Abstract <p>A disturbance propagation in a supersonic boundary layer on a straight parabolic wing is numerically simulated. Near the leading edge, a mass flow rate disturbance is introduced into the boundary layer, resulting in the formation of a first-mode wave packet, and the first-mode amplitude increases downstream. It is shown that, upon reaching a critical amplitude, the disturbance begins evolving nonlinearly and longitudinal structures appear. The nonlinear interaction of the boundary layer modes leads to the formation of a turbulent spot. The characteristics of the resulting spot with known data for gradient-free flows are compared.</p>