A Study on Turbulent Transition of Unsteady Boundary Layer Induced by Weak-Compression Wave

Abstract

A high-speed train enters the tunnel and loud noise occurs at the tunnel exit. This is due to compression wave generated by a train entering into the tunnel. It is important for developing further speed train to clarify the mechanism of the compression wave propagation, which has been strongly affected by the boundary layer characteristics. The purpose of the present study is to clarify the turbulent transition characteristics of unsteady boundary layer, which is generated by sudden started flow induced by weak-compression wave (amount of pressure change: Δp ≈ 2 kPa). The boundary layer is transited by tripping wires, and the velocity distributions are measured by a hot wire anemometer. The results show that the boundary layer transition is confirmed by spectrum analysis of the velocity fluctuation. The transition process of the boundary layer is observed by changing the position of tripping wires, and the turbulent boundary layer is maintained down to about 310 of Reynolds number based on the momentum thickness in the case of inputting the large disturbance into the boundary layer.