유동장 해석의 정확도 증진을 위한 풍상차분법의 비교 연구

김형국,김문상 한국항공대학교 2000 論文集 Vol.38 No.-

본 논문에서는 유동장 해석 결과의 정확도 증진을 위한 비점성 플럭스 계산 기법에 대한 비교 연구를 수행하였다. 플럭스를 계산하는 대표적인 방법으로 풍상차분법과 중심차분법이 있는데 최근에는 풍상차분법이 주로 사용되고 있다. 특히 풍상차분법 중에서도 FVS와 FDS의 장점만을 선택하여 개발된 AUSM 계열 기법이 많이 사용되고 있는 추세이다. 본 논문에서는 마하수 5.0으로 비행하는 무딘 물체 주위에서의 유동장을 FVS, FDS, 그리고 AUSM 계열의 풍상차분법들을 사용하여 해의 정확성을 비교 연구하였다. 본 연구를 위해서 일반 곡면 좌표계에서 유도된 2차원 압축성 오일러 방정식을 사용한 전산 프로그램을 개발하였으며, 시간 전진법으로 음해법과 양해법 모두를 사용할 수 있게 하였고 MUSCL 기법을 사용하여 2차 공간 정확도를 가질 수 있도록 하였다. 해석 결과 가장 수치적 점성 효과가 큰 기법은 FVS 기법이었으며 FDS 기법은 엔트로피 보정이 없을 경우 정체점 부근에서 carbuncle 현상이 발생하였으며 엔트로피 보정에 의해서 올바른 해를 구할 수 있었다. AUSM 계열 기법은 가장 정확한 해석 결과를 보여주었으나 AUSM 및 AUSM+ 기법의 경우 충격파 후의 압력에 overshoot 현상이 발생하였고 이런 측면에서 AUSMPW가 가장 좋은 해석 결과를 보여주었다. In this paper, a comparative study of different upwind schemes is accomplished to figure out the solution accuracy enhancement in inviscid flux calculations. The upwind schemes are more popular than the centered schemes to calculate the inviscid fluxes. The AUSM family which takes the merits of FVS and FDS is the most frequently used scheme. The flowfield around a blunt body at Mach 5.0 in inviscid flow is analyzed by using the FVS, FDS, and AUSM family schemes to compare the solution accuracy. Two-dimensional compressible Euler equations derived in general curvilinear coordinate systems are used to develop the flowfield analysis code. Implicit and explicit method are built in this code and MUSCL approach is implemented to increase the solution accuracy up to the second order in space. The most diffusive results are shown when FVS is used. The FDS shows a carbuncle phenomena near the stagnation point. This undesirable result is removed by introducing the entropy fixing technique. The AUSM family shows the best solution even though the AUSM and AUSM+ yield the overshoot pressure right after the shock. The AUSMPW is considered as the best scheme in this sense.

풍상차분법을 이용한 압축기 익렬유동 해석

권창오,송동주,강신형 대한기계학회 1994 대한기계학회논문집 Vol.18 No.3

In this paper the CSCM type upwind flux difference splitting Navier-Stokes method has been applied to study the ARL-SL19 supersonic/transonic compressor cascade flow. H-type grid was chosen for its simplicity in applying cyclic tridiagonal matrix algorithm along with conventional slip/no-slip boundary conditions. The thin-layer algebraic model of Baldwin-Lomax was employed for the calculation of turbulent flows. The test case inlet Mach No. was 1.612 and inlet/exit pressure ratio($P_2/P_1$) was 2.15. The results were compared with experimental results from current method were compared well in suction surface with the experiments and other computational results; however, not well in pressure surface. It might be due to the complex flowfields such as shock/boundary layer interaction, turbulence, and flow separation, etc. In the future, a proper turbulence modelling and adaptive grid system will be studied to improve the solution quality.

예조건화된 Navier-Stokes 방정식에서의 풍상차분법의 수치특성

길재흥,이두환,손덕영,최윤호,권장혁,이승수,Gill, Jae-Heung,Lee, Du-Hwan,Sohn, Duk-Young,Choi, Yun-Ho,Kwon, Jang-Hyuk,Lee, Seung-Soo 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.8

Numerical characteristics of implicit upwind schemes, such as upwind ADI, line Gauss-Seidel (LGS) and point Gauss-Seidel (LU) algorithms, for Navier-Stokes equations have been investigated. Time-derivative preconditioning method was applied for efficient convergence at low Mach/Reynolds number regime as well as at large grid aspect ratios. All the algorithms were expressed in approximate factorization form and von Neumann stability analysis was performed to identify stability characteristics of the above algorithms in the presence of high grid aspect ratios. Stability analysis showed that for high aspect ratio computations, the ADI and LGS algorithms showed efficient damping effect up to moderate aspect ratio if we adopt viscous preconditioning based on min-CFL/max-VNN time-step definition. The LU algorithm, on the other hand, showed serious deterioration in stability characteristics as the grid aspect ratio increases. Computations for several practical applications also verified these results.

