Investigation on the performance of an IDI engine using a novel dual swirl combustor

Abstract In order to determine the flame transfer function of a combustion system only based on isothermal flow field data, three governing mechanisms have been identified which need to be modeled: swirl fluctuations, equivalence fluctuations and velocity fluctuations excited by planar acoustic waves. This study focuses on the generation and propagation of swirl fluctuations downstream of a radial swirl combustor under isothermal conditions. Swirl fluctuations are generated experimentally by imposing acoustic perturbations. Time-resolved longitudinal and crosswise PIV measurements are conducted inside the mixing tube and combustion chamber to quantify the evolution of the swirl fluctuations. The measured flow response is decomposed using spectral proper orthogonal decomposition to unravel the contributions of different dynamical modes. In addition a resolvent analysis is conducted based on the linearized Navier-Stokes equations to reveal the intrinsically most amplified flow structures. Both, the data-driven and analytic approach, show that inertial waves are indeed present in the flow response and an inherent flow instability downstream of the swirler, which confirms the recent theoretical work of Albayrak et al. (Journal of Fluid Mechanics, 879). However, the contribution of these inertial waves to the total swirl fluctuations turns out to be very small. This is suggested to be due to the very structured forcing at the swirler and the amplification of shear-driven modes which are expected to be much more influential for this type of swirler. Overall, this work confirms the presence of inertial waves in highly turbulent swirl combustors and evaluates its relevance for industry-related configurations. It further outlines a methodology to analyze and predict their characteristics based on mean fields only, which is applicable for complex geometries of industrial relevance.

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Direct Assessment of the Acoustic Scattering Matrix of a Turbulent Swirl Combustor by Combining System Identification, Large Eddy Simulation and Analytical Approaches

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4040731 ◽

2018 ◽

Vol 141 (2) ◽

Cited By ~ 1

Author(s):

Malte Merk ◽

Camilo Silva ◽

Wolfgang Polifke ◽

Renaud Gaudron ◽

Marco Gatti ◽

...

Keyword(s):

System Identification ◽

Large Eddy Simulation ◽

Transfer Matrix ◽

Acoustic Scattering ◽

Scattering Matrix ◽

Series Data ◽

Swirl Combustor ◽

Eddy Simulation ◽

Large Eddy ◽

Analytical Approaches

This study assesses and compares two alternative approaches to determine the acoustic scattering matrix of a premixed turbulent swirl combustor: (1) The acoustic scattering matrix coefficients are obtained directly from a compressible large eddy simulation (LES). Specifically, the incoming and outgoing characteristic waves f and g extracted from the LES are used to determine the respective transmission and reflection coefficients via System Identification (SI) techniques. (2) The flame transfer function (FTF) is identified from LES time series data of upstream velocity and heat release rate. The transfer matrix of the reactive combustor is then derived by combining the FTF with the Rankine–Hugoniot (RH) relations across a compact heat source and a transfer matrix of the cold combustor, which is deduced from a linear network model. Linear algebraic transformation of the transfer matrix consequently yields the combustor scattering matrix. In a cross-comparison study that includes comprehensive experimental data, it is shown that both approaches successfully predict the scattering matrix of the reactive turbulent swirl combustor.

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Experimental Study of Transient Mechanisms of Bi-Stable Flame Shape Transitions in a Swirl Combustor

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2017-65003 ◽

2017 ◽

Author(s):

Michael Stöhr ◽

Kilian Oberleithner ◽

Moritz Sieber ◽

Zhiyao Yin ◽

Wolfgang Meier

Keyword(s):

Gas Turbines ◽

High Speed ◽

Hydrodynamic Instability ◽

Mean Flow ◽

Swirl Combustor ◽

Time Resolved ◽

Precessing Vortex Core ◽

Amplification Process ◽

Flame Shape ◽

Shape Transitions

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and 2D flame structures were measured simultaneously using high-speed stereo-PIV and OH-PLIF at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: Firstly, the linear stability analysis (LSA) of a time-varying mean flow and secondly the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flow field such that the flame re-attaches at the nozzle. In summary these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames.

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