During the second part of today’s seminar, MPhil student James Sear presented the results of his new experiments on turbulent plumes in a cross-flow. During the last few months, James has been studying what happens when a steady flux of contaminants are released into a river: the contaminants are transported by the current, while being mixed and diluted in the turbulent ambient.
James’ work builds on previous research on the dispersal of deep-sea mining sediments in the ocean, which was carried out at the Institute in the past. However, James’ experiments are the first to introduce turbulence to the background ambient, and so they give us a more complete description of the plume flow.
Exposure to short-lived, high-concentration pulses of contaminants might be just as harmful to aquatic life as the continued exposure to lower-concentration, long-lasting pollution. For this reason, James has investigated both the time-averaged and the instantaneous properties of the plumes he created in the laboratory.
His experiments have shown that the additional background turbulence may cause the plume to meander through the river: because of this, higher concentrations of contaminants might periodically be recorded in a larger portion of the river area. The effect of the background turbulence is larger when the buoyancy flux associated with the plume is small, or the mean velocity of the river flow is large.