Experimental and numerical analysis of axial flow fans

Augustyn, Ockert Philippus Hermanus (2013-12)

Thesis (MScEng)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: The majority of power stations in South Africa are located in coal rich, but arid regions where wet-cooled condenser systems are not feasible from an environmental and economic perspective. Consequently the focus on power generation cooling has shifted towards dry-cooling systems using air-cooled steam condensers (ACSC). The steam passing through the ACSC units is cooled by an air-draught, mechanically induced by large diameter axial flow fans. Consequently the effectiveness of the cooling is impacted by the performance of these fans, which ultimately affects the overall efficiency of the power plant. However, due to the large diameters (> 10 m) of these fans, their performance is predicted based on small scale test results using the fan scaling laws. The objective of this project was to develop a methodology which accurately predicts the fan performance of more than one fan configuration using computational fluid dynamics (CFD) software and validating the results with experimental tests. Four fans were considered in this study of which three were scaled fan models of large air-cooled axial fans. The performance of the scaled fan models (L1-, L2- and N-fan) were measured in a type A, BS 848 standard fan test facility. The geometries of the fans were scanned three-dimensionally to obtain 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 computational domains while implementing the multiple reference frames (MRF) and steady RANS approach. Three variations of the k-ε turbulence model were also investigated. Noticeable differences were found between the experimental and numerical results of the B-fan. Good correlations between the numerical and experimental fan static pressure, fan power and fan static efficiency were found for the two scaled model fans over a large operating range. The performance of the full scale fans, however, did not correlate well with the performance of the scaled models. It is concluded that accurate simulations of axial fans are possible although these domains require a large number of mesh elements. It is recommended that further research is carried out to investigate the relationship between full scale and small scale fan models.

AFRIKAANSE OPSOMMING: Die meerderheid steenkool kragstasies in Suid-Afrika is geleë in droë, maar steenkool ryke streke waar natverkoelde kondensor stelsels uit ʼn omgewings en ekonomiese perspektief nie geskik is nie. Die fokus in kragopwekking verkoeling het dus verskuif na droë-verkoelings stelsels en spesifiek die gebruik van lugverkoelde stoomkondensors (LVSKs). Die stoom in LVSK eenhede word verkoel deur atmosferiese lug wat meganies geïnduseer word deur groot aksiaalvloeiwaaiers. Die effektiwiteit van die verkoelingsproses word gevolglik beïnvloed deur die werksverrigting van hierdie waaiers wat uiteindelik die algehele effektiwiteit van die kragstasie beïnvloed. As gevolg van hierdie waaiers se grootte word hulle werksverrigting egter bepaal op grond van kleinskaal toetsresultate en deur gebruik te maak van die waaierskaleringswette. Die hoofdoelwit van hierdie projek was om ‘n metodiek te ontwikkel wat die werksverrigting van ʼn aksiaalwaaier akkuraat kan voorspel vir ʼn verskeidenheid opstellings, deur gebruik te maak van berekenings vloei meganika (BVM) sagteware en die resultate eksperimenteel te verifieer. Die projek het vier waaiers ondersoek waarvan drie van hierdie waaiers geskaleerde modelle van groot lugverkoelde aksiaalwaaiers was. Die werksverrigting van die geskaleerde waaiers (L1-, L2- en N-waaier) was met ‘n tipe A, BS 848 standaard waaier toetsfasiliteit gemeet. Die geometrie van dié waaiers was ook drie-dimensioneel opgemeet vir simulasie doeleindes. Die B-waaier, ‘n 8 lem aksiaalwaaier, wat ontwerp is deur Bruneau (1994) was slegs numeries ondersoek. Die L2-, N- en Bwaaier was gesimuleer in verskillende berekeningsdomeine deur gebruik te maak van die multi verwysingsraamwerk en gestadigde vloeiberekenings benaderings. Drie k-ε turbulensie modelle was ook ondersoek. Merkbare verskille tussen die eksperimentele en numeriese resultate van die Bwaaier was waargeneem. Goeie korrelasie tussen die eksperimentele en numeriese resultate van die geskaleerde waaiers vir ‘n wye bedryfsbestek was gevind. ‘n Vergelyking tussen die volskaal en kleinskaal waaiers se werksverrigting het egter beduidende afwykings aangetoon. Deur gebruik te maak van ‘n groot aantal selle in die berekeningsdomein was dit moontlik om ʼn verskeidenheid aksiaalvloeiwaaiers akkuraat te simuleer. Verdere navorsing wat die verhouding tussen volskaal en kleinskaal waaiers ondersoek woord aanbeveel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85720
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