Aerodynamic Investigations of Vehicles under High Side Wind Conditions on Bridges
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Wang, Wei
Hariharan, Sriprasanna Venkatesh
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Crosswind stability is a critical safety factor that needs to be addressed for all types of
road vehicles. However, it is especially crucial for trucks and buses due to their large lateral
areas. As a result, this makes the vehicles more vulnerable to high side forces caused
by incoming side winds. This is because of the fact that, the greater the lateral area, the
greater the sensitivity to side winds. In the absence of any shielding, the magnitude of
the resulting side force on the vehicles commuting across the bridge will be exacerbated.
In addition to side force, the yaw moment acting on the truck is also an important factor
that needs to be addressed. The lateral stability of the vehicle is mainly affected by yaw
moments. When side winds blow, the presence of a bridge structure, such as a pylon,
causes huge turbulent wake flows due to flow separation. Furthermore, when the vehicle
rides across the pylon wake, the sudden shielding effect in the wake flow region causes a
steep change in the vehicle’s side force. The pressure distribution on the surface of the
vehicles as well have continuous variation and thus result in fluctuating yaw moments.
These disturbances have an impact on the drivability and maneuverability of the vehicle.
Handling stability is extremely important for road safety. If these side wind sensitive
vehicles are traveling at high speeds, it may even cause them to roll over in severe cases.
So, it is pivotal to analyze the side wind induced aerodynamic forces and moments on
road vehicles in order to understand their impact and to provide guidance to drivers on
how to maintain the vehicle’s stability when driving in this scenario.
The road vehicle taken for this study is a truck. 3D Computational Fluid Dynamics
(CFD) simulations are performed to investigate the aerodynamic forces and moments
on the truck at different side-wind conditions. The commercial code used to simulate
the model is the StarCCM+. Initially, a steady state case is developed and solved using
Reynolds Averaged Navier Stokes(RANS) transport equations and a realizable k−epsilon
turbulence model with all necessary boundary conditions. The aerodynamic coefficients
of the truck are computed at different positions on the bridge. Individual and combined
effects of bridge structures such as deck, windshield, and pylon are investigated. Unsteady
simulations are also performed, and the results are compared to the steady-state model.
The steady state results are used as an initial solution for the unsteady model. The
unsteady model is built to simulate the motion of a truck across the bridge by using overset
mesh methodology. The simulations are run for 30, 60 and 90 degree yaw conditions. The
CFD investigations showed that the presence of deck and windshield(non-porous and
solid) reduces the side force acting on the truck by diverting the flow above with a local
re-circulation wake region beside the exposed windward surface, and thus reduces the
static pressure on the truck. On the other hand, the porous windshields increase the side
force on truck when compared against the windshields with no cut-outs. The study on
porous windshields revealed an intriguing scenario in which the presence of windshields
with more than 80% porosity increases the side force on the truck when compared to the
case with no shields.
Beskrivning
Ämne/nyckelord
Aerodynamics , Side wind effects , CFD , Overset mesh , Unsteady simulation