Effect of upstream flow deformation using plasma actuators on crossflow transition induced by unsteady vortical free-stream disturbances

• Upstream flow deformation (UFD) has been shown to be an effective technique to delay roughness induced laminar-turbulent transition at low free-stream turbulence level in three-dimensional boundary-layer flows. Beneficial steady crossflow vortex (CFV) control modes are excited and the resulting nonlinear CFVs induce a useful mean-flow distortion. We recently showed by direct numerical simulations that plasma actuators, modeled by localized steady volume forcing, can be employed to excite the UFD control modes. In the current work we investigate the same actuator set-ups to control transition caused by traveling CFVs that are excited by single unsteady vortical free-stream disturbances (FSDs) impinging on the boundary layer. FSDs of various wavenumbers and frequencies are imposed either upstream or downstream, or at the position of the actuators to also scrutinize if the volume forcing has a direct unfavorable effect on the receptivity to the FSDs that adds to the stabilization by the UFD. For all investigated cases we show that a significant transition delay is achieved.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Nyckelord

Atmospheric thermodynamics

Boundary layer flow

Boundary layers

Deformation

Fluid dynamics

Laminar boundary layer

Vortex flow

Control modes

Freestream turbulence

Laminar turbulent transitions

Plasma actuator

Steady crossflow

Three-dimensional boundary layer flows

Transition delays

Upstream flow

Actuators

Publikations- och innehållstyp

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