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Discrepancies between predicted and measured results have been reported by users of ASHRAE Standard 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 take into account the effects of centrifugal stiffening in determining propeller fan critical speeds. To determine whether this was true, ASHRAE initiated ASHRAE Research Project RP-477, "Development of a Method to Predict Vibration Response of Propeller Fans under Actual Operating Conditions." The objectives of this project were:

  1. Identify and modify, if necessary, a commercially available finite element program that runs on personal microcomputers and that takes into account centrifugal stiffening; and
  2. Use the program identified in (1) to help explain discrepancies that reportedly exist between propeller fan critical speeds oredicted in accordance with ASHRAE Standard 87.1 and the corresponding critical speeds measured on the same fans in simulated operating conditions.

This paper discusses the influence of riveted spiderto- blade connections on the vibration response of propeller fans. Experimental test results and analytical analyses using finite elementechniques indicate that the resonance frequencies of fans are significantly affected by the type and spacing of rivets, the quafity of the rivet connection, and the variations in the degree of camber and curvature of the fan blades in the vicinity where the blades are attached to the fan spider.

Citation: ASHRAE Transactions, vol. 95, pt. 2, Vancouver, BC 1989