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Hariharan Kallath,Foster Kwame Kholi,June Kee Min(민준기) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.4
The significance of low Reynolds flows increased due to the emergence of low speed flying vehicles. Therefore, the flow control methods deserve more attention. In the present study, the application of a differential temperature on the surfaces of a slotted double-element airfoil is numerically evaluated at a low Reynolds number turbulent flow condition. The main objective is to study the effects of differential temperature on the aerodynamics of the airfoil at various flap positions. Six flap positions were considered utilizing the overset meshing techniques after appropriate parameterization of the flap locations. The numerical results were validated against previous experimental results, and subsequently, the effects of the differential temperature on the aerodynamics of baseline and other configurations were clearly explained. The best configurations were identified with and without the presence of differential temperature. Moreover, it was found out that among all the considered configurations, a maximum of 4% increase in lift and 5% reduction in drag can be achieved through the application.
Shape optimization of NACA0012 using Computational Fluid Dynamics and Response Surface Methodology
Hariharan Kallath,Jun Seok Lee(이준석),June Kee Min(민준기) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
Airfoil shape optimization has been studied for a long time. The present study is related to the shape optimization of NACA 0012 airfoil profile using computational fluid dynamics and response surface methodology tools at Reynolds number 2 million, Mach number 0.15 and 10 deg angle of attack. The shape of the airfoil is parameterized differently, and a set of numerical simulations were carried out for all combinations of the parameters. The need for remeshing during CFD analysis is successfully bypassed using mesh morphing methods. Response surfaces are fitted to the drag and lift coefficient outcomes from the simulations based on several statistical criteria. Three optimization problems were formulated, and the shape of airfoil was optimized for each optimization problem. The optimized shape is compared and reported concerning the baseline shape.
A multi-objective airfoil shape optimization study using mesh morphing and response surface method
Hariharan Kallath,Jun Seok Lee,Foster Kwame Kholi,하만영,민준기 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3
Here, a distinct procedure was adopted to optimize the shape of the NACA 0012 airfoil profile for Reynolds number, Mach number, and angle of attack equal to 2e6, 0.15, and 10.24 deg, respectively. The airfoil shape was appropriately parameterized, and mesh morphing tools were used to bypass the remeshing process. Computational fluid dynamic (CFD) simulations were carried out for all combinations of selected parameters. Response surfaces were constructed for the drag and lift coefficients of the airfoil based on several statistical criteria. Subsequently, the Pareto front was used to solve the multi-objective optimization problem. Eventually, three single-objective types of optimization problems were studied. A 10 % reduction in drag coefficient was estimated for the drag minimization problem, a 22 % improvement in lift coefficient was found in case of lift maximization problem, and a 6 % reduction in drag coefficient was determined in the lift constrained drag minimization problem.
김정태,양재성,Hariharan Kallath,민준기 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.8
A multi-stage optimization with preliminary design and shape optimization has been conducted to improve the aerodynamic performance of a centrifugal fan system. In preliminary design phase, classical blade design theory and Archimedean spiral were adopted for blade and casing, respectively. The blades from preliminary design were analyzed numerically in two-dimensions for one blade. The blade that showed the best fan performance was set as the baseline for shape optimization. Mesh-morphing method was used for the shape optimization of blade and casing in two-dimensions with various optimization algorithms (Compass, Simplex, Torczon) for objective function of fan efficiency. The optimized blade and casing showed larger outlet angle and larger volume, respectively. Finally, the optimized geometries were analyzed in three-dimensions and the fan performance curve was predicted. The optimized fan system improved the fan efficiency by 5.5 % for the considered design condition in range where flow coefficient was larger than 0.07.
