• 제목/요약/키워드: Reynolds number

검색결과 2,134건 처리시간 0.074초

저 레이놀즈 수에서 이동하는 생체모사익의 추력 생성 및 추진효율 (THRUST GENERATION AND PROPULSIVE EFFICIENCY OF A BIOMIMETIC FOIL MOVING IN A LOW REYNOLDS NUMBER FLOW)

  • 최종혁;맹주성;한철희
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2009년 추계학술대회논문집
    • /
    • pp.159-163
    • /
    • 2009
  • In this paper, the fluid dynamic forces and performances of a moving airfoil in the low Reynolds number flow is addressed. In order to calculate the necessary propulsive force for the moving airfoil in a low Reynolds number flow, a lattice-Boltzmann method is used. The critical Reynolds and Strouhal numbers for the thrust generation are investigated for the four propulsion types. It was found that the Normal P&D type produces the largest thrust with highest efficiency among the investigated types. The leading edge of the airfoil has an effect of deciding the force production types, whereas the trailing edge of the airfoil plays an important role in augmenting or reducing the instability produced by the leading edge oscillation. It is believed that present results can be used to decide the optimal propulsion devices for the given Reynolds number flow.

  • PDF

The Effect of Non-condensable Gas on Direct Contact Condensation of Steam/Air Mixture

  • Lee, Hanchoon;Kim, Moohwan;Park, Suki
    • Nuclear Engineering and Technology
    • /
    • 제33권6호
    • /
    • pp.585-595
    • /
    • 2001
  • A series of experiments have been carried out to investigate the effects of non-condensable gas on the direct contact film condensation of vapor mixture under an adiabatic wall condition. The average heat transfer coefficient of the direct contact condensation was obtained at the atmospheric pressure with four main parameters ; air-mass fraction, mixture velocity, film Reynolds number, and the degree of water film subcooling having an influence on the condensation heat transfer coefficient. With the analysis of 88 experiments, a correlation of the average Nusselt number for direct contact film condensation of steam/air mixture at an adiabatic vertical wall was proposed as functions of film Reynolds number, mixture Reynolds number, air mass fraction, and Jacob number. The average heat transfer coefficient for steam/air mixture condensation decreased significantly while air mass fraction increased. The average heat transfer coefficients also decreased as the Jacob number increased, and were scarcely affected by the film Reynolds number below a mixture Reynolds number of about 245,000.

  • PDF

Effect of Reynolds number on compressible convex-corner flows

  • Chung, Kung-Ming;Chang, Po-Hsiung;Chang, Keh-Chin
    • Advances in aircraft and spacecraft science
    • /
    • 제1권4호
    • /
    • pp.443-454
    • /
    • 2014
  • An experimental study was conducted to investigate the effect of Reynolds number on compressible convex-corner flows, which correspond to an upper surface of a deflected flap of an aircraft wing. The flow is naturally developed along a flat plate with two different lengths, resulting in different incoming boundary layer thicknesses or Reynolds numbers. It is found that boundary layer Reynolds number, ranging from $8.04{\times}10^4$ to $1.63{\times}10^5$, has a minor influence on flow expansion and compression near the corner apex in the transonic flow regime, but not for the subsonic expansion flow. For shock-induced separated flow, higher peak pressure fluctuations are observed at smaller Reynolds number, corresponding to the excursion phenomena and the shorter region of shock-induced boundary layer separation. An explicit correlation of separation length with deflection angle is also presented.

POD 기법을 이용한 저 레이놀즈 수 충돌 제트의 비정상 거동 연구 (Investigation on the Unsteadiness of a Low Reynolds Number Confined Impinging Jet using POD Analysis)

  • 안남현;이인원
    • 한국가시화정보학회지
    • /
    • 제6권1호
    • /
    • pp.34-40
    • /
    • 2008
  • The flow characteristics in a confined slot jet impinging on a flat plate were investigated in low Reynolds number regime (Re$\leq$1,000) by using time-resolved particle image velocimetry technique. The jet Reynolds number was varied from 404 to 1026, where it is presumed that the transient regime exists. It is found that the vortical structures in the shear layer are developed with increasing Reynolds number and that the jet remains steady at the Reynolds number of 404. Vortical structures and their temporal evolution are verified and the results were compared with previous numerical studies.

저레이놀즈수 k-$\varepsilon$ 모델을 사용한 2차원 자연대류 난류현상에 대한 수치적 연구 (A Numerical Study on the Two-Dimensional Turbulent Natural Convection Using a Low-Reynolds Number k-$\varepsilon$ Model)

  • 강덕홍;김우승;이관수
    • 대한기계학회논문집
    • /
    • 제19권3호
    • /
    • pp.741-750
    • /
    • 1995
  • The turbulent buoyancy-driven flow in 2-dimensional enclosed cavities heated from the vertical side is numerically calculated for both cases of a Rayleigh number of 5*10$^{10}$ for air and 2.5*10$^{10}$ for water. Three different turbulence models are considered : standard k-.epsilon. model of Ozoe and low-Reynolds-number model of Lam and Bremhorst, and another low-Reynolds-number model of Davidson. The results indicate that the use of low-Reynolds number models is recommended for the indoor airflow computation, and the results from Davidson model are reasonably close to the reported experimental data. A sensitivity study shows that the amounts of wall-heat transfer and the velocity profiles with the Lam and Bremhorst model largely depend on the choice of the wall function for .epsilon..

