Investigation of large-scale cooling system fan vibration

[摘要] ENGLISH ABSTRACT: Air-cooled condenser fans operate under distorted inlet air flow conditionsthat may lead to high levels of blade vibration. Three case studies were considered where full-scale strain gauge measurements were conducted at three separate fan installations. The measurements showed high dynamic blade loading for two of these cases. Laboratory experiments confirmed that blade vibration is a function of inlet flow distortion as well as downstreamflow obstructions such as the fan bridge. These findings were used to create a potential flow simulation that can be used to determine the aerodynamic blade loading profile exerted on a fan blade as a function of its rotational position. The simulated load profile for a fan operating under distorted inlet air flow conditions was applied to a dynamically equivalent finite elementrepresentation of the fan blade. Good correlation between the simulated and measured response of the fan blade was found. Using this same load profileas excitation force in the multibody simulation of the dynamics of a complete fan system, it was found that the effect of supporting bridge stiffness is negligiblewhen compared to the effect of the ratio between the fan's rotational speed and the first natural frequency of the blades. This same result was obtained when modelling the fan system as a collection of single degree-offreedom subsystems and applying an equivalent aerodynamic load obtained from a measured response. The results obtained in this study were testedagainst the test cases where the different observations could be explained.Additionally, design recommendations could be generated based on the fan system's structural and operational parameters.

[发布机构] Stellenbosch University