Study on unsteady aerodynamic forces using a system of wind tunnels of which air streams can change speed and direction rapidly

点击翻译按钮获取中文摘要

The objectives of the present study are to develop a new wind tunnel system which can actively generate turbulent flows as well as flows of which speed and direction can change rapidly. The system consists of two wind tunnels of which fans are driven by AC servomotors controlled by computers Each wind tunnel has a square duct with 40cm x 40cm cross section and has a capacity to initiate 15 m/s speed stream only in 0.1 second. The two same wind tunnels are aligned on the floor as their air streams cross at the angle of 60 degrees. The resulting merged stream may acquire the features such as two horizontal turbulent fluctuation components, or time dependent speed and stream direction.At various combinations of two steady speeds, the two wind tunnels are driven in order to measure the steady speed and direction of the resulting merged streams. Thus, the relations between the two wind speeds and the resulting speed and direction are established. From these relations, the histories of the control voltages to generate streams of time dependent speed and direction.This facility and the control method are used to generate turbulent flows of which stream-wise fluctuation component and the lateral fluctuation component obey Karman spectra. As for the unsteady aerodynamics force measurement, a square cylinder is placed vertically in the merged streams. In streams with stepwise change of the flow speed, stronger drag forces and negative lift direction in comparison to the steady aerodynamic forces are observed. In streams with constant rate of direction change, it is observed that the aerodynamic forces at higher rate differs from the steady aerodynamic forces much more.