• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.94-99
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• 2006

As part of a Department of Defense Grand Challenge Project, advanced high performance computing (HPC) time-accurate computational fluid dynamics (CFD) techniques have been developed and applied to a new area of aerodynamic research on microjets for control of small and medium caliber projectiles. This paper describes a computational study undertaken to determine the aerodynamic effect of flow control in the afterbody regions of spin-stabilyzed projectiles at subsonic and low transonic speeds using an advanced scalable unstructured flow solver in various parallel computers such as the IBM SP4 and Linux Cluster. High efficiency is achieved for both steady and time-accurate unsteady flow field simulations using advanced scalable Navier-Stokes computational techniques. Results relating to the code's portability and its performance on the Linux clusters are also addressed. Numerical simulations with the unsteady microjets show the jets to substantially alter the flow field both near the jet and the base region of the projectile that in turn affects the forces and moments even at zero degree angle of attack. The results have shown the potential of HPC CFD simulations on parallel machines to provide to provide insight into the jet interaction flow fields leading to improve designs.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.502-507
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• 2003

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

• 한국분무공학회지
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• 제7권3호
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• pp.12-17
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• 2002

In this paper, spray and combustion characteristics of a liquid-fueled ramjet engine were experimentally investigated. The spray penetrations were measured to clarify the spray characteristics of a liguid jet injected transversely into the subsonic vitiated airstream, which is maintained a high velocity and temperature. The spray penetrations are increased with decreasing airstream velocity, increasing airstream temperature, and increasing air-fuel momentum ratio. To compensate our results of penetrations, the new experimental equation were modified from Inamura's equation. In the case of insufficient penetration, the combustion phenomenon in ram-combustor were unstable. Therefore, the temperature distribution was slanted to the low wall of the ram-combustor. These trends gradually disappeared as the length and air temperature of the combustor became longer. Combustion efficiency increased when the length of the combustor was long and the air temperature was high. Especially, stable flame region is enlarged when the length of the combustor was long and the air temperature was high. Type Abstract here. Type Abstract here.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.419-426
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• 2004

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the loss mechanism in a low-speed axial compressor operating at the design condition(${\phi}=85\%$) and near stall condition(${\phi}=65\%$). At the design condition, the flow phenomena such as the tip leakage flow and hub comer stall are similar independent of the inlet boundary layer thickness. However, when the axial compressor is operating at the near stall condition, the large separation on the suction surface near the casing is induced by the tip leakage flow and the boundary layer on the blade for thin inlet boundary layer but the hub corner stall is enlarged for thick inlet boundary layer. These differences of internal flows induced by change of the boundary layer thickness on the casing and hub enable loss distributions of total pressure to be altered. When the axial compressor has thin inlet boundary layer, the total pressure loss is increased at regions near both casing and tip but decreased in the core flow region. In order to analyze effects of inlet boundary layer thickness on total loss in detail, using Denton's loss models, total loss is scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss.

• 한국항공운항학회지
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• 제27권4호
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• pp.9-20
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• 2019

A military aircraft generally includes external stores such as fuel tanks or external arming, depending on the purpose of the operation. When a store is dropped from a military aircraft at high subsonic, transonic, or supersonic speeds, the aerodynamic forces and moments acting on the store can be sufficient to send the store back into contact with the aircraft. This can cause damage to the aircraft and endanger the life of the crew. In this study, time accurate computational fluid dynamics (CFD) with dynamic moving grid (moving and deformable mesh, MDM) technique has been used to accurately calculate store trajectories. For the verification of the present numerical approach, a wind tunnel test model for the wing-pylon-finned store configuration has been considered and analyzed. The comparison results for the ejected store trajectories between the present numerical analysis and the wind tunnel test data at the Mach number of 0.95 and 1.2 are presented. It is also importantly shown that the numerical parameter of MDM technique gives significant effect for the calculated store trajectory in the low-supersonic flow such as Mach 1.2.

