• Title/Summary/Keyword: induced drag

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Flow analysis of 3-Dimensional Power-Augmented Ram Wing in Ground Effect (3차원 PAR WIG (Powder Augmented Ram Wing in Ground Effect) 의 수치연구)

  • 곽승현
    • Journal of Ocean Engineering and Technology
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    • v.11 no.1
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    • pp.55-64
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    • 1997
  • A wing operating in close proximity to the ground exhibits a reduction in induced drag, which increase the lift/drag ratio. The poert-augmented ram (RAR) phenomenon involves directiing the efflux from forward mounted propulsion ststem under the wings, with the efflux nearly stagnated under the wings. In the present paper, 3 dimentional PAR was numerically studied by solving the Navier-Stokes equations. Pressure distribution and velocity vectors are calculated around the wing surface and the ground. Through the numerical simulation, Cp values and lift/drag ratio are carefully reviewed by changing the height/chord; 0.05, 0.1, 0.3 and 0.8. The shape of model is NACA 0012 with a span/chord ratio of 3.0. According to the numerical results, the relationship between lift/drag and height/chord is fairly reasonable.

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Influences on the Droplet Dynamics and Evaporation due to Closely Spaced Droplet Interaction (입자간의 상호작용으로 인한 입자의 운동 및 증발에 미치는 영향)

  • 이효진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.9
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    • pp.1770-1779
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    • 1992
  • The present study investigated dynamically and thermally interacting droplets in a closely spaced tandem array. By measuring the velocity and diameter of the droplet traveling along the isothermal vertical plate drag coefficients and vaporization rates of droplets at certain location were obtained. During the experiment initial droplet spacings were less than 5, and initial droplet diameters were ranged between 280 .mu.m and 700 .mu.m Drag coefficients on closely spaced droplets were placed far below the standard drag coefficient, for which it was caused turbulence induced from aforelocating droplets also narrow spaces among droplets restricted heat transfer to droplets from hot gas flow. In addition evaporated vapor entrapted between droplets was major factor in delaying droplet vaporization. With the experimental results the drag coefficient was correlated with respect to Reynolds number for the droplet as follows : $c_{D}$ =2.4/Red.$^{0.37}$

Reynolds number effects on flow over twisted offshore structure with drag reduction and vortex suppression (레이놀즈 수가 와류 감쇠 및 저항 저감형 나선형 해양 구조물 주위 유동에 미치는 영향)

  • Jung, Jae-Hwan;Yoon, Hyun-Sik
    • Journal of Ocean Engineering and Technology
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    • v.29 no.1
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    • pp.9-15
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    • 2015
  • We investigated the Reynolds number effects on the flow over a twisted offshore structure in the range of 3×103≤ Re ≤ 1 × 104. To analyze the effect of the twisted surface treatment, a large eddy simulation (LES) with a dynamic subgrid model was employed. A simulation of the cylindrical structure was also carried out to compare the results with those of the twisted offshore structure. As Re increased, the mean drag and lift coefficient of the twisted offshore structure increased with the same tendency as those of the cylindrical structure. However, the increases in the mean drag and lift coefficient of the twisted offshore structure were much smaller than those of the cylindrical structure. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted offshore structure occurred compared to those of the cylindrical cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted offshore structure achieved a significant reduction of over 96% in VIV compared with that of the cylindrical structure, regardless of increasing Re. As a result, we concluded that the twisted offshore structure effectively controlled the flow structures with reductions in the drag and VIV compared with the cylindrical structure, irrespective of increasing Re.

Numerical investigation of on-demand fluidic winglet aerodynamic performance and turbulent characterization of a low aspect ratio wing

  • A. Mondal;S. Chatterjee;A. McDonald Tariang;L. Prince Raj;K. Debnath
    • Advances in aircraft and spacecraft science
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    • v.10 no.2
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    • pp.107-125
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    • 2023
  • Drag reduction is significant research in aircraft design due to its effect on the cost of operation and carbon footprint reduction. Aircraft currently use conventional solid winglets to reduce the induced drag, adding extra structural weight. Fluidic on-demand winglets can effectively reduce drag for low-speed flight regimes without adding any extra weight. These utilize the spanwise airflow from the wingtips using hydraulic actuators to create jets that negate tip vortices. This study develops a computational model to investigate fluidic on-demand winglets. The well-validated computational model is applied to investigate the effect of injection velocity and angle on the aerodynamic coefficients of a rectangular wing. Further, the turbulence parameters such as turbulent kinetic energy (TKE) and turbulent dissipation rate are studied in detail at various velocity injections and at an angle of 30°. The results show that the increase in injection velocity shifted the vortex core away from the wing tip and the increase in injection angle shifted the vortex core in the vertical direction. Further, it was found that a 30° injection is efficient among all injection velocities and highly efficient at a velocity ratio of 3. This technology can be adopted in any aircraft, effectively working at various angles of attack. The culmination of this study is that the implementation of fluidic winglets leads to a significant reduction in drag at low speeds for low aspect ratio wings.

A Study on the Characteristics of Lift and Drag Fluctuation Power Spectral Density in a Heat Exchanger Tube Array (전열관군에서 양력과 항력 변동의 PSD 특성 연구)

  • Ha, Ji-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.2
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    • pp.712-718
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    • 2016
  • A heat exchanger tube array in a heat recovery steam generator is exposed to hot exhaust gas flow that can cause flow induced vibrations, which could damage the heat exchanger tube array. The characteristics of flow induced vibration in the tube array need to be established for the structural safe operation of a heat exchanger. Several studies of the flow induced vibrations of typical heat exchangers have been conducted and the nondimensional PSD (Power Spectral Density) function with the Strouhal number, fD/U, had been derived using an experimental method. The present study examined the results of the previous experimental research on the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array was determined from the present CFD analysis. The present CFD analysis introduced circular cylinder tube array and calculated using unsteady laminar flow for the tube array. The characteristics of lift and drag fluctuations over the cylinder tube array was investigated. The derived nondimensional lift and drag PSD was compared with the results of the previous experimental research and the characteristics of lift and drag PSD for a circular cylinder tube array was established from the present CFD study.

