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소음 상사를 이용한 직교류 홴의 유동 소음에 관한 수치해석 연구
이명성(Myungsung Lee),강성원(Seongwon Kang),허남건(Nahmkeon Hur),박정택(Jeongtaek Park) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
The flow noise of a cross-flow fan in an air conditioner indoor unit is investigated by a 2-D CFD simulation and acoustic analogy analysis. Transient flow field is obtained by solving the unsteady Reynolds-Averaged Navier-Stokes equation with the arbitrary sliding interface method to slide the grid for the relative motion of the rotating cross-flow fan. To predict the flow noise generated due to the cross-flow fan, an acoustic analogy analysis is performed with Ffowcs-Williams Hawkings model. The results show the details of transient flow field inside the air-conditioner including the typical eccentric vortex, which is appeared in the vicinity of the stabilizer. The strong interaction between the eccentric vortex and stabilizer is also well predicted, which is well known as the primary factor of the flow noise of the cross-flow fan. In order to validate the present analysis, the numerical result is compared with available experimental data such as the overall sound pressure level.
윤원혁(Wonhyuck Yoon),박근태(Keuntae Park),오세형(Sehyeong Oh),최해천(Haecheon Choi),이명성(Myungsung Lee),김주한(Joo-han Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Flow structures in a cross-flow fan at Re = 5400 based on the blade chord length and the tip velocity at the outer radius are investigated using large eddy simulation with an immersed boundary method. An eccentric vortex near a stabilizer, reverse flow between an impeller and the stabilizer, flow separation on blade suction surfaces, and a recirculation region at the corner of inflow region are observed from simulations. To analyze the effects of these flow structures on the fan performance, the variation of the torque coefficient of each blade in the azimuthal direction is examined. Consequently, the flow separation on the blade suction surfaces produces oscillatory variations of the torque coefficient along the azimuthal direction, causing degraded fan performance. Moreover, the recirculation region is shown to produce a considerable loss and the blades nearby suffer from high torque.
팽진기(Jin Gi Paeng),윤영환(Young Hwan Yoon) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.5
A ceramic monolith heat exchanger is studied to find the performance of heat transfer and pressure drop by numerical computation and ζ-NTU method. The numerical computation was performed throughout the domain including fluid region in exhaust gas-side rectangular ducts, ceramic core and fluid region in air-side rectangular duct with the air and exhaust in cross flow direction. In addition, the heat exchanger was also analyzed to estimate the performance by conventional ζ-NTU method with several Nusselt number correlations for flow in rectangular duct from literature. By comparisons of both performances by the numerical computation and the ζ-NTU method, the effectiveness by ζ-NTU method was closest to the result by numerical computation within a relative error of 2.14% when Stephan's Nusselt number correlation was adopted to the ζ-NTU method among the several correlations.
일체형 세라믹 열교환기의 전산 열응력 해석에 관한 연구
팽진기(Jin Gi Paeng),김기철(Ki Chul Kim),윤영환(Young Hwan Yoon) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.11
The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from 8 × 2 to 4 × 2, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of 4 × 2 bolt joining halls, Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.
PIV 측정을 통한 난류 구조와 핵료봉 다발의 직교류 혼합사이의 관계에 대한 연구
이준호(Jun Ho Lee),박형민(Hyungmin Park) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In a sub-channel flow between fuel rod-bundles of water nuclear reactors, the fluid flow is very important because it plays an important role in safety of the system. Especially, heat removal from the surface of the fuel element is closely related to the turbulence structure through the process of cross flow mixing. Since the structure is generated due to the gradient of streamwise velocity, turbulence properties such as mean velocity, turbulence intensity and Reynolds stress including the streamwise velocity should be measured to understand the turbulence structures. In this present study, flow in a sub-channel between a 5×5 rod bundle has been measured by applying the particle image velocimetry at Re= 10000. A relatively large gradient of the mean axial velocity appears between sub-channels due to the accelerated velocity in the core region of each sub-channel. In addition, strong turbulence is generated between sub-channels with various structures. As a result, very complex cross flows occur due to the interaction between these flow structures and it has been observed that the flow tend to be directed toward the wall except for the near-wall region.