• 한국수자원학회논문집
• /
• 제47권6호
• /
• pp.501-511
• /
• 2014

일괄형 수문모형(Lumped Model)을 활용한 홍수 유출자료의 공간확장에 영향을 미치는 강우-유출모형의 초기조건과 입력자료의 영향에 대해 연구하였다. 강우-유출모형의 초기조건으로는 기저유량 정보의 모형모의에 대한 영향과 저류함수법의 포화우량($R_{sa}$)의 공간분포에 대한 분석을 실시하였으며, 강우-유출모형의 입력자료로서 강우정보의 영향을 자료의 유무에 관련한 과거자료의 조건을 중심으로 그 영향을 분석하였다. 이를 위해 충주댐유역을 선정하였으며, 충주댐 유역을 대규모유역으로 정하고 이를 기준으로 3개 중규모유역과 22개의 소유역으로 구분하였다. 영월1, 충주댐, 영월2의 수위관측소를 70년대 수문자료 유무에 따라 중심 수위관측소로 선정하였으며 이들을 개별적 중심축으로 삼고 1993년부터 2009년까지 30개의 홍수사상을 이용해 홍수유출자료 확장의 특성을 분석하였다. 관측유출을 직접유출과 기저유출로 분류하고 산정된 기저유출을 강우-유출모의에 적용하였다. 기저유출의 적용 유무 조건하에서 세 곳의 수위관측소를 중심으로 각각의 자료 확장성을 파악하였다. 기저유출을 고려한 모델 모의시 Nash-Sutcliffe Efficiency (NSE) 값은 모델 모의 만족범위를 넘어서는 사상이 10% 이상 증가되었다. 강우에 대한 초기유출의 양을 결정하는 포화우량($R_{sa}$)의 분포는 세 곳 수위관측소의 유량값을 중심으로 중권역의 포화우량($R_{sa}$)을 최적화하는 경우, 중권역의 최적화된 포화우량($R_{sa}$) 값은 큰 차이를 보이지 않으며 포화우량($R_{sa}$) 분포가 강우사상과 유출량의 크기분포에 큰 영향을 받지 않았다. 홍수 유출자료의 강수자료 영향은 30개의 홍수사상 자료에서 자료의 이상치를 제외한 17개 홍수사상을 이용해 검증하였으며 강우자료가 많아질수록 오차 범위가 줄어듦을 보였다. 하지만, 전체 홍수사상의 규모에 비해 그 영향이 크지 않는 것으로 파악되었다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
• /
• pp.91-93
• /
• 2003

A comprehensive numerical study is carried out to investigate for the understanding of the flow evolution and flame development in a supersonic combustor with normal injection of ncumally injecting hydrogen in airsupersonic flows. The formulation treats the complete conservation equations of mass, momentum, energy, and species concentration for a multi-component chemically reacting system. For the numerical simulation of supersonic combustion, multi-species Navier-Stokes equations and detailed chemistry of H2-Air is considered. It also accommodates a finite-rate chemical kinetics mechanism of hydrogen-air combustion GRI-Mech. 2.11[1], which consists of nine species and twenty-five reaction steps. Turbulence closure is achieved by means of a k-two-equation model (2). The governing equations are spatially discretized using a finite-volume approach, and temporally integrated by means of a second-order accurate implicit scheme (3-5).The supersonic combustor consists of a flat channel of 10 cm height and a fuel-injection slit of 0.1 cm width located at 10 cm downstream of the inlet. A cavity of 5 cm height and 20 cm width is installed at 15 cm downstream of the injection slit. A total of 936160 grids are used for the main-combustor flow passage, and 159161 grids for the cavity. The grids are clustered in the flow direction near the fuel injector and cavity, as well as in the vertical direction near the bottom wall. The no-slip and adiabatic conditions are assumed throughout the entire wall boundary. As a specific example, the inflow Mach number is assumed to be 3, and the temperature and pressure are 600 K and 0.1 MPa, respectively. Gaseous hydrogen at a temperature of 151.5 K is injected normal to the wall from a choked injector.A series of calculations were carried out by varying the fuel injection pressure from 0.5 to 1.5MPa. This amounts to changing the fuel mass flow rate or the overall equivalence ratio for different operating regimes. Figure 1 shows the instantaneous temperature fields in the supersonic combustor at four different conditions. The dark blue region represents the hot burned gases. At the fuel injection pressure of 0.5 MPa, the flame is stably anchored, but the flow field exhibits a high-amplitude oscillation. At the fuel injection pressure of 1.0 MPa, the Mach reflection occurs ahead of the injector. The interaction between the incoming air and the injection flow becomes much more complex, and the fuel/air mixing is strongly enhanced. The Mach reflection oscillates and results in a strong fluctuation in the combustor wall pressure. At the fuel injection pressure of 1.5MPa, the flow inside the combustor becomes nearly choked and the Mach reflection is displaced forward. The leading shock wave moves slowly toward the inlet, and eventually causes the combustor-upstart due to the thermal choking. The cavity appears to play a secondary role in driving the flow unsteadiness, in spite of its influence on the fuel/air mixing and flame evolution. Further investigation is necessary on this issue. The present study features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous works. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is not related to the cavity, but rather to the intrinsic unsteadiness in the flowfield, as also shown experimentally by Ben-Yakar et al. [6], The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The work appears to be the first of its kind in the numerical study of combustion oscillations in a supersonic combustor, although a similar phenomenon was previously reported experimentally. A more comprehensive discussion will be given in the final paper presented at the colloquium.