Separating the contributions from air-pumping and tyre vibrations by speed dependency analysis of tyre/road noise

Traditionally tyre/road noise has been divided into low-mid frequency noise caused by tyre vibrations and high frequency noise caused by various air flow related mechanisms, "air-pumping". It has also been assumed that these two processes grow in importance with different (vehicle) speed exponents. The purpose with this work is to investigate how to extract the different noise sources by a speed exponent analysis. Such analysis tool would e.g. indicate under which circumstances it is necessary to include air flow related sources in a tyre/road noise prediction model. The results show that it is possible to extract components of tyre/road noise that grow with the speed to the power of two and four. Expecting these contributions to be connected to tyre vibrations and air flow related source mechanisms respectively, it is found that the latter are present at surprisingly low frequencies. In addition, modelled results, only taking into account noise created by tyre vibrations, also show speed exponents larger than two. It is concluded that tyre vibrations can generate noise with a range of speed exponents making it futile to separate the two main tyre/road noise source mechanisms by a speed exponent analysis