LES-based characterization of a suction and oscillatory blowing fluidic actuator

Recently, a novel fluidic actuator using steady suction and oscillatory blowing was developed for active control of high-speed turbulent flows (Arwatz et al. 2008). The suction and oscillatory blowing (SaOB) actuator converts compressed air input into pulsed bistable oscillatory blowing at the actuator outlets. The mechanism for generating bi-stable oscillatory blowing is based upon the Coandă effect and use of a feedback tube. Also, actuator geometry was found to be crucial in producing robust control outputs (Arwatz et al. 2008). The SaOB actuator has been developed and tested for several canonical flow configurations as well as for external aerodynamic control problems (Wilson et al. 2013; Schatzman et al. 2014; Shtendel & Seifert 2014; Lubinsky & Seifert 2014, 2015; Schatzman et al. 2015). These recent studies showed that the addition of steady suction in close proximity to the pulsed blowing is important in increasing the efficacy and efficiency of this flow control approach. The SaOB actuator is particularly interesting in two respects. First, generating oscillatory blowing does not involve any moving parts. Instead, a feedback tube is used to stably sustain the oscillation without additional external inputs. The length of the feedback tube is a key parameter determining oscillation frequency. Second, a suction system is employed to further increase total flow rates for a given inlet pressure. These two respects are based upon physical principles of fluid dynamics and are essential to efficiently and effectively producing oscillatory blowing. The basic mechanisms of the SaOB actuator and some of the important flow features were examined experimentally (Arwatz et al. 2008; Wassermann et al. 2013). However, detailed characteristics of unsteady flows within the actuator are not completely understood. Geometric complexity, compressibility, and the strongly turbulent nature of the internal flows make diagnostics and characterization difficult. An objective of this study is to predict the internal turbulent flows of the SaOB actuator and gain more understanding of the flow physics. A challenging part for prediction is to accurately resolve turbulent fluctuations as well as geometry of engineering complexity, both of which are important to correctly characterize the actuator. Large-eddy simulation (LES) based upon a novel unstructured-grid technique is applied to compute and characterize the internal flows within the SaOB actuator. The simulation tools are well validated for turbulent flows with multi-physics and tested to scale very well up to O(10) cores. In addition to prediction, this study targets the development of reducedorder modeling techniques for fluidic oscillators, a process which is useful if not essential for integrated simulation of aerodynamic flow control system where actuator arrays are used on complex geometries with possible great variability of important scales.