• Title/Summary/Keyword: drag performance

Search Result 451, Processing Time 0.029 seconds

A Study on the Aerodynamic Characteristic of Gunfire Damaged Airfoil (화포에 의해 손상된 날개의 공력특성에 관한 연구)

  • Lee, Ki-Young;Chung, Hyoung-Seog;Kim, Si-Tae
    • Journal of the Korea Institute of Military Science and Technology
    • /
    • v.11 no.2
    • /
    • pp.144-151
    • /
    • 2008
  • An experimental study has been conducted to investigate the effects of circular damage hole on the characteristics of airfoil performance. The damage on a wing created from a hit by anti-air artillery was modeled as a circular hole. Force balance measurements and static pressure measurements on the wing surface were carried out for the cases of having damage holes of 10% chord size at quarter chord and/or half chord positions. All experiments were conducted at Reynolds number of $2.85\times10^5$ based on the chord length. The surface pressure data show big pressure alterations near the circular damage holes. This abnormal surface pressure distribution produces shear stress that could lead to the acceleration of the structural degradation of the wing around the circular damage hole. However, in spite of the existence of circular damage holes, the measured force data indicated the only a slight decrease in lift accompanied by increase in drag compared to the results of undamaged one. The influence of damage hole on the aerodynamic performance was increased as the location of damage moved to the leading edge. The effect on the control force was insignificant when the damaged size was not large.

Effect of windshields on the aerodynamic performance of a four-box bridge deck

  • Chen, Xi;Dragomirescu, Elena
    • Wind and Structures
    • /
    • v.31 no.1
    • /
    • pp.31-41
    • /
    • 2020
  • A new type of bridge deck section consisting of four-box decks, two side decks for vehicular traffic lanes and two middle decks for railway traffic, has been experimentally investigated for determining its aerodynamic properties. The eight flutter derivatives were determined by the Iterative Least Squares (ILS) method for this new type of four-box deck model, with two windshields of 30 mm and 50 mm height respectively. Wind tunnel experiments were performed for angles of attack α = ±6°, ±4°, ±2° and 0° and Re numbers of 4.85×105 to 6.06×105 and it was found that the four-box deck with the 50 mm windshields had a better aerodynamic performance. Also, the results showed that the installation of the windshields reduced the values of the lift coefficient CL for the negative angles attack in the range of -6° to 0°, but the drag coefficient CD increased in the positive angle of attack range. However, galloping instability was not encountered for the tested reduced wind speeds, of up to 9.8. The aerodynamic force coefficients and the flutter derivatives for the four-box deck model were consistent with the results reported for the Messina triple-box bridge deck, but were different from those reported for the twin-box bridge decks.

THE ORBIT DETERMINATION OF LEO SATELLITES USING EXTENDED KALMAN FILTER (확장 칼만 필터를 이용한 LEO 위성의 궤도결정 방법)

  • 손건호;김광렬;최규홍
    • Journal of Astronomy and Space Sciences
    • /
    • v.12 no.1
    • /
    • pp.133-142
    • /
    • 1995
  • We studied the nonlinear estimation problem of extended Kalman filter and appled this method to LEO satellite system. Through this method the performance of extended Kalman filter was analyzed. There were certain presumption taken; J2 and atmospheric drag were simply considered in the dynamic model of LEO satellite and the system noise error of $\sigma_r$=150m, $\sigma_r$=10m/s was presumed in the observation data. As results of this simulation, the overall state estimation errors of extended Kalman filter were within the presumed error range and also the ability of performance was maximized when the condition was the state process noise Q has the 1/10 level of covariance matrix Po.

  • PDF

Unscented Kalman Filtering for Spacecraft Attitude and Rate Determination Using Magnetometer

  • Kim, Sung-Woo;Park, Sang-Young;Abdelrahman, Mohammad;Choi, Kyu-Hong
    • Bulletin of the Korean Space Science Society
    • /
    • 2008.10a
    • /
    • pp.36.1-36.1
    • /
    • 2008
  • An Unscented Kalman Filter(UKF) for estimation of attitude and rate of a spacecraft using only magnetometer vector measurement is presented. The dynamics used in the filter is nonlinear rotational equation which is augmented by the quaternion kinematics to construct a process model. The filter is designed for low Earth orbit satellite, so the disturbance torques include gravity-gradient torque, magnetic disturbance torque, and aerodynamic drag. The magnetometer measurements are simulated based on time-varying position of the spacecraft. The filter has been tested not only in the standby mode but also in the detumbling mode. To stabilize the attitude, linear PD controller is applied and the actuator is assumed to be thruster. A Monte-Carlo simulation has been done to guarantee the stability of the filter performance to the various initial conditions. The UKF performance is compared to that of EKF and it reveals that UKF outperforms EKF.

