Quasi-steady and unsteady actuation by surface non-thermal plasma discharge for control of a turbulent round air jet

Abstract

The dielectric barrier discharge (DBD) is a nonmechanical device able to generate electrohydrodynamic forces close to a dielectric wall. The generated “electric wind” is actually used to control airflow over various bluff bodies. In this study, a DBD actuator is investigated for the control of a round turbulent air jet. The separation along the bevel of a small angle (12°) axisymmetric diffuser is studied using LDV measurements for a 20 m s− 1 airjet velocity. The results demonstrate that a DBD actuator is suitable to separate a turbulent airflow naturally attached. Under actuation, a jet deflection of 13° is observed and the coherent structures are energized. Quasi-steady and unsteady actuations are also compared for excitation frequencies up to 400 Hz and the analysis of the turbulent spectra demonstrates that a vortex shedding could be forced at the excitation frequency (up to 160 Hz). The investigation of different duty-cycle regimes allows us to define a threshold value inducing similar flow modifications than those obtain with quasi-steady actuation but with a significant power consumption reduction of 20%. The knowledge of the separation dynamics is essential for future reactive control devices. The last part of this study is dedicated to this point. The response times of the forced separation and the natural reattachment are evaluated. The results indicate that separation is achieved in 34.5 ms and that the natural reattachment time is about 45 ms. In conclusion, this study highlights the dynamics of the separation using a single DBD actuator, and demonstrates that a jet deflection and a mixing enhancement can be performed.