VORTICAL FLOW DYNAMICS AND ACOUSTIC RESPONSE OF GAS-TURBINE SWIRL-STABILIZED INJECTORS

Open Access
Author:
Wang, Shanwu
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 30, 2002
Committee Members:
  • Domenic Adam Santavicca, Committee Member
  • Daniel Connell Haworth, Committee Member
  • James Gordon Brasseur, Committee Member
  • Vigor Yang, Committee Chair
  • Andre Louis Boehman, Committee Member
Keywords:
  • Swirling Flows
  • injector dynamics
  • POD
  • mode competition
  • large eddy simulation
  • acoustic admittance
  • acoustic respons
  • Kelvin-Helmholtz instability
  • vortex breakdown
Abstract:
The present research focuses on a time-accurate numerical simulation and analysis of the vortical flow dynamics and acoustic characteristics of gas-turbine swirl-stabilized injectors with different swirl numbers. The primary objectives are · to establish a comprehensive numerical code, validated against experimental data, to simulate turbulent swirling flows; · to explore the dominant physical processes and mechanisms involved in such flows; · to study the effects of inlet conditions, such as swirl number, on flow structures and their dynamic evolution; and · to investigate the acoustic response of injector dynamics to externally imposed excitation. The theoretical formulation is based on the complete conservation equations of mass, momentum, and energy in three dimensions. Turbulence closure is achieved by means of a large-eddy-simulation (LES) technique. The governing equations and associated boundary conditions are solved using a finite-volume approach. Both a four-step Runge-Kutta scheme and an Adam-Bashforth predictor-corrector scheme are implemented for temporal integration. A fourth-order central difference scheme along with sixth-order artificial dissipation is employed for spatial discretization of the convective terms. The code is further equipped with a multi-block domain decomposition feature to facilitate parallel processing in a distributed computing environment using the Massage Passing Interface (MPI) library. As part of the model validation effort, the numerical analysis is first implemented to study the turbulent swirling flows in a dump chamber with two different inlet swirl numbers. Good agreement with experimental data is obtained in terms of mean velocities, turbulence intensities, and turbulent kinetic energy. Results show significant effects of the swirl number on the flow evolution. The swirl number not only affects the time-mean topology of the flowfield, such as vortex breakdown, but also strongly influences the dynamic evolution of the flowfield and acoustic resonance mode of the chamber. After validation, the analysis is implemented to study the vortical flow dynamics in a gas-turbine swirl-stabilized injector as the second part of the present effort. In this flow configuration, air is radially delivered into the injector through three sets of swirl vanes, which are counter-rotating with each other. Several instability modes with well-defined frequencies, such as vortex breakdown, the Kelvin-Helmholtz instabilities in both the streamwise and azimuthal directions, helical instability, centrifugal instability, and their interactions/competitions, are observed in the flowfields. The flowfield is well organized at a low swirl number, and the vortex shedding due to the Kelvin-Helmholtz instability is the dominant mechanism for driving flow oscillations. The flow structure, however, becomes much more complex at a high swirl number, with each sub flow regime dominated with different frequencies and flow patterns. The dynamic response of the injector flow to externally imposed oscillations is examined over a broad range of forcing frequency from 400 to 13,000 Hz. The response can be conveniently characterized in terms of the acoustic admittance and mass transfer functions at the exit. Results can be used as an inlet boundary condition in analyzing the combustion instability characteristics of the main chamber. The influences of external excitations on the injector mean flow structures and turbulence properties appear to be limited. However, the unsteady flow evolution in the injector, such as the instantaneous mass flux and pressure distributions, are significantly modulated in both the spatial and spectral domains.