• 한국유체기계학회 논문집
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• 제4권1호
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• pp.7-13
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• 2001

In developing a multistage compressor, the stage matching is one of the critical design issues. The mismatching can be often observed even if each stage has been proven good and then used as part of a compression system. A good matching among the stages can be achieved by changing various design parameters (i.e., passage cross sectional areas, blades angles, stagger angles, curvature, solidity, etc.). Therefore, designers need to find out what parameters must be changed and how much. In this study, a method to search the design parameters for optimum stage matching has been used based on an 1-D mathematical model of a compressor, which uses the data obtained from the preliminary test to identify the design parameters. This methodology is applied with a two-stage axial compressor, which was originally designed for a helicopter gas turbine engine. After identifying design parameters using preliminary test data, an optimization process has been employed to achieve the best matching between the stages (i.e., maximum efficiency of the compressor at its operation modes within a given range of the rotor speed under given restrictions for required stall margins and mass flow). 3-D flow calculations have been performed to confirm the usefulness of the corrections based on the 1-D mathematical model. Calculational results agree well with the experimental data in view of the performance characteristics. Some promising results were produced through the methodology proposed in this paper in conjunction with flow calculations.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.338-353
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• 2016

Information on the surge behaviors and stall stagnation boundaries for a nine-stage axial flow compressor are summarized on the basis of analytical data in comparison with those for a single-stage one, with attention to the pressure ratio effect. The general trends of the surge loop behaviors of the pressure-mass flow are similar for both compressors including the fact that the subharmonic surges tend to appear very near the stall stagnation boundaries. With respect to the nine-stage compressor, however, the mild loops in the subharmonic surges tend to be very small in size relative to the deep loops, and at the same time, insufficient surge recovery phenomenon, which is a kind of subharmonic surge, appears also far from the stagnation boundary for relatively short delivery flow-paths. The latter is found to be a rear-stage surge caused by unstalling and re-stalling of the rear stages with the front-stages kept in stall in the stalled condition of the whole compressor, which situation is caused by stage-wise mismatching in the bottom pressure levels of the in-stall multi-stage compressor. The fundamental information on the stall stagnation boundaries is given by a group of normalized geometrical parameters including relative delivery flow-path length, relative suction flow-path length, and sectional area-pressure ratio, and by another group of normalized frequency parameters including relative surge frequencies, modified reduced resonance frequencies, and modified reduced surge frequencies. Respective groups of the normalized parameters show very similar tendency of behaviors for the nine-stage compressor and the single-stage compressor. The modified reduced resonance frequency could be the more reasonable parameter suggesting the flow-induced oscillation nature of the surge phenomena. It could give the stall stagnation boundary in a more unified manner than the Greitzer's B parameter.

• 한국항공우주학회지
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• 제39권7호
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• pp.596-604
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• 2011

원심 압축기의 원판 마찰 손실은 동력 손실의 한 종류로써, 원심 압축기의 전체 효율 향상을 위해 원판 마찰 손실을 줄여야 한다. 본 연구에서는 원심 압축기의 임펠러 디스크 면과 케이싱 사이의 축 간격 및 표면 조도 변화에 따른 원판 마찰 손실을 분석하였고, 원판마찰손실 저감을 위한 새로운 이론식을 제안하고자 한다. 원심 압축기 임펠러의 정상상태 해석을 위해서 상용 전산해석 코드인 FLUENT의 회전 좌표계와 2-equation k-${\omega}$ SST 모델을 사용하였다. CFD 해석 결과, 원심압축기 임펠러의 원판 마찰 손실은 축 간격의 변화보다는 표면조도의 변화에 더 큰 영향을 받는 것으로 분석되었다. 원심압축기 임펠러의 원판 마찰 손실을 최소화하기 위해서 축 간격은 이론적인 경계층 두께와 동일하도록 설정하고 표면조도는 최소화해야 한다.

• 한국유체기계학회 논문집
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• 제15권1호
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• pp.58-63
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• 2012

Three dimensional unsteady numerical calculations were performed to investigate unsteadiness of the tip leakage flow in an axial compressor. The first stage of the four-stage low-speed research axial compressor was examined. Since this compressor has a relatively large tip clearance, the unsteadiness of the tip leakage flow is induced. Through the results from the unsteady calculations, the process of the induced unsteady tip leakage flow was investigated. It was shown that the leakage flow that occurred at a rotor blade tip clearance affected the pressure distribution on the pressure side near the tip of the adjacent blade, thus caused the fluctuation of the pressure difference between the pressure side and suction side. Consequently, the unsteady tip leakage flow was induced at the adjacent rotor blade. The unsteady feature of the tip leakage flow was changed as the operating point was moved. The interface between the tip leakage flow and the main flow only affected the trailing edge region at the design point whereas the interface influenced up to the leading edge at the low flow rate point. As the flow rate decreased, additionally, it was seen that the vortex size of the tip leakage flow increased and the relatively large length scale disturbance occurred. On the other hand, using frequency analysis, it was shown that the unsteadiness was not associated with the rotor speed and was about 40% of the blade passing frequency. This feature was explained in the rotor relative frame of reference, and the frequency decreased as the flow rate decreased.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.101-104
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• 2010

