• Transactions of the KSME C: Technology and Education
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• v.3 no.1
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• pp.23-28
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• 2015

In this paper, we performed the design optimization dual-shell and tube heat exchanger on exhaust waste heat recovery for gas heat pump using CFD and RSM. CFD analysis is useful to design the complex structure such as double shell and tube heat exchanger. By computer simulation, engineers can assess the feasibility of the given design factors and change them to get a better design. But if one wishes to perform complex analysis on the simulation, such dual-shell and tube heat exchanger for GHP, the computational time can become overwhelming. CFD is powerful but it takes a lot of time for complex structure. Therefore, the CFD analysis is minimized by the optimization using the RSM method. As a result, the number of baffle and tube are optimized by 6 baffles and 25 tubes for heat transfer and flow friction. And then pressure drop and heat transfer is improved about 12.2%. We confirm the design optimization using CFD and RSM is useful on complex structure of heat exchanger.

• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.225-233
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• 2019

In the summer season, natural ventilation is commonly used to reduce the inside air temperature of greenhouse when it rises above the optimal level. The greenhouse shape, vent design, and position play a critical role in the effectiveness of natural ventilation. In this study, computational fluid dynamics (CFD) was employed to investigate the effect of different roof vent designs along with side vents on the buoyancy-driven natural ventilation. The boussinesq hypothesis was used to simulate the buoyancy effect to the whole computational domain. RNG K-epsilon turbulence model was utilized, and a discrete originates (DO) radiation model was used with solar ray tracing to simulate the effect of solar radiation. The CFD model was validated using the experimentally obtained greenhouse internal temperature, and the experimental and computed results agreed well. Furthermore, this model was adopted to compare the internal greenhouse air temperature and ventilation rate for seven different roof vent designs. The results revealed that the inside-to-outside air temperature differences of the greenhouse varied from 3.2 to $9.6^{\circ}C$ depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to $0.49min^{-1}$. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of $3.2^{\circ}C$ and a maximum ventilation rate of $0.49min^{-1}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.2
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• pp.107-120
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• 2021

Electric-powered distributed propulsion aircraft possess a complex wake flow and mutual interference with the airframe, due to the use of many propellers. Accordingly, in the early design stage, rapid aerodynamic and load analysis considering the effect of propellers for various configurations and flight conditions are required. In this study, an efficient panel-based aerodynamic analysis method that can take into account the propeller effects is developed and validated. The induced velocity field in the region of propeller wake is calculated based on Actuator Disk Theory (ADT) and is considered as the boundary condition at the vehicle's surface in the three-dimensional steady source-doublet panel method. Analyses are carried out by selecting an isolated propeller of the Korea Aerospace Research Institute (KARI)'s Quad Tilt Propeller (QTP) aircraft and the propeller-wing configuration of the former experimental study as benchmark problems. Through comparisons with the results of computational fluid dynamics (CFD) based on actuator methods, the wake velocity of propeller and the changes in the aerodynamic load distribution of the wing due to the propeller operation are validated. The method is applied to the analysis of the Optional Piloted Personal Aerial Vehicle (OPPAV) and QTP, and the practicality and validity of the method are confirmed through comparison and analysis of the computational time and results with CFD.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.7
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• pp.922-930
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• 2020

Marine accidents involving fishing boats, caused by a loss of stability, have been increasing over the last decade. One of the main reasons for these accidents is a sudden wind attacks. In this regard, the wind loads acting on the ship hull need to be estimated accurately for safety assessments of the motion and maneuverability of the ship. Therefore, this study aims to develop a computational model for the inlet boundary condition and to numerically estimate the wind load acting on a fishing boat. In particular, wind loads acting on a fishing boat at the wind speed profile boundary condition were compared with the numerical results obtained under uniform wind speed. The wind loads were estimated at intervals of 15° over the range of 0° to 180°, and i.e., a total of 13 cases. Furthermore, a numerical mesh model was developed based on the results of the mesh dependency test. The numerical analysis was performed using the RANS-based commercial solver STAR-CCM+ (ver. 13.06) with the k-ω turbulent model in the steady state. The wind loads for surge, sway, and heave motions were reduced by 39.5 %, 41.6 %, and 46.1 % and roll, pitch, and yaw motions were 48.2 %, 50.6 %, and 36.5 %, respectively, as compared with the values under uniform wind speed. It was confirmed that the developed inlet boundary condition describing the wind speed gradient with respect to height features higher accuracy than the boundary condition of uniform wind speed. The insights obtained in this study can be useful for the development of a numerical computation method for ships.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.445-454
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• 2022

