laser ignitor. To that end, ignition kernel formation and flame evolution characteristics were analyzed with the instrumentality of a high-speed camera (Schlieren setup), while combustion and emission properties were examined by measuring pressure and particulate emissions, respectively. The variation of pressure was also recorded to calculate (with a MATLAB code) indicated work, indicated mean effective pressure and efficiency. Results of this study revealed the linear dependence of ignition possibility to the number of pulses. Ignition possibility increased with the increasing number of pulses. It was 72.72% at 1 pulse and became 92.10% at three pulses. However, number of pulses differently affected other measured or calculated parameters. Depending on the number of pulses, improvements and deteriorations were observed in performance metrics.

Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter

The article “Combustion and emission characteristics of laser-ignited pure methane in a rapid compression machine”, written by Harun Yilmaz, Lukas Schröder, Thomas Hillenbrand and Dieter Brüggemann was originally published under exclusive license to The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2025. As a result of the subsequent decision to publish the article under the open access model, the article’s copyright notice was changed on 08 May 2025 to © The Author(s) 2025 and the article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The original article has been corrected.

Ercümen, Kadir Münir; Ceylan, Alpertunga; Aşkan, Abdulhalim; Aydin, Murat

This study investigates the low-velocity impact performance of glass fabrics impregnated with shear thickening fluids, with a focus on the effects of silica particle size and concentration. STFs were synthesized using four different average particle sizes (16 nm, 15–35 nm, 55–75 nm, and 200 nm) at three weight concentrations (40 wt.%, 52.5 wt.%, and 65 wt.%). The resulting liquids were applied to four-layer woven glass fabrics to produce twelve composite samples. All specimens were subjected to dynamic impact testing at 40 J of energy using a 20-mm hemispherical impactor. The results showed that both particle size and concentration had a significant impact on the absorption of impact energy. Sample C65, containing 55–75 nm particles at 65% w/w, showed the highest improvement in absorbed energy with a 98.1% increase over the clean weave. Interestingly, the energy absorption behavior varied with concentration for particles of varied sizes. While energy absorption improved with increasing concentration for 16 nm particles, a decrease was observed for particles ranging from 15 to 35 nm in diameter. These results highlight the critical role of optimizing STF composition, particularly nanoparticle size and concentration in enhancing the impact resistance of flexible composite fabrics. Building on this, the present work offers a systematic experimental framework that contributes to the development of advanced STF-enhanced materials for flexible impact protection applications.

Uzun, Sinem; Seyhan, Aslıhan Kurnuç

This study examines the potential of nanofluids to enhance the thermal efficiency of flat-plate solar water heating systems (SDHW) through numerical modeling using TRNSYS software. Improving the efficiency of such systems is critical for increasing the viability and sustainability of solar thermal technologies, particularly in regions with high solar potential like Türkiye. Three different nanofluids (Al2O3, TiO2, and CuO) were evaluated for their ability to improve heat transfer and system performance. Simulation results revealed that incorporating 0.1% Al2O3 into the working fluid increased the collector outlet temperature from 97 °C (with pure water) to 120 °C, indicating a 23% improvement. Comparable enhancements were observed with TiO2 and CuO nanofluids. Furthermore, collector efficiency, which typically ranges between 35 and 40% under peak solar conditions, was elevated to approximately 45% with the use of nanofluids. These findings suggest that nanofluids significantly improve thermal performance and energy conversion efficiency in SDHW systems. The results highlight the practical potential of nanofluids in advancing solar thermal technology and promoting cleaner, more efficient renewable energy solutions.

Kose, Oguz

In this paper, simultaneous longitudinal and lateral flight control is investigated for an octorotor by using stochastic optimal tuning and deep learning under differential morphing. Octorotor models for differential morphing were drawn in SOLIDWORKS drawing program. Arm lengths are randomly estimated in the algorithm. Moments of inertia changing according to morphing ratios are estimated with deep neural network. In addition, the proportional–integral–derivative controller coefficients required for both longitudinal and lateral flight according to the morphing ratios are estimated by simultaneous perturbation stochastic approximation. Considering the design performance criteria, 49.95% improvement was achieved in the total cost. The estimation of unknown parameters by optimization method and deep learning was tested in simulations, and the octorotor successfully followed the given reference angle.

Ceylan, Alpertunga; Ercümen, Kadir Münir; Aydin, Murat; Acar, Emre

This article presents a study on the rheological behavior of shear thickening fluids (STF) produced with various dispersing mediums selected according to their molecular weight, number of hydroxyl groups, branching and chain length. STF is non-Newtonian fluid behavior in which the increase in the viscosity increases with the applied shear rate. Polyethylene glycol 200, polyethylene glycol 400, 1,2-propanediol, tetraethyl orthosilicate, monoethanolamine, glycerin and diethylene glycol were used as the dispersing mediums. The steady-state rheological properties of STFs were investigated. After the rheological test, STF produced with glycerin with a concentration of 27.5% by weight gave better rheological results than STFs produced with other liquids. Although glycerin has a relatively low molecular weight, it appears that the rheological properties of glycerin are better because the STF produced with glycerin has three hydroxyl groups (3 OH−) in its structure. The critical shear rate of STF at 27.5% concentration by weight produced with glycerin is 2.39 1/s, and the peak viscosity is 732.4 Pa·s. Additionally, the weight concentration effect was also investigated. STFs were produced with polyethylene glycol 400 and 1,2-propanediol liquids at concentrations of 20%, 22.5%, 25% and 27.5% by weight. When the rheological properties of these STFs were examined, it was seen that the rheological properties improved as the concentration amount increased. For this reason, it may not be sufficient to consider only the molecular weight when choosing the dispersing medium during STF production. In addition to the molecular weight, it is necessary to consider the number of hydroxyl groups, branching and the chain length.

