© Christopher Earls Brennen


``I have travelled through great beauty
To some measure of understanding
You cannot ask for more than that.''


The financial necessity of finishing my PhD combined with the all-consuming attention that was needed to complete my thesis, led to me repeating my earlier mistake of not making timely enough preparations for the next stage of my career. Fortunately, I had created a sufficiently positive impression during my six week sojourn at the Ship Division of the National Physical Laboratory that they were willing to appoint me as a Junior Research Fellow. So it was that, in the summer of 1967, Doreen and I packed up our few meagre possessions into the decrepid Hillman hatchback that had allowed us to get around Oxford in the final few months and drove down to London to take up the postdoc at the Ship Division. I recall that even those 60 miles sorely taxed that vehicle whose steering was so disfunctional that I parked the car in the garage of our apartment in London and never took it out again; indeed it was still there when we flew away to America. So began our brief residence in the suburbs of London.

Filming the "Dam Busters" at NPL.

The National Physical Laboratory is a storied government research laboratory set up in London in 1900 to promote fundamental research in the physical sciences. Among its many other achievements, radar was invented there in 1935 (and gave the allies a great advantage during the Battle of Britain in World War II). Other notable events were Alan Turing's pioneering design for the computer while he was a staff member at N.P.L. in the 1950s. As it evolved, the Laboratory was organized into a number of divisions devoted to specific subdivisions of the physical sciences. The main site and headquarters were in Teddington, some 5 miles to the southeast of Heathrow Airport. The Ship Divison which I joined had relatively new facilities constructed in Feltham just outside the southern boundary of the airport. The other divisions that I had contact with, the Aerodynamics and Mathematics Divisions, were located in Teddington as were some of the older facilities of the Ship Division. The latter included the original ship towing tank which was opened by Lord Rayleigh in 1911 and in which ship models were towed to evaluate their drag and thus improve their shape. It became famous as the facility in which the "bouncing bomb" was developed in 1942 for the destruction of the German dams (a story told in the movie "The Dam Busters" which was partly filmed at N.P.L. in the 1950s). The newer site of the Ship Division at Feltham included some impressive facilities. These included a very large towing tank that was 25ft deep, 48ft wide, 1300ft long and floated on the shallow water table of the flatlands on which it was built. A large motorized carriage ran on rails mounted on the two sides of this tank (to keep the elevation of the carriage at exactly the same height above the water level, the rails had to follow the curvature of the earth and that curvature could be observed if one sited along the rails). The ship models were attached to this carriage and thus dragged along through the water at a series of speeds. It may be interesting to note that the proximity to Heathrow Airport of the long roof over this towing tank gave rise to some alarm. The fear was that during some hazy London winter day an airliner would mistake the roof for a runway and initiate a disaster, not only an airplane wreck but also a huge wave as the water from the ruptured tank spread throughout the surrounding built-up area.

Through helping one of my senior colleagues and mentors at the Ship Division, George Gadd, with his research I had several experiences with this towing tank. The first was the result of agreeing to help George with an experiment designed to measure the drag on a ship caused by the waves it produced. For this purpose George wanted to map out the whole wave pattern behind a ship model. To do this he constructed a huge framework attached to the carriage just behind the model and just above the waves. This frame was equipped with literally hundreds of vertical pointers that, once the carriage, frame and model were up to speed, could be lowered to just touch the water surface. In this way when the carriage came to rest at the end of the towing tank, the height of the waves over the entire region behind the model could be recorded. However, during each experimental run down the length of the towing tank it took considerable youthful agility to adjust all the pointers in the available time. This is what I was able to accomplish. Other staff members would come to watch this remarkable athletic achievement of the adjustment of over 100 pointers in less than a minute as the carriage caroomed down the length of the towing tank at over 30 miles per hour. I would leap across the frame adjusting pointers like a crazy man, only inches from being "lost at sea". I am not sure whether I ever received the recognition I deserved for this effort of behalf of science but then such is life.

The other experience with the towing tank involved more fundamental scientific discovery. It had begun to become clear that the same ship model seemed to have a significantly different measured drag when tested at different times of the year and/or in different facilities around the world. Now it so happened that at that time in the late 1960s there was much interest in the surprising effect that very small quantities of various dissolved long-chain molecules could have on the drag on an object in water. George Gadd was conducting a number of small scale flow experiments to investigate this effect using very dilute solutions of wallpaper paste and other chemicals. In a Eureka moment George realized that the algae that inevitably bloomed in the towing tank at various times during the year might be secreting organic molecules that had the same effect on the drag of the ship models. Therefore we devised a method to measure the algae content of the towing tank and were able to show that they were indeed the culprit behind that scatter in the drag measurements.

