• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.2-2
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• 2003

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.27-34
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• 2006

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.106-114
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• 2021

In the present study, we investigate the flow characteristics of a paraglider canopy with leading-edge tubercles by performing force measurement and surface flow visualizations. The experiment is conducted at Re = 3.3×10⁵ in a wind tunnel, where Re is the Reynolds number based on the mean chord length and the free-stream velocity. The canopy model with leading-edge tubercles has flow characteristics of a two-step stall, showing an earlier onset of the first stall than the canopy model without leading-edge tubercles. However, the main stall angle of the tubercled model is much larger than that of the canopy model without tubercles, resulting in a higher aerodynamic performance at high angles of attack. The delay in the main stall is ascribed to the suppression of separation bubble collapse around the wingtip at high angles of attack.

• 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.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.

• IEIE Transactions on Smart Processing and Computing
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• v.2 no.4
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• pp.240-247
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• 2013

The main aim of this study was to suppress the angular velocity against strong winds during storms and analyze the stability and performance of the phase plane method. The utilization of small-scale wind turbine system has become common in agriculture, houses, etc. Therefore, it is considered to be a scheme for preserving the natural energy or avoiding the use of fossil fuels. Moreover, settling small-scaled wind turbines is simpler and more acceptable compared to ordinary huge wind turbines. In addition, after converting the energy there is no requirement for distribution. Therefore, a much lower cost can be expected for small-scaled wind turbines. On the other hand, this system cannot be operated continuously because the small-scaled wind turbine consists of a small blade that has low inertia momentum. Therefore, it may exceed the boundary of angular velocity, which may cause a fault in the system due to the centrifugal force. The aim of this study was to reduce the angular velocity by controlling the stall factor. Stall factor control consists of two control methods. One is a shock absorber that is loaded in the junction of the axis of the blade of the wind turbine gear wheel and the other is pitch angle control. Basically, the stall factor itself exhibits nonlinear behavior. Therefore, this paper confirmed the feasibility of stall factor control in producing desirable performance whilst maintaining stability.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.2
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• pp.188-197
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• 2007

Active flow control, in the form of steady and unsteady momentum injection via jet blowing was studied. A jet was obtained by pressing a plenum inside the airfoil and ejecting flow out of a thin slot. The normal and drag forces were measured with leading edge or trailing edge blowing Jet and compared with the results obtained with no blowing. The blowing jet has been shown to improve the aerodynamic performance of the airfoil. The steady jet proved more effective than pulsating jet in these experimental conditions. Furthermore for the case of leading edge steady blowing jet, the alleviation of non-linearity in the normal force curve slope can be seen at higher angles of attack. No effective trailing edge jet was observed in this highly separated flow. This shows that the stall control is highly depends on the characteristics of the boundary layer near the jet slot.

• 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.

• Bulletin of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.88-92
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• 2001

H. Kim, B.K. Lee and C.K. Rheem have been experimentally studied to clarified the mechanism of thrust force generated by sculling motion for the propulsion of Korean small boats. The experimental investigations have been conducted under the bollard condition by installing a scull at the end of a trimming tank of towing tank. The sculling motion produced by the skilful fisherman and the resultant venerated forces have been measured in respect to the Cartesian coordinate fitted to the pivot point of the scull. ("An Experimental Study on the Propulsive Characteristics of Sculls". J. of the Soc. of Naval Arch. of Korea, Vol. 26, No. 3, 1989, pp.13-24) Through these experiments the trajectory of the blade tip and the angular displacement of the blade section have been measured as shown in Fig. 1 and 2 of this paper. And at the same time the resultant hydrodynamic force components are expressed in Fig. 3 and 4. These three dimensional data of sculling motion and generated real time force components are the unique experimental information which could clarify the thrust force generating mechanism of sculling motion. The experimental results have been reanalyzed by focusing the relation between instantaneous attack angle of blade section and the resultants real time force components. Through these investigation it is found out that the conventional imagination that the 7cull motion should be effective in generating lift force must be reconsidered because the attack angle of scull blade are too great to free from stall phenomena during the sculling operation.

• Journal of Aerospace System Engineering
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• v.7 no.3
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• pp.15-19
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• 2013

Tail wing is important to designing of civil aircrafts, because it is responsible for aircraft stability and control. Tail wing has a role in aircraft control and makes aircraft fly stably without any pilot control input. Also, designing of tail wing determine trim drag force in whole aircraft. Center of gravity(CG) of aircraft travels with various effects as placement of passenger's seats, location of cargo bay, etc. In designing horizontal tail volume, aircraft CG travel has to be considered to have margin so that it should be sized to provide adequate stability and control for the airplane's entire CG range throughout the flight envelope. Finally, it is essential to have sufficient elevator control to perform stall at forward CG for all flaps down configurations. Such stalls establish the FAR stall speed which airplane take-off and landing performance. This paper deals with the process for tail wing design regarding the aircraft CG travel and results for 95-seat type turboprop aircraft.