Seawook Lee

Numerical and Experimental Analyses for the Aerodynamic Design of High Performance Counter-Rotating Axial Flow Fans

A study was done on the numerical and experimental analyses for the aerodynamic design of high performance of the counter rotating axial fan (CRF). Front rotor and rear rotor blades of a counter rotating axial fan are designed using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. The through-flow fields and the aerodynamic characteristics of the designed rotor blades are analyzed by the matrix method and the frequency domain panel method. Fan performance curves are measured by following the standard fan testing method, KS B 6311. Three-dimensional flow fields in the CRF are analyzed by using the prism type five-hole probe. Performance characteristics of a counter-rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. The effect of the hub to tip ratio on the fan efficiency is significant compared with the effects of other design parameters such as the solidity and the taper ratio. The fan efficiency is peak at the hub to tip ratio of 0.4, which is almost same point for the front rotor efficiency and rear rotor efficiency. The magnitudes of the meridional and relative velocities on the front and rear rotors are increased with the radial direction from hub to tip. This results in the reverse pressure gradient at the blade leading edges of both the front rotor and the rear rotor. Axial velocities of the CRF, which are measured by the prism type five-hole probe, are gradually increased at the mean radius due to the flow contraction effect. At the hub region, axial velocity is gradually decreased due to the flow separation and the hub vortex compare with design results. This result induces the increment of the incidence angle and the diffusion factor of the front rotor and the rear rotor.Copyright

Unsteady Numerical Simulation of Wings with Flaperon Flying Over Nonplanar Ground Surface

A boundary-element method is developed for the conceptual design of a high-speed transportation system for flying over a nonplanar ground surface. The method is validated by comparing present results with experimental data and other numerical data. Unsteady aerodynamic characteristics of a tandem wing with the flaperon flying over the nonplanar ground surface are investigated using the present method. When a tandem wing with the flaperon flies inside the channel, the lift coefficients of the wings are increased further because the air trapped by the fence of the channel increases the ground effect On the other hand, the fence of the channel compensates for the lift decrement of the rear wing due to the wake generated by the front wing. Therefore, there is little change between the flat ground and the channel in the longitudinal stability of the wings. Moreover, because the lift increment due to the channel takes place on both sides of the wing with the same rate of increase, there is little difference between the flat ground and the channel in the lateral stability of the wings.

Effects of Inlet Turbulence Conditions and Near-wall Treatment Methods on Heat Transfer Prediction over Gas Turbine Vanes

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ωRSM turbulence model. Additionally, the RNG k-e, SSG RSM, and SST+γ-Reθ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ωRSM results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The SST+γ-Reθ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

Numerical Analyses and Wind Tunnel Tests of a Propeller for the MAV Propulsion

The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

Aerodynamic Analysis of an Arbitrary Three-Dimensional Blended Wing Body Aircraft using Panel Method

A panel method based on potential flow theory is developed for the steady/unsteady aerodynamic analysis of arbitrary three-dimensional Blended Wing Body aircraft. The panel method uses the piecewise constant source and doublet singularities as a solution. This potential based panel method is founded on the Dirichlet boundary condition and coupled with the time-stepping method. The present method uses the time-stepping loop to simulate the unsteady motion of the aircraft. The present method can solve the three-dimensional flow over the complex bodies with less computing time and provide various aerodynamic derivatives to secure the stability of Blended Wing Body aircraft. That will do much for practical applications such as aerodynamic designs and analysis of aircraft configurations and flight simulation.

Aerodynamic Analysis of the NREL Phase VI Rotor using the CFD

This paper describes aerodynamic characteristics for the NREL(National Renewable Energy Laboratory) Phase VI rotor using the Fluent which is a commercial flow analysis tool. Aerodynamic analysis results are compared with experimental results by the NREL/NASA Ames wind tunnel tests. For three velocity cases, computed results are compared with experiment results at five spanwise positions. Computed results represented good agreement with the experimental results at low velocity. Otherwise computed results in suction side represents disagreement with the experimental results at high velocity. When interval between wind turbines is 10 times of rotor diameter, CFD research is performed to calculate the wake effect.

