Laboratory Experiments
Density Current
I use laboratory experiments to understand the basic physics of environmental flows. These experiments complement field work  by offering a controlled environment where repeatable observations can be made of  mixing and dispersion in stratified and rotating flows.



Coriolis forces deflect density currents
The image on the left shows an entraining density current flowing down a steep slope into a confined basin.
The image above shows how Coriolis forces deflect a density current flowing through a curved channel. Read the article at http://www.agu.org/journals/gl/gl1017/2010GL044296/


   Our rotating platforme is based on a design generously  provided by Karl Helrich of WHOI. It was built by the U of T Physics Department machine shop. using funds provided by the Canadian Foundation of Innovation and the Ontario Research Fund.  This tablThis facility will be used to make analogue models of the influence of Corilois forces on large scale flows.

The image on the right shows how Coriolis forces deflect the interface of a density current as it flows down a channel. In a) the rotation is in the Northern hemisphere sense. in b) there is no rotation so f = 0 as at the equator, and in c) the flow is deflected in the southern hemisphere sense. The images are from the article

Cossu, R., M.G. Wells. and A.K. Wahlin (2010) Influence of the Coriolis force on the velocity structure of gravity currents in straight submarine channel systems. Journal of Geophysical Research- Oceans (in press) doi:10.1029/2010JC006208
     
Coriolis influence on density and turbidity currents Rotating Table
  
The mixing of passive tracers, such as nutrients or plankton in the ocean in often controlled by large scale eddies. I have used laboratory experiments to study such "two dimensional turbulence".

Two images from laboratory experiments are shown below.  Click here to download a movie of the laboratory experiments and here to download a movie of the numerical experiments, from our recent paper.

- M.G. Wells,  H.J.H. Clercx, and  G.J.F. van Heijst (2007)  Vortices in oscillating spin-up. J. Fluid Mech. 573, 339 - 369


Dispersion of a passive tracers                               Chemical reactions in forced 2D turbulence


2d turbulence      acid base

Below is an image from our experiments of dispersion in rotating convection, that was used in our experiments on understanding the flow in the sub-glacial Lake Vostok in Antarctica.


M.G. Wells and J. S. Wettlaufer (2008). The circulation in Lake Vostok: A laboratory analogue study. Geophysical Research Letters. 35, L0350, doi:10.1029/2007GL032162
 rotating convection

Below are images of dipole formation as a model of tidal flushing of a coastal embayment. An oscillating flow goes back and forth through a narrow gap connecting two basins and slowly flushes fluid between the two basins.

 - H.J.H Clercx , G.J.F. van Heijst, D. Molenaar and M.G. Wells (2005)  No slip walls as a vorticity source in 2D bounded turbulence. Dyn. Atmos. Oceans 40, 3-21.


dipole1    dipole3 dipole4

 

Another area of research interest is the dynamics of sediment laden flows. Below are a sequence of images taken by PhD student Remo Cossu. The images how the  propagation of a turbidity current in a laboratory experiment.

Turbidity current  


Laboratory Facilities and Equipment

The new Environmental Fluid Dynamics Laboratory consists of three newly renovated rooms in room S223 of the Science wing at UTSC.

                second room    room 3
                 Room S223f                                                                                        Room S223a


We have use a LaVision PIV-LIF flow visualisation system to measure velocity gradients and  to perfrom detailed studies of the dynamics of stratified environmental flows.

PIV camera