Steady/unsteady gas turbine combustion simulator
Abstract
A conceptual gas turbine combustion simulator is proposed to study steady and unsteady combustion phenomena at conditions relevant to aviation engines. It is intended to duplicate the flow and combustion characteristics of an aviation engine in a simple laboratory scale device in order to conduct scientific study to provide deeper insight to the complex combustion dynamics problems and other related issues. The combustion simulator is based upon the existing concept of an opposed jet flame burner. The only geometrical difference is, in this case the opposed jet burner is within a confinement. This simulator is termed as a Confined Opposed Jet Flame (COF) burner. A computational approach is used to prove the relevance of this device before developing the experimental test rig. All the computational simulations are performed using a commercial CFD package, viz. FLUENT (time steady computations) and a research CFD code, viz. GEMS (unsteady computations). COF is designed to study both non-premixed and partially premixed flames. To begin with the conceptual COF geometry was optimized by identifying the geometrical parameters that could have a major impact on flame stabilization within the defined combustion zones of COF. The next objective was to conduct a preliminary assessment to study and understand the impact of parameters like flow Reynolds number, Operating conditions, Overall equivalence ratio and a step height, on the complex combustion dynamics of COF. Flow conditions from the entire flow field were extracted from CFD results, to perform detailed analyses with computational data. Along with instantaneous and time averaged flow field plots, several other computational diagnostics were developed to study the unsteady pressure and heat release fluctuations, including power spectral density, mode shape analysis and spatially integrated results. The various types of analyses resulted in valuable insight into the causes and characteristics of unsteadiness. These diagnostics suggest that vorticity and strain rate have a critical role to play in the growth and decay of unsteadiness in the flow field. Having studied the unsteady effects of parametric variation on combustion dynamics, the next step was to find out the impact of these parameters on pollutant emission and combustion efficiency of the COF burner. Steady-state RANS computations using the detailed GRI MECH 3.0 mechanism were used for these simulations. These computations revealed the dependence of pollutant emission and combustion efficiency on the mean flow strain rate. But it will be important to find out the impact of unsteady features of the flow field like vortical structures and acoustic fluctuations on the formation and destruction of pollutant species. This preliminary study lays a basic foundation and motivation to develop the confined opposed jet flame simulator to conduct fundamental study on combustion dynamics at a wide range of operating conditions.
Degree
M.S.M.E.
Advisors
Mongia, Purdue University.
Subject Area
Mechanical engineering
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