Study on Aerodynamic Characteristics of a Launch Vehicle with Mach Number, Angle of Attack and Nozzle Effect at Initial Stage (발사초기 단계에서 발사체의 마하수, 받음각 및 노즐 효과에 따른 공력특성 연구)

  • Jeong, Taegeon;Kim, Sungcho;Choi, Jongwook
    • Journal of the Korean Society of Visualization
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    • v.17 no.1
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    • pp.34-42
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    • 2019
  • Aerodynamic characteristics for a launch vehicle are numerically analyzed with various conditions. The local drag coefficients are high at the nose of the launch vehicle in subsonic region and on the main body in supersonic region because of the induced drag and the wave drag, respectively. The drag coefficients show the similar trend with the angle of attack except zero degree. However, the more the angle of attack increases, the more dependent on the Mach number the lift coefficient is. The body rotation for the flight stability destroys the vortex pair formed above the body opposite to the flight direction, so the flow fields are more or less complicated. The drag coefficient of the launch vehicle at sea level is about three times larger than that at altitude 7.2 km. And the thrust jet at the nozzle causes to reduce the drag coefficient compared with the jetless transonic flight.

Numerical Analysis of Drag-Reducing Turbulent Flow by Polymer Injection with Reynolds Stress Model (레이놀즈응력모델을 이용한 난류의 고분자물질 첨가 저항감소현상에 대한 수치해석)

  • Ko, Kang-Hoon;Kim, Kwang-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.1
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    • pp.1-8
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    • 2000
  • A modified low-Reynolds-number Reynolds stress model is developed for the calculation of drag-reducing turbulent flows induced by polymer injection. The results without polymer injection are compared with the results of direct numerical simulation to ensure the validity of the basic model. In case of drag reduction, profiles of mean velocity and Reynolds stress components, in two-dimensional channel flow, obtained with a proper value of viscosity ratio are presented and discussed. Computed mean velocity profile is in very good agreement with experimental data. And, the qualitative behavior of Reynolds stress components with the viscosity ratio is also reasonable.

Control of Flow around an Airfoil Using Piezo-ceramic Actuators (압전세라믹 액추에이터를 이용한 익형 후류 제어)

  • Choi, Jin;Jeon, Woo-Pyung;Choi, Hae-Cheon
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.491-496
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    • 2000
  • The objective of this study is to increase lift and decrease drag of an airfoil by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and the chord length is 30cm. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number is $3{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Drag and lift are measured using an in-house 2-dimensional load cell and the surface pressures are also measured. Lift is increased by 10%, drag is reduced by 50%, and the efficiency is increased to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

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A Study of Aerodynamic Characteristics of a Car's Side-view Mirror using CFD (CFD를 이용한 자동차 사이드 미러의 공력특성 연구)

  • Min, Sun-sik;Han, Jun-Kyu;Kwon, Ki Hyun;Choi, Eun-Dong;Kim, Moon-Sang
    • Journal of Aerospace System Engineering
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    • v.2 no.2
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    • pp.46-50
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    • 2008
  • Aerodynamic characteristics, such as drag and lift, play an important role in automobile design under certain speed conditions. Such characteristics are essential to design an automobile since they are directly related to automobile's performance such as passenger safety and fuel consumption. There is a huge demand for the automobile to have safe performance at high speed. Reduction in drag is also important and it could lead to the solution of air flow induced noise and dust problems. The objective of this research is to find out the aerodynamic differences between conventional side mirror and a modified one using CFD. Although drag generated around a side mirror is only about 7% of the total drag when a car runs, it is very closely related to driver's field of vision and noise generation. CFD simulation of the flowfield around a car side-view mirror was performed using a commercial code; Gambit and FLUENT.

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A NUMERICAL STUDY ON THE EFFECT OF VEHICLE-TO-VEHICLE DISTANCE ON THE AERODYNAMIC CHARACTERISTICS OF A MOVING VEHICLE (차간 거리가 주행차량의 공력특성에 미치는 영향에 관한 수치해석 연구)

  • Kim, D.G.;Kim, C.H.
    • Journal of computational fluids engineering
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    • v.19 no.2
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    • pp.66-71
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    • 2014
  • Aerodynamic design of a vehicle has very important meaning on the fuel economy, dynamic stability and the noise & vibration of a moving vehicle. In this study, the correlation of aerodynamic effect between two model vehicles moving inline on a road was studied with the basic SAE model vehicle. Drag and lift are two main physical forces acting on the vehicle and both of them directly effect on the fuel economy and driving stability of the vehicle. For the research, the distance between two vehicles is varied from 5m to 30m at the fixed vehicle speed, 100km/h and the side-wind was assumed to be zero. The main issue for this numerical research is on the understanding of the interaction forces; lift and drag between two vehicles formed inline. From the study, it was found that as the distance between two vehicles is closer, the drag force acting on both the front and rear vehicle decreases and the lift force has same trend for both vehicle. As the distance(D) is 5m, the drag of the front vehicle reduced 7.4% but 28.5% for the rear-side vehicle. As the distance is 30m, the drag of the rear vehicle is still reduced to 22% compared to the single driving.