Attenuating the large-scale turbulent oscillations sustained by shallow cavities with a perforated lid

Abstract

Marine engineers face a challenging problem when designing recessed cavities that require perforated covers. Under certain geometric and kinematic conditions, the separated shear layers directly above the perforations support the spatial maturity of periodic large-scale structures. Intermittent spoilers attenuate the structure's maturity by interrupting communication between the shear layer and the adjacent inner cavity, but this success fails during transient flow conditions. In the far-field, the corresponding noise pulse is easily detectable. Evolutionary growth of the streamwise structures originates from small Kelvin–Helmholtz (K–H) waves within the shear layers just after separation and are sustained by a pressure feedback mechanism that occurs within the cavity itself. Herein, the resolved physics from large-eddy simulations along with the previous experimental evidence show analogous fundamental characteristics between the open and perforated covered cavities regardless of whether upstream separation is laminar or turbulent. These quantitative analogies are equally similar for lids perforated by staggered circular holes or slots that are tightly spaced in the streamwise direction. An alternative measure permits formation of the K–H waves, then successfully mitigates their streamwise growth by elongating the distance between perforations. This latter corrective measure reverses the mean resultant lid force to the preferred outboard direction.

Keywords:

• lid cavity flows
• large eddy simulation
• turbulence
• compact differencing
• oscillation modes

Acknowledgements

The author gratefully acknowledges the support of the Office of Naval Research (Dr. Ronald D. Joslin, Program Officer) Contract No. N0001408AF0002 and the In-House Independent Research Program (Mr. Richard Phillips, Coordinator) at the Naval Undersea Warfare Center Division Newport.