Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The aerodynamic performance of a mission-adaptive air inlet for a stealthy unmanned aircraft
was examined using CFX 5.5, a commercial Computational Fluid Dynamics package.
In order to ensure that the numerical results were reliable, the package was validated against
a number of flow situations for which previously-known results exist. This was done for
both external and internal flow, and in all cases the conclusion could be made that the code
produces realistic results.
The simulation of the inlet was done in two steps. A first-order design was simulated using
robust simulation parameters: the focus was on obtaining a "picture" of the flow into the inlet,
not on the quantitative values of flow variables. On account of the results of these simulations,
the design was suitably modified. This second-order design was then simulated using more
accurate simulation parameters, and the results analysed in detail. Comparative simulations
between the two design iterations showed that their pressure recoveries are similar, but that
the distortion of the velocity profile at the engine compressor face is lower for the second-order
design than for the first-order design over a significant portion of the operational range.
When compared with an idealized theoretical analysis, the numerical results showed that the
performance of the inlet was severely degraded at most operating conditions. This is mainly
due to the effects of flow separation ahead of the inlet capture plane. To alleviate this problem,
recommendations for the modification of the design are proposed.
This thesis demonstrates that CFD is a valuable tool for both qualitative and quantitative
evaluation of performance during the design process of an air inlet. / AFRIKAANSE OPSOMMING: Die lugdinamiese werkverrigting van 'n missie-aanpasbare luginlaat vir 'n radarontduikende
onbemande vliegtuig is ondersoek, deur gebruik te maak van CFX 5.5, 'n kommersiële
numeriese vloeidinamika-sagteware pakket.
Om te verseker dat die numeriese resultate betroubaar was, is die pakket gevalideer teen 'n
aantal gevalle waarvoor vooraf-bekende resultate bestaan. Dit is gedoen vir beide interne en eksterne
vloei, en die gevolgtrekking kon gemaak word dat die kode wel realistiese resultate lewer.
Die simulasie van die inlaat is in twee stappe gedoen. 'n Eerste-orde ontwerp is gesimuleer
deur gebruik te maak van robuuste simulasieparameters: die fokus hiervan was om 'n visuele
indruk van die vloeipatrone in die inlaat te kry, nie op kwantitatiewe waardes van die
vloeiveranderlikes nie. Na aanleiding van hierdie resultate van hierdie simulasies is die ontwerp
dienooreenkomstig aangepas. Hierdie tweede orde ontwerp is dan gesimuleer deur gebruik
te maak van meer akkurate simulasieparameters, en die resultate is in detail geanaliseer.
Vergelykende simulasies tussen die twee ontwerps-iterasies het gewys dat hulle drukherwinnings
soortgelyk is, maar dat die distorsie in die snelheidsprofiel by die enjin kompressor-vlak laer is
vir die tweede-orde ontwerp as vir die eerste-orde ontwerp, oor 'n beduidende gedeelte van die
operasionele bestek.
Wanneer dit met 'n ideale teoretiese analise vergelyk word, het die numeriese resultate getoon
dat die werkverrigting van die inlaat ernstig gedegradeer is by meeste operasionele toestande.
Dit kan meestal toegeskryf word aan die effekte van vloei-wegbreking voor die intreevlak
van die inlaat. Om hierdie probleem te verlig, word aanbevelings vir die aanpassing van die
ontwerp voorgestel.
Hierdie tesis demonstreer dat numeriese vloeidinamika waardevolle gereedskap is vir beide kwalitatiewe
en kwantitatiewe evaluering van werkverrigting tydens die ontwerpsproses van 'n luginlaat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53241 |
| Date | 12 1900 |
| Creators | Marais, Louwrens |
| Contributors | Thiart, G. D., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 148 p. : ill. |
| Rights | Stellenbosch University |
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