The other remarkable facility at N.P.L. Feltham was one of the largest water tunnels is the world with a circular working section some 44in in diameter. A little history is needed to put this facility in perspective. The first water tunnel in the world designed for high-speed and cavitating water flows was built at Caltech in Pasadena, California, by Robert Knapp in the 1930s. Knapp designed this tunnel using the same basic plan that had been developed for wind tunnels except, of course, the whole structure needed to be much stronger to support the much larger weight of water. However, when it was first run under conditions at which an object placed in the working section would cavitate (low pressure and high speed), a serious design flaw immediately became evident. Air came out of solution into the cavitation bubbles and, when the bubbles were convected downstream into regions of higher pressure, the vapor in the bubbles would condense but the air would remain for much longer because of the slow rate at which it would go back into solution. This rate was so slow that the air bubbles would complete the circuit of the water tunnel before being completely dissolved which resulted in the flow into the working section quickly becoming a bubbly mess that eventually eliminated any visual observations of the flow. This was a disaster that could only be fixed by major facility modifications. A crew of workmen were employed to dig a 65ft deep, 8ft diameter hole in the ground under the water tunnel and the return passage was then deflected into this steel-lined hole where it went down and up twice before returning to the original water tunnel loop. This meant that the water spent much longer at high pressure during its circuit of the facility and the air bubbles were almost completely dissolved before arriving back to the working section. This added feature needed in a high-speed water tunnel as opposed to a wind tunnel became known as a resorber and was incorporated in all subsequent water tunnel designs.

So, the design of the large 44in water tunnel at Feltham also incorporated a resorber, in this case just a very deep return leg buried some 180ft below the ground level where the working section was located. This tunnel had been completed only a year or two prior to my arrival. It was intended to complement a much smaller water tunnel that had been moved to Feltham from the Teddington site. Both were intended primarily for testing propellers for Britain's ship building industry. The problem with the large tunnel was that the cost of manufacturing the large bronze propeller models for that tunnel was prohibitive. Consequently when I arrived only the initial demonstation propeller had been manufactured and no additional propeller models were anticipated. Thus the large tunnel lay idle. Taking advantage of this situation with George's complicity, I received permission to use the tunnel for my own research purposes. Specifically, at very modest expense, I was able to construct the objects I wished to test in the tunnel. With some ingenuity I was also able to adapt existing instrumentation in the lab for my own purposes. Finally I solicited some time from the laboratory photographer who took some marvellous photographs for me. Thus I was able to devise the opportunity to do a series of very productive research investigations in the tunnel time alloted to me and those experiments, when supplemented by theoretical studies conducted later, formed the basis of a number of publications in the prestigious Journal of Fluid Mechanics. These papers greatly helped my subsequent career. In addition, it was during the middle of these investigations that I was visited by Professor Ted Wu from the California Institute of Technology, a story that belongs to the next chapter.

Fully developed cavities behind an ogive (left) and a disc (right).
Photographs taken in the Large Cavitation Tunnel at NPL, Feltham.

* * *

When Doreen, Dana and I first arrived in London, we lived in temporary accommodations in Teddington. Searching for more permanent rental accommodations was depressing because of the high rent and also difficult because Doreen was very pregnant with our second child. However, with the help of one of my other Ship Division colleagues, John English, we finally found an affordable and comfortable apartment that was part of a big house in Shepperton, an attractive suburb on the banks of the Thames about five miles south of Feltham. From there I caught the bus to Ship Divison each day for the following year and a half. The big house and the surrounding acres had been subdivided into a pleasant little development called Thamesfield Mews. The river Thames was just a few yards away as were some old pubs including "The Ship" in which we spend many happy hours. Life in Shepperton was pleasant if somewhat limited by our lack of a functional vehicle and our lack of money. Fortunately we made friends with a very nice Australian couple who occupied one of the other apartments in our complex. Delma and Demitrios Brunello were very good to us and frequently ferried us to important and neccessary appointments in their little Fiat. In this way Doreen got to her obstetric appointments at the Middlesex General Hospital, many miles away in Chelsea. However, when our second daughter, Kathy, decided to arrive, it was in the middle of the night and quite urgent so an ambulance had to be summoned; I well remember with trepidation the ambulance disappearing into the night as I had to stay home to look after Dana. In this way our second daughter, Kathy, came into the world within the sound of Bow Bells but far from any family other than her mother. She was delivered by a nurse and we were never quite sure whether that moment occurred before or after midnight which left us permanently uncertain of her real birthday (as opposed to the certain date on her birth certificate). She was a very easy and sunny child, much loved by all our friends in Thamesfield Mews. Almost every day Doreen would load Kathy and Dana into the second-hand baby carriage that we had been given and would push them about a mile, across a bridge over the Thames and into the shopping center in Walton-on-Thames where she would do our shopping, laundry, and other errands. She would make this trip even when it was freezing. Though we made the best of our life in Shepperton, I felt angry that we were not paid enough to allow reasonable living comfort. I was ready to grab any chance to improve our existence.

The Mews, Thamesfield Court, Shepperton. Dana & Kathy in Shepperton.

Last updated 10/1/01.
Christopher E. Brennen