• Proceedings of the KSME Conference
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• 2002.08a
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• pp.611-614
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• 2002

Rotating stall in vaneless diffusers of centrifugal compressor occurs in the diffuser wall due to flow separation at large inlet flow angle. For this reason, the critical inlet flow angles are suggested by several researchers. Beyond this critical angle, flow separates in the diffuser, and develops into rotating stall. This paper studied this critical flow angle. Rotating stall is measured through eight fast-response pressure transducers which are equally spaced around the circumference at the inlet and exit of a vaneless diffuser. Experiments are done from 20000rpm to 60000rpm for the diffuser stall. Two-cell structure which rotates at $6{\~}l0{\%}$ of impeller speed is fully developed at $20000{\~}40000rpm$, and three-cell structure which rotates at $7{\~}9{\%}$ of impeller speed is fully developed at $50000{\~}60000rpm$. This paper shows that the critical inlet flow angle is not constant but related with tip speed of impeller. As tip speed increases, so does the critical inlet flow angle.

• The KSFM Journal of Fluid Machinery
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• v.15 no.1
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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.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.115-119
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• 2004

The effect of a continuous blowing or suction on an oscillating 2-D NACA0012 airfoil was investigated numerically for the dynamic stall control. The influence of control parameter variation was also studied in the view point of aerodynamic characteristics. The result showed that the blowing control kept a higher lift drag ratio before stall angle but the dynamic stall angle was not exceed to without control result. As the slot position was closer to leading edge, the positive control effect becomes greater. The stronger jet and the smaller jet angel made more favorable roles on the control performance. In the cases of the suction, the overall control features were similar to those of the blowing, but dynamic stall angle was increased, i.e. suction was more effective to control dynamic stall. It was also founded that the suction control was showed better control effect as the slot position moves to trail edge within thirty percentage of chord length. In the simulation for the jet strength and the jet angle control, the same tendencies were observed to those of blowing cases.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.478-481
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• 2009

As a first step for aerodynamic analysis of vertical axis wind turbine, dynamic stall characteristics of airfoil was investigated. Dynamic stall of wind turbine airfoil is caused by severe variation of angle of attack and relative velocity of flow around airfoil. Angle of attack and relative velocity can be expressed with tip speed ratio. Variation of angle of attack is strongly dependent on the tip speed ratio. For tip speed ratio, 1.4 and free stream velocity, 15m/s, dynamic stall characteristics of wind turbine airfoil is compared with those of oscillating airfoil having same angle of attack variation.

• 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.

• The KSFM Journal of Fluid Machinery
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• v.19 no.4
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• pp.5-12
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• 2016

In this study, a parametric study on a cavity as casing treatment of a centrifugal compressor has been conducted using three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model. Two kinds of cavity were applied at choke and surge conditions, respectively, in this work. Inlet and outlet port widths, angle of outlet port, and length of cavity were chosen as the geometric parameters and investigated to find their effects on the aerodynamic performances such as adiabatic efficiency at design mass flow rate and stall margin of the centrifugal compressor. It was found that the aerodynamic performances of the centrifugal compressor were affected considerably by the four geometric parameters. The adiabatic efficiency was hardly changed by the geometric parameters, excepts for the angle of outlet port. With an increase in the angle of outlet port, the adiabatic efficiency and the stall margin decreased. The stall margin was more sensitive to the outlet port width than to the other geometric parameters. And, with a decrease in the outlet port width, the stall margin increased by 2% compared to that of the reference.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.2
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• pp.71-77
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• 1994

A serious of study is carried out to practical use of the three-slot cambered otter board improved by the authors. As the first step, we designed main plates, slots and accessories, such as holding plate, fan-shaped towing plate, normans, center ring, etc. Standing on this design, we made the simple cambered and three-slot cambered model otter board with accessories in a linear scale 6:1. and carried out model test to examine the efficiency of these boards. The obtained results can be summarized as follows: 1. On the simple cambered board with accessories, the values of the maximum shear coefficient($C _{LX}$ ). drag coefficient(($C _{D}$) and hydrodynamic efficiency($C _{L}$/$C _{D}$ ) are 1.39, 0.56, 2.48 at $22^{\circ}$ of the angle of stall respectively. 2. On the three-slot cambered board with accessories, $C _{LX}$/$C _{D}$ and $C _{I}$/$C _{D}$ are 1.67, 0.92, 1.82 at $32^{\circ}$ of the angle of stall respectively. 3.$C _{LX}$ of board with accessories is smaller 10~12% than that of only the main plate, and the angle of stall is almost same. 4. $C _{LX}$ and the angle of stall of the three-slot cambered board with accessories are greater 20% and $10^{\circ}$ than that of the simple cambered board respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.5
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• pp.1-11
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• 2006

The effects of continuous blowing on flow control and stall suppression for flows over a NACA 0015 airfoil at low Reynolds numbers were numerically investigated through its parameter variation on unstructured meshes. The aerodynamic force and moment variations due to flow control were examined, along with the stall angle-of-attack change for stall suppression. The results showed that blowing with relatively strong jet increases lift at the cost of drag increment below stall angle. Continuous blowing delays flow stall when it is implemented near the leading edge. When the blowing jet was aligned along the flow direction on the airfoil, the favorable flow control effect was most significant below the stall angle of attack.

• Wind and Structures
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• v.34 no.4
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• pp.385-394
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• 2022

Global Warming has been driven majorly by the consumption of fossil fuels. Harnessing energy from wind is viable solution towards reducing carbon footprint created due to burning such fuels, However, wind turbines have their problems of flow separation and aerodynamic stall to tackle with. In an attempt to delay the stall angle and improve the aerodynamic characteristics of the NACA 0015 symmetrical aerofoil, lateral cylindrical ridges were attached to its suction surface, at chord positions ranging from 0.1c to 0.5c. The characteristics of the original and ridged aerofoils were obtained using simultaneous pressure readings taken in a wind tunnel, at a free stream Reynolds number of R_e = 2.81 × 10⁵ for a wide range of free stream angles of attack ranging from -45° to 45°. Depending on the ridge size, a delay in stall angle varying from 5° to 20° was achieved together with the maximum increase in lift in the post-stall phases. Additionally, efforts were made to identify the optimum position for each ridge.

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.3 s.22
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• pp.116-123
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• 2005

An experimental investigation on the static and dynamic stall characteristics of elliptic airfoil was performed by PIV velocity field measurements. The flow Reynolds number was $3.13{\times}10^5$ and the reduced frequency of the pitch oscillation ranged from 0.075 to 0.125. The onset of static stall was caused by boundary layer separation which started at the trailing edge and progressed toward the leading edge. However, dynamic stall was caused by the vortex shed at the leading edge region and the flow field showed a vortex dominated flow with turbulent separation and alternate vortex shedding. The increase of reduced frequency increased the dynamic stall angle of attack and intensified the flow hysteresis in the down-stroke phase.