Ice accretion on the aircraft components, such as wings, fuselage, and empennage, can occur when the aircraft encounters a cloud zone with high humidity and low temperature. The prevention of ice accretion is important because it causes a decrease in the aerodynamic performance and flight stability, thus leading to fatal safety problems. In this study, a shape design optimization of a multi-element airfoil is performed to minimize the amount of ice accretion on the high-lift device including leading-edge slat, main element, and trailing-edge flap. The design optimization framework proposed in this paper consists of four major parts: air flow, droplet impingement and ice accretion simulations and gradient-free optimization algorithm. Reynolds-averaged Navier-Stokes (RANS) simulation is used to predict the aerodynamic performance and flow field around the multi-element airfoil at the angle of attack 8°. Droplet impingement and ice accretion simulations are conducted using the multi-physics computational analysis tool. The objective function is to minimize the total mass of ice accretion and the design variables are the deflection angle, gap, and overhang of the flap and slat. Kriging surrogate model is used to construct the response surface, providing rapid approximations of time-consuming function evaluation, and genetic algorithm is employed to find the optimal solution. As a result of optimization, the total mass of ice accretion on the optimized multielement airfoil is reduced by about 8% compared to the baseline configuration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.9
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• pp.599-608
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• 2022

Urban air mobility (UAM) equipped with rotor system is subject to ground effect at vertiport during takeoff and landing. The aerodynamic performance of the aircraft in ground effect should be analyzed for the safe operation. In this study, The ground effects on the aerodynamic performance and wake structure of the quadcopter electric vertical takeoff and landing (eVTOL) configuration equipped with coaxial counter-rotating propellers were investigated by using the lattice Boltzmann method (LBM). The influence of the ground effect was observed differently in the upper and lower propellers of the coaxial counter-rotating propeller system. There was no significant change in the aerodynamic performance of the upper propeller even if the propeller height above the ground was changed, whereas the averaged thrust and torque of the lower propeller increased significantly as propeller height decreased. In addition, the amplitude of the thrust fluctuation tended to increase as the propeller height decreased. The propeller wake was not sufficiently propagated downstream and was diffused along the ground due to the outwash flow developed by the ground effect. The impingement of the rotor wakes on the ground and a fountain vortex structure were observed.

• Wind and Structures
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• v.34 no.1
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• pp.127-136
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• 2022

In this work a multi-fidelity non-intrusive polynomial chaos (MF-NIPC) has been applied to a structural wind engineering problem in architectural design for the first time. In architectural design it is important to design structures that are safe in a range of wind directions and speeds. For this reason, the computational models used to design buildings and bridges must account for the uncertainties associated with the interaction between the structure and wind. In order to use the numerical simulations for the design, the numerical models must be validated by experi-mental data, and uncertainties contained in the experiments should also be taken into account. Uncertainty Quantifi-cation has been increasingly used for CFD simulations to consider such uncertainties. Typically, CFD simulations are computationally expensive, motivating the increased interest in multi-fidelity methods due to their ability to lev-erage limited data sets of high-fidelity data with evaluations of more computationally inexpensive models. Previous-ly, the multi-fidelity framework has been applied to CFD simulations for the purposes of optimization, rather than for the statistical assessment of candidate design. In this paper MF-NIPC method is applied to flow around a rectan-gular 5:1 cylinder, which has been thoroughly investigated for architectural design. The purpose of UQ is validation of numerical simulation results with experimental data, therefore the radius of curvature of the rectangular cylinder corners and the angle of attack are considered to be random variables, which are known to contain uncertainties when wind tunnel tests are carried out. Computational Fluid Dynamics (CFD) simulations are solved by a solver that employs the Finite Element Method (FEM) for two turbulence modeling approaches of the incompressible Navier-Stokes equations: Unsteady Reynolds Averaged Navier Stokes (URANS) and the Large Eddy simulation (LES). The results of the uncertainty analysis with CFD are compared to experimental data in terms of time-averaged pressure coefficients and bulk parameters. In addition, the accuracy and efficiency of the multi-fidelity framework is demonstrated through a comparison with the results of the high-fidelity model.

