Adaptive Mesh Refinement for Computational Aeroacoustics

Abstract

This thesis describes a parallel block-structured adaptive mesh refinement (AMR) method that is employed to solve some computational aeroacoustic problems with the aim of improving the computational efficiency. AMR adaptively refines and coarsens a computational mesh along with sound propagation to increase grid resolution only in the area of interest.While sharing many of the same features, there is a marked difference between the current and the established AMR approaches. Rather than low-order schemes generally used in the previous approaches, a high-order spatial difference scheme is employed to improve numerical dispersion and dissipation qualities. To use a highorder scheme with AMR, a number of numerical issues associated with fine-coarse block interfaces on an adaptively refined mesh, such as interpolations, filter and artificial selective damping techniques and accuracy are addressed. In addition, the asymptotic stability and the transient behaviour of a high-order spatial scheme on an adaptively refined mesh are also studied with eigenvalue analysis and pseudospectra analysis respectively. In addition, the fundamental AMR algorithm is simplified in order to make the work of implementation more manageable.Particular emphasis has been placed on solving sound radiation from generic aero-engine bypass geometry with mean flow. The approach of AMR is extended to support a body-fitted multi-block mesh. The radiation from an intake duct is modelled by the linearised Euler equations, while the radiation from an exhaust duct is modelled by the extended acoustic perturbation equations to suppress hydrodynamic instabilities generated in a sheared mean flow. After solving the near-field sound solution, the associated far-field sound directivity is estimated by solving the Ffowcs Williams-Hawkings equation. The overall results demonstrate the accuracy and the efficiency of the presented AMR method, but also reveal some limitations. The possible methods to avoid these limitations are given at the end of this thesis.

A high-order low-Mach number AMR construction for chemically reacting flows

“…The numerical solution is compared against an analytical one to assess the effect of approximate preservation of flux continuities. This may be considered to be a reacting flow analog of the acoustic pulse test performed in [16] for much the same purpose. Later, we re-examine the same problem in a more stringent context, by subjecting a premixed flame to a large, vortically-induced stretch and investigating its effect on the spatial distribution of radicals.…”

Efficient Computation of Spinning Modal Radiation Through an Engine Bypass Duct

“…The code was extended to work on a distributed-memory parallel machine using a message passing interface library and supported body-fitted meshes to solve aeroacoustic problems of practical significance, for example, acoustic radiation from a general aeroengine intake [12]. Spectral analysis proved the stability of the employed high-order spatial schemes on an adaptively refined mesh [28]. The pseudospectra method [29] could analyze transient stability under an AMR environment.…”

“…In an earlier work [28], a block-structured AMR code was constructed and tested against benchmark problems on rectangular meshes. The code was extended to work on a distributed-memory parallel machine using a message passing interface library and supported body-fitted meshes to solve aeroacoustic problems of practical significance, for example, acoustic radiation from a general aeroengine intake [12].…”

Adaptive Mesh Refinement Computation of Acoustic Radiation from an Engine Intake

“…In our previous work [10] the method of AMR was used in the computation of acoustic radiation along and away from an unflanged cylindrical duct. In this work the method is extended to a generic aeroengine intake with a realistic background mean flow, as shown in Fig.…”

“…It is well accepted that block-structured AMR requires less programming efforts and is computationally more effective than cell-structured AMR with respect to communication costs and memory requirements. In this work we extend our earlier effort [10] where a block-structured AMR code was constructed and tested against benchmark problems on rectangular meshes. In order to solve aeroacoustic problems of practical significance, e.g.…”