Reynolds-Number-Effects and their Influence on Flow Induced Vibrations

Kurzfassung

Engineering structures are often composed of more or less bluff bodies as for example bridge decks, towers or cables. The sections of the individual elements can be sharp-edged or rounded. A main point of the lecture is the question: In which case does the Reynolds No. play a significant role, in particular concerning their influence on the propensity to flow induced vibrations. The paper reviews the results of experiments carried out over a wide range of Reynolds numbers on 2-D sections. The bodies are circular cylinder, a bridge section, and a thick airfoil at high angle of attack. In all cases, variation of Re No. led to dramatic changes in the force coefficients and St No., caused by changes in the topological structure of the separated flow. Concerning the circular cylinder, the possibility will be discussed, that due to the drag crisis in the critical Re No. range selfexcited oscillations can occur. This effect - similar to galloping oscillations - can perhaps lead to wind induced cable vibrations. The important results are, that there are 2-D sections that behave as a bluff- or stremalined body, depending on Re, and that slender bodies with sharp-edged cross-sections may also suffer pronounced Re No. effects.