A pipeline is often considered as the most convenient, efficient and economical mode of transporting liquids likes petroleum, natural gas, and water etc. Damages to this pipeline can cause loss of resources and the contents can also be harmful to the environment. In order to minimise the damages brought to the environment and the loss of resources, rapid non-destructive detection of pipeline leakage is indispensable. In previous works, acoustic wave propagation based methods were used in leakage detection in a pipe without flow. In this study, the acoustic wave method and a modal frequency technique are used to detect leakage in a pipeline system in the presence of mean flow velocity. Computational fluid dynamics (CFD) analysis was employed to simulate acoustic wave propagation in air-filled pipes with leakage in the presence of mean flow velocity. Furthermore, experimental testing was conducted to validate some of the numerical results. The experiment performed consisted of the measurement of acoustic wave propagation in a straight air-filled pipe with leakage. The CFD analysis of fluid-filled pipe can be used to simulate the acoustic wave propagation and acoustic wave reflectometry of a fluid-filled pipe with leakage of different sizes in the presence of flow. Also, the measured signal of acoustic wave propagation in the pipeline from the experiment can be decomposed and de-noised to identify and locate leakages of different sizes.