# A New Procedure to Design an Open Circuit Blowing Subsonic Moist-Air Wind Tunnel
## 1 Introduction  
In the recent past, several engineers have evinced special interest in different engineering applications like wind tunnel tests for civil constructions and their effects on different structures [1, 2]. Further, most of these wind tunnels were of the open-loop type [3]. However, on analysing the climatic environments, different outdoor regions were observed to present different weather conditions. Thus, interestingly, it was noted that not only did the outdoor air velocity influence wind energy conversion, but new parameters, including the relative humidity of moist air, also needed to be considered in the design and operation of such applications. Different relative humidity conditions of outdoor air in humid regions like that in Calicia (Spain) are listed in Figures 1-4[4]. Such relative humidity clearly influences the flow of moist air, particularly affecting the density and enthalpy of moist air, as shown in Figure 5. Similarly, different applications were designed and employed in the case of dry air. Dry air is used in wind turbines, cars, planes and nearly all devices involving moist-air aerodynamics. Europe is recognised as the world leader in wind energy, and many new regions will experience a definite increase in wind power installation once 100 MW wind generating capacity is achieved [5, 6]. To analyse the behaviour of different wind turbines, wind tunnels and computational fluid dynamic (CFD) simulations need to be applied. Wind tunnels have commonly been described as equipment designed to obtain air-flow conditions tosimulate similar ambiences for comparative study [7]. In this context, several wind tunnels in the past were evaluated and developed, but none of them presented the moist air control system. Moist air needs to be assessed in conditions similar to real conditions in outdoor environments. Generally, wind turbines are commonly associated with horizontal-axis wind turbines (HAWT). However, several new concepts need to be developed and understood when wind farms are designed in the future. Vertical-axis wind turbines (VAWT) are clearly more advantageous when compared with horizontal-axis wind turbines, which are omnidirectional, meaning they can work under different wind directions, require lower maintenance, and begin working under low wind speeds of 3 m/s. Just last year, a new application of wind concentrators enhanced the performance coefficient of the vertical-axis wind turbines. Figure 1: Relative humidity of outdoor air in Galicia (Spain). Figure 2: Outdoor air temperature in Galicia (Spain). From the beginning, for a VAWT with a typical Savonius rotor model, a convergent nozzle was used instead of the flat plate suggested by [PERSON] in 1977 [8]. What is more, increasing the power yield in relation to the rotor-swept concentrators is proposed [9], producing acceleration in the flow velocity by employing a diffuser duct and a funnel. In particular, the Savonius rotor is an example of a solution previously investigated [10; 11]. Other researchers developed experiments to improve the performance of the Savonius wind rotor by curtain arrangement [12], leading to a power coefficient increase of 38.5%. Furthermore, the advantages of VAWTs' blades and their attachments are that they have a lower cost, are more rugged in operation, and since most VAWT working parts that may require maintenance are placed at ground level, they will be easily accessible according to [13; 14]. Finally, to implement VAWTs' wind energy conversion during low wind velocity, it is necessary to consider the conditions behind and in front of the converter [15]. Figure 4: Outdoor air enthalpy in Galicia (Spain). Figure 3: Outdoor air velocity in Galicia (Spain). Based on these previous works [16], a vertical axis wind turbine concentrator design and test were set up considering one more parameter, the moist air density, as a fundamental way to increase wind turbine power conversion, showing that the wind concentrator was tested under different moist air densities and an input air velocity around 3 m/s.