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Present work demonstrates the complete numerical modeling and experimental validation of transient incompressible two-phase flow during vacuum infusion (VI) in the presence and absence of high permeability media (HPM) considering gravity effects. Coupled flow modeling based on continuity equations, Darcy's law for porous media flow, including gravity effects with level set front tracking algorithm, has been developed on the multiblock-structured grid with higher-order finite-difference framework to predict the spatio-temporal preform saturation during infusion with/without HPM on the complex mold configurations. The model-predicted instantaneous change in pressure, thickness elevation, fill time, flow front positions, and influence of gravity have been validated with experiments for horizontal and vertical flat plates using pressure sensors and digital cameras. For the first time, the complete modeling and experimentation of transient VI in the presence or absence of HPM, including gravity, shows the ability to predict realistic preform saturation during VI in different mold geometry. [ABSTRACT FROM AUTHOR]

The present work focuses on the formulation of transient incompressible resin flow during vacuum-assisted resin transfer moulding using level set front tracking method in a multi-block structured grid within a finite difference framework. Initially, the relation between compaction pressure and fibre volume fraction ( V f ) has been established by conducting compression tests using a universal tensile machine under dry and wet conditions. In-plane permeability has been characterised as a function of V f using three thicknesses of unidirectional carbon fabric (4, 8 and 12 plies). A pressure data acquisition system and a non-contact out-of-plane displacement measurement setup have been developed using a single lens camera to conduct the vacuum infusion experiments. The numerical model prediction of the instantaneous change in pressure, displacement, and fill time has been validated with the experiments for the three different thickness of unidirectional preform in a flat plate and a plate with a centrally located hole during vacuum infusion. The coupled transient flow model with the level set interface propagation in a multi-block framework shows a good agreement with vacuum infusion experiments. The proposed transient vacuum infusion flow model, compaction relation with V f , permeability and experimental setup show the potential to capture realistic flow physics during vacuum infusion on different mould configurations. [ABSTRACT FROM AUTHOR]

Coherent flame oscillations generated by large-scale flow instabilities have been shown to significantly influence combustor performance and thermoacoustic instability. This study examines the influence of turbulence intensity on the large-scale dynamics of rod-stabilized flames. Instability in the flow field of a bluff-body stabilized flame, which is a function of mean shear in the flow field, turbulence intensity of the incoming flow, and the location of the flame with respect to the shear layer, manifests as coherent vortex shedding. However, this vortex shedding is not self-excited if the flow is globally stable, as is often the case in reacting flows. In this experiment, time-resolved, three-component velocity measurements from high-speed stereoscopic particle image velocimetry are taken at three turbulent inlet flow conditions and at three bulk flow velocities. To identify whether these instabilities occur, the velocities fields are filtered using a wavelet transform around select spectral bands and then decomposed using proper orthogonal decomposition to extract the most energetic motion in the flow; this filtering method retains any time-dependent, intermittent behavior. The results show that vortex shedding is intermittent and the degree of intermittency is dependent on the in-flow turbulence level. Although all the cases tested were determined to be globally stable, variations in the flow velocity change the structure of the flame and flow, which alters the receptivity of the flow to turbulent perturbations. As a result, the strength and regularity of vortex shedding increase with increasing turbulence level and increased receptivity, indicating that the system is a noise-forced globally-stable oscillator. [ABSTRACT FROM AUTHOR]