**3.6. Power plant**

The main aim of the power plant is to maintain the flow running inside the wind tunnel at a constant speed, compensating for all the losses and dissipation. The parameters that specify it are the pressure increment, *Δp*, the volumetric flow, *Q*, and the power, *P*. Once the test chamber cross-section surface, *STC*, and the desired operating speed, *V*, are fixed, and the total pressure loss coefficient, *ζ*, has been calculated, all those parameters can be calculated using:

$$
\Delta p = \frac{1}{2} \rho \cdot V \,^2 \cdot \zeta$$

$$
Q = V \cdot S\_{TC}$$

$$
P = \Delta p \cdot \frac{Q}{\eta} \,^{\prime}$$

an optimum design of these elements, at least in the case of corner 1 and 2, has a significant

W**ent**

W**exit**

H**ent**

H**exit**

**Corner vanes**

**Vanes flap**

**Flow direction**

In order to allow a preliminary estimation of the pressure loss in the corners we will follow the method presented in Diagram 6.33 from Idel´Cik (1969) mentioned above. In this approach, we take an average number of vanes, *n*= 1,4\**S*/*t1*, *S* being the diagonal dimension of the corner, where *t1* is the chord of the vane. The pressure loss coefficient is given by the expression:

*ζM* depends on *r*/*Went*, and its values are 0,20 and 0,17 for *r*/*Went* equal to 0,20 and 0,25, respective‐ ly.Asaresult,thecorrespondingvaluesof*ζ*are0,226and0,198respectively,alwayswithrespect to the dynamic pressure at the entrance. This proves the validity of the recommendations given

The main aim of the power plant is to maintain the flow running inside the wind tunnel at a constant speed, compensating for all the losses and dissipation. The parameters that specify it

before with regard to the value of the curvature radius and the length of diffusor 1.

impact on the wind tunnel performance.

**Figure 7.** Scheme of a wind tunnel corner, including vanes, flaps and nomenclature.

**Corner radius**

16 Wind Tunnel Designs and Their Diverse Engineering Applications

*Went* .

*<sup>ζ</sup>* <sup>=</sup>*ζ<sup>M</sup>* <sup>+</sup> 0,02 <sup>+</sup> 0,031\* *<sup>r</sup>*

**3.6. Power plant**

where *ρ* is the operating air density and *η* the fan efficiency, accounting for both aerodynamic and electric motor efficiencies.

In order to reduce the cost of this part by roughly one order of magnitude, we propose to use a multi-ventilator matrix, as presented in Figure 8, instead of a more standard single ventilator power plant configuration. The arrangement of this matrix will be discussed later.

**Figure 8.** Layout of a multi-fan power plant.

According to our experience, for a closed circuit wind tunnel eventually including settling chamber screens or/and a honeycomb, the total pressure loss coefficient is in the range of 0,16 to 0,24. Consequently, in the case of 1,0 m2 test section area and 80 m/s maximum operating speed, assuming an average value of *ζ* to be in the range mentioned above, and for a typical value of *η* equal to 0,65, the data specifying the power plant are:

*Δp*= 785 Pa, Q= 80 m3 /s, P= 100 kW.

In this case we could use a 2,0m diameter fan specially designed for this purpose or 4 com‐ mercial fans of 1,0 m diameter, producing the same pressure increment, but with a volumetric flow of 20 m3 /s each. The latter option would reduce the total cost because the fans are a standard product.
