Thesis (PhD (Mechanical Engineering))--University of Stellenbosch, 1990. / Leaves printed on single pages, preliminary pages i- viii and numbered pages 1-1-R5. Includes bibliography, list of tables and figures and list of appendices. Digitized at 330 dpi black and white PDF format (OCR),using KODAK i 1220 PLUS scanner. / ENGLISH ABSTRACT: A numerical procedure for predicting the effect of inlet flow distortions on the
performance of axial flow fans is proposed. The study is aimed specifically at
fans of low solidity and low hub-to-tip ratios, which have attained some
importance with the advent of large directly air-cooled power stations in
certain arid regions of the world. The numerical model is an extension to
cylindrical polar coordinates of the SIMPLEN algorithm that has been developed by the author previously.
The algorithm is implemented in a computer code, FLOVAX, which solves the
incompressible Navier-Stokes equations, augmented by the k-Ɛ model of
turbulence, on a computational domain that is aligned with the cylindrical polar
coordinate system. Several relatively simple flow problems are solved to verify
the code: laminar stagnation flow, laminar flow near a rotating disk, turbulent
flow near a propeller, turbulent flow through an abrupt axisymmetric expansion,
and turbulent swirling flow in an annulus. Good agreement is obtained between
the numerical solutions and the corresponding analytical, empirical or published
experimental and numerical results.
Some experimental results are also presented: measurements of shaft power,
volume flow rate and static pressure rise were taken in a setup comprising an
axial flow fan mounted in the wall of a wind tunnel. The wind tunnel was used
to provide flow across the fan intake, thus establishing distorted inflow
conditions. Detailed measurements of the velocity and static pressure
distributions in the duct downstream of the fan rotor were also performed. It
is clear from the results that flow across the intake of the test fan has a
detrimental effect on its performance in that an increased amount of power is
necessary to deliver the same flow rate as with no crossflow.
In the numerical predictions, blade element theory is used to model the thrust
and torque exerted by the fan blades on the air. The numerical results
generally confirm the results of the experiment, although the increase in power
is underestimated: an increase of only approximately half of the measured
increase is predicted. Several recommendations for improvement of the numerical
procedure are made. / AFRIKAANSE OPSOMMING: 'n Numeriese prosedure vir die voorspelling van die invloed van versteurings in inlaatvloei op die werking van aksiaalwaaiers word daargestel. Die studie is spesifiek gemik op waaiers van lae soliditeit en lae lempunt-tot-naafverhoudings. Waaiers van hierdie tipe het belangrikheid verwerf sedert die onlangse totstandkoming van groot lugverkoelde kragstasies in sekere droe werelddele. Die numeriese model is 'n uitbreiding na silindriese poolkoordinate van die SIMPLEN-algoritme wat voorheen deur die skrywer ontwikkel is. Die algoritme word geimplementeer in 'n rekenaarkode, FLOVAX, wat die onsamedukbare Navier-Stokes-vergelykings, aangevul deur die k-Ɛ-turbulensiemodel, oplos op 'n berekeningsgebied wat saamval met die silindriese poolkoordinaatstelsel. Verskeie relatief eenvoudige vloeiprobleme word opgelos ter verifikasie van die kode: laminere stagnasievloei, laminere vloei op 'n roterende skyf, turbulente vloei deur 'n propeller, turbulente vloei deur 'n aksiaalsimmetriese vernouing, en turbulente roterende vloei in 'n annulus. Goeie ooreenstemming tussen die numeriese oplossings en die ooreenstemmende analitiese, empiriese of gepubliseerde eksperimentele en numeriese resultate is verkry. Eksperimentele resultate word ook aangebied: metings van asdrywing, volumevloei en statiese drukstyging is geneem in 'n opstelling wat bestaan het uit 'n aksiaalwaaier wat in die wand van 'n windtonnel gemonteer is. Die windtonnel is gebruik om versteurde-invloei-toestande te genereer in die vorm van dwarsvloei oor die waaier-inlaat. Snelheids- en statiese drukverdelings in die kanaal stroom-af van die waaierrotor is ook gemeet. Dit blyk duidelik uit die resultate dat die dwarsvloei oor die inlaat van die toetswaaier 'n nadelige uitwerking het op die werking daarvan in die opsig dat meer drywing nodig is om dieselfde vloeitempo te handhaaf as wat die geval is sonder dwarsvloei. Vir die numeriese voorspellings word van lem-element-teorie gebruik gemaak om die stukrag en draaimoment wat deur die waaier op die lug uitgeoefen word, te modelleer. Die numeriese resultate bevestig oor die algemeen die eksperimentele resultate, alhoewel die drywingstoename onderskat word met sowat die helfte van die gemete toename. Verskeie aanbevelings ter verbetering van die numeriese prosedure word gemaak.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5747 |
| Date | 03 1900 |
| Creators | Thiart, G. D. |
| Contributors | Von Backstrom, T. W., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | [208] p. : ill. |
| Rights | University of Stellenbosch |
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