Author(s): Claudia Reibenwein; Reinhard Prenner; Helmut Bir
Linked Author(s):
Keywords: Vortex shedding; Turbulence level; Free-stream turbulence; Wake of cylinders; Froude's law of similitude; Dynamic similitude; Model-family; Hydraulic experiments
Abstract: Due to problems in identifying the resonance frequency of prototype structures, e. g. trashracks or gates, which can be forced to vibrate by flow-induced mechanisms, it was of vitally interest to verify Froude’s law of similitude applied to the conversion of frequencies on basis of model experiments. Vortex shedding frequencies in the wake of stationary mounted smooth circular bars (Reynolds numbers 2⋅103 - 2⋅104) were investigated experimentally in a water channel. Special emphasis was put on adopted measures to reduce the turbulence level of the approaching flow, taking results of investigations into account, formerly conducted in wind tunnels. It can be demonstrated, that the incoming turbulence of the approaching flow has a considerable influence on the evaluation of results. The adding of flow-soothing screens enables a significant reduction of the turbulence intensity of the approaching flow conditions. By means of a model-family vortex frequency calculations were carried out to obtain information about the verification of Froude’s similitude related to the frequency scale. The model-family consists of circular bars with a scale-range 1: 1 up to 1: 5. In comparison to former model tests on square plates to a scale of 1: 1 up to 1: 2, 5, it was possible to extend the scale-range in the present study. The shedding frequency was measured by means of an ADV- probe, which was positioned in the convective wake of the profiles.
Year: 2005