Low-frequency vibrations in control valves are a rare phenomenon that can lead to excessive pipeline vibrations and potential shutdown of operations. Due to the complexity of the flow through a control valve, the parameters that lead to the low-frequency vibrations are not established. In several of the documented cases, pipe bends were located directly upstream of the control valve and potentially this is one of the parameters that contribute to the vibrations. A well-known flow phenomenon that occurs in pipe bends is the formation of a pair of counter rotating Dean vortices. It has been shown previously that these vortices do not remain symmetric and instead the stagnation point between the two vortices oscillates back and forth. The oscillation of the Dean vortices is at a Strouhal number that is approximately one order of magnitude lower than what is typically seen for the frequency of the shear layer vortices. It is proposed here that when low-frequency vibrations occur in a control valve with pipe bends located upstream, the potential cause is the oscillation of Dean vortices. In this paper large-eddy simulation (LES) is performed on a 90-degree pipe bend at a Reynolds number of 80,000 using the open source CFD code OpenFOAM. The ratio to the curvature radius of the pipe axis to the pipe diameter is 2. The objective of performing this simulation is to verify the low-frequency oscillation of the Dean vortices occur at this Reynolds number and to determine to what extent pressure fluctuations caused by the Dean vortices extend downstream. It is postulated that if a control valve is positioned sufficiently close to a bend, the low-frequency pressure oscillations originating from the Dean vortices can enter the valve chamber and be amplified to an extent that potentially causes pipeline vibrations. It is shown in the simulation that the Dean vortices oscillate at a low-frequency and they influence the pressure several pipe diameters downstream of the bend. Dynamics mode decomposition (DMD) is applied to the flow field to extract a mode of the flow structures at the low-frequency. Simulations are performed using simplified geometry of a control valve and it is found that there is additional low-frequency content to the pressure spectrum in the chamber of the valve when a bend is placed directly upstream. The amplitude of the pressure oscillations within the valve chamber are substantially higher than what is seen in the upstream pipes. Vortex shedding occurs in the chamber of a valve, due to the flow navigating the sharp bend at the valve inlet. It is shown that the vortex shedding occurs at a high-frequency and therefore can not be the direct cause of the low-frequency vibrations. Recommendations are given for the length of pipe downstream of a bend needed to reduce the impact of the oscillating Dean vortices.          


On the Potential for Low-Frequency Control Valve Vibrations Being Caused by Upstream Oscillating Dean Vortices

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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