  • PDF

Performance Verification of LEO Satellite Propulsion System based on Early On-orbit Operation Analysis (초기 궤도운용 분석 기반 저궤도 지구관측위성 추진시스템 성능 검증)

  • Won, Su-Hee;Chae, Jongwon;Kim, Sukyum;Jo, Sungkwon;Jun, Hyoung Yoll
    • Journal of Satellite, Information and Communications
    • /
    • v.11 no.1
    • /
    • pp.58-62
    • /
    • 2016
  • The satellite propulsion system provides the required thrust to insert a satellite into the desired orbit after separation from the launch vehicle and to control orbit inclination or compensate altitude loss due to drag after inserted into the desired orbit. The on-orbit performance of LEO satellite propulsion system according to operation mode was verified based on the results analysis for early on-orbit operation. The temperature trends of components and tubing were checked and the resultant trends were within the normal range as well.

Design of air-cooled waste heat removal system with string type direct contact heat exchanger and investigation of oil film instability

  • Moon, Jangsik;Jeong, Yong Hoon;Addad, Yacine
    • Nuclear Engineering and Technology
    • /
    • v.52 no.4
    • /
    • pp.734-741
    • /
    • 2020
  • A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.

A Study on the Configuration Design and the Performance Analysis of the 20kW HAWT based on BEMT (BEMT를 적용한 20kW 수평축 풍력터빈 형상설계 및 성능해석)

  • Kang, Ho-Keun;Nam, Cheong-Do;Lee, Young-Ho;Kim, Beom-Seok
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.30 no.6
    • /
    • pp.669-676
    • /
    • 2006
  • The optimum design and the performance analysis software called POSEIDON for the HAWT (Horizontal Axis Wind Turbine) is developed by use of BEMT, which is the standard computational technique for prediction of power curves of wind turbines. The Prandtl's tip loss theory is adopted to consider the blade tip loss. The lift and the drag coefficient of S-809 airfoil are predicted via X-FOIL and the post stall characteristics of S-809 also are estimated by the Viterna's equations.$^{[13]}$ All the predicted aerodynamic characteristics are fairly well agreed with the wind tunnel test results. performed by Sommers in Delft university of technology. The rated power of the testing rotor is 20kW(FIL-20) at design conditions. The experimental aerodynamic parameters and the X-FOIL data are used for the power Prediction of the FIL-20 respectively The comparison results shows good agreement in power prediction.

Experimental Investigation of the Hydrodynamic Force Acting on Ship Hull and Rudder in Various Wave Direction

  • Nguyen, Van Minh;Nguyen, Tien Thua;Seo, Juwon;Yoon, Hyeon Kyu;Kim, Yeon Gyu
    • Journal of Advanced Research in Ocean Engineering
    • /
    • v.4 no.3
    • /
    • pp.105-114
    • /
    • 2018
  • In the past, traditional methods of research on ship maneuvering performance were estimated in calm waters. However, the course-keeping ability and the maneuvering performance of a ship can be influenced by the presence of waves. Therefore, it is necessary to understand the maneuvering behavior of a ship in waves. In this study, the force acting on a moving ship and a rudder behind the model ship will be performed in regular waves in Changwon National University (CWNU). In addition, the prediction force acting on the rudder in calm waters was carried out and compared with those of Computational Fluid Dynamics (CFD). Model test in regular wave was performed to predict the force acting on the ship and the rudder behind the model ship in various wave directions. The effects of wavelength and wave direction on hydrodynamic forces acting on the ship hull versus rudder angle is discussed.

Performance Analysis of the NREL Phase IV Wind Turbine by CFD (CFD에 의한 NREL Phase IV 풍력터빈 성능해석)

  • Kim, Bum-Suk;Kim, Mann-Eung;Lee, Young-Ho
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2008.03b
    • /
    • pp.652-655
    • /
    • 2008
  • Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-${\varepsilon}$ model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(k-${\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

  • PDF

SELECTION OF THE OPTIMAL POSITION OF THE FLAP FOR THE IMPROVEMENT OF AERODYNAMIC PERFORMANCE (공기역학적 성능 향상을 위한 플랩의 최적 위치 선정)

  • Kang, H.M.;Park, Y.M.;Kim, C.W.;Lee, C.H.
    • Journal of computational fluids engineering
    • /
    • v.18 no.4
    • /
    • pp.41-46
    • /
    • 2013
  • The selection of the optimal position of the flap was performed in order to improve the aerodynamic performance during the take-off and landing processes of aircraft. For this, the existing airfoils of the main wing and flap are selected as the baseline model and the lift coefficients (cl) according to angle of attacks (AOA) were calculated with the change of the position of flap airfoil. The objective function was defined as the consideration of the maximum cl, lift to drag ratio and cl at certain AOA. Then, at 121 experimental points within $20mm{\times}20mm$ domain, two dimensional flow simulations with Spalart-Allmaras turbulence model were performed concerning the AOA from 0 to 15 degree. If the optimal position was located at the domain boundary, the domain moved to the optimal position. These processes were iterated until the position was included in the inside of the domain. From these processes, the flow separation at low AOA was removed and cl increased linearly comparing with that of the baseline model.