Methodologie voor stromings-structurele-akoestische voorspelling in een vroeg ontwerpstadium van leidingen

Tackling noise generated by flow duct systems—such as those in HVAC installations and industrial machinery—is of utmost importance for acoustic comfort and regulatory compliance. These systems act as efficient acoustic waveguides, allowing noise to propagate with minimal dissipation, while excitation of structural vibrations in the duct walls causes radiation of 'break-out' noise. Therefore, flow duct noise is inherently multiphysical, involving aerodynamic, acoustic, and structural interactions. Conventional mitigation strategies, often based on empirical guidelines and implemented late in the design process, lack predictive accuracy and lead to suboptimal solutions, certainly at low frequencies. To address this, predictive modeling during early-stage design is essential, enabling noise control to be integrated alongside primary objectives such as aerodynamic efficiency, mass reduction, compactness, and robustness. This research aims to predict flow duct noise during early-stage design for low-speed turbulent airflow in thin-walled ducts. Two key challenges to reach this goal are inherent to early-stage design, namely the necessity of (i) a low computational cost to allow a broad 3D study in limited time and (ii) a high accuracy to make well-considered design decisions. To overcome these challenges, two objectives are pursued: (i) create a 3D simulation tool incorporating essential interactions at an acceptable computational cost, and (ii) establish a methodology for estimating realistic structural boundary conditions of flexible wall joints, which strongly influence low-frequency vibro-acoustic behavior, but are unknown during early-stage design. For the first objective, a fully coupled mathematical model is deemed computationally prohibitive for early-stage design. Therefore, simplifying assumptions are introduced: low acoustic and structural amplitudes compared to the aerodynamics allow one-way aero-acoustic and aero-elastic interactions, whereas the confined configuration requires a two-way vibro-acoustic coupling. Linear acoustics and elasticity are assumed. The fluid domain is modeled with a hybrid Computational Aero-Acoustic approach, which splits the domain into a source region and a propagation region. The propagation region models the convective effects by computing the aerodynamic mean flow with the incompressible Navier-Stokes equations and the acoustic propagation with the Linearized Euler Equations (LEE). The LEE are solved in the time domain, enabling frequency domain analysis via impulse response. The structural domain is represented by linear elasto-dynamic plate or shell equations. A partitioned coupling strategy is implemented using the open-source library preCICE, linking an in-house LEE solver with a structural solver to capture two-way vibro-acoustic interactions. Verification on an academic case demonstrates accurate prediction of vibro-acoustic behavior under aero-acoustic convective effects compared to analytical and finite element models. The partitioned coupling of the LEE with structural dynamics for efficient simulation of two-way vibro-acoustic interactions in flow ducts constitutes the first contribution to the state of the art. The second objective addresses the lack of reliable structural boundary conditions in early-stage design. Oversimplified assumptions such as clamped or simply-supported conditions lead to significant inaccuracies, particularly at low frequencies: in this frequency range, an accurate prediction of the vibro-acoustic interaction, visible in the spectrum as distinctive peaks due to the low modal density, is necessary for effective mitigation.} To improve the structural boundary conditions, an indirect estimation methodology is developed, leveraging acoustic two-port measurements of a prototype duct segment. The two-port method characterizes the duct's input-output acoustic behavior, abstracting from acoustic boundaries imposed by the unknown larger duct system. It is assumed that a flow does not affect the structural boundary conditions and only influences the pre-tension. By defining an objective function based on the difference between measured and simulated two-port metrics, structural boundary conditions—modeled with linear, frequency-, and mesh-independent parameters—are updated without direct measurement. This approach is tested on a rectangular duct with one flexible wall, achieving a 45% improvement in matching transmitted acoustic power ratios compared to conventional assumptions. Based on the Modal Assurance Criterion, it is confirmed that vibro-acoustic modes can be accurately reproduced with the updated numerical model, with an average eigenfrequency prediction error of 1.86%. Robustness is demonstrated through numerical studies varying material properties and through predictive validation on modified configurations, such as added cavities. This underlines the merits of the developed indirect methodology for estimating structural boundary conditions of flexible wall joints, which constitutes the second contribution to the state of the art. In summary, this research delivers two key advancements for early-stage design of flow duct systems: (i) a computationally efficient simulation tool capturing dominant multiphysical interactions, and (ii) a robust methodology for estimating structural boundary conditions critical to low-frequency noise prediction. Together, these contributions enable effective noise control strategies to be integrated early in the design process, avoiding costly late-stage modifications and improving acoustic comfort in practical engineering applications.