Computer simulation of wind interaction with street video display.

 

Purpose: Flow simulation, visualization and estimation of the main aerodynamical characteristics of a two-sided street video display under interacting with wind according to [1-2].

 

Schematic view of the display is shown in Fig. 1 as a 3D solid CAD model. 2-sided video display has a supporting frame with a form of non-symmetrical prism with sizes 8.34 x 6.6 m (surface area from each side is equal to 55 m2). The display is mounted on a vertical post with a height of 5.1 m. Total height of the setup is 12 m, weight – 10.6 t, height of gravity center is 8.4 m. The setup bottom is attached to a basement plate and fixed on the ground.

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Fig. 1 CAD-model of the display

Computer simulation based of numerical solution of 3D gas dynamics equations with account for turbulence of external wind flow has been performed. In the far field a logarithmic profile of wind velocity in atmospheric boundary layer was assumed according to standardized wind loading ([1] for the 1-st type of wind region ( Moscow, landscape type “A”). The simulation was done in a domain of parallelepiped shape 200 x 200 x 100 m (Fig. 2) on a hybrid volume mesh with 3 M cells (tetrahedral, prismatic and pyramids)

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Fig. 2 Calculation domain

A fragment of the mesh on the surface of the video display and the ground is shown in Fig. 3.

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Fig. 3 A fragment of the mesh on the surface of the display and the ground.

 

Two values of velocity at 10 m altitude were used in the simulations. The first value (19.4 m/s) corresponds to an operational wind pressure of 230 Pa [1] for logarithmic velocity profile. The second value (35.75 m/s) gives an extreme total wind load of 780 Pa for the setup [3] accounting for pulsatory component, calculated by the method [1]. Four wind directions in perpendicular plains (north-south and east-west) were simulated with a range of Re numbers of 10-20 M.

Figures 4-15 show visualization of simulation results for different wind directions.  Velocity, pressure and energy of turbulent pulsations in middle plains are shown. Arrows represent wind directions in far field with logarithmic velocity profile in the boundary layer.

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Transversal flow around the display

Wind speed 19.4 m/s at h=10 m

Wind speed 35.75 m/s at h=10 m

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Fig . 4 Flow field

 

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Fig. 5 Wind pressure

 

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Fig. 6 Energy of turbulent pulsations

 

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Fig. 7 Wind pressure on   the windward side of the display

 

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Fig. 8 Flow field

 

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Fig. 9 Wind pressure

 

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Fig. 10 Energy of turbulent pulsations

 

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Fig. 11 Wind pressure on   the windward side of the display

 

Longitudinal flow around the display

Wind speed 35.75 m/s at h=10 m

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Fig. 12 Flow field

 

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Fig. 13 Wind pressure

 

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Fig. 14 Energy of turbulent pulsations

 

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Fig. 15 Wind pressure on  the windward side of the display

 

As it is well known form the theory geometrically the display is a high-drag body with several sharp edges and flat windward side with low extension. This shape leads to detachments of the flow and formation of long recirculation zones. Such flow patterns are clearly seen on the flow fields (Fig. 4, 8, 12) and can also be proved by distributions of kinetic energy of the turbulent pulsations (Fig. 6, 10, 14).

Analysis of simulation results allowed to estimate aerodynamic friction of the display for transversal and longitudinal flow directions in the range of Re = (10-20)x106. Estimated values of Сх are 1.07-1.18 (the value of friction force is divided by wind pressure on the height of 10 m and the  surface area of the windward side of the display). For comparison, a friction coefficient of a disk located perpendicular to a flow direction is 1.1.

According to [1]  estimation of wind load for plain-shape constructions located perpendicular to the flow is based on the friction coefficient С=1.4. Therefore, when [1] used for strength estimation of similar shaped objects exposed to the wind load, extra safety factor of 10-15% is added to the real values of wind load.

 

Bibliography

 

  1. SNIP 2.01.07-85. Loading and coercion. Construction standards and rules. Moscow, 1985
  2. STO 36554501-015-2008. Standard of organization. FGUP “NITH  “Construction”, Moscow, 2008
  3. Two-sided display with the size 8.34x6.6 m Н=12 m. Metallic frames 55111. Calculation of constructions. OOO NIPI PRONSTALKONSTRUKTHIYA, Moscow, 2008.
Moscow 2009

 

Published with approbation of the customer.

Wind speed 19.4 m/s at h=10 m