Wind tunnel of a mixed circuit: closed (at closed throttles) when the air flowing out from the tunnel tube through the outlet returns to the tunnel tube through the return channel above the beginning part of working section; open (at open throttles) when the air inflowing into the inflow comes from outside the building by an air scoop located above the inflow on the building roof and is exhausted also outside the building by an air launcher located behind the fan. The open air circuit in the wind tunnel is applied mainly in the case of visualisation investigations.
These elements are designed to take over the stream either returning through the return channel or taken above the building roof by external air scoop and direct it respectively, making the stream homogeneous and of a very low turbulence before the inflow to the working section.
The basic geometric dimensions of the working section are: width – 2.20 m; height – from 1.40 m at the beginning and 1.60 m at the end of the working section; length – 10 m. Formation of the mean wind velocity profile and atmospheric turbulence takes place in the first part of the working section at the length of 6 m by use of respective turbulization networks, barriers, spires and blocks of respective geometry and an automatic controlled height. Four characteristic segments each of 2.5 m long can be distinguished in the working section. The side walls of the front segment are full (with windows) 2.20 m apart. The other segments have slotted side walls (with horizontal controlled slots aiming at diminution of the so called blockage effect) 2.20 m apart and full side walls with windows 3.40 m apart. In the third and fourth segments of the working section there are two round rotational tables 2 m in diameter. The first one is designed mainly for examination of flow around phenomena and their visualization and for examination of snow precipitation and snow redistribution phenomena. The other rotational table is designed mainly for aerodynamic and aeroelastic tests of buildings and structures. In the upper part of the working section there is an equipment for fixing all kinds of measurement probes and their controlled movements at the whole working section in directions x, y, z. The roof of the working section may change its position in the direction up and down; this permits to control the gradient of static pressure in the working section. In the back part of the working section there are two aerodynamic balances for measurements of aerodynamic forces and moments: one of six-components for vertical models, the other of three-components for horizontal models. The working section is ended with a cascade of horizontal airfoil profiles that reduces the influence of vortices generated by the fan on an air flow in the area of the rotational table.
The diffuser with the net protecting the fan
The diffuser which is behind the working section is of a rectangular shape at the beginning part and of a circular shape at the end part (cross-section of the fan) and its length is equal to 5 m.
The axial fan, single-stage of efficiency 0.8-0.9, the outer diameter 2.72 m and the velocity of the end of the fan blade up to 100 m/s, is located on the suction side of the wind tunnel.
System of supply and rotation control
The engine of the alternate current, shorted, driving the fan with a power of 200 kW, of nominal revolutions 750 rpm and supply voltage 220V, controlled by inverter.