Browsing by Author "Muiyser, Jacques"
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- ItemInvestigation of large-scale cooling system fan vibration(Stellenbosch : Stellenbosch University, 2016-12) Muiyser, Jacques; Els, Danie J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Air-cooled condenser fans operate under distorted inlet air flow conditions that 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 downstream flow 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 element representation of the fan blade. Good correlation between the simulated and measured response of the fan blade was found. Using this same load profile as 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 negligible when 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 tested against 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.
- ItemSimultaneous measurement of air flow conditions and resultant blade and gearbox loading at large-scale cooling system fans(Stellenbosch : Stellenbosch University, 2012-12) Muiyser, Jacques; Els, D. N. J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Axial flow fans used in large-scale air-cooled steam condensers (ACSCs) may operate under distorted inflow conditions. These conditions occur due to the prevailing wind conditions, the presence of buildings, and the location of the fan within the ACSC. Fans located on the periphery of the ACSC are affected the most due to their exposure to strong winds and the inner fans drawing in air past them. Distorted inflow conditions cause varying fan blade and gearbox loading conditions. The purpose of the investigation was to simultaneously measure the inlet air flow and the resultant blade and gearbox loading conditions of a single fan located on the periphery of a large-scale ACSC. Inlet and heat exchanger bundle outlet air flow velocities were measured using a combination of ultrasonic and propeller anemometers while blade loading was measured with strain gauges attached at the neck of the specific blade being monitored. Strain gauges were also attached to the low-speed fan shaft to measure gearbox loading. Measurements were recorded over a period of 8 days where it was found that increased wind resulted in increased air flow in the axial direction of the fan, which then caused a reduction in average blade loading. This was due to a decreased static pressure rise over the fan. The fan blade was found to vibrate at its own natural frequency of 6 Hz when excited by the variable aerodynamic loading. The aerodynamic loading was extracted from the measured data and was found to correlate well with previous experimental work performed by Bredell et al. (2006a). Shaft bending stresses and torque were found to oscillate at the fan’s rotational frequency of 2Hz with a large torque exerted on the shaft during fan start-up.