• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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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.

• 대한기계학회논문집B
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• 제26권8호
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• pp.1123-1131
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• 2002

An experimental study on the performance and instability development characteristics of a centrifugal compressor equipped with a cambered variable diffuser has been performed with varying diffuser vane angles. The test was conducted at the design speed of 20,800 rpm and the 80% design speed of 16,640 rpm for 5 diffuser angles : 65$^{\circ}$, 70$^{\circ}$, 75$^{\circ}$, 77.5$^{\circ}$, 80$^{\circ}$ The steady performance test results showed that choking mass flow rate decreases and total pressure ratio increases with a narrowed surge margin as the diffuser vane angle increases. Unsteady pressures were measured using high-frequency pressure transducers at the inducer and the diffuser throat to investigate the instability phenomena such as rotating stall and surge inside the compressor. From the unsteady measurements, it is found that the transient process from rotating stall to surge was mainly affected by diffuser angles. The results of the present study can be applied to the instability control of the centrifugal compressors using a variable diffuser.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1997년도 강연회 및 연구개발 발표회 논문집
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• pp.159-165
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• 1997

• 한국축산시설환경학회지
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• 제14권2호
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• pp.75-80
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• 2008

High concentration of $NH_3$, $CO_2$, and lots of dust are found in modern densely raising stall system, as results, they provide a negative influence on animal and lamer health, and production ability. Therefore, it is necessary to keep clean the inside of stall air to increase the productivity. A wet type air cleaner has been developed to clean the stall air. The work principle is that the inside air are sucked through the fan, and the rotating discs make a water into a fineness spray and blows into the stall. The spray can take the dust, $NH_3$, and odor from the stall inside air and give back to the circulating water, which can be refreshed in 2 hours interval. In the Present study, we measured the $NH_3$, dust, odor, temperature and humidity in a swine stall that were installed two wet air cleaners with 700 fattening swine with on-mode and off-mode of wet air cleaners. In fall, the concentrations of $NH_3$ in off-mode stall were maximum 24 ppm and minimum 16 prm, and the average was 18.2 ppm. However in on-mode stall the $NH_3$ concentrations were maximum 7ppm and minimum 1ppm, and the average was 2.7ppm. The concentration of $NH_3$ in on-mode was 74% lower than off-mode stall. Odor was measured by olfactometer. In the off-mode stall, the odor unit was 3,800 OU/$m^3$, but in the on-mode stall the odor unit was 2,100 OU/$m^3$ Odor removal efficiency was about 45% in on-mode stall. The dust measure was divided into 3 categories, $PM_{10}$, $PM_{2.5}$ and $PM_{1.0}$. Whereas the $PM_{10}$ showed no significant differences between the tests, $PM_{2.5}$ and $PM_{1.0}$ in the fine particle range reduced remarkably in the on-mode.

• 한국항공우주학회지
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• 제30권7호
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• pp.20-28
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• 2002

본 연구에서는 로터의 후류 효과 및 실속 후 특성을 고려하여 30kW급 상반회전 풍차 시스템에 대한 공력성능 해석을 수행하였다. 기본 공력이론은 모멘텀 이론과 2차원 준정상 공기력 이론을 통합한 형태를 사용하였다. 로터의 후류영향을 고려하기 위해 축소형 풍차 블레이드 모델에 대한 풍동시험 결과를 적절히 이용하였으며, 이로부터 보조로터를 지난 후류의 축속도 및 각속도 성분을 결정하였다. 또한, Glauert의 최적 작동판 이론과 Prandtl의 익단손실 효과를 고려하여 30kW급 풍차 시스템에 대한 최적 시위 및 비틀림 분포를 구하였으며, 기존의 단일 로터 시스템과의 공력성능 비교를 통하여 상반회전 풍차 시스템의 효율성 및 우수성을 입증하고자 하였다.

• International Journal of Fluid Machinery and Systems
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• 제5권1호
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• pp.1-9
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• 2012

In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitation-number region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1383-1388
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• 2004

The flow characteristics in the blade passage of a low speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. The tip leakage vortex interfaces with blade pressure surface, and results in high velocity fluctuation near the pressure surface. From the relative velocity distributions near the rotor tip, large axial velocity decay is observed at near stall condition, which results in large blockage compared to that at the design condition. Througout the flow measurements using a quasi-orthogonal measuring points to the tip leakage vortex, it is noted that the radial position of the tip leakage vortex is distributed between 94 and 96 percent span for all flow conditions. High spectrum density due to the large fluctuation of the tip leakage vortex is observed near the blade suction surface below the frequency of 1000 Hz at near stall condition.

• Wind and Structures
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• 제13권2호
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• pp.127-144
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• 2010

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.202-205
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• 2011

A rotating propeller of turboprop aircraft gives much effect on the aerodynamic characteristics of wing such as lift, moment and stall. Specially, a rotating propeller changes the lift and moment characteristics when aircrafts are in landing or take-off condition. In the present paper, 3-dimensional Navier-Stokes simulations for the interaction of propeller and wing were carried out. For rotating propeller, unsteady sliding mesh method was used to simulate a relative motion. For the power effect analysis in landing and take off configurations, double slotted flap was also considered and the aerodynamic characteristics were investigated. It was shown that the propeller slipstream enhanced the lift slope including maximum lift and this enhancement was more dominant with high lift device.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.