On Hydroelastic Plug Valve Vibration

Abstract

<p> The research reported in this thesis concentrated on experimentally investigating and theoretically modelling self-excited valve vibrations. In particular the jet-flow inertia mechanism has been studied. Experimentally, this has been achieved by allowing water to discharge from a constant head tank into a pipeline through a simple plug valve. The plug valve was restrained so that axial vibrations of the plug valve could occur. Using this equipment the conditions for which the valve was stable and unstable was obtained. Further experimental investigation using a Laser Doppler Anemometer allowed for recording of instantaneous fluid discharge during the valve limit cycles. In addition the records of the instantaneous pressure difference and valve opening allowed for instantaneous discharge coefficient calculations. Although no trends in these instantaneous discharge coefficients were apparent, these particular experiments allowed for improved modelling of the valve vibration. </p> <p> Dimensionless nonlinear differential equations were derived to describe general flow control devices. A stability analysis of these differential equations showed that at large fluid inertias that the instability that arises is one of divergence, hence a quasistatic stability analysis is valid. Numerical integration of the differential equations of motion was used to predict limit cycles as well as valve stability. </p> <p> The divergence formula derived for large fluid inertia was found to coincide with the corresponding experimental results. Other predictions were found to generally agree with experimental results. Discrepancies which did arise were attributed to waterhammer. Hence the theory derived was concluded to be fundamentally correct. Recommendations for further research include inclusion of waterhammer in the model and investigation of local flow effects. </p>