This thesis deals with the exhaust noise generated from reciprocating internal combustion engines. The exhaust gas propagates as nonlinear waves and the voricity flow convects with subsonic speed. The exhaust noises are generated due to the acceleration of the gas through the exhaust valve, moving periodically, and due to the flow separation near the valve. the main objective of this paper is to identify the mechanism of generation and propagation of these waves.
Compressible Navier-Stokes equations are solved numerically for the exhaust stroke of axisymmetric model having a single cylinder and a single exhaust valve. A diagonal implicit algorithm is used for space and $δ^k$ -Correction is used to improve the time accuracy. thompson's nonreflecting boundary condition is applied to the exhaust exit and unsteady deforming mesh algorithm is employed to simulate the periodic motion of the piston and valve.
The large compressive pressure wave is generated due to the initial pressure difference in the exhaust stroke through the valve and wavelets of small amplitude are followed, which are conjectured as noise due to the flow separation. At the end of the exhaust stroke, expansion waves are generation due to pressure drop in the cylinder of the engine.