Modeling Fluidelastic Instability of Tube Bundles Subjected to Two-Phase Flows

Fluidelastic instability (FEI) is the most important mechanism of flow-induced vibration in nuclear heat exchangers, with the potential to cause severe tube damage, efficiency losses, and safety concerns. While FEI has been extensively studied in single-phase flows, its manifestation in two-phase conditions remains less understood due to the added complexity of void fraction variations, interphase slip, and flow regime transitions. This thesis advances the modeling of two-phase FEI through the development of two novel semi-analytical approaches. The first, a Control Volume (CV) model, discretizes the flow path between the tubes, known as flow channel, into stationary cells whose size varies with tube displacement. Each control volume is assigned a void fraction consistent with statistical distributions, and interphase slip is incorporated to capture differences in phase velocities. The second, a Layer model, represents the flow channel as layers of varying void fraction moving with the bulk flow velocity. Both models were validated against experimental air–water data across a full range of void fractions, demonstrating strong agreement with critical velocity measurements and improved prediction compared with the homogeneous equilibrium model. While the CV model offered enhanced accuracy in predicting average tube displacement, the Layer model achieved similar predictive capability with significantly reduced computational cost, making it more practical for large-scale applications. Building on this, the Layer model was extended to simulate multiple flexible tubes in a parallel triangular array. The simulations revealed important bundle dynamics, including stochastic tube motion in stable conditions, synchronization and phase-dependent amplification of instability in the unstable regime, and earlier onset of instability compared with single-tube systems due to the influence of stiffness-controlled mechanisms. Overall, the models developed in this work provide computationally efficient and physically representative tools for predicting two-phase FEI in nuclear steam generators. The findings enhance fundamental understanding of flow–structure interactions in tube bundles and offer valuable guidance for the design of safer, more efficient, and cost-effective nuclear heat exchangers

Grantor dc:publisher

University of Guelph

Author dc:creator

• Farani Sani, Hossein

Advisor dc:contributor.advisor

• Hassan, Marwan

• flow regimes
• two-phase flow
• fluiedelastic inability
• flow-induced vibration

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10214/29400

OAI record oai:identifier

https://atrium.lib.uoguelph.ca/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Aatrium.lib.uoguelph.ca%3A10214%2F29400