Pressure Pulsation Caused by Vortex Shedding from a Perforated Plate with Holes

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The pressure fluctuations accompanying the occurrence of the lock-in caused by the vortex shedding from the perforated plate were examined experimentally. Measurements were also made on the pressure fluctuations caused by the lateral vibration of the perforated plate excited axially by the piezoelectric element. The results are summarized as follows :(1) The occurrence of lock-in is significanfly affected by the flexural rigidity of the perforated plate. When this phenomenon is caused, the pressure fluctuation is considerably increased.(2) As the thickness of the perforated plate is increased, the lock-in velocity range shifts to a higher velocity, while the frequency of pressure fluctuation shows only a slight change.(3) The lock-in velocity range, as well as the frequency and amplitude of the pressure fluctuation during the occurrence of lock-in, depends on both the pipe length upstream and downstream from the perforated plate.(4) When the lock-in occurs, the in-phase lateral vibration of the perforated plate is generated. The plate displacement has a phase lag with respect to the differential pressure across the plate.(5) The pressure mode shapes in the pipe during the occurrence of lock-in agree quite well with those of the pressure fluctuation caused by the lateral vibration of the perforated plate excited axially by a piezoelectric element.(6) When the pressure fluctuation due to the issuing of unstable jets from the perforated plate is reflected at the pipe ends and transmitted back to the plate, the differential pressure fluctuation across the plate is increased. This differential pressure fluctuation causes the lateral vibration of the plate. By the resulting flow fluctuation, the pressure fluctuation is further amplified.