Experimental study of effects of wicks and boundary conditions on thermal performance of heat pipes
Foster Kwame Kholi,Hariharan Kallath,Alberto Mucci,Man Yeong Ha,Jason Chetwynd-Chatwin,민준기 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1
The inherent two-phase heat transport of heat pipes (HPs) is progressively being examined for potential uses. These thermal devices are affected by many operating factors, prompting this study to investigate the effects of different types of wicks and working conditions on the time-dependent thermal behavior. Primarily, the effects of different wick performances were investigated under various operating conditions. The resulting surface temperatures depicted in the time to steady performance and the dry-out behavior revealed the conditions to improve the HPs design. The thermal resistance decreased from 0.6 K/W (at 25 W) to 0.05 K/W (at 200 W) by increasing the HP diameter from 6 to 10 mm; these values are relative to those of copper rods, which decrease from 2.70 K/W (at 25 W) to 0.40 K/W (at 200 W). Nonlinear and linear temperature responses were recorded when the HPs diameter and length were varied. Compared to conventional mesh and groove wicks, the composite groovesintered, mesh-sintered, and groove-mesh wicks recorded lower thermal resistance with distinctively faster startup times, lower startup temperatures, better temperature uniformity and less dynamic instability. Tilting the HPs relative to the horizontal position lessens failure tendencies. Usually, dynamic responses are typically first-order under the conditions studied. Hence, proper sizing of HPs and correct wick selection can improve their performance.
Foster Kwame Kholi,Alberto Mucci,Hariharan Kallath,하만영,Jason Chetwynd-Chatwin,민준기 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6
Previous correlations that have been used to predict the heat transfer performance of pulsating heat pipes (PHPs) offer limited thermal predictions within a narrow range of fluid-filling ratios and PHP inclinations. In this paper, a novel semi-empirical correlation with improved scope is proposed, with an increased range of fluid-filling ratios and PHP inclinations. The proposed correlation employs the dimensionless numbers governing the thermohydrodynamic operation of PHPs, and achieved ±30 % accuracy when predicting selected experimental data, showing reasonably good agreement. Unlike previous correlations, the new correlation can be used for different working fluids, geometrical aspect ratios, and heat loads. A comprehensive assessment of the relative significance of the correlation parameters on the total heat transfer performance is discussed. The new correlation with its flexible application range is expected to assist in faster and more enhanced thermal predictions as interest in PHPs grows.
Alberto Mucci,Foster Kwame Kholi,Hariharan Kallath,Thierry Sibilli,June Kee Min(민준기) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.1
Experimental studies on gas turbines face severe difficulties in obtaining an accurate and representative model of the internal environment. High temperature and pressure in the core flow require specific test rigs to guarantee the safety and representativeness of the experiment. Moreover, complexities arise when testing novel designs. Due to increasing concerns about flying gas turbines environmental footprint, the Advisory Council for Aeronautics Research in Europe (ACARE) proposed a reduction in aircraft emissions. From a concept proposed by the NEW Aero Engine Core (NEWAC) grant, we developed a methodology to test a novel Cooled Cooling Air Heat Exchanger (CCAHX) system at real steady-state operative conditions. The method involves the creation of one- and three-dimensional Computational Fluid Dynamics (CFD) models to support the experiment and verify the safety of the testing environment. The study presents the steps required to achieve this test, which involves the correct definition of an ε-NTU method for the one-dimensional model and a correct design of the three-dimensional exchange model. Additionally, the CFD model provides insight into the CCAHX operations, showing the temperature gradient inside the bulk structure and inducing further studies on the unit. The experiment reached the required temperature reduction and induced testing in case of a cooling failure to verify the structural safety of the CCAHX device.
Foster Kwame Kholi,Jaehyun Park(박재현),Hyo Je Son(손효제),Hariharan Kallath,Michael Klingsporn,Jason Chetwynd-Chatwin,June Kee Min(민준기) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4
This study examined the cooling performance of a fuel-cooled oil cooler (FCOC) under typical operating conditions. The oil cooler can fail due to the congealing of oil in the FCOC core at low-temperature conditions, which could be recovered by de-congealing the oil flow. The de-congealing time can be affected by changes in oil pressure and temperature conditions, flow re-routing, and malfunctioning of the oil bypass valve (OBV). In this study, we proposed a prediction model for the transient oil de-congealing phenomenon in the FCOC. The numerical procedure was based on the one-dimensional (1D) flow and thermal network analysis and the effectiveness (ε)-NTU method. The commercial code was customized to implement the de-congealing phenomena. Pre-defined empirical correlations and property corrections aided the modeling of the detailed de-congealing process. Moreover, the 3D CFD temperature contours provided a visual insight into the internal flow inside the FCOC core during the de-congealing process. An experimental study was conducted in parallel to validate the prediction result. Both experimental and numerical methods showed a loss of cooling when the OBV fails. The oil temperature and pressure, and flow directions affect the de-congealing process. The present model proved useful for various oil cooler configurations that are difficult to investigate experimentally and could quickly provide oil de-congealing results.