Influence of fluid compressibility on the vibration of pipe conveying fluid

Fluid compressibility is often neglected in the vibration analysis of pipes conveying fluid, and its effects on the dynamic characteristics of the pipe are an unknown issue. In this study, the fluid bulk modulus is incorporated for the first time to develop a more comprehensive dynamic model of the pipe that considers fluid compressibility, which is validated through the absolute nodal coordinate formulation. The effects of internal pressure, flow velocity, and pipe geometry parameters on natural frequencies are investigated by comparing with the conventional incompressible model. It is found that ignoring fluid compressibility has a minimal effect on the vibration characteristics of rigid pipes but significantly affects the natural frequencies of flexible pipes, leading to a striking drop in the prediction accuracy of their natural frequencies. Additionally, the value of the critical flow velocity is significantly overestimated. Interestingly, the natural frequency of the rubber pipe exhibits a non-monotonic variation with internal pressure, initially increasing and then decreasing. Error analysis reveals significant differences between the models, especially for flexible pipes and high-pressure conditions. The limits of the incompressible fluid assumption are defined. Based on the characteristics of the pipe and operating conditions, a criterion for modeling the pipe dynamics to determine whether a fluid can be compressed is established in this study.