• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.181-186
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• 2009

The objective of this study is ensuring safety of cabin when the blade impacts into a obstacle by verifying safety of the rotor mast and the transmission using impact loads calculated from the simulation. The rotor mast shall not fail and the transmission shall not be displaced into occupiable space when the main rotor composite blade impact into a 8 inch rigid cylinder in diameter on the outer 10% of the blade at operational rotor speed. To calculate the reaction loads at the spherical bearing and lead-lag damper, blade impact analysis was performed with FE model consist of composite blade, tree(or rigid cylinder) using elastic-plastic with damage material and several contact surfaces which were created to describe a progress of actual failure. Also, the reaction loads were investigated in change of blade rotation speed and pitch angle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1080-1088
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• 2009

An actuator using piezoceramic material was designed in order to perform a flow control for flat plate flow. Boundary layer measurements were carried out to explore the flow disturbances by the designed actuator that was activated at low excitation frequency(15Hz). The mean velocity and fluctuation in the boundary layers were measured at $x/{\delta}^*=31.9$ downstream from the actuator tip by a one-dimensional hot-wire probe(55P14). Results reveal that low- and high-velocity regions were observed in the vicinity of the actuator center and in the outer area of the actuator respectively, and the formation of counter-rotating streamwise vortices was predicted. The fluctuations were persistently found in the outer part of the actuator and an inflection point in the spanwise gradient of the streamwise velocity was observed. Boundary layer instability was amplified at both the actuator excitation frequency and the T-S wave frequency when the actuator was excited at low frequency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1073-1079
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• 2009

The proper orthogonal decomposition (POD) method can identify principal modes that optimally capture the energy content from large multi-dimensional data set. In this study unsteady pressure fields on the rotor blade surface of a helicopter in forward flight are expressed by a reduced order model based on the POD method. Special modes containing high energy are analyzed to investigate the aerodynamic characteristics in more efficient way. The CFD simulation of flowfields around helicopter rotor blade in hovering motion is also conducted to validate its prediction with experimental result. In the process 7 modes containing energy ratio 99% from 240 snapshots information are identified and utilized to construct a reduced order model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.782-789
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• 2018

Multi-Function Display (MFD) of Korean Utility Helicopter (KUH) displays image information(navigation, flight, topographical and maintenance information) delivered from Mission Computer (MC) during flight operation. The abnormal display of MFD such as flickering phenomenon was identified in the system development. It was solved by improving the shielding performance of the DVI cable and changing the DVI cable installation path at the first mass production. However, it was occurred again when the aircraft was operated for one or two years after delivery. It was also identified in the evaluation process of the derivative helicopters. Therefore, a comprehensive review of the aircraft system level has been performed to solve the problem of MFD malfunction at first and then a design improvement plan was derived by improving the DVI cable. In this paper, the causes of MFD anomalies are analyzed and also the process of design improvement are summarized. The validity of the improvement has been verified through the DVI cable assembly comparison test, SIL/ground/flight test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.43-53
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• 2020

The effect of the relative location between pre-swirl nozzle and receiver hole on the performance of radial on-board injection type pre-swirl system was analyzed. In this study, tendency of the change of discharge coefficient and temperature drop efficiency were analyzed for 20 design points through the combination of 5 pre-swirl nozzle location and 4 receiver hole location. Discharge coefficient of system tended to be similar to the pressure ratio of the pre-swirl nozzle. System performance variation occurred as the flow structure in the cavity was affected by the surface, and the influence of the stationary surface is greater than that of the rotating surface. Discharge coefficient of system changed -1.39% to 1.25% and temperature drop efficiency changed -5.41% to 2.94% refer to reference design point.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.712-719
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• 2019

This paper explores an implementation of finite element analysis and experiment in the design process of a tape spring hinge used for various CubeSat missions. Tape spring hinges consist of short-length hardened-steel strips with one-sided curvature, and thus the behavior is subject to large deformation with unpredicted non-linearity. Precise dimensions of a commercial tape spring are traced by the use of high-resolution digital camera, and thin-shell FEM analysis is conducted using ABAQUS program. Based on the rotation-moment analysis suggested in previous studies, parametric analysis is conducted by adjusting the contributing factors such as strip thickness and the subtended angle of the cross section. Finally the behaviors are investigated by both analytical and non-linear finite element methods, and the results are compared with the simple measurements. Further studies suggest a possible application in dynamic characteristics of hinges during CubeSat operations.

• Journal of Aerospace System Engineering
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• v.13 no.3
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• pp.56-63
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• 2019

Performance analyses were performed on a propeller developed for use in a PAV (Personal Air Vehicle) under 600 kg Maximum Take-Off Weight (MTOW). The actuator disc theory and CFD analyses were used to estimate the hovering time with regards to MTOW variation for a given battery weight. The interference induced power factor kint was introduced to account for the effect of flow interference between the propellers and to estimate the performance of counter-rotating propellers. The Maximum Figure of Merit (FM) value of the propeller pitch was determined and the design RPM range for the required power inversely obtained from the CFD results. Previous research indicate that the flight time of large multi-copter is limited by the available battery energy density. Similarly, the propeller pitch settings and spacing are important factors in reducing the kint value.

• Journal of Aerospace System Engineering
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• v.13 no.1
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• pp.1-10
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• 2019

The flow characteristics in a stirred tank are very useful in a wide variety of industrial applications. Generally, the flow pattern, power consumption and mixing time in stirred vessels depend not only on the design of the impeller, but also on the tanks' geometry and internal structure. In this study, the analysis of an unstable and unsteady complicated flow characteristics generated by the interaction between the baffle shape and impeller were performed using the ANSYS FLUENT LES Turbulence Model. The study compared the predictions of CFD with the interaction between two types of rotating impellers (axial and radial flows) and the shapes of three baffles. The results of the comparison verified that the design model showed a relatively efficient trend in the mixing flow fields and characteristics around the impeller and baffles during agitation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.187-194
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• 2019

The off-axis Infra-Red(IR) seeker is mounted on the nose cone side of the anti-air high speed missile to alleviate thermal shield effect due to aerodynamic heating. The seeker output can not be regarded as the Line-of-Sight(LOS) rate any more as missile's roll motion to keep the target tracking is associated. In this paper, we propose a method to calculate the LOS rate for off-axis seeker on a 2-axis gimbal. Firstly, true LOS rate equations are analytically derived but not implementable because boresight error rate is not measurable. And then the first order lag approximation to obtain boresight error rate is proposed. The proposed LOS rate calculation method can compensate the coupling effect by considering the rotations of missile and gimbal. The performance of the proposed method is verified via full nonlinear 6-DOF(Degree of Freedom) simulations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.204-211
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• 2019

The analysis on two-phase flow in a Lean Direct Injection(LDI) combustor has been investigated. Linearized Instability Sheet Atomization(LISA) and Aerodynamically Progressed Taylor Analogy Breakup(APTAB) breakup models are applied to simulate the droplet breakup process in hollow-cone spray. Breakup model is validated by comparing penetration length and Sauter Mean Diameter(SMD) of the experiment and simulation. In the LDI combustor, Precessing Vortex Core(PVC) is developed by swirling flow and most droplets are atomized along the PVC. It has been confirmed that all droplets have Stokes number less than 1.0.