Fluid Dynamics Lab

Overview of PhD Research

I undertook my PhD in the Fluid Dynamics Laboratory where I investigated the flushing of embayments.

I have also written an article about my research called A Current Problem for Plus magazine (an online maths magazine aimed at 14-18 year-olds).

Flushing of Embayments

I am interested in how the sea moves around in coastal bays. As the sea flows past a bay it can force the water in the bay to move round in a circle. This "recirculation" of the water can cause things to become trapped in the bay for long periods of time. This may be extremely important when trying to decide where to build your sewage pipe, and how long you need to make it! One of the interesting things about this problem is that the flow past the bay changes direction with the tide. This makes the outcome more difficult to predict. I am investigating flows in bays in three ways: making measurements of the flow in a real bay, using a laboratory tank to set up a scale model, and modelling the flow using a computer code.


With the help of staff from the Brixham Environmental Laboratory, velocity measurements were taken in Blackpool Sands (Devon) in July 2002 and 2003. These measurements showed tidal driven circulation in the bay. More details of the 2002 fieldwork are given here.

Laboratory Experiments

I did some experiments in a flume tank in the lab. This tank allows me to change the direction of the water flow - like a real tide.

I released food colouring into the water which shows how the flow can trap pollutants near to the coastline. I also put small bits of paper onto the water surface to show me how the water moves. Finally I used a technique to tell me where the water surface deforms. A dip in the surface shows an eddy (try stirring your cup of tea and you will see this).

lab experiment

Dips in the water surface show where the eddies are.


I wrote a computer code which models the flow around a bay. This picture is showing "vorticity" which is a measure of how much the water is rotating.

Dipole generated by reversing flow.

In this picture the tide has just changed direction. The eddy which developed in the bay is swept out and joins with a new eddy being generated at the corner.


My research was sponsored by the NERC (Natural Environment Research Council) and the Brixham Environmental Laboratory which is part of AstraZeneca.

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Last updated: 5th April 2005
F.C. Elwell

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