Siyambaş, Yusuf; Memiş, Fatih; Turgut, Yakup

Duplex stainless steels have a two-phase microstructure containing both ferritic and austenitic phases and have high strength, hardness, and corrosion resistance. However, these properties complicate chip formation during machining and make chip control difficult. Lack of chip control during the turning process negatively affects machining efficiency, quality, and safety. Inadequate chip control results in an inability to manage unwanted chip formation, especially long and tangled chips. This affects both machine operations and workpiece quality. Therefore, machining parameters need to be optimized and carefully examined to ensure chip control. The objective of this study was to detect the optimal combination of processing parameters for decreasing cutting force and surface roughness throughout the turning of AISI 2205 duplex stainless steel. To attain this goal, the experiments used the Taguchi L18 orthogonal array experimental design. Two distinct chip breaker forms of cemented carbide cutting inserts (NR4, NM4), three distinct feed rates (0.1–0.2–0.3 mm/rev), and three distinct cutting speed (180–210–240 m/min) values were used as machining parameters. As a consequence of the study, the lowest cutting force and surface roughness were obtained at NR4 insert, 0.1 mm/rev feed rate and, 210 m/min cutting speed. Using the entropy weighted-TOPSIS approach, a multi-objective optimization process was carried out for surface roughness and cutting force. As a result of the optimization approach, the sequence of experiments in which the most suitable processing parameters were obtained was determined. Anova study shows that feed rate is the most efficient parameter for both surface roughness and cutting force. To forecast processing outputs, mathematical models were constructed utilizing the response surface method. In summary, the findings from this study can contribute to the improvement of the productivity required by the industry in turning AISI 2205 duplex stainless steel.

Siyambaş, Yusuf; Turgut, Yakup

In metal-based additive manufacturing, laser power, scanning speed, hatching distance and layer thickness are important manufacturing parameters. These parameters are very important in terms of microstructure, mechanical properties and surface quality of the final product. For this reason, it is very important choosing these parameters correctly in the production process. One of the common approaches used to optimize these parameters is volumetric energy density. In this study, product quality improvement in additive manufacturing of AlSi10Mg alloy was focused, and test pieces were produced at different volumetric energy densities. The parts were manufactured according to the Taguchi L9 orthogonal array experimental design. Three different laser powers (250–300–350 W), three different scanning speeds (900–1000–1100 mm/s), three different hatching distances (0.17–0.19–0.21 mm) and constant layer thickness values were used as manufacturing parameters. The performance properties of the manufactured parts were investigated in terms of mechanical properties and surface roughness. As a result of the study, it was observed that the mechanical properties of the samples produced at very high and very low volumetric energy densities decreased and the surface roughness increased. Maximum mechanical properties within the produced samples were obtained at 55.82 J/mm3 volumetric energy density, and minimum surface roughness was obtained at 54.46 J/mm3 volumetric energy density. For mechanical properties and surface roughness, multiple response optimization was performed with Taguchi-based Grey relational analysis method. According to the experimental results, optimum manufacturing parameters for additive manufacturing of AlSi10Mg alloy; it was obtained as 350 W laser power, 1100 mm/s scanning speed, 0.19 mm hatching distance and 55.82 J/mm3 volumetric energy density, which is the interaction of these parameters. The mechanical properties and surface roughness obtained graphically were supported by fracture surface images and microstructure studies. With multiple response optimization, 30.15% improvement was achieved in performance indicators. In addition, it has been demonstrated that volumetric energy density can be used as an important evaluation tool in determining product quality.

Demirtaş, Salih; Ozturk, Hasan

The high-speed railways require more viaduct than a conventional railway. When the viaduct is subjected to high-amplitude vibrations for a long time, the fatigue-induced crack formation can occur. The presence of a crack changes the stiffness of the structure. Depending on the location of the crack, the reduction effect in stiffness varies. In this study, the presence of a single crack in a multi-storey frame structure, which is considered as a viaduct model, has been investigated. Effects of crack location on the dynamic response are investigated via 3D velocity-crack location-dynamic magnification factor (or maximum displacement) graphs. The train is modelled as a four-axle two-bogie multi-body system with 10 DOF and moving at a constant speed. The finite element method, based on Euler–Bernoulli beam theory, is used to simulate the vibrations of the coupled vehicle-structure system. Wilson-theta time integration scheme is used to solve the equation of motion. It has been determined that when the crack is located at the midpoint of the top beam, the highest effect on the dynamic response is observed.