• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.66-71
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• 2008

Two cases with circumferential grooves were designed for a transonic compressor, and 3-D numerical simulations were conducted for stall mechanism at three representative speeds. A conclusion can be drawn from the comparison between compressors with or without casing treatment that: with the rising of rotation speed, stall margin increases dramatically under the help of casing treatments, and the case with middle grooves has reasonable compromise between stall margin increment and efficiency cutting. At lower speed, the increment reduces, and grooves at the back of blade tip have more influence on stall margin. Further investigation shows there is a transition in mechanism of compressor stall with the decline of rotational speed: at high rotation speed, the expansion of stall margin mainly results from the suppression of tip leakage vortex by casing treatments, yet it benefits more from the depression of boundary layer separation from suction surface of blade tip.

• 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.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.91-98
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• 2017

Performance of a low speed axial compressor is enhanced through a proper configuration of blade row tip injection and casing treatment of groove type. Air injectors were mounted evenly spaced upstream of the blade row within the casing groove and were all aligned parallel to the compressor axis. The groove, which covers all the blade tip chord length, extends all-round the casing circumference. Method of investigation is based on solution of the unsteady form of the Navier-Stokes equations utilizing $k-{\omega}$ SST turbulence model. Extensive parametric studies have been carried out to explore effects of injectors' flow momentums and yaw angles on compressor performance, while being run at different throttle valve setting. Emphasis has been focused on situations near to stall condition. Unsteady numerical analyses for untreated casing and no-injection case for near stall condition provided to discover two well-known criteria for spike stall inception, i.e., blade leading edge spillage and trailing edge back-flow. Final results showed that with only 6 injectors mounted axially in the casing groove and at yaw angle of 15 degrees opposite the direction of the blade row rotation, with a total mass flow rate of only 0.5% of the compressor main flow, surprisingly, the stall margin improves by 15.5%.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1441-1445
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• 2008

Insect flight is adapted to cope with each circumstance by controlling a variety of the parameters of wing motion in nature. Many researchers have struggled to solve the fundamental concept of insect flight, but it has not been solved yet clearly. In this study, to find the most effective flapping wing kinematics, we conducted to analyze CFD data on fixing some of the optimal parameters of wing motion such as stoke amplitude, flip duration and wing rotation type and then controlled the deviation angle by fabricating wing tip motion. Although all patterns have the similar value of lift coefficient and drag coefficient, pattern A(pear-shape type) indicates the highest lift coefficient and pattern H(pear-shape type) has the lowest lift coefficient among four wing tip motions and three deviation angles. This result suggest that the lift and drag coefficient depends on the angle of attack and the deviation angle combined, and it could be explained by delayed stall effect.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.55-61
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• 2008

The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.27-36
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• 2014

This paper presents a numerical investigation of the effect of the rotation speed on the performance in a transonic axial compressor with the dihedral stator. Four stator geometries with different stacking line variables were tested in the flow simulations over the whole operating range. It was found that a large shroud loss at the rotor outlet and the subsequent shroud corner separation in the stator passage occurred at low mass flow rate with the 100 % design speed. The hub dihedral stator could suppress the shroud loss region and consequently improve the stall margin. In case of the 70 % design speed condition as the mass flow rate decreased, it was seen that the high loss region was placed at the midspan of the rotor passage. The dihedral stator slightly affected the local diffusion factor, but the performance of the compressor was not changed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.2
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• pp.60-67
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• 2018

Recently, environment-friendly cultivation technology is popular. A cultivator is useful for turning over the stall bedding in a poultry farm. In this study, a rotary-based cultivator with a rechargeable battery was developed for eco-friendly management of broiler chickens. From the results of the test run, the clustered stall bedding was approximately divided into up and down layers. Through experimental evaluation, the working width was more than 60 cm, and the noise was less than 80 dB. The output of the motor was 400 W, and the speed of rotation was 3000 rpm. Electric battery type cultivators are expected to be widely used in the livestock industry.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.506-511
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• 2009

Insect flight is adapted to cope with each circumstance by controlling a variety of the parameters of wing motion in nature. Many researchers have struggled to solve the fundamental concept of insect flight, but it has not been solved yet clearly. In this study, to find the most effective flapping wing dynamics, we conducted to analyze CFD data on fixing some of the optimal parameters of wing motion such as stoke amplitude, flip duration and wing rotation type and then controlled the deviation angle by fabricating wing tip motion. Although all patterns have the similar value of lift coefficient and drag coefficient, pattern A(pear-shape type) indicates the highest lift coefficient and pattern H(pear-shape type) has the lowest lift coefficient among four wing tip motions and three deviation angles. This result suggest that the lift and drag coefficient depends on the angle of attack and the deviation angle combined, and it could be explained by delayed stall and wake capture effect.

• International Journal of Fluid Machinery and Systems
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• v.3 no.3
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• pp.211-220
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• 2010

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.43-46
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• 2008

Quad-Rotor, which consists of four blades, performs a flight task by controling each rotation speed of the four blades. Quad-Rotor blade making no use of cyclic pitch or collective one is a type of fixed-wing as different from helicopter blade. Although, Quad-Rotor is simple and easy to control for those reasons, blade configuration of the fixed wing is one of the critical factors in determining the performance of Quad-Rotor. In the present study, coefficients for thrust and power of Quad-Rotor blade were derived from the data acquired by using 6-component balances. Firstly, Measurements for aerodynamic force were conducted at various pitch angles (i.e., from 0$^{\circ}$ to 90$^{\circ}$ with the interval of 10$^{\circ}$). The blade used in this experiment has aspect ratio of 6 and chord length of 35.5 mm. Secondly, assembled-blade, which was an integral blade but divided into many pieces, was used in order to test aerodynamic forces along twist angles. The curve of thrust coefficient along pitch angle indicates a parabola form. Stall which occurs during wind tunnel test to calculate lift coefficient of airfoil does not generate. When deciding the blade twist angle, structural stability of blade should be considered together with coefficients of thrust and power. Those aerodynamic force data based on experimental study will be provided as a firm basis for the design of brand-new Quad-Rotor blade.