Abstract:
Most heavy goods vehicles in service today are fitted with add-on aerodynamic
devices. The most common of which is the cab-mounted roof deflector. Such devices
provide appreciable drag savings, however, they are often not optimised for the
trailer. When a wind yaw angle is present, their savings also diminish as the yaw
angle increases.
The work conducted within this thesis investigated the possibility of using an
adjustable deflector for active flow control. The optimum deflector height for a given
trailer height was initially investigated using wind tunnel testing. The variation of
this optimum with yaw angle and container separation was then investigated. From
the results a 3D look-up table was generated.
A control scheme was proposed that used the 3D look-up table requiring only
three measurable inputs. The three inputs required were: the wind yaw angle, the
container height and the container separation. A pressure differential located on
the deflector was found to linearly relate to the wind yaw angle. This relationship
allowed on-road measurement of the wind yaw angle and therefore enabled the
development of a prototype controller.
Extensive on-road testing and unsteady computational simulation were conducted.
The results obtained indicated a mean yaw angle magnitude of around
5 perturbed by four fundamental low frequencies. These frequencies were identified
in the runs conducted over the test period and an average frequency established.
Higher frequency disturbances were attributed to the wakes of leading heavy goods
vehicles and were filtered by a suitably chosen numerical filter.
Finally, an estimation of the efficiency of the active device was made using a
combination of simulation and full scale testing.
From the results obtained, an optimised deflector generated an average drag reduction
of 7.4%. An estimated additional drag reduction of 1.9% over the optimised
deflector was predicted through use of an active system.
