Design and development of a precision flow perturbation device

• Main Author: Arwinder Singh.
• Other Authors: Ng Heong Wah
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/54095
• Institution: Nanyang Technological University

This project entailed the design of a perturbation device which would disturb a free jet at a prescribed amplitude and frequency that can be altered using the device. The device was designed with the idea of a piston-crank mechanism in mind where a link can be connected at increasing radii of the disc in order to increase the displacement of the piston and the frequency of the perturbation. This device was then designed using Solidworks along with the stand for the motor so that it can be kept at an elevated level with respect to the pipe on which perturbation will be carried out. The second part of this project consists of a flow visualisation study of a free jet that was excited at different frequencies. Elliptic and rectangular nozzles were used. From knowledge gained from literature review of past studies done on excited nozzles it was found that jets, when excited at their characteristic frequencies, will exhibit structures of higher coherency and vortex pairing will occur more regularly. This found to be true for both the nozzles of AR=3. From the analysis, the author postulated that the characteristic frequency for the elliptic nozzle was between St=0.31 and St=0.60 and for rectangular nozzles, in the region of St=0.50, This was in line with previous studies conducted by Gutmark and Grinstein(1999) and Husain and Hussain(1993) where characteristic frequencies of asymmetric nozzles of AR=3 was postulated to be in the region of St=0.50. In the final part of this project, a numerical study was conducted on a two dimensional pipe flow that was simulated to be perturbed at increasing amplitudes. These perturbations were carried out by introducing a sinusoidal velocity input whose velocity fluctuated about a mean velocity of 0.1m/s. These fluctuations were dependent of the amplitude of the flow. However, the study did not bear fruit as the simulations flows perturbed at increasing amplitudes were exactly the same which in theory is definitely not the case.