Driven Cavities

Just like blowing over a soda bottle, air (or water) flowing across an open cavity will induce unsteady pressures and create noise.  But open cavities are essential in many engineering design problems.  Examples include car sunroofs, aircraft bomb bays, recessed sensors and weapon bays, and submarine ballast tank vents.  Designers are therefore tasked with providing cavities that minimize drag, noise, and vibration.

Proper design of the cavity’s volume, shape, and edge treatments can eliminate many of these problems.  But the flows involved are inherently viscous, vortical, and turbulent, and only RANS can resolve all the physics that impact unsteadiness.  The two movies on this page show a series of three cavities lined up in the principal flow direction.  The top movie shows contours of velocity magnitude resulting from the shapes as originally received by AFT for analysis.  The bottom movie shows flow after AFT completed the redesign process.  Unsteadiness (and therefore noise) is virtually eliminated, and drag is reduced about 12%.  Changes to the geometry were limited to only those exterior regions between cavities.