Hybrid Noise Simulation for Enclosed Configurations

• Main Author: Lackhove, Kilian
• Format: Others
• Language: en
• Published: 2018
• Online Access: http://tuprints.ulb.tu-darmstadt.de/7611/1/Dissertation_Kilian_Lackhove_2018-07-24.pdf; Lackhove, Kilian <http://tuprints.ulb.tu-darmstadt.de/view/person/Lackhove=3AKilian=3A=3A.html> : Hybrid Noise Simulation for Enclosed Configurations. Technische Universität, Darmstadt [Ph.D. Thesis], (2018)

Future air traffic regulations are going to further limit the noise and pollutant emissions of aero engines in a way that can only be met by the comprehensive migration towards lean premixed combustion based aero engine designs. Compared to conventional rich-quench-lean setups, these next generation combustion systems are more prone to thermoacoustic instabilities caused by combustion noise. For this reason, improved methods for the prediction and investigation of combustion noise and thermoacoustic instabilities are required. Consequently, a hybrid Computational Aeroacoustics (CAA) method is devised, implemented and applied to two enclosed, reactive configurations in this work. The method comprises a low Mach number flow solver, a dedicated acoustics tool and a coupling layer, which bridges the different numerical schemes and physical phenomena. In addition to traditional aeroacoustic problems, the method is applicable to enclosed configurations with complex geometries, while maintaining the favorable computational efficiency of common hybrid methods. Its key components are the newly developed acoustics solver and the corresponding coupling layer. For the description of the reacting flow field, an established, finite volume based flow solver is equipped with the coupling interface. By employing the high order spectral/hp element method in a discontinuous Galerkin formulation, the CAA solver efficiently accounts for acoustic wave propagation in complex, three-dimensional geometries. Its implementation is focused on stability and flexibility to allow for an easy adaption to industrial applications, such as combustion noise. This is achieved by solving the unconditionally stable Acoustic Perturbation Equations (APE) and using a set of Riemann solvers that can operate on variable density base flows. The developed coupling layer enables bi-directional communication of both solvers at run-time, without limiting their spatial and temporal resolutions, even when applied to coinciding domains. Their different length scales and discretization methods are overcome by a linear interpolation in time and a spatial, implicit low pass filter, that operates on an intermediate representation of the flow fields. The applicability of the hybrid CAA method is investigated by means of two laboratory scale combustors of increasing complexity. The first setup features a half-dump combustor, that facilitates a basic validation of the CAA solver and the coupling. It is shown that the short length scale base flow fields are sufficiently represented in terms of the CAA expansion by the coupling layer. In the obtained acoustic fields, the behavior of the system's first eigenmode is well reproduced. The instigation of a second eigenmode was not observed in the experimental noise spectrum but is in agreement with a similar hybrid CAA simulation. The second configuration is a pressurized burner, operated by a swirl stabilized, premixed flame. It is already beyond the capabilities of most available CAA tools and features most phenomena present in industry scale combustion systems. In the considered frequency range, the prevalent eigenmode is very well predicted. Independent of the acoustic governing equations, the developed method is estimated to require less than a fifth of the computational effort of a direct noise simulation for the considered configuration.