At sound levels encountered in musical wind instruments the oscillating flow at the tube termination can produce periodic local non-linear flow effects. PIV is used to measure the complex flow at the termination of a model wind instrument for a range of sound levels and geometries. POD analysis is then applied to the velocity maps, and the ability of the technique to separate the acoustic flow from the induced non-linear flow is assessed. The percentage of kinetic energy in the upper POD modes is used to indicate the strength of the non-linear flow effects and this is found to be dependent on the Strouhal number of the flow. Acoustic streaming is also analysed from the PIV data. The ratio of streaming velocity to acoustic particle velocity is found to depend on the Strouhal number.