• Journal of the Korean Institute of Gas
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• v.24 no.2
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• pp.1-8
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• 2020

Centrifugal pump is a facility that transfers energy to fluid through centrifugal force, which is usually generated by rotating the impeller at high speed, and is a major process facility used in many LNG production bases such as vaporization seawater pump, industrial water and fire extinguishing pump using seawater. to be. Currently, pumps in LNG plant sites are subject to operating conditions that vary depending on the amount of supply desired by the customer for a long period of time. Pumps in particular occupy a large part of the consumption strategy at the plant site, and if the optimum operation condition is not available, it can incur enormous energy loss in long term plant operation. In order to solve this problem, it is necessary to identify the performance deterioration factor through the flow analysis and the result analysis according to the fluctuations of the pump's operating conditions and to determine the optimal operation efficiency. In order to evaluate operation efficiency through experimental techniques, considerable time and cost are incurred, such as on-site operating conditions and manufacturing of experimental equipment. If the performance of the pump is not suitable for the site, and the performance of the pump needs to be reduced, a method of changing the rotation speed or using a special liquid containing high viscosity or solids is used. Especially, in order to prevent disruptions in the operation of LNG production bases, a technology is required to satisfy the required performance conditions by processing the existing impeller of the pump within a short time. Therefore, in this study, the rotation difference of the pump was applied to the ANSYS CFX program by applying the modified 3D modeling shape. In addition, the results obtained from the flow analysis and the curve fitting toolbox of the MATLAB program were analyzed numerically to verify the outer diameter correction theory.

• Journal of Bio-Environment Control
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• v.15 no.4
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• pp.296-305
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• 2006

The heterogeneity of crop transpiration is important to clearly understand the microclimate mechanisms and to efficiently handle the water resource in greenhouses. A computational fluid dynamic program (Fluent CFD version 6.2) was developed to study the internal climate and crop transpiration distributions of greenhouses. Additionally, the global solar radiation model and a crop heat exchange model were programmed together. Those models programmed using $C^{++}$ software were connected to the CFD main module using the user define function (UDF) technology. For the developed CFD validity, a field experiment was conducted at a $17{\times}6 m^2$ plastic-covered mechanically ventilated single-span greenhouse located at Pusan in Korea. The CFD internal distributions of air temperature, relative humidity, and air velocity at 1m height were validated against the experimental results. The CFD computed results were in close agreement with the measured distributions of the air temperature, relative humidity, and air velocity along the greenhouse. The averaged errors of their CFD computed results were 2.2%,2.1%, and 7.7%, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.12
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• pp.1102-1139
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• 2002

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 2000 and 2001 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. (1) Most of fundamental studies on fluid flow were related with heat transportation of facilities. Drop formation and rivulet flow on solid surfaces were interesting topics related with condensation augmentation. Research on micro environment considering flow, heat, humidity was also interesting for comfortable living environment. It can be extended considering biological aspects. Development of fans and blowers of high performance and low noise were continuing topics. Well developed CFD technologies were widely applied for developing facilities and their systems. (2) Most of papers related with heat transfer analysis and heat exchanger shows dealt with convection, evaporation, and channel flow for the design application of heat exchanger. The numerical heat transfer simulation studies have been peformed and reported to show heat transfer characteristics. Experimental as well as numerical studies on heat exchanger were reported, while not many papers are available for the system analysis including heat exchanger. (3) A review of the recent studies on heat pump system shows that performance analysis and control of heat pump have been peformed by various simulations and experiments. The research papers on multi-type heat pump system increased significantly. The studies on heat pipe have been examined experimently for change of working characteristics and strut lure. Research on the phase change has been carried out steadily and operation strategies of encapsulated ice storage tank are reported experimentally in several papers. (4) A review of recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. Evaporation and condensation heat transfer characteristics are investigated for tube shapes and new alternative refrigerants. Studies on components of refrigeration/air conditioning system are carried to examine efficiency for various compressors and performance of new expansion devices. In addition to thermophysical properties of refrigerant mixtures, studies on new refrigerants are also carried out, however research works on two-phase flow seemed to be insufficient. (5) A review of the recent studies on absorption cooling system indicates that heat and mass transfer phenomena have been investigated to improve absorber performance. Various experimental data have been presented and several simulation models have been proposed. A review of the recent studies on duct and ventilation shows that ventilation indices have been proposed to quantify the ventilation performance in buildings and tunnels. Main efforts have been focused on the applications of ventilation effectiveness in practice, either numerically using computational fluid dynamics or experimentally using tracer gas techniques. (6) Based on a review of recent studies on indoor thermal environment and building service systems, research issues have mainly focused on many innovative ideas such as underfloor air-conditioning system, personal environmental modules, radiant floor cooling and etc. Also, the new approaches for minimizing energy consumption as well as improving indoor environmental conditions through predictive control of HVAC systems, various activities of building energy management and cost-benefit analysis for economic evaluation were highlighted.