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Discrepancies between predicted and measured results have been reported by users of ASHRAE 87.1-1983 "Method of Testing Dynamic Characteristics of Propeller Fans - Aerodynamically Excited Fan Vibration and Critical Speeds." It was believed that these discrepancies were associated with the fact that the standard did not properly take into account the effects of centrifugal stiffening in determining propeller fan critical speeds. The dynamic response of propeller fans was studied using finite element analysis to account for centrifugal stiffening of the blades. The Southwell coefficients were calculated from finite element analysis results at two speed, 0 and 52 rad/sec. This procedure was shown to improve the accuracy of critical speed predictions substantially. It was found that the finite element analysis can be carried out with a model of either the complete fan or a single blade with appropriate boundary conditions.

 

KEYWORDS: vibration, fan blades, fans, calculating, standards, USA, analysis, measuring, speed, operations, properties.

Citation: ASHRAE Transactions, vol.96, pt. 1, Atlanta, 1990