Computational Study of Near-Wall Flow Control Flap with Pulsed Inlet Velocity

The dynamic layering method was used to modulate a 3D moving and deforming Computational Fluid Dynamics (CFD) mesh surrounding a wall-mounted flow control geometry that oscillated sinusoidally. The dynamic mesh contained only hexahedral elements and could absorb large boundary displacement while maintaining mesh quality. This proof-of-concept model was the first step toward creating a CFD simulation of small, hinged features in shark skin called "denticles". Embedded primarily in the viscous sublayer, bristled denticles inhibit boundary layer separation, which enables the shark to maneuver with greater agility. However, sliding mesh interfaces might lead to unreliable results near the flow controller surface. Therefore, the researchers conducted several simulations that showed how the model behaves with various time step sizes, momentum spatial discretization schemes, and gradient reconstruction methods. It was found that the interfaces did not affect the drag acting on the flow controller, and the solution methods and controls did not significantly impact the results. The model was also run with a pulsed inlet fluid velocity at numerous frequencies and phase shifts with the purpose of emulating what happens when a bristling denticle experiences bursts of turbulence from the buffer layer. It was shown that the drag was greatest when the pulsed inlet velocity frequency and flow controller oscillation frequency were equivalent and in phase, and it was minimized when the phase was shifted 180 degrees.