Aerodynamic characteristics of a mission-adaptive stealthy air inlet

Marais, Louwrens (2003-12)

Thesis (MScEng)--Stellenbosch University, 2003.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53241
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