Jul 15

Supersonic cafe

[Disclosure: I was attending last night’s Science Cafe in my role as Manager of Science City Bristol.]

At last night’s Science Cafe, a broad group of Bristolians heard about CFD, Pitch drips, carbon footprint of cows, and road spray from lorries; all from a talk about a 1,000mph rocket car!

Pitch drop experiment on Wikipedia

Pitch drop experiment on Wikipedia

Computational Fluid Dynamics is the particular research discipline of Dr Clare Wood and Dr Ben Evans from Cardiff University. Clare began with a basic introduction to CFD, some of the history of the Navier-Stokes equations and the other uses they get put to. This was where the Pitch Drop came in; an experiment started in 1930 to measure the viscosity of pitch (which looks like a solid), there have been 8 drips of pitch since then as it very slowly flows into the catching beaker. Unfortunately, no one has ever witnessed a pitch-drip, there was a technical hiccup with the video feed [requires Windows Media Player] on the last drop (28 November, 2000). Clare also talked about ‘proper’ science and using CFD to model blood flow in hearts and the bio-medical applications.

Ben then picked up the topic and began talking about the pressure waves that develop as you move from sub-sonic through to super-sonic. A major challenge is the incredible pressure that will occur around the rear wheels as the third shock wave develops. This is potentially so strong it could physically lift the back-end of the car into the air, obviously a bad thing at 1,000mph!

There’s a limit to what can be done with the mini-winglets that are being used to trim the car aerodynamically, so Ben and the CFD team are leading the engineering design changes to the rear suspension & underside to try and reduce these pressure waves to make the car safe to drive. There was some more about the research development of new CFD algorithms and the promo-video (embedded at the end of this post).

After a short break, the Q&A began. The first question was about the environmental impact of a 1,000mph rocket car with follow up comments about the 19th Century’ness of a fast car. Although this wasn’t Ben’s area of specific expertise its obviously something that comes up fairly regularly. An environmental economist (or something like that) has looked at the car, the project and worked out their carbon footprint for the whole 4 year project. Apparently it comes to around 4 cows farting for a year; now I’d never entered the term “cow fart” into Google before this morning (who would) but it seems quite a research topic, even the Telegraph are reporting it!

As to the choice of a rocket car (rather than a green car); this had been intended from the outset to be an engineering adventure. The car & the 1,000mpt target are almost incidental, the primary aim is to get children (and the young at heart) excited about science & engineering and thinking about careers in the sciences. Rockets are still exciting to young kids!

The topics moved around and one that came up was the legacy of the project, what will we have after the final run (other than a very expensive museum exhibit)? Ben explained that much of the research involved in the CFD modelling is directly transferable. The example he used was how spray is formed at the back of lorries in the rain. One of the challenges of Bloodhound is the generation of a dust spray from the wheels and shock wave, and modelling how this mix of air & particles grows and affects the car. The same physics are (they think) involved in road spray from lorries, but no one has developed a good model of how spray forms and moves around the lorry. When you drive into this spray, in overtaking for example, it can be a real safety hazard, by modelling this and proposing different designs for the lorries, they might be able to reduce this spray and improve road safety.

There were tons of other questions (about an hour’s worth), it was a really great evening. Thanks to John and At-Bristol for hosting and to Bob Foster for his Science Cafe website where I found out about the event from Bob’s Calendar.