Gas turbine combustors typically have been designed through *ad hoc* and heuristic guidelines based on trial-and-error experimentation. This iterative combustor design process raises research and development costs. Computational fluid dynamics (CFD) simulations of turbulent combustion has made considerable progress. For example, original engine manufacturers (OEMs) utilize CFD extensively to guide some of the combustor design processes. Nevertheless, CFD has been limited to a few sample simulations that may not be representative of the entire design space. In turn, this leads to a localized optimal design that may not represent the global optimum. In addition, many of these design approaches do not consider the gas turbine engine enclosure or the plenum environment in which testing will be performed for two reasons. First, the combustor design has been considered insensitive to the enclosure.  Second, excluding the enclosure minimizes the size of the computational domain which reduces computational costs.

In a design process that does not contemplate the combustor enclosure (i.e., “truncated geometry”), the discharge coefficients of the inlet jets are intrinsically unity. Consequently, an optimized combustor without enclosure would need to have the holes resized before manufacturing to account for flow separation (i.e., lower discharge coefficient). A design optimization procedure was implemented to resize the holes of a combustor liner for practical applications. A combustor geometry evaluated without an enclosure was to be reformulated within an enclosure. The objective functions of the combustor with enclosure involved targeting the flow splits of the combustor without enclosure. Latin Hypercube Sampling (LHS) design of experiments (DOE) was utilized to obtain at least a pure quadratic response surface (RS). These were computed using Genetic Aggregate (GA). These RS were, in turn, evaluated by a multiple objective genetic algorithm (MOGA) optimizer. The focus of this study was a small-scale cavity-stabilized combustor. Steady, compressible three-dimensional simulations are performed using a multi-phase Realizable k-e Reynolds-averaged Navier-Stokes (RANS) approach. Combustion-turbulence interaction is modeled with flamelet progress variable (FPV) and Beta-presumed probability density function (PDF). There are eleven input and output parameters corresponding to the combustor hole sizes and associated mass flow rates. The RS obtained with GA were principally of the Kriging kind (with constant and linear trends and damped sinusoid and Gaussian kernels). A combustor hole mass flow rate was mainly determined by its hole size but was also influenced by the other holes. The combustor flow split non-linearity shows that increasing a hole size increases its mass flow rate, but simultaneously decreases another hole flow rate. This was also verified by sensitivity analysis. Due to this non-linearity, matching flow splits between geometry without and with enclosure is challenging and may not be possible for some situations. Thus, it is concluded that optimization of the combustor geometry without the enclosure is not the best route. Rather, it would be better for the geometry to be optimized with the enclosure included in order to account for flow separation and non-linear influence of the combustor holes on the flow field.


Effects of Combustor Enclosure Flow Path on Combustor Design

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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