• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.699-708
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• 2021

In this paper, the aerodynamic and aeroacoustic characteristics that vary depending on the rotation axial distance between the upper and lower rotor, which is one of the design parameters of the coaxial rotor, is analyzed in the hovering condition using the computational fluid dynamics. Aerodynamic analysis using the Reynolds Averaged Navier Stokes equation and the aeroacoustic analysis using the Ffowcs Williams ans Hawkings equation is performed and the results were compared. The upper and lower rotor of the coaxial rotor have different phase angle which changes periodically by rotation and have unsteady characteristics. As the distance between the upper and lower rotors increased, the aerodynamic efficiency of the thrust and the torque was increased as the flow interaction decreased. In the aeroacoustic viewpoint, the noise characteristics radiated in the direction of the rotational plane showed little effect by axis spacing. In the vertical downward direction of the axis increased, the SPL maintains its size as the frequency increases, which affects the increase in the OASPL. As the axial distance of the coaxial rotor increased, the noise characteristics of a coaxial rotor were similar with the single rotor and the SPL decreased significantly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.75-82
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• 2006

Tiltrotor aircraft can fly about twice faster and several times further than conventional helicopters. These aircraft provide advantages preventing compressibility of advancing side and stall of retreating side of blades because they take forward flight with tilting rotor systems. However, they have limit on forward flight speed because of the aeroelastic instability known as whirl flutter. First, the parametric study on the aeroelastic stability of the isolated rotor system has been performed in this paper. And the effects of pitch-link stiffness, gimbal spring constant, and precone angle on the whirl flutter stability of Smart-UAV have been investigated through CAMRAD II analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.197-209
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• 2018

In this study, numerical analyses on Quad Tilt Rotor(QTR) are carried out to investigate the interference effect of components and effect of operating condition during forward flight. Actuator Surface Method(ASM) which is implemented in an open source CFD code, OpenFOAM, is used to calculate the flow field around QTR with high computational efficiency. The lift of the front and rear wing is found to increase or decrease depending on the rotation direction of the rotor. At the rear wing, the interference effects of the front and rear rotor appear as a combined manner. Performance change due to the phase difference is found to be insignificant. For both rotors, the locally higher thrust is generated by the blockage effect of the wing. The interference effect of wake from the front nacelle contributes to higher local thrust for the rear rotor compared to the front rotor. And it is observed that the amplitude of thrust oscillation can decrease depending on the phase difference between the rotors. Aerodynamic performances of both rotors and the entire aircraft were compared and analyzed for various operating conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.92-97
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• 2006

A critical speed analysis is performed for a 30 ton thrust turbopump considering the casing structural flexibility. A full three-dimensional finite element method including rotor and casing is used to predict rotordynamic behavior. Rotor alone model and rotor-casing coupled model with fixed-fixed and free-free boundary conditions are calculated to investigate the effects of the casing structural flexibility. The stiffness of ball bearings are applied as unloaded and loaded values to consider rotor operating conditions in vacuum and real engine respectively. From the results of the numerical analyses, it is found that the effect of the casing structural flexibility reduces the critical speeds of the turbopump. Especially, the loaded rotor condition with higher bearing stiffness is affected dramatically rather than the unloaded rotor condition with lower bearing stiffness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.37-45
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• 2012

This study investigates the pressure leakage characteristics of a desiccant rotor with a brush-type air seal. Through a pressure leakage experiment, a correlation equation for the leakage air flow rate is obtained as a function of the air seal area and pressure difference. Using this equation, an air leakage model for the desiccant rotor is developed. By comparing simulation results with the experimental results for the desiccant rotor, the accuracy of the air leakage model is demonstrated. A performance test of a desiccant rotor with various air flow rates is carried out. Using the air leakage model, the effective mass flow rate and air leakage rate are found. In addition, the characteristics of the air leakage are analyzed for a desiccant cooling system using the developed air leakage model.

• Aerospace Engineering and Technology
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• v.4 no.1
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• pp.39-44
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• 2005

To validate the rotor performance analysis, 3D Computational Fluid Dynamics(CFD) analysis was performed for tilt rotor aeroacoustic model(TRAM). Also, 3D vehicle with rotating rotors was simulated for rotor power effect analysis. Multiple reference frame(MRF) and sliding mesh techniques were implemented to capture the effect of rotor revolution. CFD results were compared with the wind tunnel test results to validate their accuracy. At helicopter mode, CFD analysis predicted lower thrust than the wind tunnel test but CFD results showed good agreement with the test result at cruise mode. Rotor power effect decreased the lift but did not change drag and pitching moment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.653-660
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• 2009

A helicopter rotor brake system stops or reduces the speed of the rotor by transforming the kinetic energy into the heat energy. The frictionally generated heat has a considerable effect on the frictional property of material itself and causes the change of the friction coefficient which may affect the breaking time significantly. In this paper, to take into account the effect of change of friction coefficient according to temperature on braking time, thermo-mechanically coupled analysis is carried out by commercial software ABAQUS. Further, simple theoretical equation is derived considering thermo-mechanical behaviors. The predicted braking times both from theoretical and numerical methods are compared and validity of proposed theoretical equation is investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.523-531
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• 2012

The performance simulation of a desiccant rotor, which is a core component of a desiccant cooling system, was conducted on the basis of a theoretical solution of the heat and mass transfer process in the rotor. The simulation model was validated by comparing simulation results with experimental data; reasonable agreement was observed. The effect of the rotation speed on the performance of the desiccant rotor was investigated for various operation conditions: temperature (50 to $70^{\circ}C$), humidity ratio (0.01 to 0.02 kg/kg DA), and flow rate of regeneration air. The optimum rotation speed was determined from the maximum moisture removal capacity (MRC) of the desiccant rotor, and it was found to vary with the operation conditions. Further, the correlation for the optimum rotation speed was determined by regression analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.456-462
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• 2015

The objective of this study was to develop an advanced pump technology using tornado and axial pumping principles without priming water. The developed rotor type slurry pump consisted of an electric motor, driving shaft and coupling, a rotor, an impeller, suction and discharge pipes. For the clean water test, the experimental results are presented for the discharge flowrate, electric power input and vacuum pressure with the rotor design parameters as a function of the motor rpm. The slurry discharge characteristics with the solid concentration of the cement slurry was performed. As the rotor diameter and height increase, the discharge flowrate and electric power input increase while the vacuum pressure in the suction pipe decreases. The rotor thickness had no significant effect on the discharge flowrate and electric power input. Slurries with more than 18 % solid concentration, which is the development factor, can be pumped.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.48-54
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• 2020

Numerical analysis was carried out to analyze the flow fields and mechanical output of a rotor for various positions and inlet flow rates in a shroud, and it was compared with experimental data. Rotor and seawater current largely affects the flow field characteristics in the shroud system. Especially the mechanical output of the rotor increased with axial position near the center of the cylinder, and it gradually decreased close to the entrance and exit. Also, the rotor output increased with the inlet velocity. Axial and angular momentum of flow along the cylinder region rapidly increased and reached a peak, and then decreased as it passed through the rotor, while there was no significant change in the cylinder region. It is expected that these results can be used as applicable design data for the development of the tidal power generation system.