최근 무인기 혹은 소형 항공기들에 대한 수요가 증가함에 따라 소형 터보제트 혹은 터보팬 엔진의 수요가 꾸준히 증가하고 있다. 이러한 소형 엔진은 요구 추력을 달성하면서 크기와 무게를 줄이는 것이 가장 중요한 설계 인자인데, 이는 곧 비추력(Thrust to Weight) 값이 매우 높음을 의미한다. 비추력 값이 높은 엔진을 설계하기 위해서, 압축기 혹은 터빈 등의 핵심구성품의 경우 크기를 줄이고 단수를 줄이는 방법이 가장 효과적이다. 특히 축류압축기의 경우 일반적으로 다단으로 구성하는데 여러 단으로 구성된 압축기 중에서 단수를 줄이고 남은 단에서의 압력비를 높이는 '고부하 압축기'를 채용함으로써 이러한 문제를 해결할 수 있다. 최근 국내에서도 축류형 압축기에 대한 개발의 필요성이 꾸준히 제기되고 있으며, 이에 본 논문에서는 고부하 축류형 압축기의 설계 및 성능 리뷰 중 주요한 사항에 대해 소개하고자 한다.

• 조명전기설비학회논문지
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• 제22권3호
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• pp.34-39
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• 2008

The purpose of this paper is characteristic analysis of multi-disk axial-gap pm motor for turbo compressor. The axial-gap permanent magnet motor has shown a growing interest in high-speed application for its high-efficiency, compact size and low vibration characteristics due to core-less structure. To achieve high-power, the axial-gap PM motor has multi-disk structure of stator and rotor disk. Because of its complicated magnetic flux path, it is not easy to calculate a dynamic characteristics using finite element analysis. In this paper, the simplified 2-D unfolded model to predict EMF characteristic is presented. To verify thesuggested 2-D unfolded model analysis of back-EMF characteristic was calculated and compared 3-D finite element. Finally the proposed method is verified by experimental results and shows good agreement with test results.

• 한국유체기계학회 논문집
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• 제17권5호
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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.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1210-1218
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• 2004

Experimental study was performed to investigate the flow behavior in boundary layer on the blade suction surface of a multi-stage axial flow compressor, which was focused on the third stage of the 4-stage Low Speed Research Compressor. Flow measurements in the boundary layer were obtained using a boundary layer hot wire probe, which was traversed normal to the blade suction surface at small increments by the probe traverse specially designed. Detailed boundary layer flow measurements covering most of the stator suction surface were taken and are described using time mean and ensemble averaged velocity profiles. Amplitude of the velocity fluctuation and turbulence intensity in the boundary layer flow are also discussed. At midspan, narrow but strong wake zone due to passing wake disturbances is generated in the boundary layer near the blade leading edge for the rotor blade passing period. Corner separation is observed at the tip region near the trailing edge, which causes to increase steeply the boundary layer thickness.

• 한국유체기계학회 논문집
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• 제11권6호
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• pp.54-63
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• 2008

A study on the flow characteristics in a 4-stage axial compressor and the behavior of rotating stall was experimentally performed at the third-stage rotor and stator rows in order to investigate its performance and instability of the compression system. The pressure losses generated due to the leakage flow at a tip clearance and a shroud seal clearance and the wake flow near the trailing edge of a blade were taken into consideration to estimate the causes of performance drop of the low speed research compressor(LSRC) in Seoul national university. In addition, the measurement of rotating stall was conducted with hot-wire probes and the existence and propagation of stall cell could be confirmed through fast Fourier transform and cross-correlation analysis.

• 한국유체기계학회 논문집
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• 제15권1호
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• pp.52-57
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• 2012

Stall inception characteristics are researched to understand stall well. To realize different stall inception patterns, IGV stagger angle was changed. At design IGV stagger angle, spike, which is short length scale, is observed. Decreasing IGV stagger angle, spike changes to mode, which is long length scale, and further decreasing get multi cell. Compressor maps for each IGV stagger are shown to compare different stall inceptions. The characteristics of both spike and mode are confirmed in this experiment. Furthermore, transient from spike to mode is find. multi cell has 4cells and is little bit faster than mode. and multi cell shows 2nd, 3rd characteristics on compressor map.