Flow-Sound-Structure Interaction in Spring-Loaded Valves

Abstract

This thesis provides a comprehensive investigation of flow-sound-structure coupling in spring-loaded valves subjected to air flow. While they are commonly used in a multitude of applications, these types of valves have been found to experience severe vibrations when interaction is present among the structure, the hydrodynamic field, and the acoustic field for a range of operational valve structural characteristics, flow parameters, and connected piping length.

The first part of this investigation was aimed at characterizing experimentally the valve’s dynamic behaviour and the parameters affecting the onset of self-excited instability. The occurrence of instability was mainly driven by the presence of acoustic feedback: the connected length of piping had to be sufficiently long, with a longer pipe correlating to more severe vibrations. In addition, it was found that the valve’s oscillation frequency depends on the modal characteristics of the combined valve piping system, rather than the structural natural frequency alone. Furthermore, an increase in the valve’s spring stiffness caused the vibrations to become more severe. Meanwhile, other parameters such as initial spring preload force and valve plate area only had moderate effects on the stability behaviour of the valve.

The second part of the investigation sought to develop a theoretical model that could simulate the valve’s response when subjected to air flow while considering the effects of acoustic feedback and impact on the seat and limiter. Thus, a structural model of the valve was developed based on a single-degree-of-freedom model of the system with impact computed based on a pseudo-force method. The hydrodynamic field relied on a one dimensional unsteady Bernoulli description of the flow. Finally, the acoustic interaction was accounted for using the one-dimensional wave equation resolved using a finite difference scheme. The model has demonstrated remarkable agreement with the experimental results. It has shown an ability to predict the modal characteristics of the system as well as correctly predict the effect of increased stiffness or increased piping length on vibration amplitude.

The final part of the investigation consisted in designing countermeasures to mitigate the effects of this self-excited instability mechanism. A concentric Helmholtz-type cavity resonator, an orifice plate, and an anechoic termination are placed at the downstream side of a model valve which were seen to be unstable in the experimental and modelling phases of the investigation. All tested devices were able to eliminate the self excited instability mechanism. The applicability and robustness of each of these methods were discussed.