범람 모의를 위한 이동경계조건

인태훈,이봉희,조대희,조용식 한국수자원학회 2003 한국수자원학회논문집 Vol.36 No.6

지진해일 또는 조석과 같은 파의 거동을 수치모의할 때 해안선의 위치는 파랑의 움직임에 따라 끊임없이 이동하게 된다. 따라서, 이를 수치모형에 효과적으로 반영하기 위해서는 수치모형의 경계선을 파랑의 움직임에 따라 이동시켜야 한다. 본 연구에서는 경사지형을 계단지형으로 단순화한 이동경계조건에 대해 해안선의 이동을 보다 정확히 모의하기 위하여 천수방정식의 비선형항을 2차 정확도의 풍상차분기법으로 차분화하여 해석하였다. 개발된 수치모형을 검증하기 위하여 바닥마 A shoreline, which has no the water depth, moves continuously as waves rise up and recede. Therefore, a special boundary treatment is required to track properly the movements of the shoreline in numerical modeling of the behavior of tsunamis or tides near

천음속/초음속 압축기 익렬에서 Shock-Boundary Layer 상호작용의 수동적 제어에 의한 성능 향상 연구

김상덕,권창오,사종엽,Kim, Sang-Deok,Gwon, Chang-O,Sa, Jong-Yeop 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.9

In this paper the CSCM type upwind flux difference splitting Navier-Stokes method has been applied to study the ARL-SL19 transoni $c^ersonic compressor cascade flow. First, the general characteristics of baseline cascade flow were analyzed. At freestream Mach n.1.612 and exit/inlet pressure ratio 2.15, the results from current laminar flow were compared well in suction surface with the experiment; however, not well in pressure surface. Second, numerical study of the transoni $c^ersonic compressor cascade flow demonstrated the effectiveness of a passive control by the various size cavities. A cavity under the shock foot point at the suction surface of the blades was used as a passive control. The passive control of shock-boundary layer interaction by a cavity reduced total pressure losses. The effect of cavity length and depth was studied. The total pressure loss was reduced by about 10% and the isentropic efficiency was improved slightly. The effect of cavity depth in current study(d/l = 0.05, 0.02) was not found strong. Further adequate turbulence modeling and TVD schemes would help to capture the shock more accurately and increase the effectiveness of the current shock-boundary layer interaction study using upwind flux difference splitting computational methods.thods.

하이브리드탄의 항력 및 유동해석

이상길,이동현 한국군사과학기술학회 2000 한국군사과학기술학회지 Vol.3 No.2

Three dimensional, compressible, mass weighted averaging of Favre, Navier-Stokes system with k-$\varepsilon$ turbulence, is numerically discretized to compute three dimensional multiple jet interaction flow fields for a hybrid projectile containing three rocket motors in the ogive section. Numerical flow field computations have been made for angled nose jets and rockets at supersonic speed using multiblock structured grid. The jet conditions include very high jet to free stream pressure ratio and high temperature. It is shown that the strength of nozzle stagnation pressure affects the flow field near the side nozzle and the high stagnation pressure increases total amount of drag by a few percent. However, minor drag loss due to the pressure drag might be fully overcomed by an additional axial thrust. The results of present study can be applied for the design of future hybrid projectile.

예조건화 기법을 이용한 화학반응 난류 유동장 해석

송봉하(Bong-Ha Song),최윤호(Yun-Ho Choi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6

??The computations of chemically reacting turbulent flows are performed using the preconditioned Navier-Stokes solver coupled with turbulent transport and multi-species equations. The flowfields encountered in the vast majority of combustion applications take place at low speeds. Choi and Merkle’s preconditioning technique is used to overcome the convergence difficulties occurred at these low speed flows. The low-Reynolds number k?ε turbulence model proposed by Chien is used for turbulent flow predictions. Two numerical schemes, the implicit upwind ADI and DDLGS algorithms are used and are validated through the comparisons of computational and experimental results for H2/O2 reacting turbulent shear flow. Preconditioning formulation based on the ADI algorithm shows better convergence characteristics than that of other numerical techniques considered, such as preconditioned system using DDLGS algorithm and nonpreconditioned system using ADI or DDLGS algorithm.