Evolution of pantograph noise directivity at increasing speeds

In February-March 2018 a set of tests were undertaken to confirm the acoustic performance of high speed rolling stock fleets. These tests were carried out on behalf of HS2 on the ADIF high speed network near the village of Las Inviernas (Guadalajara, Spain). The test site was chosen so that three conditions would be fulfilled. First, maximum speed up to 350 km/h ought to be reachable during tests in dedicated mode. Second, a complete catenary arch ought to be present in the site so that it could be used as a support for installation of a number of microphones. Third, a flat and almost levelled terrain with almost semi-anechoic characteristics should be found in the surroundings of the track. Among other tests, the evolution of pantograph noise emission with respect to speed was studied, for the same unit of a dedicated Siemens Velaro E running at different speeds from 250 km/h to 350 km/h. This paper shows the evolution observed in the directivity emission pattern as observed by the microphones installed in the catenary portal. A theoretical discussion about the physical aero-acoustic phenomena justifying the observed evolution is presented together with the experimental results.