Circulation Control using Discrete Jets*

Traditional circulation control (CC) for lift enhancement utilizes a nominally '2-D' control jet / sheet issued tangentially over the curved trailing edge of an airfoil.  It utilizes the Coanda effect to entrain and turn the outer flow and alter the stagnation point and stagnation streamline, thereby augmenting the airfoil's circulation and lift.  The present flow control approach introduces the segmented '3-D' array of flow control jets for the first time in place of the '2-D' control with the main objective of reducing the flow control input requirement for a given increment in lift.  A scaling relative to the active flow control area between the 2-D and 3-D flow control approaches indicates the 3-D flow control higher effectiveness in the lift increment relative to the active flow control area.  It is the tradeoff between the increased 3-D jets effectiveness and reduced total active area compared to the 2-D jet that determines which approach effects the higher total lift increments.  Depending on this balance, it is shown that the 3-D flow control may require tens of precents less flow control input than its 2-D counterpart.  Lastly, the proposed scaling for the 3-D flow control effectiveness indicates the guiding parameters for the flow control elements sizing and distribution.