Time evolution of the velocity field amplitude in the y direction, as measured by the kλ = 12π mode of the Fourier transform of v_y, for some of the KH instability tests described in Sect. 3.1. Each panel refers to KH simulations performed with the same Mach number, the initial conditions set-up being given in Table 1. Within each panel, the different curves are for AC-SPH runs with different simulation parameters, as specified in Table 2. The black solid line indicates the expected linear-theory growth rate.