Subsonic wind tunnel design

In this thesis, wind tunnel design and requirements are investigated in further and CFD simulations are carried out for different designs. EDS Atmospheric Boundary Layer Wind Tunnel is designed and constructed by EDS Engineers and it is currently being used in order to measure wind forces on buildings. The purpose of this thesis is adapt EDS Wind Tunnel into a wind tunnel with a higher velocity profile in the test section, using the fans and the current contraction design. Three different test section dimensions are considered and investigated with this thesis. First test section(TS-1) dimensions are decided as 1x2x2 meters. A second contraction is added right after the EDS Wind Tunnel's contraction. Second contraction for TS-1 design is generated using basic splines with a CAD program. First simulations for TS-1 consisted of mesh independency study, turbulence model comparison and contraction shape comparison and desicion. Mesh independency study was carried out with a coarse mesh of 3.9 million cell count and a fine mesh of 5.3 million cell count and the results showed that 3.9 mesh was enough to get stable CFD results. Turbulence model comparison was carried out between the most appropriate two models; k-ε and k-ω models and results showed that two models gave very similar results and it is decided to use k-ε for further simulations because it is more appropriate for swirling flows. Three other contraction shapes (3rd order, 5th order and 7th order polynomial) investigations are added to simple spline design and all four contraction shapes are compared with eachother depending on the CFD simulation results. Selection criteria was the test section inlet flow quality; uniformity and angularity of the flow. Results showed that 7th order polynomial shaped contraction supplied the best flow quality but the flow quality was still not enough for a wind tunnel test section so it is decided to insert a second screen in the settling chamber. CFD simulations are carried out for the three test section designs TS-1(1x2x2 m), TS-2(0.75x2x2 m) and TS-3(1.5x2x2 m) designs without the diffuser section. Results showed that TS-2 design gave the best test section inlet flow quality results. TS-1 design test section inlet flow quality results were in the allowable range. TS-3 gave the worst results because of the low contraction ratio and were not appropriate for a wind tunnel. Full CFD simulations are also carried out for the three designs in order to compare pressure losses in the components of the each tunnel. Results showed that TS-3 design had the lowest pressure losses and TS-2 had the highest pressure losses. The narrower the test section dimensions got, the higher the pressure losses became. Good flow quality results at the test section inlet are achieved for TS-1 and TS-2 designs. It is also decided that blowing type wind tunnels are highly turbulent and settling chamber and contractions might not be enough to reduce turbulence levels.