The simulation of transient cross-wind gusts and their aerodynamic influence on passenger cars
The unique University of Durham transient cross-wind facility has been developed such
that sharp edged, finite length, cross-wind gusts with a relative yaw angle of 22' can be
developed at the rate of 1000/hr. This cross-wind facility uses the transient interaction
of two wind tunnel jets to create these gusts, with the fully automated, rapid, repeatable
gust production process allowing ensemble averaging to significantly improve data
The cross-wind gust characteristic, as observed for the empty working section, has some
inherent problems. A yaw angle undershoot, and more importantly, an overshoot occur
at the leading edge of the gust. A transient total pressure overshoot is also observed at
the leading edge of the gust. Computational fluid dynamics (CFD) simulations of the
empty working section have replicated these anomalies, and suggestions are proposed
for their elimination.
Two aerodynamic models were tested in this facility, each being subjected to transient
cross-wind gusts of 10 model lengths. Both models exhibited significant transient force
and moment overshoots. These overshoots were found to be a consequence of delayed
pressure development in regions of separated flow, with full flow development requiring
up to seven model lengths of cross-wind gust.
These results, which cannot be replicated by any steady testing procedure, confirm the
requirement for transient testing, if transient forces and moments are required.