Low Speed Wind Tunnel

In general, the wind tunnels are the devices which provide an airstream flowing under controlled conditions for external/internal flow simulations in the laboratory. The most fundamental experiments undertaken in the wind tunnel are the force/heat transfer measurement and flow visualization on aerodynamic models. The flows generated in the test section of the tunnel may be laminar/turbulent, steady/unsteady etc. The other features may be study of boundary layer separation, vortex flow generation etc. The low speed wind tunnels limit their speed to 50-60 m/s and based on the need, the tunnel may be designed. Depending on the discharge of the air flow to atmosphere or recirculation of air, it is classified as open or closed circuit wind tunnels (Fig. 8.1.1).

Fig. 8.1.1: Schematic representation of wind tunnel: (a) open circuit wind tunnel;

(b) closed circuit wind tunnel.

Remarks for open/closed circuit wind tunnel

• •  In a closed circuit wind tunnel, the high quality flow can be assured in the test section and power requirement is less as compared to open circuit wind tunnel. However, it is not suitable for smoke flow visualization and incurs high capital/construction cost.

•  An open circuit wind tunnel is more adaptive for flow visualization experiments because due to its direct connection with the atmosphere. In order to assure the flow quality in the test section, one needs to install special devices such as flow straightener explicitly aligning the flow axially. Of course, it requires more power as compared to closed circuit wind tunnel.