KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBSTACLE IN A STEADY, UNIFORM WIND

(a) Flow round a section of a tall rectangular building in a steady,uniform wind. (b) Vortices on the roof of a rectangular building.

a)

b)

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

• Region B’BCDD’- Separated flow forming the wake• Inside the wake the wind flow is very turbulent (turbulence intensity up to 40%)• BB’ and DD’- shear layers (the greatest level of fluctuating component)• Corner vorticies on the roof are responsible for the high peak suction near the edges of buildings (important for ventilation system)

OBSTACLE IN A STEADY, UNIFORM WIND

Flow structure in the wake behind the plate

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBSTACLE IN A STEADY, UNIFORM WIND

Visualization of the flow behind the rectangular obstacle

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBSTACLE IN A STEADY, UNIFORM WIND

Drag coefficient for an obstacle of rectangular cross-section

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBSTACLE IN A STEADY, UNIFORM WIND

wind directionSharp corners Rounded corners r/h=0.25

2.0 1.2

1.55 1.5

1.5 0.6

2.0 1.6

1.2 1.1

2.0 1.3

Drag coefficients for objects with sharp and rounded corners

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBSTACLE IN A STEADY, UNIFORM WIND

Influence of the rounded corners

OBJECT IN TURBULENT INCIDENT FLOW

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

Two main effects of the inlet turbulence:• The separated flow can re-attach at D’. The second separation occurs at C, so the boundaries of the wake are B’BCC’• Shear layers BB’ and CC’ are thickened.

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

OBJECT IN TURBULENT INCIDENT FLOW

Influence of turbulence untensity on drag coefficient

EFFECT OF SHEAR IN INCIDENT WIND

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

The effects of shear in the inclined wind on the flow round a building. (a) Stream lines. (b) Vortex lines.

Upstream of an obstacle in a shear flow on the ground (boundary layer) a vortex is found which creates a down-wash on the front face of the obstacle. Explanation: Vortex lines swept in by the inclined flow are “piled” up. Swirling flow exists downwind on either side of the building.

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

EFFECT OF SHEAR IN INCIDENT WIND

Turbulent boundary layer separation in front of a building. Plan view shows trajectories at ground level.

KINEMATICAL STUDY OF THE FLOWAROUND SURFACE-MOUNTED OBSTACLES

EFFECT OF SHEAR IN INCIDENT WIND