Wind Tunnel Documentation And The Wake Of Two Non-parallel Cylinders

Wind tunnels are an indispensable part of the aircraft development work. Theyplay an important role in aviation and aerospace engineering researches and have beenwidely used in many domains. The work of this subject mainly tests the performance ofthe wind tunnel installed recently at the Institute for Turbulence-Noise-VibrationInteraction and Control, Harbin Institute of Technology, Shenzhen Graduate School,including velocity distribution, boundary layer thickness, turbulence intensity, wallvibration frequency, etc.The wind tunnel has two different test sections replaceable,0.8×1.0m and0.5×0.5m, each has a length of5.5m. At0.69m away from the contraction, dependingon the free-stream velocity, the boundary layer thickness and turbulence intensity are16~26mm and0.16%~0.42%, respectively for0.8×1.0m section and9~23mm and0.13%~0.4%, respectively for0.5×0.5m section. While wall vibration frequency was25~45Hz for all the windows, wall vibration rms amplitude (Arms) was less than0.12mm at all wind speeds except at wind speed of30m/s where Armsis maximum, about0.14~0.16mm for big wind tunnel. Wall vibration frequency was40~65Hz for topwalls and15~50Hz for the side walls, Arms was about0.3mm regardless of windspeed for small wind tunnel.Then test the wake of single cylinder and St is found to be constant in thespanwise length for L=175~850mm which proves wind tunnel is symmetric and hasgood performance. Furthermore, the wake is examined of two non-parallel (includedangle15) circular cylinders in tandem and side-by-side orientations at Re=5.65×104.There are four cases for tandem arrangement and side-by-side arrangement, see thethird part of second chapter. Strouhal number measurements are performed at differentspanwise length of the cylinders. Bistable flow regime in the first case is much longer,S/D=2.5~3.5, while that in parallel case is S/D=4.0at the same Re. For the second case,no bistable flow was observed, St escalating continuously from0.15to0.185when S/D was increased from2.0to3.0. For the3rd case, two St of0.105and0.15were identifiedat S/D=1.2to1.9. Bistable flow appears at S/D=2.2to2.9. For the forth case, biasedflow appears at S/D=1.2to2.0with St corresponding to narrow wake being muchhigher (St=0.65~0.2) compared to that (St=0.3~0.2) for parallel cylinders. There arealso two St of0.1and0.2at S/D=2.0to2.7, indicating another type of bistable flow orbiased flow.