How much of Red Bull's problem with the RB21 is due to its wind tunnel?

Chris Watson poses this month’s question, asking if the difficult handling of the Red Bull RB21 is down to the Formula 1 team using an outdated wind tunnel.

Christian Horner, prior to his departure from the squad, was quoted as saying: “When you get to the finer elements of a set of regulations like this, the wind tunnel we have is a relic of the Cold War, so it has its limitations, which is why we’ve invested in a new tunnel that’s in the process of being constructed.”

He implied many times that this was the fundamental problem behind Red Bull's difficulties. The tunnel the team uses is at what was the Royal Aircraft Establishment, a facility established after the Second World War and which flourished during the 1950s.

There were a number of wind tunnels on the site but the 13 feet by nine feet tunnel, which among other things carried out a lot of the experimental work on Concorde, is the tunnel still used today by Red Bull. 

The dimensions refer to the width and height of the working section, the area where the model is mounted. These are critical dimensions as ideally there should be no interference of the wake coming off the car, vertically or sideways, with the walls of the tunnel.

This requires a large working section and for F1 work it is best to keep the blockage to around 3% of the working section area. The Red Bull tunnel dimensions suggest this is closer to 5%, not a big problem but perhaps not ideal. That said there are many other F1 tunnels with similar blockage ratios.

This tunnel was unique when built in that it had a ‘rolling road’ – a moving belt that represented the ground and hence allowed studies to be made of aircraft during take-off and landing. Of course, a moving ground is essential for racing car aerodynamic studies, but the belts used today are much more sophisticated than those from the 1950s.

The same is true of the wind tunnel balance, used for measuring the forces and moments on the model. Both of these fundamental parts of the wind tunnel will have been replaced by Red Bull and will be state of the art.

Experimental work on the Anglo-French Concorde project took place in what is now the Red Bull wind tunnel

Photo by: Philippe Collard / Unsplash

The final element of the mechanical part of the wind tunnel is the model motion system. One of the advantages of wind tunnel experiments over computational fluid dynamic simulations is that during a single wind tunnel run the model is moved to a variety of positions, not just various ride heights, but the model can also pitch roll and yaw.

This gives a plethora of information but, with the restrictions placed by the FIA, it is necessary to have an efficient motion system and teams now use what is termed ‘continuous motion’.

Rather than moving the model to a fixed position, acquiring data, and then moving to another position, the model is continuously moving, and data is acquired as a single stream. Once again, there is no reason why the best motion system could not be fitted to a tunnel built many years ago.

So, this leaves us with thinking about the quality of the air passing over the model. This needs consistency: the air velocity should be constant throughout the working area, it should have low turbulence, the static pressure should be constant and the boundary layer should be thin.

I can imagine it is quite hard to keep the air temperature constant even during a single tunnel session, let alone trying to keep the same temperature in January and August

All of these should be reasonably easy to achieve in a good tunnel. In addition, the air temperature needs to be constant, and this is not so easy to achieve. Basically, the power driving the fan that moves the air in the tunnel once it is up to speed is converted to heat.

Some of this is absorbed by the thermal mass of the tunnel itself, some is radiated from the tunnel walls, but a significant amount is dissipated in a cooling system normally built into the turning vanes at the tunnel corners.

It is here that the Red Bull tunnel may be deficient in that it’s built of concrete and hence has a huge thermal mass. I can imagine it is quite hard to keep the air temperature constant even during a single tunnel session, let alone trying to keep the same temperature in January and August.

So, the tunnel may not be ideal, but it is not deficient. There’s much that can be improved if building a new wind tunnel. For example, an open jet tunnel may be a better compromise for the high and wide wakes that emanate from an F1 car as well as being a better configuration for using particle imaging velocimetry, a technique for visualising and recording the flow patterns of the air.

Perhaps the real answer lies in the fact that Racing Bulls uses the same tunnel and, while its car may not have the outright aerodynamic performance of the RB21, it is a car that appears to have benign aerodynamic characteristics. The new tunnel will be good, but I think Red Bull also needs to look elsewhere.

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It had long been Horner’s contention that the root cause of Red Bull’s issues was the “relic of the Cold War” used by the team

Photo by: Red Bull Content Pool