The Critical Condition for Occurrence of Fluttering of Membrane Suspended in Uniform Air Flow

Very flexible membrane specimens, four fabrics and a thin film, which had been suspended each between windward and leeward supporting bars with a sag in a wind tunnel showed an existence of fluttering state in the respective flow speed region. In the fluttering state each specimen had a minimum flow speed UF2. The mechanical condition on which the fluttering state can occur at UP2 is one of critical condition. An equation which expresses the critical condition was induced theoretically assuming that the condition of static equilibrium of specimen's self weight and the lift should be satisfied at UP2. Then the equation was modified referring the experimental results. This modified equation is very simple one that has three non dimensional variables, which are Fronde number, mass ratio and sag ratio.