Boundary Layer Separation Control With Fluidic Oscillators

Abstract

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to “repair” the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and is therefore more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% rms of the average operating at nondimensional blowing frequencies (F+) in the range of 0.6<F+<6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared with optimal steady blowing. Particle image velocimetry velocity and vorticity measurements have been performed, which show no large-scale unsteadiness in the controlled boundary layer flow.

The time-resolved natural flow field of a fluidic oscillator

“…In recent years, these devices have gained renewed interest as flow control actuators. Numerous studies have demonstrated their potential for separation control (e.g., Seele et al 2009;Cerretelli and Kirtley 2009;Phillips and Wygnanski 2013;Woszidlo et al 2014), combustion control (e.g., Guyot et al 2009), and noise control (e.g., Raman and Raghu 2004). Although fluidic oscillators have been successfully employed for flow control, the information available on their fundamental internal and external dynamics remains limited.…”

Parameters Governing Separation Control with Sweeping Jet Actuators

“…Although discovered more than fifty years ago at the Harry Diamond Research Laboratories, these devices have mostly been operated with liquids as a working fluid [34,35] (e.g., windshield washers, sprinklers, shower heads, Jacuzzis, etc.). Only in recent years has this concept been applied in conjunction with active flow control (e.g., separation [36,37] , noise [38,39] , and a) b)…”

“…Several active and passive concepts to provide the oscillatory character of the emitted jet have been proposed, including selfinduced feedback [43] and external control [42,[44][45][46][47] designs. Early actuators for flow control used a splitter in the outlet nozzle [36,40,55] , which forced the jet to exit through discrete outlets ( Figure 1a) instead of having a continuous sweeping range ( Figure 1b). …”

“…In recent years, significant aerodynamic improvements were achieved with the type of actuators shown in Figure 1b by controlling flow separation over the flap of several two-dimensional (NACA 0015 [2,53,54] , NACA 0021 [56] , V-22 airfoil [37] , diffuser model [36] , DU96 airfoil [55] , and ADVINT airfoil [58][59][60] ) and three-dimensional models (finite wing and 1/10 th scale, powered V-22 model [37] , and a -wing configuration [57] ).…”

Pneumatic sensors based on colliding curved wall jets

“…generation of microbubbles [9]) or capability of controlling fluid flows past bodies (e.g. flow separation and transition into turbulence on aeroplane wings [10] or turbine blades [11]). No-moving-part oscillation generators collaborating with pneumatic sensors became also recently popular in no-moving-part fluidic pumps [12,13] handling very dangerous liquids (e.g.…”