Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637079
Title: Vortex formation in the flow around a lifting aerofoil
Author: Gorman, J.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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Abstract:
This thesis presents an investigation of vortex formation in the flow around a lifting aerofoil both with and without acoustic forcing. The chord Reynolds number range covered is from 3000 to 300000. At low chord Reynolds number, (3000 to 20000), and low incidence, (0 to 8°), vortex formation in the flow around an aerofoil has been studied in a water tunnel. Stability theory and in particular the concepts of absolute and convective instability are applied to the aerofoil wake. It is found that for non zero incidence a region of absolutely unstable flow is associated with the separation bubble. Koch's (1985) global mode selection criteria is applied to the wake and is found to give good agreement with the experimentally measured vortex formation frequency. This implies the existence of a critical profile in the wake which, in conjunction with the aerofoil trailing edge, traps energy at the vortex formation frequency. At higher chord Reynolds numbers, (17000 to 300000), the vortex formation characteristics of the aerofoil are further examined both with and without the excitation of an acoustic resonance. Detailed phase averaged measurements of the aerofoil wake are made allowing examination of its structure during resonance. A novel scheme for the accurate measurement of vortex phase is introduced, based on comparison of vortical structure of the vortex formation region using two-dimensional cross-correlation. The results obtained support a modified version of the acoustic resonance excitation mechanism proposed by of Arbey and Bataille (1983). Vortex street structures considerably different to the classic Kármán vortex street are observed. For antisymmetric streets, the vortex spacing ratio h/l is shown to be widely different from the theoretical value of 0.281 obtained by von Kármán and Rubach.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.637079  DOI: Not available
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