Experimental Investigation of the Flow Field and the Heat Transfer on a Scaled Cooled Combustor Liner With Realistic Swirling Flow Generated by a Lean-Burn Injection System

Abstract

Lean burn swirl stabilized combustors represent the key technology to reduce NOx emissions in modern aircraft engines. The high amount of air admitted through a lean-burn injection system is characterized by very complex flow structures such as recirculations, vortex breakdown and processing vortex core, that may deeply interact in the near wall region of the combustor liner. This interaction and its effects on the local cooling performance make the design of the cooling systems very challenging, accounting for the design and commission of new test rigs for detailed analysis. The main purpose of the present work is the characterization of the flow field and the wall heat transfer due to the interaction of a swirling flow coming out from real geometry injectors and a slot cooling system which generates film cooling in the first part of the combustor liner. The experimental setup consists of a non-reactive three sector planar rig in an open loop wind tunnel; the rig, developed within the EU project LEMCOTEC, includes three swirlers, whose scaled geometry reproduces the real geometry of an Avio Aero PERM (Partially Evaporated and Rapid Mixing) injector technology, and a simple cooling scheme made up of a slot injection, reproducing the exhaust dome cooling mass flow. Test were carried out imposing realistic combustor operating conditions, especially in terms of reduced mass flow rate and pressure drop across the swirlers. The flow field is investigated by means of PIV, while the measurement of the heat transfer coefficient is performed through Thermochromic Liquid Crystals steady state technique. PIV results show the behavior of flow field generated by the injectors, their mutual interaction and the impact of the swirled main flow on the stability of the slot film cooling. TLC measurements, reported in terms of detailed 2D heat transfer coefficient maps, highlight the impact of the swirled flow and slot film cooling on wall heat transfer.

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

“…The Nusselt numbers were normalized with respect to the Dittus-Boelter correlation (Eq. 2) for fully developed turbulent pipe flow and the result is reported as an enhancement (augmentation) along the combustor wall as done by previous researchers [19][20][21][22][23][24].…”

“…The normalized flow field within the combustor for the different mass flows was approximately self-similar for the range of Reynolds numbers measured and for the swirl number of the fuel nozzle (0.74 ). The self-similarity in combustor flows has also been reported for other burner geometries and fuel nozzles [36,24]. For this reason, only the normalized flow field for the case is shown in Figure 12.…”

“…A consistent observation was also made by Dellenback et al [14] for different swirl and Reynolds numbers, with their peak heat transfer on average step heights (0.16 for their setup) upstream of their re-attachment point. This mismatch has not been reported in more recent investigations of annular combustor models [22,24]. The mismatch could be due to an increased tangential and axial shear, analogous to increased transport of energy per the Reynolds analogy, as the flow turns back from the reattachment point into the corner recirculation.…”

“…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. Their results include the effects of neighboring nozzles and of the cooling film at the start of the liner.…”

Numerical analysis of the dynamic flame response of a spray flame for aero-engine applications

“…The PERM injector, investigated in this paper, is a double swirler airblast atomizer developed to achieve partial evaporation inside the inner duct and rapid mixing within the combustor, optimizing the location and stability of the flame. Further details about the PERM injector can be found in papers by Kern et al and Andreini et al 1,2 Other studies on the flow field generated by a PERM injector and its interaction with the cooling system at combustor walls can be found in Andreini et al and Mazzei et al 3,4 One of the most critical issues of lean combustion technology is the possible occurrence of combustion 1 Department of Industrial Engineering, University of Florence, Italy 2 Combustor Technology, GE Avio S.r.l., Rivalta di Torino, Italy instabilities related to a coupling between pressure oscillations and unsteady heat release. Such instabilities may damage the combustor's components and limit the range of stable operating conditions.…”