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Stenotic Flows: Direct Numerical Simulation,Stability and Sensitivity to Asymmetric ShapeVariations
KTH, School of Engineering Sciences (SCI), Mechanics.
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Flow through a sinuous stenosis with varying degrees of shape asymmetry andat Reynolds number ranging from 250 up to 800 is investigated using direct numericalsimulation (DNS), global linear stability analysis and sensitivity analysis.The shape asymmetry consists of an offset of the stenosis throat, quantifiedas the eccentricity parameter, E. At low Reynolds numbers in a symmetricgeometry, the flow is steady and symmetric. Our results show that when Reynoldsnumber is increased, the flow obtains two simultaneous linearly stablesteady states through a subcritical Pitchfork bifurcation: a symmetric stateand an asymmetric state. The critical Reynolds number for transition betweenthe states are found to be very sensitive to asymmetric shape variations, thusbifurcation can also occur with respect to eccentricity for a given Reynoldsnumber. The final state observed in the DNS can be either nearly symmetricor strongly asymmetric, depending on the initial condition. When eccentricityis increased from zero, the symmetric state becomes slightly asymmetric,flow asymmetry varying nearly linearly with eccentricity. When eccentricityis increased further, the nearly symmetric state becomes linearly unstable. Alinear global stability analysis shows that the eigenvalue sensitivity to eccentricityis of the second order, this is also confirmed by preliminary sensitivityanalysis. For higher Reynolds numbers, the asymmetric solution branch displaysregimes of periodic oscillations as well as intermittency. Comparisons aremade to earlier studies and a theory that attempts to explain and unite thedifferent numerical and experimental results within the field is presented.

Place, publisher, year, edition, pages
2014. , 57 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-205652OAI: oai:DiVA.org:kth-205652DiVA: diva2:1089907
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Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2017-04-21Bibliographically approved

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  • apa
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