Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.
Deep cavity configuration at subsonic velocity could be
found in many industrial processes, ranging from windows and
sunroofs in automobiles and over space between two
consecutive train vehicles. These cavities may induce
aeroacoustic couplings between the cavity shear layer
oscillations and the acoustic modes of the installation. This
aero-acoustic coupling can leads to serious damages of vehicles
due to resonance of high pressure fluctuation level around the
cavity. The study of deep cavity at low velocity presents a great
practical interest to suppress acoustic noise. In spite of
numerous studies devoted to the cavity and its control, very few
of them relate to the deep cavity configuration at low velocity.
The focus of the present study is to apply a passive control to
the case of the deep cavity flow at relatively low velocities. A
Detailed Experimental study of flow over a deep cavity was
conducted towards understanding the attenuation of tones using
a spanwise cylinder. The cavity length-to-depth aspect ratio is
L/H = 0.2. Single hot-wire measurements characterized the
incident turbulent boundary. A “no control” cavity was
compared with a similar configuration using a cylinder on the
leading edge of the cavity. Parametric changes of the spanwise
cylinder such as the distance from the wall are studied.
Maximum control across the range of studied velocities occurs
for a particular position of the spanwise cylinder. Reductions in
sound pressure levels (SPL) of up to 36 dB were obtained.
Moreover, a shaped cylinder was also studied and shows that
the attenuation of tones is not due to high frequency pulsing as
suggested in literature, but to an increase of the cavity shear
layer thickness due to change in the mean axial velocity
profiles.
