Browsing by Author "Louw, Francois George"
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- ItemInvestigation of the flow field in the vicinity of an axial flow fan during low flow rates(Stellenbosch : Stellenbosch University, 2015-12) Louw, Francois George; Von Backstrom, T. W.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Large axial flow fans (≈9 m in diameter) are used in air-cooled heat exchangers (ACHEs). Adverse inflow conditions occur in these systems, especially near the periphery of the air-cooled heat exchanger (ACHE) platform, affecting reduced flow rates through the fans located in these regions. The focus of the present study is to investigate the flow field in the vicinity of an axial flow fan during these low flow conditions, by means of experimentation and numerical analyses. A 1.542 m diameter model of an axial flow fan, termed the B2a-fan, is constructed and tested in a British standard 848, type A test facility to obtain its characteristic curves. A wireless system to conduct blade surface pressure measurements (BSPMs) on both the pressure and suction sides of a fan blade is also developed and implemented. An eighth sector of the fan is modelled using the commercial CFD code, ANSYS Fluent 14.0, for a range of flow rates. Pearson correlation factors of RP; Fs = 0:997 and RP; Fs = 0:990 are obtained for the respective characteristic curves of fan static pressure and static efficiency. Factors of RP;BSPM & 0:990 are obtained for more than 90% of the BSPMs along circumferential sections of a blade, at different radii. These correlations validate the numerical model. Flow field visualizations show that the flow field becomes more unstable as the flow rate through the fan is decreased with considerable increases in radial velocity. Instability starts near the blade root and progressively moves towards higher blade spans with a decrease in flow rate. A deviation occurs between the numerically calculated blade sectional lift and drag characteristics and the two-dimensional NASA LS 0413 aerofoil data at low flow rates. The highest blade sectional lift coefficients occur near the hub and decrease towards higher blade spans. An Euler turbo-machinery analysis of the flow field data shows that the component of Coriolis power is close to zero at near-design flow rates, whereas the aerodynamic power component is almost equal to the total power applied by the fan. However, as the ow rate decreases a gradual inversion of this characteristic is observed. Lastly, a new simplified fan model in the form of an actuator-disc model (ADM) is developed, termed the Reverse engineered empirical actuator-disc model (REEADM). This model implements the blade sectional lift, drag and radial force coefficients calculated from the CFD data. The results obtained from this model provides a fair comparison to the experimental fan characteristics at near-design flow rates, but a deviation is observed for low flow rates, although an improvement is made compared to the original ADM.