Active control of flow structure and unsteady aerodynamic force of box girder with leading-edge suction and trailing-edge jet

Abstract

An experimental study was conducted to investigate the control effectiveness and underlying mechanism of the leading-edge suction and trailing-edge jet (LSTJ) for a box girder at a Reynolds number of 2.08×104. Four circular holes were machined in the leading edge and the trailing edge of the box girder to induce steady LSTJ flow. The strength of the LSTJ is described by a dimensionless suction/jet momentum coefficient. Pressure taps around the surface associated were used with a digital sensor array system to acquire the pressure distribution of the test model. The aerodynamic forces, which macroscopically represent the control abilities of the LSTJ, were calculated based on the surface pressure distribution. The pressure measurements indicate that the fluctuating pressure on the surface near the trailing edge was attenuated and the root-mean-square value of the lift, drag, and moment forces reduced with LSTJ control. In addition to the surface pressure measurements, particle image velocimetry (PIV) was used to obtain the flow fields of the box girder model with and without LSTJ control. Both the pressure measurement and PIV results show that a certain value of the suction/jet momentum coefficient can ensure optimum control effectiveness of the LSTJ. Moreover, the LSTJ was found to push the unsteady flow structure further downstream in the model wake. A data-processing method of dynamic mode decomposition was used to illustrate the LSTJ mechanism. The energy and Strouhal number of the main mode of the LSTJ controlled case were found to differ from the uncontrolled case. The topological structure of the main mode extracted from the flow field also showed a significant variation. Linear stability analysis of the wake flow field indicates that the control method of LSTJ changes the region of unstable flow notably. Moreover, the control effectiveness of the LSTJ at various wind angles of attack was confirmed in the present study.