A master thesis from Aalborg University
Large Eddy Simulation On Vortex Shedding For A Helical-Twisted Cylinder Subjected To Crossflow
Author(s)
Term
4. semester
Education
Publication year
2020
Submitted on
2020-06-16
Pages
69 pages
Abstract
Helical-twisted cylinders are used in safety applications. Due to its imperfect cross-section a better grip is achieved. In this Master thesis, a LES turbulence model is made to predict the behavior of vortex shedding on helical-twisted profiles. A numerical model for a circular cylinder is investigated and compared to several configurations of the groove’s height (e) and pitch (p). This comparison is carried out in order to find the design in which the suppression of vortex-induced vibrations is optimized. Simulations are done by subjecting the body of six different cylinders to an air crossflow, with a Reynolds number of 3.7·10^4. The aerodynamic force coefficients are also recorded for the evaluation of the vortex shedding reduction mechanism. It is found that the helical-twisted profile with p/D = 1 and e/D = 0.05 effectively mitigate the vortex shedding frequency by 16%, in comparison to the circular cylinder. This is related to the damping of the fluctuating lift forces and their spanwise correlation. Therefore, improvements in the three- dimensional disturbance by the near wall wake are achieved. With regard to the other helical-twisted pipe configurations, they are proven to be insufficient for this matter, thus concluding that deeper or larger cavities can lead to an exacerbation of the vortex shedding phenomena. Nevertheless, damping of the lift force amplitude fluctuations is achieved for the cases of p/D = 1 e/D = 0.2, p/D = 2 e/D = 0.1 and p/D = 0.5 e/D = 0.1.
Keywords
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