Curve squeal in sharp curves: effect of multiple wheel/rail contact points

Curve squeal is one of the most annoying noise problems related to the operation of trains, trams, and metros in urban environments. It typically occurs in sharp curves, which are very common in urban areas, and is disturbing for both passengers and people in proximity to the line. Curve squeal is characterized by a loud tonal noise that usually occurs close to the natural frequencies of the wheel. It is generally attributed to the self-excited vibration of the wheel, as a result of the contact phenomena taking place at the wheel/rail interface during curve negotiation. An experimental campaign has been carried out on a sharp tramway curve to measure noise emission due to curve squeal. This revealed that different squealing frequencies and noise levels were generated by two different tramcars of the same type. The presence of a second contact point between the flange back of the leading inner wheel of one of the tramcars and the groove rail was found to be the reason behind these dissimilar experimental results. Thus, the aim of this work is to assess the role of the flange back contact condition on the excitation of squeal noise. A curve squeal prediction model is formulated in the frequency domain to include the presence of multiple wheel/rail contact patches. Numerical simulations reveal that this contact condition can significantly alter the squealing frequencies involved, similarly to what is observed in the pass by sound pressure measurements. The contact on the flange back is found to promote mode-coupling mechanisms in the proximity of close pairs of wheel vibration modes. These results suggest that the potential presence of multiple contacts between wheel and rail should be considered to obtain reliable curve squeal predictions.