Time evolution of the convective velocity u_conv in two series of 2.5D simulations with radiative diffusion: the simulations of convective penetration with mass entrainment from the radiative envelope (‘core + envelope’) and similar simulations without the radiative envelope (‘core only’). All of the simulations have the boost factor b = 10⁴. The time axis shows simulation time as a fraction of the thermal timescale τ_th(b). Each data point corresponds to a time average over 0.005τ_th. The right vertical axis shows the corresponding Mach numbers computed using the reference sound speed c_ref = 7.96 × 10⁷ cm s⁻¹. Grid resolution is given in terms of the dimensionless radial grid spacing Δr such that a grid with N_r = 1024 in the ‘core + envelope’ case has Δr = 1.