Large Eddy Simulation of Flow Over a Flat-Window Cylindrical Turret with Passive Flow Control

This work presents multiple high-order implicit large eddy simulations (ILES) of flow over a cylindrical turret with a flat window oriented at three angles (90, 100, and 120 degrees). For the 100 degree case, an additional computation was performed with a row of five pins inserted upstream of the turret to passively control flow separation. The ILES computations were obtained using a well-validated high-order Navier-Stokes flow solver employing a 6-order compact spatial discretization in conjunction with a 8-order lowpass spatial filter. Simulations were executed on a massively parallel computing platform using a high-order overset grid methodology on meshes with approximately 55 million nodes. Results from this simulation were compared to data from an experimental study performed at the University of Notre Dame. Overall, solutions compared favorably to experimental time mean and fluctuating velocity profiles as well as the overall flow structure at all three angles. Pins inserted upstream of the flat aperture generate spanwise structures in the time-mean flow that energize the boundary layer and reduce the size of the separation bubble at the leading edge of the flat window. Reducing the size of this separation region led to an overall decrease in the turbulent kinetic energy over the remainder of the window. Additionally, flow sheds from the pins at a discrete frequency similar to that observed in another LES simulation for a finite-height cylinder. This study demonstrates the ability of ILES to successfully reproduce complex flow physics over a flat-window turret with various levels of separation. Additionally, it provided valuable insight into the flow physics of pins and how they control flow separation which is critical in reducing aero-optical aberrations.

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