Helical Flow in Sinuous Submarine Channels

Jasim Imran and M. Ashraful Islam
Civil and Environmental Engineering, University of South Carolina, Columbia, SC

Helical motion in a river is produced by the local imbalance between two competing forces - centrifugal force caused by channel curvature and pressure difference force due to the water surface tilt. Similar imbalance of forces exist in meandering submarine channels. Secondary circulation or helical flow is, therefore, expected to occur in meandering submarine channels as well. However, the nature of helical flow in submarine channels has remained largely unknown due to the lack of well designed experimental study. Recently, we have carried out experimental measurement of the flow field in single and multiple bend submarine channel models with rectangular as well as trapezoidal cross sections placed at the bottom of a large laboratory tank. We considered both confined and unconfined flow and the current was driven by excess density provided by either dissolved salt or silt in suspension. Instantaneous velocity data were collected using 3-D micro ADV. The velocity data show that when the flow remains confined within the channel, two cells of secondary circulation form. The bottom circulation cell forms between the channel bed and the position of the maximum streamwise velocity and has the sense of rotation similar to that observed in fluvial channels. The upper circulation cell has the opposite sense of rotation. If, however, spilling occurs at a bend apex thus creating a lateral convection towards the outer overbank area, the upper circulation cell tends to disappear.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas