• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.12
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• pp.1071-1078
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• 2015

Numerical computations were performed to investigate the effects of pintle stroke, altitude, and bore on the performance of an external pintle thruster. Results show that under-expansion flow occurs always, independent of pintle stroke. An external pintle thruster shows good performance in that it is capable of good amount of thrust control, while aerodynamic loads are increased due to shock waves on the pintle support. When altitude is increased to 20 km, the nozzle exit velocity, Mach number, thrust as well as aerodynamic loads are increased. Bore increases aerodynamic load 5.9%, and therefore pintle shape without bore is preferred for lower aerodynamic load of a pintle in order to actuate the pintle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.728-733
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• 2008

Unsteady aerodynamic analysis of an air-pressure-levitated high-speed ground vehicle moving over the nonplanar ground surface are performed using the boundary-element method. The potential flow solution is included in a time-stepping loop and the wake is captured as part of the solution. When the vehicle moving inside the channel, the lift coefficient and the pitching moment coefficient of the vehicle are increased further because the air trapped by the channel increases the ground effect. In other words, the nonplanar ground surface such as the channel decreases further the longitudinal stability of the vehicle. On the other hand, there is little difference between the ground and the channel in the lateral stability of the vehicle because the lift increment due to the nonplanar ground surface such as the channel takes place on both sides of the wing with the same rate of increase.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.10
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• pp.745-752
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• 2020

A numerical study was carried out to evaluate the aerodynamic characteristics of the supersonic grid fins installed on SpaceX Falcon 9. The unit-grid-fin concept was utilized for more efficient and simpler 3-D steady flow calculations. Pre- and post-correction processes that accounted the interference effects by the angle of attack of the missile, the influences of the outer frame of the grid fin and the connecting rods were improved in the study, and it was demonstrated that the present correction method was more accurate as compared to previous studies. Finally, the present approach was applied to evaluate the aerodynamic characteristics in transonic/supersonic flights of SpaceX Falcon 9 with various angle of attacks.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.2
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• pp.81-89
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• 2019

In this study, wind tunnel test on Quad-Tilt Propeller which has tandem wings is carried out to analyze the aerodynamic interference effect of front wing and propeller on rear wing during forward flight. Using 6-axis balance system, forces and moments of whole aircraft were measured and using strain gauge at wing root, bending moments were measured to observe change of aerodynamic force of each wings. A 12-hole probe was used to measure the flow field in the wing and propeller wake. Flow characteristics were observed qualitatively through flow visualization experiment using tuft and smoke. To measure the aerodynamic interference by elements, the influence of front wing and propeller on rear wing was analyzed by changing the wings and propellers mount combination.

• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.63-71
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• 2023

In the present study, the effect of pitch amplitude on the unsteady aerodynamics of a NACA 0012 airfoil is numerically investigated. When the frequency ratio is equal to 1.0, airfoil pitching with 20 and 30 degrees of pitch amplitude shows almost small lift generation, but the lift is significantly increased in case of 10-degree pitch amplitude. When the frequency is 0.5, the lift coefficients have large values, and the lift increases with a decrease in pitch amplitude. When the frequency ratio is 1.0, the airfoil generates large thrust. The thrust decreases as the pitch amplitude decreases. When the frequency ratio is 0.5, drag is generated for the 30-degree pitch amplitude, but the thrust is generated for 10-degree pitch amplitude. In future, the effect of heave amplitude on the unsteady aerodynamics of the airfoil will be studied.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.47-53
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• 2004

An Experimental investigation into the effects of the blowing jet type and jet orientation on the aerodynamic characteristics over an elliptic type airfoil is explored. This study is aimed at expanding the data base of blowing jet application in separation control of elliptic airfoil. Present data includes: surface pressure, blowing jet exit velocity measurements and integrated aerodynamic loads. The experiments were performed for an elliptic airfoil at Reynolds number $8.22{\times}10^5$. The improvement of effects of pulsed jet on the increase of aerodynamic characteristics was significant for the post-stall angle. For reduced mass flow rates, pulsed jet allowed considerably higher lift to be generated. The jet orientation also showed dominant parameter on the separation control Positive jet angle delay or avoid separation, whereas negative jet angle promotes it.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.2
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• pp.134-143
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• 2014

A significant degradation in the aerodynamic performance of wind turbine system can occur by ice accretion on the surface of blades operated in cold climate. The ice accretion can result in performance loss, overloading due to delayed stall, excessive vibration associated with mass imbalance, ice shedding, instrumental measurement errors, and, in worst case, wind turbine system shutdown. In this study, the effects of ice accretions on the aerodynamic characteristics of wind turbine blade sections are investigated on the basis of modern CFD method. In addition, the computational results are used to predict the performance of three-dimensional wind turbine blade system through the blade element momentum method. It is shown that the thickness of ice accretion increases from the root to the tip and the effects of icing conditions such as relative wind velocity play significant role in the shape of ice accretion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.535-543
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• 2014

A computational simulation for a nonslender BWB UCAV configuration with rounded leading edge and span of 1.0m was performed to analyze its aerodynamic characteristics. The freestream is 50m/s over -4 to 26 degree A.o.A.s. Reynolds number based on the mean chord length is $1.25{\times}10^6$. 3D multi block hexahedral grids are used which allow good grid quality and ease to capture boundary layer. ${\gamma}-Re_{\theta}$ model as well as $k-{\omega}$ SST model is employed to assess the effect of transition for flow behavior. Drag and lift of the UCAV were well predicted while $C_M$ is under predicted at high angle of attacks and influenced by the turbulence models strongly. After assessing pressure distribution, skin friction lines and velocity field around the UCAV configuration, it was found that transition effect should be considered to enhance the prediction of aerodynamic behavior by a vortical flowfield.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.475-484
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• 2012

Numerical investigation is performed to understand the effects of thickness uncertainty of a supporting airfoil due to manufacturing processes on the aerodynamic characteristics of an airfoil used for measuring data in a wind tunnel testing. This is done by comparing the coefficients of lift, drag and moment of the airfoils. In this work, the airfoil model consists of three parts, one located in the center for measuring and two outer parts used for supporting. The study is carried out with a NACA64-418 airfoil and the turbulence model of Transition SST. It is found that the effect of thickness uncertainty of the airfoils used for supporting is not significant to the performance of the test airfoil at various angles of attack and Reynolds numbers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.185-195
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• 2021

The flapping-wing micro air vehicle (FW-MAV) in this study utilizes the cambered wings made of quite flexible material. Similar to the flying creatures, the present cambered wing uses three different materials at its leading edge, vein, and membrane. And it is constrained in various conditions. Since passive rotation uses the flexible nature of the wing, it is important to select an appropriate material for a wing. A three-dimensional fluid-structure interaction solver is developed for a realistic modeling of the cambered wing. Then a parametric study is conducted to evaluate the aerodynamic performance in terms of the elastic modulus of leading edge and vein. Consequently, the elastic modulus plays a key role in enhancing the aerodynamic performance of FW-MAVs.