Computational acoustics of confined turbulent flows: Swirl combustor and venturi cavitation
Abstract
It has been well established that flame generated sound is the origin of combustion instabilities in swirl combustors featuring lean premixed flames. Understanding of aeroacoustics in swirl combustors can help understand better the control/suppression of these combustion instabilities. Large eddy simulation (LES) featuring high-order numerics and non-reflecting boundary conditions has been developed to study aeroacoustics of swirl combustors. The code has been validated for three different cases. LES results were found to be in reasonable agreement with the available experimental data. An important objective of this study was also to assess the accuracy of hybrid approach to predict aeroacoustics of swirl combustors. Ffocws Williams-Hawkings (FWH) equation gives poor predictions for far-field sound in swirl combustors. The poor predictions of FWH are due to the strong convection effects in the far-field region of swirl combustors which are not accounted in this equation. Linearized Euler equations (LEE) which account for the convection effects were considered. LEE predictions of far-field sound were validated using the directly computed sound from LES. LEE predictions of far-field sound are found to be in reasonable agreement with LES results. Additional noise in the high frequency region is observed in LEE which is due to the lack of viscous effects in this set of equations. A major road block in the efficiency of high speed hydraulic devices is the formation of cavitation. A better understanding of cavitation and its control is necessary for higher efficiency of these hydraulic devices. The LES code was modified to study cavitating flow in a venturi-type geometry. Flow acceleration due to area contraction and recirculation due to area expansion are qualitatively captured. Local vorticity is intensified by the vapor in cavitating regions. Dilatation and baroclinic torque terms are identically zero for the non-cavitating flows, however are non-zero for cavitating flows with dilatation term being about two orders of magnitude larger than the baroclinic torque term.
Degree
Ph.D.
Advisors
Frankel, Purdue University.
Subject Area
Mechanical engineering
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