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수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사
전용준(Yong Joon Jun),배중헌(Joong Hun Bae),유정열(Jung Yul Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.
A-mode 영역에서 교란유동장에 놓인 원형실린더 후류의 유동공진 현상
김수현(Soo Hyeon Kim),배중헌(Joong Hun Bae),유정열(Jung Yul Yoo) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Lock-on phenomenon in the wake of a circular cylinder is investigated at the Reynolds number of 220 (Amode instability regime) using direct numerical simulation. For lock-on, the sinusoidal perturbation, whose frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. In order to analyze the vortex structure, the power spectra of the streamwise velocity signal and orthogonal enstrophies are investigated. It is observed that the three-dimensional vortex structure behind the circular cylinder turns into two-dimensional one due to the perturbed velocity. And this change causes the jump of the Strouhal number from the stable regime (A-mode instability regime) to the unstable regime (extrapolated from twodimensional shedding regime) in the Strouhal-Reynolds number relationship. As a result, the vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.
수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사
전용준(Yong Joon Jun),배중헌(Joong Hun Bae),유정열(Jung Yul Yoo) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.9
Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.
수직원형관내 초임계압 물의 난류 열전달에 관한 직접수치모사
이상훈(Sang Hoon Lee),배중헌(Joong Hun Bae),유정열(Jung Yul Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Turbulent flow and heat transfer to water at supercritical pressure flowing in vertical pipes is investigated using direct numerical simulation (DNS). A conservative space-time discretization scheme for variabledensity flows at low Mach numbers is adopted in the present study to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point. The fluid properties at these conditions are obtained using PROPATH and used in the form of tables in the simulations. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proved to play an important role in turbulent flow and heat transfer at supercritical state. Depending on the degree of buoyancy influence, turbulent heat transfer may be enhanced or significantly deteriorated, resulting in local hot spots along the heated surface.