Taylor's hypothesis convection velocities from mass conservation equation

We propose to use the continuity equation to calculate convection velocities provided by the Taylor hypothesis for flow structures crossing a measurement plane. This is carried out in Fourier space to identify a velocity associated to each frequency. High-speed PIV experimental data of an axisymmetric mixing layer is used to implement the method. We show that as expected the Taylor hypothesis fails for the lowest frequencies and predicts the convection velocity to be close to the mean velocity for the higher ones. The method is compared to one of the definitions proposed by Del Álamo and Jiménez [J. Fluid Mech. 640, 5 (2009)].