• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.78-92
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• 1994

Thermal performance of pipe network of continuous heating system controlled by thermostat and flow control valve was simulated in consideration of radiation heat transfer and solved by linear analysis method. Thermal performance of real apartment building with radiant floor heating system was simulated by equivalence heat resistance-capacity method. This method enables to simulate the unsteady variation of temperature or each element of building. Heat transfer characteristics of each element were also investigated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.751-767
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• 1994

Recent developments of S.I. engine, aiming to higher power, better fuel economy, lower air pollution and better driveability, have much focused on the importance of the role of computer simulation in engine research and development. In this point of view, improving engine performance requires finding some means to improve volumetric efficiency. Up to now there have been several attempts to optimize the intake and exhaust system of internal system of S.I. engine by computer simulation. There appear to be few studies available, however, of such simulation & experimental studies applied to the optimization of exhaust manifold configuration. In this study, gas exchange & power process of 4 cylinder S.I. Engine was studies numerically & experimentally, and governing equation of a one-dimensional unsteady compressible flow and combustion process were respectively solved by a characteristics method and 2-zone model. The aim of this study is to predict and investigate the influence of pressure wave interaction at the exhaust systems on engine performance with widely differing exhaust manifold configuration.

• Wind and Structures
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• v.24 no.5
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• pp.447-464
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• 2017

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

• The KSFM Journal of Fluid Machinery
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• v.6 no.4 s.21
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• pp.14-20
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• 2003

In this study an analysis of the flow characteristics in three types of turbo-fans for a vacuum cleaner was performed by using CFD. The characteristics of three models calculated for various rotating speed for flow rates are obtained and compared with measured data. The mixing plane approach is applied to compute the flow between impeller and diffuser. The results show that the model that is modified to reduce fan noise gives stable flow characteristics in operating range than the original model, with both models show similar performance characteristics at the range of high flow rate. Since in the modified model it takes much longer for an impeller blade to pass a diffuser blade than in the original model, and the peak pressure at BPF can be relieved, it is anticipated that the modified model give much lower noise level with similar performance than the original one, which remains to be verified by unsteady computation and measurements. The good agreement between the predictions and measurement results confirms the validity of this study.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.631-634
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• 2002

The study of the flow characteristics in two types of turbo-fans for a vacuum cleaner was performed in a previous study. In present study an analysis of a new modified model to reduce fan noise was performed by using CFD. The characteristics of three models calculated for various rotating speeds and flow rates are obtained and compared with available measured data. The results show that the modified model gives stable flow characteristics in operating range than the original model, while both models show similar performance characteristics at the range of high flow rate. Since in the modified model it takes much longer for an impeller blade to pass a diffuser blade than in the original model, and thus the peak pressure at BPF can be relieved, it is anticipated that the modified model gives much lower noise level with similar performance than the original one, which remains to be verified by unsteady computation and measurements.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.31-40
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• 2021

Modern aircraft are high-performance and lightweight. Thus, the characteristics of the flexible structure appear and affect flight performance or limit it. These flexible characteristics need to be analyzed from the early stages of aircraft design. To this end, a program to analyze the dynamic and static behavior of flexible aircraft has been developed and the results are presented. Based on the multi-body dynamics simulation technique, rigid flight mechanics, structural vibrating behavior, and unsteady aerodynamics have been developed and integrated. Lastly, the level flight and the turn flight of the flexible characteristic aircraft have been analyzed using this integrated simulation program.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.7-15
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• 2014

In the present study, a computational analysis of the flow in a centrifugal blower is carried out to predict a performance and to explain noise characteristics of the blower. Unsteady, 3D Navier-Stokes equations were solved with k-${\varepsilon}$ turbulence model using CFX software. CFD results were compared with the experimental data that is acquired from an experiment conducted with the same blower. The pressure fluctuation in the blower was transformed into the frequency domain by Fourier decomposition to find the relationship between flow behaviors and noise characteristics. Sound pressure level (SPL) which is obtained from wall pressure fluctuation at impeller outlet represents relative overall sound level of the blower well. Sound spectra show that there are some specific peak frequencies at each mass flow rate and it can be explained by flow pattern.

• Journal of Mechanical Science and Technology
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• v.16 no.3
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• pp.344-353
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• 2002

A reliable computational heat transfer model has been investigated to define the heat transfer characteristics of a spray column direct contact heat exchanger, which is often utilized in the process involving counterflows for heat and mass transfer operations. Most of the previous studies investigated are one-dimensional unsteady solutions based on rather fragmentary experimental data. Development of a multidimensional numerical model and a computational algorithm are essential to analyze the inherent multidimensional characteristics of a direct contact heat exchanger. The present study has been carried out numerically and establishes a solid simulation algorithm for the operation of a direct contact heat exchanger. Operational and system parameters such as the speed and direction of working fluid droplets at the injection point, and the effects of aspect ratio and void fraction of continuous fluid are examined thoroughly as well to assess their influence on the performance of a spray column.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.536-541
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• 2001

A high resolution digital cinematic Particle Image Velocimetry(PIV) has been developed. The system consists of a high speed CCD camera, a continuous Ar-ion laser and a computer with camera controller. To improve the spatial resolution, we adopt a Recursive Technique for velocity interrogation. At first, we obtain a velocity vector for a larger interrogation window size based on the conventional two-frame cross-correlation PIV analysis using the FFT algorithm. Based on the knowing velocity information, more spatially resolved velocity vectors are obtained in the next iteration step with smaller interrogation windows. The correct velocity vector at the first step is found to be critical, so we apply a Multiple Correlation Validation(MCV) technique in order to decrease the spurious vectors. The MCV technique turns out to improve SNR(Signal to Noise Ratio) of the correlation table. The developed cinematic PIV method has been applied to the measurement of the unsteady flow characteristics of a Rushton turbine mixer. A total of 3,245 instantaneous velocity vectors were successfully obtained with 4 ms time resolution. The acquired spatial resolution corresponds the performance of the conventional high resolution digital PIV system using a $1K{\times}1K$ CCD camera.

• Wind and Structures
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• v.23 no.4
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• pp.301-311
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• 2016

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using $k-{\varepsilon}$ standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.