On the Use of Power-Based Parameters for Blowing Active Flow Control Systems

Boundary-layer control (BLC) of turbulent flows aims to compensate for mean frictional losses on a frozen configuration, while active flow control (AFC) seeks to alter the mean flow by exploiting instabilities. Since AFC performance is judged by the energy required to achieve a prescribed goal, it must be introduced into the aircraft design process at the early conceptual stages. For blowing applications, deciding whether to draw from engine bleed or install smaller compressors adjacent to the actuators is an important system-level consideration that requires the separation of the loss in the air supply system from the input that triggers and amplifies the exterior flow instabilities. The current paper exposes the inadequacy of the momentum coefficient that has primarily been used in the past to assess AFC efficacy and recommends two easily measurable fluid power coefficients to replace it. These enable direct comparisons of actuator efficiencies and system efficiencies, creating a link between the physics of flow control and system integration. This link is demonstrated first on a two-dimensional configuration that uses steady blowing, which is later extended to the use of sweeping jet actuators on a modular swept wing of finite aspect ratio.