The vortex instability at a side branch connection in a piping system may establish an acoustic standing wave in closed branch lines leading to vibration problems. The Energy Institute (EI) screening method for avoiding such resonance works by ensuring that the fundamental acoustic natural frequency of the side branch is larger than the EI calculated excitation frequency. The EI screening method ignores the possibility that the side branch acoustic natural frequency is significantly lower than the main line excitation frequency. Allowing for this possibility, an alternative screening method is proposed based on the fact that side branch resonances occur across a Strouhal Number range of 0.3-0.6. The minimum and maximum permissible length of the side branch is then calculated based on these bounds. The presented case study demonstrated that the new screening method reduced the systems identified at risk and provided sensible solutions based on the overall branch length to avoid resonance. This provides a practical alternative to the restrictive short branch length generated by the EI screening.
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