Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

Abstract

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak GenerationNowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360 deg nonreactive combustor simulator (CS) representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles, allowing the investigation of the hot streaks transport through the high pressure (HP) stage. First, a true scale three injector annular sector of the CS without turbine is assembled and tested at the University of Florence. To generate the hot steaks, the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple, and hot wire anemometers. This paper presents the design process and instrumentation of the trisector CS, with a special focus on large Eddy simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual Reynolds averaged Navier Stokes (RANS) approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry (HWA) measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.

Design of a Centrifugal Compressor Test Rig

“…The development of combustor dates back to as early as 1950's and continues till date. Koupper et al, [11] the varied demands being the prime reason for such continuous developments. With the evolution of Axial turbines and compressors, the development in combustor saw a shift from Tubular type [12] to Can -annular (Tubo-annular) types [11,13].…”

“…Koupper et al, [11] the varied demands being the prime reason for such continuous developments. With the evolution of Axial turbines and compressors, the development in combustor saw a shift from Tubular type [12] to Can -annular (Tubo-annular) types [11,13]. As the combustor's design is influenced by numerous parameters ranging from swirler dimensions [11], effusion cooling holes & their inclinations and the main flow direction [14], the need for optimization increases according to the application.…”

“…The influence of parameters on the main design were initially determined only by experimental studies. However, with the development of numerical simulation and computational sources, the studies have shifted from mere flow visualization studies [15] to optimization [11].…”

“…Simmone et al, [17] conducted extensive CFD simulation to investigate the effects of Non-uniform temperature profile in a turbine blades with much higher accuracy (0.8% deviation). Finally, Koupper et al, [11] were successfully able to optimize the annular combustor for a high pressure turbine with as many as 38 million cells for a sector of the Combustor. Also the Turbulence handling has evolved from a simple closure for RANS equation in [14] to highly complicated and time consuming LES as found in the works of Koupper et al, [11] with a time step of 0.24 micro seconds.…”

Turbulence intensity measurements across a NGV cooled cascade with representative Lean Burn combustor outflow

“…The three sector configuration was adopted to make the central sector flow field less sensitive to the presence of the lateral walls. Details of the CFD-aided design process and of its experimental verification can be found in the works of Bacci et al (2018b) and Koupper et al (2014).…”