• Title/Summary/Keyword: air drag

Search Result 259, Processing Time 0.03 seconds

이온풍을 이용한 실린더 뒤의 후류 제어 (The wake flow control behind a circular cylinder using ion wind)

  • 현기탁;전중환
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2002년도 학술대회지
    • /
    • pp.459-462
    • /
    • 2002
  • Many active and passive flow control methods have been studied since decades, but there are only few works about flow control methods using ion wind. This paper presents an experimental study on the wake control behind a circular cylinder using ion wind, a bulk motion of neutral molecules driven by locally ionized air of corona discharge. Experiments are done f3r different electrohydrodynamic numbers - the ratio of an electrical body farce to a fluid Inertial force - from 0 to 2 and for the Reynolds number ranging from $4{\times}10^3\;to\;8{\times}10^3$. Pressure distributions over a cylinder surface are measured and flow visualizations are carried out by smoke wire method. Flow visualizations confirm that ion wind affects significantly the wake structure behind a circular cylinder and pressure drag could be dramatically reduced by the superimposing ion wind.

  • PDF

액적이 있는 비점성 공기유동 모델을 이용한 구름속의 천음속 에어포일 수치해석 (NUMERICAL SIMULATION OF A TRANSONIC AIRFOIL IN THE CLOUD WITH THE DROPLET-LADEN INVISCID AIR FLOW MODEL)

  • 염금수;장근식;백승욱
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2011년 춘계학술대회논문집
    • /
    • pp.291-293
    • /
    • 2011
  • In this paper, the problem of transonic aerodynamic characteristics of a NACA0012 airfoil is numerically investigated in the inviscid gas-droplet two-phase flow with the compressible two-fluid model. In the present study, the airfoil flight in the cloud is simulated by taking account of the viscous drag of the droplets, the heat transfer, the phase change, and the droplet fragmentation The two-fluid equation system is solved by the fractional-step method and the WAF-HIL scheme. The effects of size and volume fraction of the droplets on the flow characteristics of the airfoil in the cloud are elaborated and discussed.

  • PDF

철도터널의 환기특성에 관한 연구 (The Characteristics of Ventilation in Railway Tunnel)

  • 유지오;신현준;이호석
    • 한국터널지하공간학회 논문집
    • /
    • 제2권2호
    • /
    • pp.22-31
    • /
    • 2000
  • 철도터널에서 오염물질의 거동은 열차의 운행조건 및 터널의 구조 등과 같은 다양한 인자에 의해 영향을 받아 매우 복잡한 양상을 보이게 된다. 본 연구에서는 SES프로그램을 수정하여 해석한 농도계산을 이용하여 철도터널에서 오염물질의 거동특성을 구명하고, 터널의 단면적, 길이 및 열차의 항력계수, 주행속도가 터널의 최대풍속 및 오염농도에 미치는 영향에 대한 분석결과를 제시하였다.

  • PDF

폐쇄형 풍동 시험부내의 진동하는 익형 주위 유동에 대한 비정상 벽면효과 연구 (UNSTEADY WALL INTERFERENCE EFFECT ON FLOWS AROUND AN OSCILLATING AIRFOIL IN CLOSED TEST-SECTION WIND TUNNELS)

  • 강승희;권오준;홍승규
    • 한국전산유체공학회지
    • /
    • 제10권2호
    • /
    • pp.60-68
    • /
    • 2005
  • For study on the unsteady wall interference effect, flows around a forced oscillating airfoil in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The Spalart-Allmaras one-equation model is employed for the turbulence effect. The computed results of the oscillating airfoil having a thin wake showed that the lift curve slope is increased and the magnitude of hysteresis loop is reduced by the interference effects. Since the vortex around the airfoil is generated and convected downstream faster than the free-air condition, the phase of lift, drag and pitching moment coefficients was shifted. The pressure on the test section wall shows harmonic terms having the oscillating frequency contained in the wail effect.

전기동력무인기 유연날개 플러터 해석 (Flutter Analysis of Flexible Wing for Electric Powered UAV)

  • 이상욱;신정우;최용준
    • 한국소음진동공학회:학술대회논문집
    • /
    • 한국소음진동공학회 2014년도 추계학술대회 논문집
    • /
    • pp.189-192
    • /
    • 2014
  • Recently, development of electric powered UAV for high altitude and long endurance mission has been conducted worldwide. Long endurance requirement necessitates high lift over drag (L/D) aerodynamic characteristics and lightweight structures, leading to highly flexible wings with high aspect ratio. These highly flexible wings increase the danger of catastrophic aircraft failure due to flutter, which is a dynamic aeroelastic instability occurring from the interaction of aerodynamic, inertial, and elastic forces acting on the aircraft flying through the air. In this paper, flexible wing for electric powered UAV whose skin is fabricated using mylar film for lightweight design is briefly explained. In addition, flutter analysis procedures and results for the flexible wing in order to substantiate the aeroelastic stability requirements are presented.

