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Modeling cavitation phenomenon can be a challenging prospect for numerical solvers because the available cavitation models require a fine-tuning of model parameters and a good quality mesh in cavitating zones. Cavitation often occurs in complex geometries such as nozzle injection systems, marine propellers or gear pumps and creating a good quality mesh in such geometries need high skill and enough time. Overset mesh simplifies the overall meshing process in complex geometries by allowing separately generated good quality component meshes, which later overlap on each other to form actual flow domain. The aim of this study is to validate the accuracy of the overset method for cavitating flow problems using a multi-phase RANS flow solver and a homogeneous mixture model. Cavitating flow inside a circular throttle injection system is validated against experiment where mass flow rates at the outlet are compared at different inlet pressures. Flow past a fully submerged wedge-shaped hydrofoil is analysed for different cavitation numbers and multiple angles of attack, where cavity shapes for both overset and non-overset meshes are compared with experimental images. Furthermore, supercavitation phenomenon for the flow past a circular disk is investigated where cavity length and cavity radius are validated against the empirical correlations proposed by different authors. This study also highlights the best practices for Schnerr-Sauer and Zwart-Gerber-Belamri cavitation models available in ANSYS Fluent with overset mesh.

This work simulates a laboratory-scale 3D methane/air burner, which features a bluff body stabilized, lean partially premixed flame experiencing strong limit cycle oscillations. A thin steel liner is installed around the combustion chamber, which heavily interacts with the flow field and produces large amplitude structural deformation via Fluid-Structure Interactions (FSI). An unsteady RANS approach uses the Shear Stress Transport turbulence model and a Flamelet Generated Manifold combustion model to predict the thermoacoustic oscillations in the turbulent reacting flow. The solver also has a built-in finite element Structure Model, which solves the structural governing equations simultaneously with the CFD-computed, finite volume flow equations. This way, a fully coupled, two-way FSI simulation can be performed to predict the thermoacoustic instabilities and the associated solid deformations in the burner. Overall, the predicted strongest pressure oscillation and wall displacement modes (frequency and amplitude) are all in good agreement with the experimental data across different operating conditions. The established workflow may support realistic gas turbine combustor design and prognosis.

Overset method is validated for different free surface flow applications to demonstrate its capabilities and benefits over traditional dynamic mesh approach. An overset mesh consists of a set of overlapping component meshes, which allows complex geometries to mesh with lesser effort. Interpolation methods are enforced at internal boundaries to ensure a continuous solution in overlapping component zones. Overset methodology is not perfectly mass conservative by its design. Present study in this regard, demonstrates the benefit of higher order interpolation method on simulation accuracy and mass conservation. The simulation results for various case studies involving static and moving overset meshes are validated against analytical, experimental and equivalent non-overset mesh results using ANSYS Fluent. Finite volume method (FVM) with pressure based coupled solver is used to solve Reynolds Averaged Navier Stokes equations. Free surface flow is modeled using Volume of Fluid Method (VOF) which capture interfaces between immiscible fluids. Pseudo-transient method is adopted for steady state applications to get better robustness. A pure advection of slotted circle is simulated where its revolution is forced along the static overlapping zone, final shape and position is compared with initial state after one revolution. A non-linear Stokes wave with high steepness is propagated in a numerical wave tank which contains multiple static overlapping zones in the vicinity of free surface, where simulation results of free surface and velocity profiles are verified against analytical profiles. Flow over a bump for subcritical to subcritical and subcritical to supercritical regimes are verified against analytical results. Flow over a submerged hydrofoil using static overset mesh is validated against experimental result for free surface profile. A rotating gear case involving moving overset mesh is compared with sliding mesh results for free surface and pressure profiles. A case involving transient heave oscillation of floating cylinder is validated with theoretical, experimental and equivalent dynamic mesh results.

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