Inconsistency

Firstly, a bit of exciting news. I got an email from the organisers of WREC a week ago saying that I was awarded the best paper in the hydropower applications section of the conference, which was fantastic news. I've now been invited to write up the paper for Renewable Energy Journal, which I'll do over the coming weeks.

Notice on WREC Website for best papers

Certificate for best paper in hydropower applications at WREC

I wish sometimes things would be a bit simpler. I've been doing a lot of testing recently, and by that I mean sitting in the lab hours on end recording torque and speed readings at different positions. Each run of the turbine I do takes about half an hour, when you allow for getting the right flow rate to produce the right head at the nozzle, then waiting for all the air to purge from the system before actually recording the data, which may only take about 10 minutes or so. However, I have managed to be fairly productive, and got all the variables extreme testing that I wanted to do done. I then went on to consistency testing and found that my results are fairly consistent, less than 5% variation which is quite good. But this has also shown a problem. During the initial testing I managed to get a maximum efficiency of about 85%, during the extremes testing this was down to 80% and now during this consistency testing I've got up to 88%. Why is this variation happening?

Well, I think I've found what it is due to, slight changes in position. With the jet a little bit too high, the efficiency drops off quickly, and with my aiming system, I've not been able to be more accurate in position than about 5mm. I've also found that all the pipe I have is slightly bowed, so when it is rotated about its clamped position it gives hits the cups in different positions. Now I know what's going on, I can at least fix the rotation of the pipe and so should be able to make this more consistent. It is quite frustrating though…

Photo of the testing as the jet hits the cup

I've decided to look at the angle the jet hits the cup at as well, an reduced angle would mean increased change in momentum at the cup giving more torque and power, but may have an adverse effect in terms of how the jet interacts with the cup, as it may cut it off earlier. Whereas, with an increased angle there will be less momentum of the water in the direction of rotation, but it may be able to enter the cup better, ensuring more of the water works towards generating the power. So, I'll have to do these experiments, a further set of 24.

A couple of third year undergraduates here had done some work on cup design and had designed what they thought would be a more efficiency cup, so I had this rapid prototyped and tested it against the standard cups. We got a good step change in efficiency. Unfortunately, however, I managed to break them, I didn't design out all the stress razors, and the cups fractured along one of the plastic layers which is really frustrating. But still, a bit positive that it provided an increase in efficiency.

Rapid prototyped cups

Comparison with bought in cups

I've been busy outside uni as well, being me. I was in Paris at the beginning of the month for my friend Olly's 'this-isn't-a stag-party-it's-more-of-a-pre-wedding-bash'. There are three of us best men, but as we're all fairly quiet it wasn't a raucous bash. In fact Olly organised it himself - and we went out to a restaurant to eat from their tasting menu - 5 courses with 5 different wines. The food was amazing, pricey too. Then I spent a week being backstage at the Redgrave for Sweet Charity. It was fantastic fun, I do enjoy doing things that are completely different from my day job, and this certainly was. However, it did mean I spent the week being totally knackered! The day after it all finished, Hannah did the Race for Life [race for life] in Bath and so I stood around in the rain for a couple of hours watching people walk and run around 5kms. I think they managed to raise a lot of money, so that was brilliant.

Eating the tasting menu at a good (but pricey) restaurant in Paris (L-R me, Olly - the groom, Olly's brother Andrew)

I'm off to Nepal now for a week, my Nepali sister is getting married so I'm off to be at that. I actually have a trip planned for the middle of July too, that time is for a month, but I had bought the tickets before I knew about the wedding, and I have to be back for the beginning of July for Olly's wedding. All go still!

SAM

Back to work…

After the excitement of being in Sweden, the last couple of weeks have been fairly boring. Work has been mainly consisted of testing, I've been doing a more accurate test regime, looking at the extremes of all my variables to see which are most important and which may affect the efficiency of the turbine most. To do this, I've had to modify the rig slightly, so I can more accurately measure and move angles and positions. I've a series of 12 tests to do now, which will map out the combination of variables that is most important. This should be finished in the next week hopefully…

I've also been getting further frustrated by the analytical modelling. I still seem to unable to model it using the different physical effects that are quantifiable. I've tried another method over the last couple of weeks, using the cup as the stationary coordinate system and sweeping a stream of water particles in and out, but that still brings up inconsistencies which I really can't get my head around. I think the only option I really have open to me now is use experimentally derived constants to match the theory with the experiments. Definitely not ideal and not really what I wanted to do, but I will do this so that I can have a model to progress on to the next stage and then try again later to derive the whole thing from geometry and fluid mechanic equations.

I've also been looking at the electrical side of the project a little more. At WREC I met someone who presented a paper on parallel connected inverters and he gave me some pointers about how to model these types of systems, so I've done a lot of reading on these and the concept of virtual impedance control schemes for inverters.

On the more fun side of things, I've been getting ready for another musical, this time Sweet Charity with Bristol Musical Comedy Club (BMCC). This is the first time for a long time I've worked with a new company, which is fun, although getting to know how different people do things is quite hard at first. BMCC don't have a parish hall that they're based in, so perform in professional theatres, this time it's the Redgrave Theatre. This is going to be another new experience for me, setting up and working in a proper professional theatre. I've spent the last few weeks visiting the rehearsals and building some of the set, which has been good fun - I enjoy getting my hands dirty, it makes sitting at a computer for the rest of the day more bearable.

I went down to Cornwall for a few days for my Mum's birthday, which was great. I really haven't visited home as much as I should have over the last few months, so it was fantastic for all my family to be in one place again.

Mum and her birthday cake (don't count the candles!)

The next few weeks are going to be fairly hectic I think. Alongside all the work I'm doing at uni, I'm off to Paris for my friend's 'this-isn't-a stag-party-it's-more-of-a-pre-wedding-bash', then there's the performance of Sweet Charity in the first week of June, straight after coming back from Paris, then after a week's rest and relaxation, I'm off to Nepal for a short visit to go to Rachhu's wedding before returning for three weeks and then back to Nepal for my annual month-long trip. I've got to try and wrap up all the turbine work before I head away as they're going to be doing some modifications in the Hydrolab, which is annoying. Finger's crossed it all goes well!

SAM