Active flow control on the 25°Ahmed body using a new unsteady jet

•A new unsteady jet using semi-sinusoid signal is applied to form a flow control method.•The new unsteady jet overcomes the drawbacks of the traditional synthetic jet and increases the efficiency of the drag reduction.•The influence of the control frequency on control efficiency is taken into considerations.•The mechanism of the drag reduction through deviating and stabilizing the shear layers by the unsteady jet is found and interpreted.