Keywords

Transition to turbulence, Co-existence of laminar and turbulent flow, Isosceles triangular duct, Wall pressure fluctuations

Abstract

An experimental investigation was performed to ascertain the nature of turbulence in a narrow apex angle isosceles triangular duct. The study involved the design and construction of a low noise, low turbulence wind tunnel that had an isosceles triangular test section with an apex angle of 11.5[degrees]. Experiments involved the measurement of velocity fluctuations using hot wire anemometry and wall pressure fluctuations using a condenser microphone. Measurement of the velocity fluctuations reconfirms the coexistence of laminar and turbulent regions at a given cross section for a range of Reynolds numbers. The laminar region is concentrated closer to the apex while the turbulent region is found closer to the base. The point of transition is a function of the Reynolds number and moves closer to the apex as the flow rate is increased. Moreover, it was found in this investigation that traditional scaling of the turbulent statistical quantities do not hold good in this geometry. Although velocity fluctuations showed distinctive flow regimes, no such distinction could be seen in the dynamic wall pressure data. The nature of the dynamic wall pressure was uniform throughout the entire cross section suggesting that wall pressure fluctuations, unlike the velocity fluctuations, are able to travel from the base to the apex, without being damped. This implies that the relationship between the velocity and the pressure fluctuations applicable in the other systems does not hold well in a narrow apex angle isosceles triangular duct. Further, the typical scaling relationships applied to wall pressure spectra of other geometries doesn't apply in this scenario and the ratio of the RMS pressure fluctuation to the mean shear is much higher compared to a flat plate or pipe flow situation.

Notes

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Graduation Date

2007

Semester

Fall

Advisor

Kapat, Jayanta

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical, Materials and Aerospace Engineering;

Degree Program

Mechanical Engineering

Format

application/pdf

Identifier

CFE0001955

URL

http://purl.fcla.edu/fcla/etd/CFE0001955

Language

English

Release Date

December 2007

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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