Efficiency Enhancement in Active Separation Control Through Optimizing the Duty Cycle of Pulsed Jets

Abstract

This paper is concerned with active separation control in a one-sided diffuser test section using pulsed wall jets. Particular focus is laid on the two timescales defining the periodic forcing signal, which are the pulse duration and the time delay between successive pulses . The latter is addressed in a dedicated type of experiment where forcing is terminated abruptly as the flow is allowed to evolve into its natural, separated state. Lasting for a duration approximately 50 times the convective time , this transient process is largely independent of initial forcing conditions. The onset of reverse flow near the diffuser foot is shown to occur after a characteristic separation time of only for a variety of actuation signals when a mean momentum input of is exceeded. Setting the forcing signal according to these flow-inherent quantities is demonstrated to reliably prevent the recurrence of mean reverse flow throughout the actuation period. For such parameter combinations, a systematic reduction of the required mass flow is feasible by reducing the pulse duration , and thereby the duty cycle. Thus, is associated with an equal or even superior control authority compared to the typically used case in the current setup, although only one-third of the mass flow is required. The results presented in this paper therefore promote significant efficiency gains in active boundary-layer control by optimizing the duty cycle of pulsed-jet actuators.