A 26 percent drag reduction through tailored fairings, rear-end boat tail and wheel arch treatments. This poses around a 13 percent reduction in fuel usage at motorway speeds.
Original tanker design showing significant turbulence between tractor and trailer, also seen behind the trailing edge of the tanker
A simple 8 wheeler tanker model was created and used to set a baseline for drag force at a nominal road speed of 56 mph. Using the new-to-market cloud computing power and software available to JMR Analytical, the various flow regimes that contributed to excessive vehicle drag were identified. A number of schemes were put forward to augment the airflow characteristics in a way which would help reduce the high pressure bubble in front of the tractor unit and in front of the tanker trailer. Similarly, ideas were put forward to feed air into the low pressure wake towards the rear of the vehicle. After an iterative process of design and simulation, the optimum combination of design changes were identified.
The optimised tanker showed improved flow in several ways:
1. The fairing above the tractor unit prevented the airflow from hitting the forward face of the tanker trailer. This reduced the drag created by this face. It also had positive effects elsewhere on the vehicle that had previously been negatively affected by the scattered airflow trapped between the tractor and trailer. The fairing was a bespoke design for this tanker, allowing the airflow to remain attached and clean for much more of the length of the trailer.
Revised design showing improved flow around tractor unit, reduced turbulence between tractor and trailer and also improved trailer wake
2. Rear end drag was massively reduced by boat-tailing the rear of the tanker. This gentle diffusion of free stream flow into the low pressure bubble behind the tanker caused much more organised flow in an area which had previously seen large amounts of flow recirculation. Another effect of this boat-tailing was to reduce the area of the rear face of the tanker. Any low pressure acting on the rear face would now be acting upon a smaller area.
3. The wheelarch treatment was seen to reduce turbulence created by the rotating wheels, by free stream air hitting the edges of the wheels and tyres and to reduce the bleeding of free stream air into the air pocket under the tanker where it could join the complex underbody flow and meet bluff faces.
Forces acting on all truck faces are measured over the course of the simulation. By comparing the forces in the “X” direction (forces pushing forwards and rearwards on the vehicle) we can compare the drag force created by one truck model to another.
In the first plot we can see the net drag force on all tanker faces are 1798N, in the second we see that this figure has been reduced to 1137N. Incidentally, in the resultant plot we can also observe that the drag calculation is quite a stable one and has converged after only 400 iterations, adding further credence to the reliability of the final figure.
Force plot of the original tanker design Indicating a drag force plot of 1798N
Force plot of the modified tanker design indicating a drag force of 1137N