T H E E U R O J E T E J 2 0 0 www.engineeringnews.co.nz 21 birthplace of the Finite Element Method, each CFD analysis of even minor configuration changes would take about 30 hours. Consequently homing in on an acceptable shape configuration took nearly three years. It is difficult to summarise where the project is, given the complexity of the engineering and logistical challenges, but the first shakedown really signals the end of the design phase and the start of the development phases. At Newquay Bloodhound only reached 210mph, but this was constrained by the length of the runway, the fact that it was on tarmac and the car was on 'runway' wheels borrowed from an English electric lightning jet fighter. Coming up over the next two years are tests to 600, 800 and finally 1000mph assuming all goes well during the previous increments. “We are intending to go faster in 2018,” says Richard Nobel, Bloodhound project director. “The tricky bit is to validate the CFD and to run to supersonic and collect data, plus you have to make sure it's stable.” The CFD used special code developed by the University of Swansea, which used over a hundred million finite elements for the CFD simulation. “You can't use a wind tunnel to verify the CFD as there is no tunnel available that goes to 1000mph with a moving ground plane even with scale effects,” continues Mr Nobel. “Instead we used the reciprocal and used a rocket sled as we needed to validate the analysis before starting to build.” The reciprocal of the wind tunnel moves the object through the air not the air over the object. There are several rocket sled test tracks for testing armaments and jetfighter cockpits around the UK. “We found one that wanted to use up some rockets that were close to their expiry date,” says Mr Nobel. “We used 200 rockets for 13 runs of the rocket sled and thankfully the data correlation to the CFD was a straight line.” a desert bed, with potentially variable weather and wind conditions, is no simple task - having the support crew in exactly the right place at the right moment is critical to making the second run in the time required. Stopping a 7¾ tonne jet car is not as simple as it sounds either - there are air brakes, two parachutes and wheel brakes to be deployed - again these things have to happen at exactly the right time in a particular sequence. Deploying the supersonic parachute too early could rip it to shreds and negate its effect, which means that the other braking mechanisms have to provide all the deceleration, increasing the stopping distance to six maybe seven miles. This extra distance could mean the car could run off the end of the desert at worst, but it would also effect where the pitstop is performed and crucially it places the car further from the measured mile, which could mean the car runs out of fuel before completing the second run. The other tricky bit is that the jet has to be shut down manually, before the end of the measured mile to achieve the optimum deceleration. A jet doesn't work like a mechan- Each of the high speed tests needs a different configuration of power/propulsion units as the thrust requirements are different. It's well known that drag increases with the square of the speed in turbulent flow, but the power required, increases with the cube of the speed. So double the speed, the drag increases four-fold and the power required increases eight-fold. The Eurojet EJ200 jet engine produces nine tonnes of thrust and it should be sufficient alone for the 600mph tests. The 800mph tests will require the jet and a single monopropellant rocket, but 1000mph will need the jet and three rockets. Unfortunately, the three rockets require more space than the single rocket, so significant rear suspension changes need to be made to repackage for them. But lessons learned from the previous testing need to be incorporated into the ultimate speed configuration. The total thrust required to 1000mph is 20 tonnes with a thrust to weight ratio is about 2½ times. The car in 1000mph trim is about 7¾ tonnes in weight. The first rocket for the 800mph tests is a mono propellant rocket. “We basically decompose peroxide to steam plus oxygen - there is no combustion for the thrust,” says Mark Chapman, Bloodhound engineering director. “This is a three stage, multiple chamber rocket with three stages feeding a single nozzle producing 4 tonnes of thrust. For 1000mph instead of decomposing to steam and oxygen there is a fuel element in the hybrid rocket that is burning to produce 10 to 12 tonnes of thrust. Both rockets need the same amount peroxide - one tonne peroxide in 17 seconds.” One of the most significant challenges in the development phase is perfecting the Bloodhound pitstop. The FIA rules stipulate that for a valid record, the vehicle has to go through a measured mile in two directions within an hour. Simple enough, but that hour starts as the car trips the start of the first measured mile. So, after eight seconds (the first mile) the car needs to decelerate and stop (usually taking in excess of 5½ miles), get turned round and refuelled with jet and rocket fuel and be on its way to trip the start of the second measured mile within the hour. Unlike an F1 pitstop, where there is a simple 5 metre box to hit at 80kph, figuring out where that box is after a run of up to 1000mph, on
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