Aeroacoustical study of the TGV pantograph recess

The general focus of this aerodynamic noise research, induced by turbulent incompressible flow, is to improve our knowledge of acoustic production mechanisms in the TGV pantograph recess in order to be able to reduce the radiated noise. This work is performed under contract with SNCF as a part of the German-French Cooperation DEUFRAKO K2, and is supported by French Ministries for Transport and Research. Previous studies on TGV noise source locations (DEUFRAKO K) have identified the pantograph recess as one of the important aerodynamic noise sources, for speeds higher than 300 km/h, due to flow separation. The pantograph recess is a very complex rectangular cavity, located both on the power car and the first coach roofs of the TGV, and has not been studied before due to the complex shapes. Its aeroacoustic features are investigated experimentally in a low-subsonic wind tunnel, on a realistic 1/7th scale mock-up both with and without pantographs. Flow velocities, estimated with hot-wire anemometry, and parietal visualizations show the flow to reattach on the recess bottom wall and to separate again at the downstream face. Wall pressure fluctuations and "acoustic" measurements using 1/4 and 1/2 in microphones respectively are also measured to qualify the flow: no aerodynamic or acoustic oscillations are observed. The study indicates that the pantograph recess has a different behaviour compared to the usual cavity grazing flows. (C) 2000 Academic Press.