• Advances in aircraft and spacecraft science
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• 제8권4호
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• pp.303-330
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• 2021

The paper discusses the effect of the winglets on the aerodynamic and aeroacoustic performance of Boeing 737-800 aircraft by numerical approach. For this purpose, computational fluid dynamics and fluent commercial software are used to solve the compressible flow governing equations. The RANS method and the K-ω SST turbulence model are selected to simulate the subsonic flow around the wing with acceptable accuracy and low computational cost. The main variables of steady flow around the simple and blended wing in constant atmospheric conditions are computed by numerical solution of governing equations. The solution of the acoustic field has also been accomplished by the broad-band acoustic source model. The results reveal that adding a blended winglet increases the pressure difference near the wingtip,which increases the lift force. Also, the blended winglet reduces the power and magnitude of vorticities around the wingtip, which reduces the wing's drag force. The effects of winglets on aerodynamic forces lead to a 3.8% increase in flight range and a 3.6% increase in the maximum payload of the aircraft. Also, the acoustic power level variables on the surfaces and fields around the wing have been investigated integrally and locally.

• 한국전산유체공학회지
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• 제15권2호
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• pp.7-13
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• 2010

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 5.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}10^6$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental datum in the low aspect ratio cavity (L/D = ~4.5). In the high aspect ratio cavity, however, there are other low dominant frequencies of the leading edge shear layer with the dominant frequencies of the feedback mechanism.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• 한국항공우주학회지
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• 제36권4호
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• pp.337-345
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• 2008

연구에서는 NACA4412익형으로 이루어진 주날개에 NACA0012플랩이 장착된 아음속 벽면효과 모형(SWIM)의 날개 표면 3차원 압력 분포를 압력감응페인트를 이용하여 시험적으로 연구하였다. 한국항공우주연구원의 아음속 풍동에서 레이놀즈수 3.1x105의 조건에서 시험 모형의 받음각 변화에 따른 날개 윗면 및 아랫면의 압력 분포를 측정하였다. 그 결과 받음각이 증가함에 따라 날개 윗면에서의 최저 압력 지점이 뿌리에서 끝단으로 이동을 하는 것을 관찰하였고, 날개 끝단의 뒷전에서도 끝단 와류를 일으키는 압력이 매우 낮은 지점도 관찰되었다. 그러나 실속각 이후인 받음각 15도의 경우 끝단 뒷전에서는 압력이 낮은 지점이 계속 관찰되었으나 그 이외의 부분은 스팬 방향 압력 분포가 편평하였다. 압력감응페인트와 더불어 압력공을 사용하여 날개의 코드 방향 2차원 압력분포도 측정 하여 비교하였고 두 시험에서 측정된 각 압력계수들의 차이의 평균은 약 0.077임을 확인하였다.

• 천문학회보
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• 제43권1호
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• pp.45.1-45.1
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• 2018

Formation of filaments and subsequent dense cores in ISM is one of the essential questions to address in star formation. To investigate this scenario in detail, we recently started a molecular line survey namely 'Filaments, the Universal Nursery of Stars (FUNS)' toward nearby filamentary clouds in Gould Belt using TRAO 14m single dish telescope equipped with a 16 multi-beam array. In the present work, we report the first look results of kinematics of a low mass star forming region L1478 of California molecular cloud. This region is found to be consisting of long filaments with a hub-filament structure. We performed On-The-Fly mapping observations covering ~1.1 square degree area of this region using C18O(1-0) as a low density tracer and 0.13 square degree area using N2H+(1-0) as a high density tracer, respectively. CS (2-1) and SO (32-21) were also used simultaneously to map ~290 square arcminute area of this region. We identified 10 filaments applying Dendrogram technique to C18O data-cube and 13 dense cores using FellWalker and N2H+ data set. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that filaments in L~1478 are velocity coherent and supercritical. Especially the filaments which are highly supercritical are found to have dense cores detected in N2H+. Non-thermal velocity dispersions derived from C18O and N2H+ suggest that most of the dense cores are subsonic or transonic while the surrounding filaments are transonic or supersonic. We concluded that filaments in L~1478 are gravitationally unstable which might collapse to form dense cores and stars. We also suggest that formation mechanism can be different in individual filament depending on its morphology and environment.