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Modal Analysis of Supersonic Flow Separation in Nozzles

Ragnar Lárusson (Institutionen för tillämpad mekanik, Strömningslära)
Gothenburg : Chalmers University of Technology, 2017. ISBN: 978-91-7597-542-9.
[Doktorsavhandling]

Operating a convergent-divergent nozzle under overexpanded conditions can lead to supersonic flow separation in the divergent section of the nozzle. In this case, an attached oblique shock wave forms at the separation base. The sudden pressure rise across the shock wave can cause damaging lateral pressure forces, or side-loads, to act on the nozzle if the separation line is asymmetric. Such asymmetry can be caused by downstream instabilities stemming from turbulence, external excitation or periodic modes. In this thesis the applicability of applying modal decomposition methods to supersonic nozzle flows was investigated. Axisymmetric RANS and URANS simulations of nozzle flows were investigated using the Arnoldi algorithm and the Dynamic Mode Decomposition,respectively. The Arnoldi method relies on a linearized flow solver and has the advantage of being able to detect asymmetric modes on two dimensional grids. The DMD, however, is a snapshot-based algorithm which needs no explicit linearization of the flow dynamics. Results show that these methods can successfully be applied to supersonic nozzle flows with separation and strong shocks. For example, the Arnoldi method predicted a helical screeching mode with impressive accuracy and The DMD analysis on perturbed 2D URANS flow field was able to detect modes linked to transonic resonance. Finally, Detached Eddy Simulations (DES) on a separated flow inside a Truncated Ideal Contoured Nozzle were performed for two separate nozzle pressure ratios (NPR’s). The simulated sideload were lower than experimentally measured values but within uncertainty range. A three dimensional DMD analysis was performed on the DES data and revealed a strong ovalization mode at the lower NPR and a helical mode which could be linked to a peak in side-load spectrum at the higher NPR.

Nyckelord: Dynamic Mode Decomposition,CFD, Arnoldi, Separated Nozzle Flow, Hybrid RANSLES, Modal Analysis



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Denna post skapades 2017-02-13. Senast ändrad 2017-02-16.
CPL Pubid: 248086

 

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Institutioner (Chalmers)

Institutionen för tillämpad mekanik, Strömningslära (2005-2017)

Ämnesområden

Energi
Transport
Teknisk mekanik
Rymd- och flygteknik
Strömningsmekanik och akustik

Chalmers infrastruktur

Relaterade publikationer

Inkluderade delarbeten:


Linear Stability Analysis Using the Arnoldi Eigenmode Extraction Technique Applied to Separated Nozzle Flow


Comparison of Eigenmode Extraction Techniques for Separated Nozzle Flows


Investigation of Screech in Supersonic Jets Using Modal Decomposition


Hybrid RANS-LES Simulation of Separated Nozzle Flow


Dynamic Mode Decomposition Applied to a Detached-Eddy Simulation of Separated Nozzle Flow


Examination

Datum: 2017-03-10
Tid: 10:00
Lokal: Virtual Development Laboratory, M-huset.
Opponent: Professor Abdellah Hadjadj, Department of Mechanical Engineering, National Institute for Applied Sciences, France

Ingår i serie

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie 4223