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A Linearized Navier-Stokes Equations Methodology for Aeroacoustic and Thermoacoustic Simulations

Time: Fri 2021-02-05 10.00

Location: Zoom webinar, register at: https://kth-se.zoom.us/webinar/register/WN_CH8p_GMmR8iM-5_kzaQ2fg, Du som saknar dator/datorvana kan kontakta sboij@kth.se / Use the e-mail address if you need technical assistance, Stockholm (English)

Subject area: Engineering Mechanics

Doctoral student: PhD student Wei Na , Marcus Wallenberg Laboratoriet MWL

Opponent: Professor Niklas Andersson,

Supervisor: Susann Boij, Linné Flow Center, FLOW, VinnExcellence Center for ECO2 Vehicle design, Competence Center for Gas Exchange (CCGEx), Farkostteknik och Solidmekanik, Marcus Wallenberg Laboratoriet MWL; Gunilla Efraimsson, Linné Flow Center, FLOW, VinnExcellence Center for ECO2 Vehicle design, Farkost- och flygteknik, Teknisk mekanik

Abstract

Aeroengine noise is one of the dominating noise sources in today’s aircraft. Reduction of the aeroengine noise is related to multiphysics phenomena, and that is subject to different mechanisms, e.g., the coupling between turbulence, flame and sound waves. Here, the noise propagating from and interacting with different components of aeroengines with different mechanisms is studied. A numerical methodology solving the linearized Navier-Stokes equations in frequency domain(LNSE) is extended and applied in different applications.

In the compressor, the sound scattering at the tube row heat exchangers in the presence of cross-flow is of interest. When the flow passes through the contraction by two cylinders, there is a strong separation around the cylinder, a jet flow and shear layers are formed. At the shear layers, vorticities are generated and the energy is transferred between the acoustic mode and the vorticity mode, which may lead to the dissipation or amplification of the acoustic energy. Therefore, the numerical methodology LNSE including the energy equation is used to investigate the flow-acoustic interaction in presence of a mean cross-flow.

In order to reduce the fan noise in aeroengines, acoustic liners are used as wall treatments during the sound transmitting from the duct. Thus, in the thesis, a numerical methodology named “unified LNSE approach” is proposed to simulate the acoustic properties of a hybrid liner in an efficient way without compromising the accuracy. The unified LNSE approach allows solving the Helmholtz equation in regions with plane wave propagation and simultaneously solving the LNSE in regions where the acoustic attenuation due to viscothermal losses is significant.

Thermoacoustic instabilities arise when the heat release fluctuations and the acoustic perturbations are in phase. When thermoacoustic instabilities occur, it will lead to a high-level tonal noise that might result in mechanical failure of the combustor chambers. In the thesis, the numerical methodology is developed for prediction of thermoacoustic instabilities. The numerical methodology solving the Helmholtz equation in combination of the flame n - τ model with the low Mach number assumptions is implemented as well.

There are direct and indirect combustion noise in a combustion chamber. The direct combustion noise is mainly caused by the unsteady heat release rate. The indirect combustion noise is due to entropy fluctuations generated in combustion chambers interacting with the accelerating mean flow. In this process, the energy is transferred from the entropy modes to acoustic modes. In this thesis, the entropy wave in a one-dimensional converging nozzle is simulated to analyze the acoustic entropy interactions. 

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Last changed: Jan 27, 2021