Why Momentum Input Should Not Characterize Active Flow Control

Momentum coefficient that characterized Active Flow Control (AFC) should be replaced by a power coefficient consisting of the product of mass flow and pressure coefficients. This quantity is easily measurable in contrast to the momentum coefficient that requires additional assumptions for its determination. It resembles parameters defining compressors and it facilitates quantitative rating of actuators. Additional pressure measurements enable the assessment of power losses in the air supply system that may exceed the power delivered by the actuators. The use of power consumed by AFC enables the evaluation of various actuation systems including passive devices that increase the drag throughout the entire flight while being only useful at low speed or at extreme maneuvers. There are many parameters defining AFC system, but at the end of the day its power consumption determines its value.