Reflection coefficient at an end of an unflanged duct without flow is derived analytically and compared with the previous one. With this reflection coefficient the case in which there is a mean flow is investigated and the reflection coefficient for such case is also found theoretically. Using this coefficient the sound pressure distribution in the duct is obtained with a flow velocity ranging from Mach Number 0 to 0.1.
An experiment is executed with both ends of the duct open without flow. The result is compared with the analytical solution, which shows very good agreement with each other. In addition analytical relations have been formulated between the sound pressure deviation and the flow velocity at specific frequency.