Study of Flow and Convective Heat Transfer in a Simulated Scaled Up Low Emission Annular Combustor

Abstract

Modern dry low emissions (DLE) combustors are characterized by highly swirling and expanding flows that makes the convective heat load on the gas side difficult to predict and estimate. A coupled experimental–numerical study of swirling flow inside a DLE annular combustor model is used to determine the distribution of heat transfer on the liner walls. Three different Reynolds numbers are investigated in the range of 210,000–840,000 with a characteristic swirl number of 0.98. The maximum heat transfer coefficient enhancement ratio decreased from 6 to 3.6 as the flow Reynolds number increased from 210,000 to 840,000. This is attributed to a reduction in the normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.98 for the Reynolds number range investigated. The location of peak heat transfer did not change with the increase in Reynolds number since the flow structures in the combustors did not change with Reynolds number. Results also showed that the heat transfer distributions in the annulus have slightly different characteristics for the concave and convex walls. A modified swirl number accounting for the step expansion ratio is defined to facilitate comparison between the heat transfer characteristics in the annular combustor with previous work in a can combustor. A higher modified swirl number in the annular combustor resulted in higher heat transfer augmentation and a slower decay with Reynolds number.

Investigation of isothermal convective heat transfer in an optical combustor with a low-emissions swirl fuel nozzle

“…The realizable k-ε turbulence model [34] was used for the analysis of the combustor flow for Reynolds numbers up to with respect to the combustor diameter. The RNG k- turbulence model was considered initially as suggested by Patil et al [19,22] for swirling flows; however the results using the realizable k- model showed better convergence and resulted in more realistic velocity and heat transfer distributions.…”

“…The work of these authors included isothermal convective heat transfer measurements supplemented by numerical simulations and flow characterization using particle image velocimetry (PIV). The work by Patil et al [22] reported Nusselt numbers several times higher than those obtained from the Dittus-Boelter equation, suggesting that the correlation underestimates the convective heat loads within burners. Recent work by Andreini et al [24] and Lorenzo [25] have also experimentally and computationally studied the isothermal convective heat transfer and flow within combustors using a three swirl nozzle combustor model.…”

“…Investigators [19,22,23] typically place the heater on a thermally insulating surface (foams/cork with W m -1 K -1 ) to minimize the heat loss and any three dimensional conduction effects. This is unfortunately not applicable for the quartz liner, as its thermal conductivity equals 1.4 W m -1 K -1 [30] at ambient conditions.…”

“…While combustor cooling technologies have been studied extensively in the open literature [17,18], information on combustor heat loads is lacking. Combustor convective heat transfer has been studied by Ekkad and coworkers for both can [19,20,21] and annular [22,23] combustor geometries, using approximated swirlers representative of industrial fuel nozzles. The work of these authors included isothermal convective heat transfer measurements supplemented by numerical simulations and flow characterization using particle image velocimetry (PIV).…”

Stability analysis forn-periodic arrays of fluid systems

“…The ubiquity of fluid systems characterized by an n-periodic arrangement of identical units or by multi-periodic geometric features has spawned a great deal of analyses and simulations: flow in wavy or grooved channels [9,15,16,40] or past arrays of roughness elements and vortex generators [6], acoustics in periodic wave-guides [1], energy extraction from an buoy array [12] and, of course, flow in turbomachines [8,13,14,20,23,24,30] and combustors [5,28,29,31,38,39,45] are but a few examples that fall under this category. Not surprisingly, specific analysis and simulation techniques that efficiently address this periodicity have been developed, in particular for turbomachinery applications, typically describing blade-to-blade dynamics, aeroelastic properties, and rotor-stator interactions.…”