Experimental and numerical analysis of axial flow fans

[摘要] ENGLISH ABSTRACT: The majority of power stations in South Africa are located in coal rich, but aridregions where wet-cooled condenser systems are not feasible from anenvironmental and economic perspective. Consequently the focus on powergeneration cooling has shifted towards dry-cooling systems using air-cooledsteam condensers (ACSC). The steam passing through the ACSC units is cooledby an air-draught, mechanically induced by large diameter axial flow fans.Consequently the effectiveness of the cooling is impacted by the performance ofthese fans, which ultimately affects the overall efficiency of the power plant.However, due to the large diameters (> 10 m) of these fans, their performance ispredicted based on small scale test results using the fan scaling laws.The objective of this project was to develop a methodology which accuratelypredicts the fan performance of more than one fan configuration usingcomputational fluid dynamics (CFD) software and validating the results withexperimental tests. Four fans were considered in this study of which three werescaled fan models of large air-cooled axial fans. The performance of the scaledfan models (L1-, L2- and N-fan) were measured in a type A, BS 848 standard fantest facility. The geometries of the fans were scanned three-dimensionally toobtain the models for simulation purposes. The other fan considered was an 8-bladed axial fan designed by Bruneau (1994) and referred to as the B-fan.Simulations were carried out for the L2-, N- and B-fan for different computationaldomains while implementing the multiple reference frames (MRF) and steadyRANS approach. Three variations of the k-ε turbulence model were alsoinvestigated.Noticeable differences were found between the experimental and numericalresults of the B-fan. Good correlations between the numerical and experimentalfan static pressure, fan power and fan static efficiency were found for the twoscaled model fans over a large operating range. The performance of the full scalefans, however, did not correlate well with the performance of the scaled models. Itis concluded that accurate simulations of axial fans are possible although thesedomains require a large number of mesh elements. It is recommended that furtherresearch is carried out to investigate the relationship between full scale and smallscale fan models.

[发布机构] Stellenbosch University