• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.7
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• pp.629-634
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• 2005

This paper performed to predict vertical temperature distribution and air flow near cold heat source in the mass merchandising store. At the height of 150 cm, the vertical air temperature difference between the results of CFD and of measurement field showed $10\%$ near the refrigeration zone and $8.8\%$ near the freezing zone. Therefore, it regarded as appropriate for the using CFD to investigate airflow near the heat sources. The 3 kinds of CFD model were divided by the disposition of diffuser/exhaust and diffuser air temperature. At the refrigeration and freezing zone in the Model 2 and 3, the temperature difference between the front and the back of human model were showed $6.8^{\circ}C\;and\;3.9^{\circ}C$ with diffuser air temperature $17^{\circ}C$ and were showed $6.8^{\circ}C$ and $4^{\circ}C$ with diffuser air temperature $19^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.668-676
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• 1991

Turbulent flows around tube banks and in the diffuser were studied using a non-orthogonal boundary fitted coordinate system and the modified K-.epsilon. turbulence model. In these cases, many problems emerge which stem from the geometrical complexity of the flow domain and the physical complexity of turbulent flow itself. To treat the complex geometry, governing equations were reformulated in a non-orthogonal coordinate system with Cartesian velocity components and discretised by the finite volume method with a non-staggered variable arrangement. The modified K-.epsilon. model of Hanjalic and Launer was applied to solve above two cases under the condition of strong and mild pressure gradient. The results using the modified K-.epsilon. model results in both test cases.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.485-490
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• 2000

This paper dipicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equation in a domain that extends form the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for subsonic/sonic ejector systems, the ejector throat area, the mixing section configuration, and the ejector throat length were changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratio, the effects of the design factors on the flow are discussed.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.422-427
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• 2000

The design of low-solidity vaned diffusers and the effect on the performance of a turbocharger compressor is discussed. The effect of vane number and turning angle was investigated while maintaining a basic design with a leading edge angle of $70^{\circ}$, leading and trailing edge radius ratios of 1.1 and 1.3. All results are compared with those obtained with the standard vaneless diffuser configuration and it was shown that all designs increased and shifted the pressure ratio to reduced flowrates. Despite the low-solidity configuration none of the vane designs provided a broad operating range, and the vane leading edge angle was not main factor that system went into the surge condition. The diffuser of higher trailing edge angle improved the flow range for the compressor to operate at lower flow region.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.5
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• pp.397-403
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• 2005

The thermal comfort of occupants is directly related to several environmental factors such as velocity of air flow, turbulence intensity and temperature distribution of indoor air. The purpose of this study is to evaluate the indoor air flow and temperature distribution in office area using under-floor air-conditioning system (UFAC System) based on the results from physical measurements and to perform a Computer Fluid Dynamics (CFD) under the same condition of inlet and outlet as field measurement. The results from the CFD simulation are similar to those from the field measurement. The results show that UFAC system is provide proper indoor condition for occupants.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.105-110
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• 2010

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser (SED). This paper aims at the improvement in HAT facility by focusing attention on the vertical firing rocket test stand with shock generators. Shock generators are mounted inside the SED for improving the pressure recovery. The results clearly showed that the performance of the ejector-diffuser system was improved with the addition of shock generators. The improvement comes in the form of reduction of the starting pressure ratio and the vertical height of test stand. It is also shown that shock generators are useful in reducing the total pressure loss in the SED.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.2
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• pp.269-276
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• 2001

This paper dipicts the computational results for the axisymmetric subsonic/sonic ejector systems with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-Averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the ejector diffuser exit. In order to obtain practical design factors for subsonic/sonic ejector systems, the ejector throat area, the mixing section configuration, and the ejector throat length were changed in computations. For the subsonic/sonic ejector systems operating in the range of low operation pressure ratio, the effects of the design factors on the flow are discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.11
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• pp.16-22
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• 2020

This study was aimed at analyzing the velocity and pressure changes in the airflow corresponding to different configurations of a diffuser for three types of cars. According to the flow results of the three automotive models, in model 3, the vortex was formed slightly upward on the outlet plane, whereas in models 1 and 2, the vortex was generated lower than that in model 3. The values of the pressure distribution in model 3 were larger than those for models 1 and 2 on the planes located at the same distance from the end of the rear part. The maximum turbulent kinetic energies in models 1 and 2 occurred at a location lower than that in model 3. The shape corresponding to the airflow that enhanced the driving performance was determined through the flow analysis.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.281-286
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• 2004

The vacuum cleaner motor runs on very high speed for the suction power. Specially, the motive power is provided by the impeller being rotate on very high speed. And centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed or the impeller and small gap distance between the impeller and diffuser, the centrifugal fan makes very high noise level at BPF and harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, the unsteady flow data is needed. And Noise cause is dividing to fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, measuring method has been used to measure vibration by the accelerometer; this method has been not measured for the vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This paper was purposed on the accurate analysis, using laser vibration analyzer,. By using this measured data of noise cause against the difficult part in old times, we would like to use for the design of silent fan motor.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.346-352
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• 2009

The objective of the present work is to improve numerical predictions of unsteady turbulent swirling flows in the draft tubes of hydraulic power plants. We present Large Eddy Simulation (LES) results on a simplified draft tube consisting of a straight conical diffuser. The basis of LES is to solve the large scales of motion, which contain most of the energy, while the small scales are modeled. LES strategy is here preferred to the average equations strategies (RANS models) because it resolves directly the most energetic part of the turbulent flow. LES is now recognized as a powerful tool to simulate real applications in several engineering fields which are more and more frequently found. However, the cost of large-eddy simulations of wall bounded flows is still expensive. Bypass methods are investigated to perform high-Reynolds-number LES at a reasonable cost. In this study, computations at a Reynolds number about 2 $10^5$ are presented. This study presents the result of a new near-wall model for turbulent boundary layer taking into account the streamwise pressure gradient (adverse or favorable). Validations are made based on simple channel flow, without any pressure gradient and on the data base ERCOFTAC. The experiments carried out by Clausen et al. [1] reproduce the essential features of the complex flow and are used to develop and test closure models for such flows.