Numerical methods are mostly used to predict the acoustic pressure inside duct systems. In this paper, the development of a numerical method based on the convected Helmholtz equation to compute the acoustic pressure inside an axisymmetric duct is presented. A validation of the proposed method was done by a comparison with the analytical formulation for simple cases of hard wall and lined ducts. The effect of the flow on the acoustic pressure inside these ducts was then evaluated by computing this field with different Mach numbers.

The mean flow characteristics in a curved channel are really different from those in a straight channel. The main cause is the existence of secondary flow within the flow in the curved channel. This paper will discuss the differences in mean flow characteristics due to changes in the bed topography in the curved channel. Acoustic Doppler Velocimetry (ADV) measurements have helped to analyse characteristics of the mean flow on flat and eroded beds in a 180° curved channel. Sand (mean diameter d ₅₀ = 0.001 m and specific gravity Gs = 2.65) was selected as the bed material. The condition of flow in the approach section was steady and uniform with 0.159 m depth. One of the mean flow characteristics in the curved channel is the free surface superelevation due to the presence of centrifugal force. The second is the circular motion toward the inner-bank region at the lower layer and toward the upper layer outer-bank region. The cause of the circulation is the difference in centrifugal forces between the two layers. The magnitude of velocity near the bed surface is more significant than the flow near the water surface. This causes erosion in the outer bank region and deposition in the inner bank region. In general, tangential velocity vθ in flat bed is greater than its tangential velocity in eroded bed. The maximum velocity path in a flat and eroded bed of the curved channel resembles a sinusoidal curve, where the minimum value is located at 90° and 120° of the curve.