TITLE:
Aerodynamic Sound Radiated from Longitudinal and Transverse Vortex Systems Generated around the Leading Edge of Delta Wings
AUTHORS:
Shigeru Ogawa, Jumpei Takeda, Taiki Kawate, Keita Yano
KEYWORDS:
Aerodynamic Noise, Delta Wing, Longitudinal Vortex, Transverse Vortex, CFD
JOURNAL NAME:
Open Journal of Fluid Dynamics,
Vol.6 No.2,
June
21,
2016
ABSTRACT: Flow around the front pillar of an automobile is typical of a flow field with separated and reattached
flow by a vortex system. It is known that the vortex system causes the greatest aerodynamic
sound around a vehicle. The objective of the present study is to clarify the relationship between
vortical structures and aerodynamic sound by the vortex system generated around the front pillar.
The vortex system consists of the longitudinal and the transverse system. The characteristics of
the longitudinal vortex system were investigated in comparison with the transverse one. Two
vortex systems were reproduced by three-dimensional delta wings. The flow visualization experiment
and the computational fluid dynamics (CFD) captured well the characteristics of the flow
structure of the two vortex systems. These results showed that the longitudinal with the rotating
axis along mean flow direction had cone-shaped configuration whereas the transverse with the
rotating axis vertical to mean flow direction had elliptic one. Increasing the tip angles of the wings
from 40 to 140 degrees, there first exists the longitudinal vortex system less than 110 degrees,
with the transition region ranging from 110 to 120 degrees, and finally over 120 degrees the
transverse appears. The characteristics of aerodynamic sound radiated from the two vortex systems
were investigated in low Mach numbers, high Reynolds number turbulent flows in the lownoise
wind tunnel. As a result, it was found that the aerodynamic sound radiated from both the
longitudinal and the transverse vortex system was proportional to the fifth from sixth power of
mean flow velocity, and that the longitudinal vortex generated the aerodynamic sound larger than
the transverse.