정사각단면을 갖는 $180^{\circ}$ 곡관내의 2차 모멘트 난류모형에 관한 연구 (Study on the Second Moment Turbulence Model in a Square Sectioned $180^{\circ}$ Bend)

  • 김명호;염성현;최영돈
    • 대한기계학회논문집
    • /
    • 제18권5호
    • /
    • pp.1203-1217
    • /
    • 1994
  • In the present study, in order to analyze a turbulent flow in a square sectiond 180.deg. bend, Kim's low Reynolds number second moment turbulence closure is adopted. In this model, turbulence model constants in the wall region are modified as functions of turbulent Reynolds number by use of near wall turbulent universal properties based on Laufer's experimental results of Reynolds stress distriburions. Algebraic stress model and Reynolds stress equation model are used to verify the low Reynolds number second moment closure. The application of the present low Reynolds number algebraic stress model to the prediction of a square sectioned 180.deg. bend flow gives improved velocities and Reynolds stresses profiles compared with those obtained by using the van Driest mixing length model and present low Reynolds number Reynolds stress equation model.

매끈한 관내 공기유동에서 유량과 속도분포에 관한 실험적 연구 (An Experimental Study on the Flow-rate and Velocity Profile of Air Flow in the Smooth Pipe)

  • 박상언
    • 한국유체기계학회 논문집
    • /
    • 제5권4호
    • /
    • pp.54-60
    • /
    • 2002
  • Experimental study was conducted to obtain the air velocity profiles in turbulent pipe flow. The acrylic smooth pipe (${\phi}=80mm$) was used for the test section of the flow loop. It was known that the velocity profiles of turbulent flow were different with Reynolds numbers and the viscous sublayer was usually quite thin. The following conclusions were drawn from the experimental investigations. Maximum velocity of the pipe center and flow-rate are useful for the duct design on the spot. The velocity profiles of high Reynolds number was flatter than those of low Reynolds number. It was known that the exponent, n, for power-law velocity profiles was $6{\sim}9$ depending on Reynolds number ranging from $10^4$ to $10^5$ in the turbulent flow, However, in this experiment study, it was $9{\sim}14$ depending on Reynolds number ranging from 17,000 to 123,727 in the turbulent flow, and $1.7{\sim}3.5$ depending on Reynolds number ranging from 2,442 to 4,564 in the transition region.

저 Reynolds수 에 있어서의 원통주위의 흐름에 관한 연구 (A Study on the Flow around the Circular Cylinder at Low Reynolds Number)

  • 이은선;송강섭
    • 한국항해학회지
    • /
    • 제9권2호
    • /
    • pp.43-63
    • /
    • 1985
  • As a circular cylinder has a comparatively simple shape and becomes a basic problem for flows around other various shapes of bodies, the problem of two-dimensional viscous flow around the circular cylinder has been investigated, both theoretically and experimentally. But not a few problems are left unsolved. It is well known that the calculations are successfully made with the approximations of Stokes or Oseen for very low Reynolds numbers, but as Reynolds number is increased, Oseen's approximations as well as Stokes's ones become more and more remote from the exact solution of the Navier-Stokes equations. Therefore, in this paper, the authors transform the Navier-Stokes equations into the finite difference equations in the steady two-dimensional viscous flow at Reynolds number up to 45, and then solve the solution of the Navier-Stokes equations numerically. Also, the authors examine the accuracy of the solution by means of flow visualization with aluminum powder. The main results are as follows; (1) The critical Reynolds number at which twin vortices begin to form in the rear of the circular cylinder is found to be 6 in the experiment and 4 in the numerical solution. (2) As Reynolds number is increased, it is proved that the ratio of the length of the twin vortices to the diameter is grown almost linearly, both experimentally and numerically. (3) Separation angle is also increased according to reynolds number. But it is found that it would converge into 101.3 degrees, both experimentally and numerically.

  • PDF

레이놀즈 수가 낮은 영역에서 와류발생기를 적용한 핀-관 열교환기 성능평가 (Performance Evaluation of Finned Tube Heat Exchanger with Vortex Generators in a Low Reynolds Number Regime)

  • 곽경민;송길달
    • 설비공학논문집
    • /
    • 제18권2호
    • /
    • pp.151-157
    • /
    • 2006
  • The present paper reports the method for evaluation of heat-transfer performance of finned tube heat exchangers in a low Reynolds number regime (Re = $160\~800$) and also reports the data of heat transfer and pressure loss taken from a finned tube heat exchanger with/without vortex generators (VGs) installed as a heat-transfer enhancement device. The evaluation is based on the modified single blow method conducted in a specially designed low Reynolds number duct. Three different test core geometries, i.e., fin only, fin-tube without VGs and that with VGs, are studied here. The data of heat transfer and pressure loss taken from the fin only geometry agree well with the empirical correlations, thus validating the present method as used for low Reynolds number regime. The data taken from the finned tube geometries with and without VGs are presented and compared to examine the effect of VGs in the low Reynolds number regime.

고도에 따른 발사체의 레이놀즈수 영향성 연구 (The Reynolds Number Effects on the Projectile with an Altitude Change)

  • 양영록;허상범;이영민;조태환;명노신;박찬우
    • 한국군사과학기술학회지
    • /
    • 제12권5호
    • /
    • pp.683-688
    • /
    • 2009
  • A research was conducted about the Reynolds number effect on the projectile with an altitude change. The atmosphere conditions change in accordance with an altitude change. It effects the Reynolds number. To confirm how the phenomena affect the trajectory of the projectile, a computer program is designed with an altitude and a range considered. The MISSILE DATCOM which is based on the semi-empirical method was utilized to get aerodynamic coefficients. The result shows that the Reynolds number considerably changes as the altitude change. It causes to change the drag coefficient of the projectile. As the Reynolds number decreases, the skin friction drag increases significantly. It causes to decrease the maximum altitude and the range.