This page contains a Flash digital edition of a book.
This close-up of the Red Bull exhaust outlet shows how the floor is being blown directly ahead of the rear wheel with the exhaust pointing to the inside edge of the rear tyre to stop the vortex interfering with the flow through the diffuser. Note the cut out just ahead of the wheel where the flow will go down


Shown in white at the bottom of the picture, the McLaren diffuser covered with a ceramic thermal barrier coating


we have a large accumulator for the storage of compressed air and this is fed directly into the strut, then into the model. In both wind tunnels, the


compressed air lines are fed down the main strut and into the model via the cockpit. In wind tunnel one, the air lines terminate at the air amplifiers, which are located in the engine region. The air amplifiers use the compressed air to entrain additional flow, which is drawn from the roll hoop and then fed into the tailpipes. In wind tunnel two, the supply is simpler, with the compressed air lines being directly connected to the tailpipes.’ However, it is not really


possible to replicate the gas temperatures in the wind tunnel. ‘Doing the temperatures is very difficult,’ admits Lola’s Julian Sole. ‘We have a cooler in our tunnel but, once you start pumping


hot gases in, you are working it overtime. I’m not sure anyone in F1 is doing that.’ Herbert elaborates: ‘It is


not possible to heat the model scale tailpipe flow. We cannot simultaneously replicate a scale equivalent of both the speed and mass flow of the full-size car in the wind tunnels. Therefore,


A further iteration of the exhaust blown floor, as seen on the Mercedes, showing the attachments to channel airflow through the diffuser


It would seem, then, that van


Rees was right in that the only real way to get a full simulation of the heated gases is to either run the car on a track and see what happens – which is not simulation at all – or to use CFD. ‘We use CFD to visualise


the flows,’ continues Herbert, ‘and we use our PIV (Particle


“We cannot replicate a scale


equivalent of both the speed and mass flow of the full-size car in the wind tunnels”


based on our experience, as well as a lot of testing and configuring, we know the appropriate level to set the wind tunnel tailpipe velocity to replicate actual exhaust gas behaviour.’


Image Velocimetry) technology to ensure a good correlation between tunnel results and CFD modelling, in the same way we use PIV to enhance the accuracy of our CFD for other aerodynamic work. CFD can also be used


to assess whether the plume impinges on the tyre surface and, if necessary, to simulate the thermal effects on the air around the tyre.’


THERMAL MANAGEMENT As Herbert hints, the temperature of the gas has more than an influence on the dynamic properties of the exhaust plume. It also has significant implications for the materials and structures of the car itself. Exhaust temperatures of 650-1000degC are commonplace and any team contemplating a blown diffuser has to take this into account. There are several different solutions available to help cope with this, including gold foil wrapping or thickening of carbon fibre structures, but ceramic coatings such as those offered by the Oxfordshire-based firm, Zircotec, are now an essential


July 2012 • www.racecar-engineering.com 69


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89