The performance of a zero-net-mass-flux Jet and Vortex Actuator (JaVA) was numerically investigated in a two-dimensional-cross-flow flat-plate laminar boundary layer. The JaVA is an active flow control device that can be used for flow separation control and thus can delay/prevent boundary layer separation. In this study, an unsteady, incompressible flow solver has been used to study the flow fields generated by a JaVA in a water channel. Detailed quantitative information about the performance of the JaVA on a flat-plate boundary layer is obtained. JaVA-induced boundary-layer profiles are clearly 'fuller' at the wall and hence more resistant to flow separation. The 'positive' effects of the JaVA with different operating regimes on various boundary-layer flow characteristics such as displacement thickness, shape factor and the friction coefficient are presented in this study. Selecting the appropriate governing parameters in conjunction with cross-flow properties, the velocity profile can be tuned in a boundary layer to delay or prevent separation. (C) 2013 Elsevier Masson SAS. All rights reserved.