• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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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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• 1997.02a
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• pp.159-165
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• 1997

• Journal of Animal Environmental Science
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• v.14 no.2
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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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.20-28
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• 2002

In this paper, the aerodynamic performance prediction of a 30kW counter-rotating (C/R) wind turbine system has been made by using the momentum theory as well as the two-dimensional quasi-steady strip theory with special care on the wake and the post-stall effects. In order to take into account the wake effects in the performance analysis, the wind tunnel test data obtained for a scaled blade are used. Both the axial and rotational inductions behind the auxiliary rotors are determined through the wake model. In addition, the optimum chord and twist distributions along the blades are obtained from the Glauert's optimum actuator disk model considering the Prandtl's tip loss effect. The performance results of the counter-rotating wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the counter-rotating wind turbine system.

• International Journal of Fluid Machinery and Systems
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• v.5 no.1
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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.

• Proceedings of the KSME Conference
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• 2004.11a
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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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• v.13 no.2
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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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• 2011.05a
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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.

• Proceedings of the KSME Conference
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• 2003.11a
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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.