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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.
박남은(N.E. Park),우철훈(C.H. Woo),유광재(G.J. Ryu) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
HALO/HAHO are methods of delivering personnel, equipment and supplies from a transport aircraft at a high altitude via free-fall parachute insertion. HALO(High Altitude-Low Opening) and HAHO(High Altitude-High Opening) are also known as Military Free Fall. In the HALO technique, the parachutist opens his parachute at a low altitude after free-falling for a period of time, while in the HAHO technique, the parachutist opens his parachute at a high altitude just a few seconds after jumping from the aircraft. The HALO parachutist jumps from the helicopter at fast forward flight to avoid attack from the enemy. The trajectory of skydiving shows down/backward falling. The skydiver could be humped against external protuberance around aft fuselage of the helicopter at moment of jumping. The configuration design is needed to consider about crash skydiver against fuselage or the flight manual has to describe speed limitation during HALO. The helicopter pitch attitude of fuselage and downwash from rotor is become different by forward flight speed. In this paper, the helicopter attitude and the rotor blade motion were simulated by HOST(Helicopter Overall Simulation Tool) to use input data to CFD(Computational Fluid Dynamics) for HALO simulation. The rotor blade was modeled by actuator disk method and the interference analysis was performed including skydiver, fuselage and rotor downwash. The human body was modeled 95% height size and 5% weight of human database for conservative simulation. The analysis results of interference with skydiver and fuselage, drag coefficients by attitudes of diving, external forces of sky diver were inputted to equations of motion to calculate the diving trajectory. The forward flight speed was suggested from the trajectory simulation to avoid crash against with protuberance of helicopter.
전산공력소음해석을 통한 UH-60 제자리비행 공력소음 연구
박남은(N.E. Park),우철훈(C.H. Woo),최건묵(G.M. Choi),김철호(C.H Kim),이석준(S.J. Yee) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4
The helicopter development technology is improved by the increasing of computing power and advanced test facilities. The increasing efficiency of fuel consuming by the developing of improved lift-to-drag rotor system is the major issue, the noise reduction for ecology(civil area) and increase of survivability to reduce noise detection(battlefield) also are important. This investigation shows the helicopter external noise flight test methods, conventional military helicopter's(UH-60) experimental results and the numerical modeling method for aero-acoustic of rotor blade and the result of CAA(Computalional Aero-Acoustic) for main rotor blade.
헬리콥터 로터 블레이드 제빙시스템 설계를 위한 블레이드 제빙해석 기법 연구
박남은(N.E. Park),우철훈(C.H. Woo),이석준(S.J. Yee),이재복(J.B. Yi),임태균(T.G. Lim) 한국전산유체공학회 2013 한국전산유체공학회 학술대회논문집 Vol.2013 No.5
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. Generally, the engine intake and the pitot sensor are adapted 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 is always active heater mat in icing condition; the deicing system is run alternately by on/off time sequence to avoid ice accretion on blade. Especially, due to the composite blade is weak by heat, over heat could make weak brittleness of blade. Thus, the de-icing system should be designed not only eliminate the ice on leading edge but also not damage the blade by heat source. 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 result shows good estimations of icing region and ice thickness. In this study, de-icing situation is simplified that the blade surface adjoin with ice and thermal conduction occur at that interface. To analysis of convection on exterior surface of ice and internal heat power from heater mat by numerical method, discrete computational nodes of ice covered blade and consider phase change at the interface blade and ice. The numerical analysis result compared with ice wind tunnel test data of the blade to evaluate. The numerical method results show similar with experimental data about time to eliminate the ice and temperature of off-time range.
박남은(N.E. Park),우철훈(C.H. Woo),이상기(S.G. Lee),이석준(S.J. Yee) 한국전산유체공학회 2008 한국전산유체공학회 학술대회논문집 Vol.2008 No.-
The development technology for the helicopter is improved by the increasing of computing power and advanced test facilities. The increasing efficiency of fuel consuming by the developing of improved lift-to-drag rotor system is the major issue, the noise reduction for ecology(civil area) and increase of survivability to reduce noise detection(battlefield) also are important. This investigation shows the classification of helicopter external noise and requirements, the noise flight test methods, the numerical modeling method for aero-acoustic of rotor blade and the result of CAA(Computational Aero-Acoustic) for main rotor blade.