Leesang Cho

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

Wake Shapes Behind Wings in Close Formation Flight Near the Ground

The unsteady evolution of trailing vortex sheets behind wings in close formation flight near the ground is simulated using a discrete vortex method The ground effect is included by an image method The method is validated by comparing computed results with other numerical results. For a lifting line with an elliptic loading, the ground has an effect of moving wingtip vortices laterally outward and suppressing the development of vortex evolution The gap between wings in close formation flight has an effect of moving up wingtip vortices facing each other For wings flying in parallel, the ground effect causes the wingtip vortices facing each other to move up, and it makes the opposite wing tip vortices to move laterally outward When there is a relative height between the wings in ground effect, right-hand side wingtip vortices from a mothership move laterally inward.

Aerodynamic Design and Analysis of a Propeller for a Micro Air Vehicle

AU-80 propeller and its modified version, U-75 propeller, are used for a micro air vehicle. The performance characteristics of a U-80 propeller and a U-75 propeller have not much known in the published literature. Thus, their aerodynamic characteristics are investigated using a lifting surface numerical method. The lifting surface method is validated by comparing computed results with measured data in a wind tunnel. From the computed results, it is found that the U-75 propeller produces larger thrust with higher efficiency than the U-80 propeller. To enhance the performance of these propellers, a new propeller is designed by following the sequential design procedures with the design parameters such as hub-tip ratio, maximum camber and its position, and chord length distribution along the radial direction. The performance of the designed propeller is shown to be improved much comparing with those of both the U-80 and U-75 propellers.

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.

Experimental Study on the Aerodynamic Characteristics of a Two-Stage and a Counter-Rotating Axial Flow Fan

Experiments were done for the comparison of performance and flow characteristics between a two -stage axial flow fan and a counter-rotating axial flow fan. Each stage of the two -stage axial flow fan used fur the present study has an eight bladed rotor and thirteen slater blades. The front and the rear rotor of the counter - rotating axial flow fan have eight blades each and are driven by coaxial counter ro latins shafts through a gearbox located between the rear rotor and the electric motor. Both of the two axial fan configurations have identical rotor blades and the same operating condition fur the one -to-one comparison of the two. Performance curves of the two configurations were obtained and compared by varying the blade pitch angles and axial gaps between the blade rows. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fa n flow characteristics were measured using a five-hole probe by a non-nulling method. The velocity profiles between the hub and tip of the fans were measured and analyzed at the particular operating condition s of peak efficiency, minimum and maximum pressure coefficients. The peak efficiency of the counter-rotating axial fan was improved about 2% respectively, compared with the two stage axial fan. At the minimum pressure coefficient point of the two stage axial fan, the fan inlet flow patterns show that axial velocity highly decreased in the vicinity of the blade tip region. Also, the reverse flow took place at the blade tip.

Optimal Design for a Conic Winglet of a Dual Type Combined Fan

In this study, the conic winglet which is made by rotating wing tip airfoil by each 3 axis is applied to the dual type combined fan to reduce the wing tip leakage loss. Computational Fluid Dynamics is used to calculate the loss and optimum technique is used to get minimum loss. Optimization results shows that total pressure loss coefficient was reduced by 3.4 %, and optimization model was a bended shape at the end of wing forward to pressure side.

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.

Aerodynamic Characteristics Analysis of Small Two-Stage Turbo Blower Using CFD

Aerodynamic characteristics of the small two-stage turbo blower were investigated using commercial CFD tool(ANSYS CFX Ver. 14.5) in this paper. Turbo blower, which is a centrifugal type of turbomachinery, is used in various industries. It is used for application that required high static pressure rising at relatively small volumetric flow rate. In order to understand the mechanism of static pressure rising, the aerodynamic characteristics of the small two-stage turbo blower are analyzed at high rotating speed in this study. The k-ω SST turbulence model, which is good at prediction of adverse pressure gradient flows, was applied. The CFD results of the turbo blower are validated by performance test. The static pressure rising of the turbo blower is nonlinearly increased over the first stage and the second stage. The secondary flow occurred at guide vanes, between the casing and the first impeller shroud, and the bottom of the impeller disk. As a result, It is required that whole fluid area is analyzed to predict aerodynamic characteristics of small two-stage turbo blower. and the result should be selected with considering for error from experiment and CFD.

Aerodynamic Analysis of the Blended Wing Body Type MAV using the Time-Domain Panel Method

A time-domain panel method based on the potential flow theory and the time-stepping method is developed to predict the steady/unsteady aerodynamic characteristics of FM07, which is the BWB (Blended-wing body) type MAV. In the aerodynamic analyses, we used two types of the initial model(Case I) and the improved model(Case II), which is moved the gravity center toward the rear and has larger aspect ratio. In the steady aerodynamic analyses, it is revealed that improved model has higher lift to drag ratio(L/D) and more stable pitch characteristic than those of the initial model. In the unsteady aerodynamic analyses for sudden acceleration motion similar to the launch phase of MAV, it seemed that there is a rapid increase of the lift coefficient after the launch and unsteady results are good agreed compare with steady results in just a few times. In the analysis for pitch oscillation motion, which is occurred at the cruise condition of the FM07, it shows that unsteady aerodynamic coefficients looped around steady results and the improved model has more sensitive aerodynamic characteristics.

Aerodynamic Analysis of the Helicopter Rotor Using the Time-Domain Panel Method

Recently, aerodynamic analysis of the helicopter rotor using computational fluid dynamics (CFD) is widely carried out with high accuracy. But, it is very long time to calculate aerodynamic performances and it is difficult to simulate the wake shape of the helicopter rotor using CFD analysis. In this research the time-domain panel method, which uses a numerical technique based on the piecewise constant source and doublet singularities, is applied to the analysis and prediction of the unsteady aerodynamic characteristics of helicopter rotor in a potential flow. And the free wake model is used for wake simulation. The results of present method are compared with the results of experiment of a helicopter rotor in hover and in forward flight. Results show good agreement with the experimental results.Copyright