  Modelling flow and acoustics in a constricted duct at low Mach numbers is
important for investigating many physiological phenomena such as phonation,
generation of arterial murmurs, and pulmonary conditions involving airway
obstruction. The objective of this study is to validate computational fluid
dynamics (CFD) and computational aero-acoustics (CAA) simulations in a
constricted tube at low Mach numbers. Different turbulence models were employed
to simulate the flow field. Models included Reynolds Average Navier-Stokes
(RANS), Detached eddy simulation (DES) and Large eddy simulation (LES). The
models were validated by comparing study results with laser doppler anemometry
(LDA) velocity measurements. The comparison showed that experimental data
agreed best with the LES model results. Although RANS Reynolds stress transport
(RST) model showed good agreement with mean velocity measurements, it was
unable to capture velocity fluctuations. RANS shear stress transport (SST)
k-{\omega} model and DES models were unable to predict the location of high
fluctuating flow region accurately. CAA simulation was performed in parallel
with LES using Acoustic Perturbation Equation (APE) based hybrid CAA method.
CAA simulation results agreed well with measured wall sound pressure spectra.
The APE acoustic sources were found in jet core breakdown region downstream of
the constriction, which was also characterized by high flow fluctuations.
Proper Orthogonal Decomposition (POD) is used to study the coherent flow
structures at the different frequencies corresponding to the peaks of the
measured sound pressure spectra. The study results will help enhance our
understanding of sound generation mechanisms in constricted tubes including
biomedical applications.
