• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.60-65
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• 2001

The projectile afterbodies for zero-lift drag reduction has been analyzed using the Navier-Stokes equations with the $\kappa-\epsilon$ turbulence model. The numerical method of a second order upwind scheme has been used on unstructured adaptive meshes. Base drag reduction methods that have been found effective on axisymmetric bodies include boattailing, base bleed, base comustion, locked vortex afterbodies and multistep afterbodies. In this paper, the charateristics of turbulence flow have been studied for geomeries of multistep afterbodies. The important geometrical and flow parameters relevant to the design of such afterbodies have been identified by number, length and height of step. The flow over multistep afterbodies has been analyzed including expansion waves, recompression waves, recirculating flow, shear flow and wake flow. The numerical results have been compared and analyzed with the experimental datum.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.138-143
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• 2001

An experimental model to enhance the mixing of parallel supersonic-subsonic jet ($M_1$=1.78 and $M_2$=0.30) is simulated with a numerical technique by modeling the wall-mounted cavity to a boundary condition of oscillating pressure. The computed pilot pressure distributions along three representative cross sections show a good agreement with the equivalent experimental data. The irradiation of acoustic wave in the ultrasonic range causes the mixing augmentation of jet and wake due to the transfer of vibration energy between fluid particles.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.895-903
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• 2004

In this paper are presented the blade vibration characteristics at the starting conditions of the low pressure multistage axial compressor of heavy-duty 100 MW gas turbine. Vibration data have been collected through strain gauges during aerodynamic tests of the model compressor. The influences of operating modes at the starting conditions are investigated upon the compressor blade vibrations. The exciting mechanisms and features of blade vibrations are investigated at the surge, rotating stall, and buffeting flutter. The influences of operating modes upon blade dynamic stresses are investigated for the first and second stages. It is shown that a high dynamic stress peak of 120 MPa can occur in the first stage blades due to resonances with stall cell excitations or with inlet strut wake excitations at the stalled conditions.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.253-256
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• 2006

BEMT나 wake method와 같이 2-D 에어포일의 데이터를 성능과 하중 해석에 이용하는 기법의 경우 에어포일 데이터의 정확도는 전체 결과에 큰 영향을 미친다. 풍력 블레이드와 같은 회정익에서는 2-D 에어포일 데이터를 실험 등을 통하여 정확히 얻어서 적용 시키더라도 예측 결과는 실제값과 큰 차이를 보이는 경우가 많다. 이는 회전익의 유동 특성에 의해 발생하는 실속 지연의 효과로 인한 것이며 이것은 입력에 사용되는 에어포일 데이터에는 반영되지 않으므로 자체적인 보정이 필요하다. 본 연구에서는 이러한 문제를 해결하기 위해 현재 제시되어 있는 실속 지연 모델을 살펴보고 이를 불레이드의 성능과 하중 해석에 저용시켜 보아 그 유효성에 대하여 살펴보았다.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.63-71
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• 2001

The objective of this work is to elucidate the details of two key factors dominating the droplet buring behavior in sprays : droplet-droplet interaction and convective flow. The combustion of a one-dimensional linear droplet array with a convective flow has been studied. A one-step, second order model was employed to simulate the chemical reaction in the combustion process. Results for droplet arrays burning at two Reynolds numbers, 50 and 100, two horizontal droplet spacings, 5 and 11 radii, and two vertical droplet spacing, 2 and 4 radii, were obtained. The results indicate the droplet burning behavior is affected by Reynolds number, droplet-droplet spacing, and the relative location of droplets in the array. Droplet-droplet interaction was found to be strong for arrays with smaller droplet spacing.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.223-226
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• 2006

Computational Study of a sphere subjected to free stream flow and simultaneously subjected to spinning motion is carried out. Three dimensional compressible Navier-Stokes equations are solved using fully implicit finite volume scheme. SST(Shear Stress Transport) $k-{\omega}$ turbulence model is used. Aerodynamic characteristics being affected are studied. Validation of the numerical process is done for the no spin condition. Variation of drag coefficient and shock wave strength with increase in spinning rate is reported. Changes in the wake region of the sphere with respect to spinning speed are also observed.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.73-76
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• 2007

The present paper describes the results of performance analysis for UH-60A rotor blade in hover. For the numerical simulations, commercial CFD software, FLUENT was used with Spalart-Allmaras turbulence model. The flow solver was based on node based scheme and second order spatial accuracy options was used for simulations. For the enhancement of wake capturing capability, high resolution grid was used around tip vortex region. Granting that somewhat over prediction of thrust was observed near blade tip region, performance was well correlated with experimental data within 3% accuracy in the operating region. Finally it was shown that the present flow solver can be used for preliminary performance analysis tool for hovering helicopter rotor blades.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1552-1558
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• 2002

The blade leading edge is modified to control the secondary flow generated in the turbine cascade with fence by intensifying the suction side branch of the horseshoe vortex. The incompressible Navier-Stokes equations are numerically solved with a high Reynolds number k-$\varepsilon$ turbulence closure model for investigating the vortical flows in the turbine cascade. The computational results of total pressure loss coefficients in the wake region are first compared with experiments for validation. The structure and strength of the passage vortex near the suction surface are examined by testing various geometrical parameters of the turbine blade leading edge.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.151-154
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• 2006

In the present paper, hovering performance analyses of proprotor and helicopter rotor blades were performed by using FLUENT software. As a proprotor, TRAM(Tilt Rotor Aeroacoustic Model) was selected and performance analysis was carried out with mesh adaptation for more elaborate solution. As a helicopter rotor blades, two bladed Caradonna and Tung's rotor and four-bladed BO-105 helicopter rotor blades were selected. In case of Caradonna and Tung's rotor, vortex trajectory was compared with experimental data to inspect the vortex convection capability of the present flow solver. For the final case, performance of BO-105 helicopter rotor blades was investigated and compared with experimental data. After performance analyses of proprotor and helicopter rotors, it was shown that the present solver showed reasonable vortex strength, wake geometry and thurst coefficient distributions. But power coefficient was somewhat overestimated about $10%{\sim}15%$ regard less of mesh adaptation.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.783-786
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• 2002

The unsteady turbulent flow characteristics of NACA4406 airfoil at close proximity to the pound are numerically investigated, especially focused on the noise generation mechanism near the blunt trailing edge. The unsteady two-dimensional compressible Wavier-Stokes equations with a Spalart-Allmaras turbulence closure model are solved by the 6th-order compact scheme and the 4th-order Runge-Kutta scheme. The computation shows a noise generation by a feedback mechanism at the blunt tailing edge, where the acoustic-fluidic coupling occurs between the wall-reflected sound waves and the periodically disturbed turbulent shear layer.