Abstract: A dielectric barrier discharge ( DBD) plasma actuator was placed near the flow separation point at the end of the 25° Ahmed automobile model． Through wind tunnel test，the effects of different excitation voltages on the aerodynamic drag coefficient of the model when the excitation frequency was 9 kHz，the maximum drag reduction rate when the wind speed was 10 ～ 25 m /s and the optimum excitation voltage corresponding to this time were stu- died． The flow field map measured by PIV and the pressure value of the tail bevel measured by PSI pressure scan- ning system shows that when DBD is switched on，the flow velocity around the exciter and near the wall surface of the inclined surface is increased，the tail flow separation area is decreased，and the pressure at the pressure mea- surement point on the tail bevel is increased． According to the measurement results of the balance sensor，the maxi- mum drag reduction rate ( 7． 28% ) can be obtained when the experimental wind speed is 15 m /s and the corre- sponding optimal excitation voltage is18． 5 kV． The DBD exciter has an effect of drag reduction by reducing the pressure drag of the model． With the increase of the excitation voltage，the aerodynamic drag coefficient presents a tendency that decreases first and then keeps steady． Therefore，there was an optimum excitation． With the increas- ing wind speed，a higher excitation voltage is required to achieve a better drag reduction effect．

Key words: automotive engineering, aerodynamics, active drag reduction, dielectric barrier discharge, wind tun- nel test