• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.2
• /
• pp.118-124
• /
• 2012

The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.6
• /
• pp.893-901
• /
• 2002

Effect of boundary layer thickness on the flow characteristics around a rectangular prism has been investigated by using a PIV(Particle Image Velocimetry) technique. Three different boundary layers(thick, medium and thin)were generated in the Atmospheric Boundary Layer Wind Tunnel at Pusan National University. The thick boundary layer having 670 mm thickness was generated by using spires and roughness elements. The medium thickness of boundary layer($\delta$=270 mm) was the natural turbulent boundary layer at the test section floor with fairly long developing length(18 m). The thin boundary layer($\delta$=36.5 mm) was generated on the smooth panel elevated 70cm from the wind tunnel floor. The Reynolds number based on the free stream velocity(3 ㎧) and the height of the model(40 mm) was 7.9$\times$10$^3$. The mean velocity vector fields and turbulent kinetic energy distributions were measured and compared. The effect of boundary layer thickness was clearly observed not only in the length of separation bubble but also in the location of reattachment point. The thinner the boundary layer thickness, the higher the turbulent kinetic energy Peak around the model roofbecame. It is strongly recommended that the height ratio between the model and the approaching boundary layer thickness should be encountered as a major parameter.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.12
• /
• pp.1165-1172
• /
• 2009

The laminar boundary layer along a streamwise corner formed by two flat plates intersecting at right angle is measured by using Particle Image Velocimetry(PIV) technique. The free stream velocity ranges from 2.96m/s to 3.0m/s. The angle of incidence of the corner is set to 1.2 degree providing slightly favourable pressure gradient to ensure a laminar flow in the corner region. A round shape leading edge is used and the length of the model is about 1000mm. In the bisector plane, the measurement data show separation type velocity profiles having an inflection point which is a typical characteristic of laminar corner boundary layers. As the distance away from the bisector plane increases, velocity profiles are found to change into the Blasius profile. The change completes around half length of the boundary layer thickness in the bisector plane away from the bisector plane along the plate. In the bisector plane, the growth characteristic of the boundary layer thickness and the approximate similarity of velocity profiles are confirmed from the measurement data.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.2
• /
• pp.181-189
• /
• 1985

The effect of the Coriolis force on the 2-D turbulent boundary layer which is developed in the side wall of the rotating rectangular flow channel was investigated. In this study, we measured mean velocities, turbulent velocity components(axial as well as lateral ones) and Reynolds stresses of the turbulent boundary layer. For high Reynolds number flows, the turbulent boundary layer without pressure gradient is hardly affected by the rotation. For low Reynolds number flows, however, the shearing stress at suction side decreases. Consequently, the velocity near the wall become slower so that the thickness of the viscous sublayer expands. On the other hand, the velocity near the wall at pressure side turns out increased.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.4
• /
• pp.453-460
• /
• 2005

Experiments were conducted to investigate the effect of the surface roughness on the flat plate turbulent boundary layer. The square rods were installed at the leading edge to make surface roughness. The particle image velocimetry was used to measure the mean velocities and velocity fluctuation component. All measurements were made over a range of w/k=1. 2 5 and $Re_x=80.000{\sim}360,000$. Friction velocity was measured by using Clauser plot method. The level of turbulent intensities on roughness surface appears more strongly than that of turbulent intensities on flat plate. A correlation of boundary layer thickness in term of $Re_x$ and w/k are presented.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.661-667
• /
• 2001

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7. According to a wake-passing through the cascade, two velocity deficits appear near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit is caused by a periodic wake and the second one appears after some delayed time. The second velocity deficit may be interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreases the duration time of separation appearance and the lesser loss of aerofoil is resulted.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.740-745
• /
• 2000

Effects of porous fences on the wind erosion of sand particles from a triangular pile were investigated experimentally. The porous fence and sand pile were installed in a simulated atmospheric boundary layer. The mean velocity and turbulent intensity profiles measured at the sand pile location were well fitted to the atmospheric boundary layer over the open terrain. Particle motion was visualized to see the motion of windblown sand particles qualitatively. In addition, the threshold velocity were measured using a light sensitive video camera with varying the fence porosity ${\varepsilon}$. As a result, various types of particle motion were observed according to the fence porosity. The porous wind fence having porosity ${\varepsilon}=30%$ was revealed to have the maximum threshold velocity, indicating good shelter effect for abating windblown dust particles.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.2
• /
• pp.219-226
• /
• 2002

This paper is concerned with the effects of periodically approaching upstream wakes on cascade-flow and loss. The reduced frequency of the periodic wakes was varied in the narrow range from 0.5 to 0.7 Corresponding to a wake-passing through the cascade, two velocity deficits appeared near the boundary layer contour in the downstream from about 60% chord-length. The first velocity deficit was caused by a periodic wake and the second one appeared after some delayed time. The second velocity deficit was interpreted as the results of reattachment of flow-separation. The higher reduced frequency decreased the duration time of separation appearance and the lesser losses of blade were resulted.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.30 no.2
• /
• pp.109-115
• /
• 1994

This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into near the buffer layer of turbulent boundary layer on flat plate. The concentrations of micro bubble distribution in the boundary was calculater by eddy viscosity equations in the governing equations. When near region of the buffer layer of turbulent boundary layer is filled with micro-bulle of air and viscous of the region is kept low, the velocity profile in the near region should be changed substantially. Then the Reynolds stress in the region becomes less, which guide to lower velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

• Journal of applied mathematics & informatics
• /
• v.25 no.1_2
• /
• pp.67-83
• /
• 2007

The characteristics of steady two-dimensional laminar boundary layer flow of a viscous and incompressible fluid past a moving wedge with suction or injection are theoretically investigated. The transformed boundary layer equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method. The effects of Falkner-Skan power-law parameter (m), suction/injection parameter ($f_0$) and the ratio of free stream velocity to boundary velocity parameter (${\lambda}$) are discussed in detail. The numerical results for velocity distribution and skin friction coefficient are given for several values of these parameters. Comparisons with the existing results obtained by other researchers under certain conditions are made. The critical values of $f_0$, m and ${\lambda}$ are obtained numerically and their significance on the skin friction and velocity profiles is discussed. The numerical evidence would seem to indicate the onset of reverse flow as it has been found by Riley and Weidman in 1989 for the Falkner-Skan equation for flow past an impermeable stretching boundary.