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단일 공동 주위의 2차원 및 3차원 초음속 난류 유동 분석
우철훈(C.H. Woo),김재수(J.S. Kim) 한국전산유체공학회 2005 한국전산유체공학회지 Vol.10 No.4
The unsteady supersonic flow over two- and three-dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k-ω turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in the cavity. An explicit 4th order Runge-Kutta scheme and an upwind TVD scheme based on the flux vector split with the van Leer limiters are used for time and space discritizations, respectively. The cavity has a L/D ratio of 3 for two-dimensional case, and same L/D and W/D ratio of 1 for three-dimensional case. The Mach and Reynolds numbers are 1.5 and 450000 respectively. In the three-dimensional flow, the field is observed to oscillate in the ‘shear layer mode’ with a feedback mechanism that follows Rossiter's formula. In the two-dimensional simulation, the self-sustained oscillating flow has more violent fluctuation inside the cavity. The primary fluctuating frequencies of two- and three- dimensional flow agree very well with the 2nd mode of Rossiter's frequency. In the three-dimensional flow, the 1st mode of frequency could be seen.
우철훈(C.H. Woo),김재수(J.S. Kim) 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.4
High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation, reattachment, shock waves and expansion waves. The general cavity flow phenomena includes the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the k-ω turbulence model . The cavity model used for numerical calculation had a depth(D) of 15㎜ cavity aspect ratio (L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyzed and compared with the results of Rossiter's Eq.
로터 블레이드 제빙 시스템 설계를 위한 예측 코드 개발 및 결빙 풍동 시험
우철훈(C.H. Woo),김경삼(K.S. Kim),이석준(S.J. Yee),이재복(J.B. Yi),임태균(T.G. Lim),김정일(J.I. Kim),박남은(N.E. Park) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
When the helicopter is flighting through icing condition, the ice could be accreted on fuselage and blades. The ice on blade could deform the blade configuration and increase the weight of blade. The unstable motions of blade make decreasing of performance, handling quality and structural stability due to the abnormal weight increase and configuration change. The helicopter deicing system is required to avoid risk by icing. To protect the icing, the anti-icing system or the deicing system is used. Generally, the intake, the pitot sensor are adapted the anti-icing system, but the rotor blade uses deicing system because the large size heater mat of blade needs a lot of power consumption. The anti-icing system always actives heater mat in icing condition; the deicing system is run alternately by on/off time sequence to avoid ice accretion on blade. The design concepts of deicing system are needed estimation of heater mat location, scheduling on/off time sequence to avoid ice accretion, fixing of power consumption of heater mat. First of all, the icing region estimation on blade is needed to design of rotor blade deicing system. In this paper, air flow field and multi-phase fluid analysis was performed by the commercial CFD s/w, SC/Tetra to calculate the collection efficiency around objects. The ice accretion analysis was performed by developed in-house code, ASTROD based on Messinger thermodynamic model. The computation results show good estimation of ice accretion shape and ice thickness. The development of computational tool for icing/deicing is just one part of deicing system design process. The understanding of physical phenomenon of icing and deicing on blade surface is needed for design of deicing system. The icing/deicing wind tunnel test was performed to evaluate the function of deicing system of rotor blade that showed the phase changing on blade surface from ice to water at 0℃. And the deicing system design information was acquired from experimental results by on/off time scheduling.
김재수,우철훈,김종록,김태훈,이상수 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.2
고속으로 운항하는 비행체에는 구조상 바퀴간이나 폭탄장착부 등에 공동이 존재하게 되며, 난류 전단층에 의한 심한 압력진동과 공진현상이 일어나게 된다. 이러한 공진 현상들은 공동 주위의 구조물에 손상을 줄 수 있으며, 공기역학적 성능 및 안정성에 나쁘게 작용할 수가 있다. 본 논문에서는 비정상, 압축성의 2차원 축대칭과 3차원 Unsteady Reynolds -Averaged Navier-Stokes(RANS)방정식에 k- u난류 모델을 적용하여 종방향 진동이 지배적인 세장비(L/D)가 3인 공동에 폭비(W/D)를 1~5까지 증가시키며 수치 계산을 수행하였다. 이를 Rossiter 공식에 기초한 무차원 진통수와 Xin Zhang and Edwards의 실험결과로 비교 및 검증하였다. 그리고 2차원과 3차원의 각기 다른 유동현상을 SPL값을 이용한 FFT분석과 streamline을 통하여 비교 분석하였다. High-speed flight vehicles have cavities such as wheel wells and bomb bays. Supersonic cavity flow of high Reynolds number is characterized by pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the k-u turbulence model to the unsteady, compressible, two dimensional and three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations. The Strouhal numbers of the cavities were compared and verified by Rossiter's equation and experimental values of Xin Zhang and Edwards. The cavity model used for numerical calculation had a depth(D) of 15mm, cavity L/D of 3, width to depth ratio(W /D) was 1.0 to 5.0 for three dimensional analysis. Based on the PSD(Power Spectral Density) analysis of the pressure variation at the cavity floor, the dominant frequency was reasonable in comparison to the results of Rossiter and Xin Zhang & Edwards.