• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.10-20
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• 2002

The present paper investigates methods to control dynamic stall using an optimal approach. An unsteady aerodynamic sensitivity analysis code is developed by a direct differentiation method from a two-dimensional unsteady compressible Navier-Stokes solver including a two-equation turbulence model. Dynamic stall control is conducted by minimizing an objective function defined at an instant instead of integrating for a period of time. Unsteady sensitivity derivatives of the objective function are calculated by the sensitivity code, and optimization is carried out using a linear line search method at every physical time step. Numerous examples of dynamic stall control using control parameters such as nose radius, maximum thickness of airfoil, or suction show satisfactory results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1247-1254
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• 1998

The vaneless diffusers are widely used in industrial centrifugal compressors which are required to operate within a wide flow range. When very high pressure gases are handled by centrifugal compressor. rotating stall is a serious problem because of the occurance of large aerodynamic exciting forces. Rotating stall mostly often occurs in the impellers but it can occur in vaneless diffusers as well. In this experimental study, the rotating stall in vaneless diffuser with radial type centrifugal impeller was measured by changing the flow rate with I-type, X-type hotwire. As the result, it was cleared which type of rotating stall of the impeller stall would occur and how many stall cells would appear relating with the flow rate. As the flow rate reduced, the propagation speed of rotating stall was reduced. But the stall cell number unchanged with respect to the flow rate.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.16 no.3
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• pp.1-6
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• 2008

The stalling speed flight test of light airplane, ChangGong-91, was performed to acquire the certification. With power-off engine condition, the wings level stall flight tests were conducted at the aircraft configuration of various flap angle - clean, 20degree, and full flap, respectively. They were performed considering with the combination of the maximum and minimum test weight, and forward and afterward center of gravity. The stalling speeds and the minimum speeds of light airplane were determined from the results of flight test. Also, the appropriateness of stall warning speeds are evaluated through the flight test measures. The airplane is recoverable only with pitch control and engine throttle from stall state without exceptional operation.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.70-77
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• 1998

The rise in pressure across the impeller blade of an axial flow fan depends on the angle of attack. At a low back pressure, the air volume will be large and the angle of attack is small. The gradual increase of the back pressure approached stall zone which is not stationary but travels blade to blade passage. In consequence, a region occurs around these blades with large vibration in the flow. To avoid these stall operation, the stall detector in the axial flow fans has been designed to detect stalling condition with a manometer or differential pressure switch by electric mechanism.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.834-839
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• 2003

In the present study, the performance characteristics and the number of stall cells during rotating stall of a centrifugal air compressor were experimentally investigated. If the flow coefficient is lower than 0.150, the static pressure at impeller inlet is higher than that at inlet duct And reverse flow is observed under these flow coefficient region. Maximum adiabatic efficiency is obtained for the tested compressor around flow coefficient 0.128, and it is independent of compressor rotating speed. The number of stall cells and their rotational speeds are distinctive features of the rotating stall phenomenon. The present study is mainly concerned with the number of stall cells and their rotational speeds. The interpretation method of visualization is based on the pressure distribution in the circumference pressure fields while plotting the pressure and its harmonics variations in time in polar coordinates.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.625-630
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• 2014

연료전지의 성능을 결정짓는 가장 중요한 변수 중의 하나는 각 스택의 채널에 얼마나 균일하게 연료를 공급할 수 있느냐이다. 본 연구에서는 네 가지의 모델을 사용하여 연료전지 매니폴드 형상에 따른 최적 설계를 수행하였다. 위 네 가지 모델은 각기 다른 기하학적 형상을 가지며 Edison CFD를 이용하여 형상 내의 유동을 비교하였다. 초기 모델에서는, 입구부에서 매니폴드로 유입되는 유동의 확산이 잘 일어나지 않아 각 채널의 질량유량이 불균일한 분포를 보였으며 특히 속도가 빠른 중심 영역의 채널에 많은 연료가 유입되었다. 이를 위한 디퓨져 모델링이 제안되었으며 실속이 최소한도로 발생할 때 채널당 질량유량이 가장 균일하다고 가정하였다. 이를 위해 다양한 디퓨져 각을 가진 모델을 사용했고, 이론상으로 실속이 발생하지 않는 형상에서 가장 균일한 분포를 보임을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.153-161
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• 1998

This study describes the results of the analysis of measured rotating stall signal in a centrifugal compressor with vaneless diffuser. Unsteady flow and rotating stall in vaneless diffuser were investigated by measuring of unsteady velocity fluctuation using hot-wire anemometer. Experiments were carried out in several impeller rotating speeds, at different radius ratios. Single hot -wire was used to study the characteristics of rotating stall. As a result, the abrupt rotating stall was detected at all measured impeller rotating speeds and the several flow coefficients which are less than 0.16. The number of the stall cell was one at all measured rotational speeds, and the rotating direction was the same as that of the impeller. As the flow rate decreased, the profile of the phase averaged radial velocity component with time changed from a sawtooth to a sine wave.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.37-39
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• 2010

Aerodynamic analysis was done for a fuselage and wing configuration of a mid-sized aircraft using 3-dimensional Navier-Stokes solver. Various turbulent models including a transitional SST were implemented to observe a dynamic stall as well as cruise characteristics. Also, different mesh moving methods were evaluated. Flow hysteresis which causes dynamic stall was investigated through flow field investigations.

• 베이커리
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• no.6 s.359
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• pp.66-69
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• 1998

• 프린팅코리아
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• s.3
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• pp.47-47
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• 2002