Comparative Study of Near-Wall Treatment Methods for Prediction of Heat Transfer over Gas Turbine Nozzle Guide Vane

* Dept. of Mechanical Engineering, Hanyang Univ., ** Dept. of Mechanical Design and Production, Konkuk Univ.,*** Korea Aerospace Research Institute, **** Dept. of Mechanical Systems Engineering, Hansung Univ., (Received January 3, 2014 ; Revised May 19, 2014 ; Accepted May 19, 2014)Key Words: Gas Turbine Nozzle Guide Vane(가스터빈 노즐 가이드 베인), Near-Wall Treatment Method(벽면처리 방법), Transition Model(천이모델), Conjugate Heat Transfer(복합열전달) 초록: 난류모델에서 벽면처리법이 터빈 노즐 베인의 열전달 예측에 미치는 영향을 비교·분석하였다. 본 연구를 위해 NASA의 C3X 터빈 노즐 베인을 사용하였다. 벽함수 방법, 저레이놀즈수 방법, 천이모델을 사용하여 베인 표면에서의 압력 및 온도를 해석하였다. 해석 결과 터빈 노즐 베인의 중간 압력분포는 각 벽면처리법에 따른 차이 없이 실험값과 잘 일치하였다. 그러나 터빈 노즐 베인의 온도와 열전달 계수는 각 벽면처리법에 따라 큰 차이를 보였다. 전반적으로 저레이놀즈수 방법과 천이모델은 벽함수 방법에 비해 온도 및 열전달 계수 예측에 특별한 이점을 보이지 않았으며, 벽함수 방법을 적용한 레이놀즈응력 난류모델이 터빈 노즐 베인 표면의 온도 및 열전달 계수를 비교적 잘 예측하였다.Abstract: The comparative analysis of near-wall treatment methods that affect the prediction of heat transfer over the gas turbine nozzle guide vane were presented. To achieve this objective, wall-function and low Reynolds number methods, and the transition model were applied and simulated using NASA´s C3X turbine vane. The predicted turbine vane surface pressure distribution data using the near-wall treatment methods were found to be in close agreement with experimental data. However, the predicted vane metal temperature and heat transfer coefficient displayed significant differences. Overall, the low Reynolds method and transition model did not offer specific advantages in the prediction of temperature and heat transfer than did the wall-function method. The Reynolds stress model used along with the wall-function method resulted in a relatively high accuracy of prediction of the vane metal temperature and heat transfer coefficient.

Study on Tip Clearance Effect of a Counter-Rotating Ducted Fan for VTOL UAV

The tip clearance effect on counter-rotating ducted fan of VTOL UAV in hovering condition, was investigate using computational analysis. The SST turbulence model is employed in this study. The numerical results of baseline model are validated by wind tunnel test in hovering and forward conditions. It is observed that if tip clearance of one rotor in the counter-rotating ducted fan increase then the thrust coefficient of another rotor increases. In Addition to this, when the tip clearance of the rear rotor increases, the thrust of the ducted fan is improved due to increasing of average total pressure at exit plane.

Numerical Analysis for Internal Leakage Flow Characteristics of Damped Bypass Valve

A numerical analysis for the internal flow was carried out in order to analyze the leakage flow characteristics inside the damped bypass valve. This research has found that the valve characteristics became stable at above a specific temperature. Very small amount of leakage flow was occurred. But there was no effect in temperature. The more temperature fell, the more maximum pressure rate was increased.

Steady/Unsteady Cavitating Flow Analysis of Pilot Valve in Flight Actuator System Using Dynamic Moving Mesh

A numerical analysis of steady/unsteady flow applying cavitation model and moving mesh method was carried out in order to analyze flow and response characteristics inside the pilot valve which controls the flight actuator system. The flow of the valve was assessed according to operation temperature and time. This research has found that valve characteristics became stable at above a specific temperature and the cavitation affected valve`s performance. Internal pressure and response characteristics of the valve were analyzed and flow characteristics of steady and developed unsteady flow were confirmed to be matched each other.