  • PDF

Bioinspired Nanoengineering of Multifunctional Superhydrophobic Surfaces

  • Choi, Chang-Hwan
    • 한국표면공학회:학술대회논문집
    • /
    • 한국표면공학회 2015년도 추계학술대회 논문집
    • /
    • pp.102-133
    • /
    • 2015
  • Nature, such as plants, insects, and marine animals, uses micro/nano-textured surfaces in their components (e.g., leaves, wings, eyes, legs, and skins) for multiple purposes, such as water-repellency, anti-adhesiveness, and self-cleanness. Such multifunctional surface properties are attributed to three-dimensional surface structures with modulated surface wettability. Especially, hydrophobic surface structures create a composite interface with liquid by retaining air between the structures, minimizing the contact area with liquid. Such non-wetting surface property, so-called superhydrophobicity, can offer numerous application potentials, such as hydrodynamic drag reduction, anti-biofouling, anti-corrosion, anti-fogging, anti-frosting, and anti-icing. Over the last couple of decades, we have witnessed a significant advancement in the understanding of surface superhydrophobicity as well as the design, fabrication, and applications of superhydrophobic coatings/surfaces/materials. In this talk, the designs, fabrications, and applications of superhydrophobic surfaces for multifunctionalities will be presented, including hydrodynamic friction reduction, anti-biofouling, anti-corrosion, and anti-icing.

  • PDF

디지털 풍동을 활용한 풍력 발전기 날개 단면 형상 개발에 관한 연구 (A Study on the Development for the Airfoil of Wind Turbine Blade using Digital Wind Tunnel)

  • 강덕훈;우영진;이장호
    • 한국유체기계학회 논문집
    • /
    • 제15권5호
    • /
    • pp.42-47
    • /
    • 2012
  • Newly updated wing shape to apply small vertical wind turbine is tested with digital wind tunnel in this study. Digital wind tunnel is designed to reduce length of wind tunnel and also to maximize its area of test section. Same DC fans of ninety six are installed in the end side of its rectangular duct and air can be blown out to the other side to have uniform flow with same electricity power. New wing is concluded using experimental plan and analysis with 4-parameters and 3-levels, and tested with digital wind tunnel. It shows better performance in lift to drag ratio, and can applied to the wind turbine for the higher torque and lower thrust.

난류 경계층의 표면 마찰력 감소화 (Reduction of Skin Friction Force for Turbulent Boundary Layer)

  • 김시영
    • 수산해양교육연구
    • /
    • 제5권2호
    • /
    • pp.128-137
    • /
    • 1993
  • This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into buffer layer of turbulent boundary layer on flat plate. The buffer layer of boundary was specified by minus velocity gradient of law of the wall. When the buffer layer region of turbulent boundary layer is filled with micro-bubble of air and viscous of the region is kept low, the velocity profile in the region should be changed substantially. Then the Reynolds stress in the buffer layer region becomes less, which guide to higher velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

  • PDF

간단한 교시용 수리실험장치에 관한 연구 (A Study on Some Simple Apparatus to DemotlBtrate Hydraulic Principles)

  • 유한열
    • 한국농공학회지
    • /
    • 제7권1호
    • /
    • pp.843-849
    • /
    • 1965
  • Some simple devices to demonstrate important hydraulic principles to students are necessitated in fluid mechanics or hydraulics classes. These devices should\ulcorner be easy to make and operate with inexpensive cost. The writer has studied some simple demonstrhation apparatus of hydraulic principles which were made with cheap materials. The purpose of this paper is to present the results of the study. In this paper, hydraulic principles that can be demonstrated by using these apparatus are described, the plans of them are presented, and how to make them and what materiaIs to be used are briefly explained. An axial-flow fan is a device with which the flow of air is supplied for several purposes. It consists of a duct, a fan and a guide vane. It may be possible to demonstrate the principles of propeIler,drag force, lift, etc.

  • PDF

하드 디스크 드라이브용 패드 슬라이더의 트라이볼로지 특성에 관한 실험적 연구 (Experimental Analysis of Tribological Performances of Padder Slider in HDD)

  • 홍수열;좌성훈;고정석;이형재
    • Tribology and Lubricants
    • /
    • 제17권4호
    • /
    • pp.312-320
    • /
    • 2001
  • In magnetic hard disk drives, higher areal recording density requires reduction of head-disk spacing. To overcome the increase of stiction associated with reduction of head-disk spacing, a padder slider, which adds pads to slider's air bearing surface, can be one of the practical solution for sub 20 nm flying height, and even for near contact recording. This study investigated the tribological characteristics of a padder slider. A padder slider took off slowly but showed less friction force than a normal slider. The hot/dry CSS test and drag test indicated that pad wear of a padder slider was negligible. The tribological performance of disk is an important factor to be considered. In particular, less carbon overcoat layer of the disk will result in higher stiction and wear in slider/disk interface. In conclusion, a padder slider shows encouraging tribological performances for practical use in HDD.