Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Mechanical and Manufacturing Engineering

First Advisor

Mr. C. Gibbons

Second Advisor

Dr. S. McCarthy


Textile air-distribution systems are air permeable materials used for air delivery applications where problems associated with solid steel ducting, such as condensation, local draughts, noise and hygiene are to be eliminated. The aim of this project was to investigate the causes of duct wall vibration in textile air-distribution systems. This was undertaken by consideration of the three aspects of a fluid dynamics problem; a) theoretical analysis, b) experimental analysis and c) analysis using Computational Fluid Dynamics.

The aspect of textile air-distribution systems is still at an infancy stage and no publicised research was encountered in this area. Thus, the approach taken was to investigate flow situations for solid duct configurations and then to apply these design criteria to textile ducting. The theoretical analysis revealed several possible sources of duct wall vibration.

Experimental investigations showed that the main causes of the duct wall vibrations were due to the fan. At the exit from a centrifugal fan, a cut-off section exists causing air delivery from as little as half of the diffuse duct. This causes a large positive velocity profile in the upper section of the diffuse duct, with a negative profile in the lower section of the duct. There is a high degree of turbulence following the cut-off section. This turbulence decreases along the length of the duct, and is further decreased if a perforated plated or a textile cone is placed after the fan. The frequency of the fundamental mode of vibration and possible sources of resonance were also calculated.

The FLUENT Computational Fluid Dynamics software package was utilised to model the tested configurations. These models show the same trends as the experimental results. From these models, a clear picture of the flow situation for each case is evident.

Upon completion of this project, the importance of adhering to fan manufacturer’s design guidelines and basic duct design principles is apparent. To avoid the adverse effects of the centrifugal fan cut-off, a solid walled duct, of a length equivalent to 4 duct diameters, should be placed after the cut-off section.


Submitted to the National Council for Educational Awards, January 1997

Forbairt (ARP/92/115)

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