Graduate Seminar in Fluid Mechanics

February 9, 2018 @ 4:00 pm – 5:00 pm
132 Gilman Hall

4:00 pm Presentation (New Time)

 Modeling and Simulations of Fused Deposition Modeling”

 Presented by HUANXIONG XIA (Adviser: Prof. Tryggvason)

A fully resolved model is developed for FDM (Fused Deposition Modeling) process, one of the well-known additive manufacturing processes, to understand the underlying physical behaviors, where the objects are built by depositing filaments of hot polymers that fuse together when they solidify. The process is embedded in a hexahedral computational domain, where both the polymer and the ambient air are included. A finite volume/front tracking method and one-fluid formulation are used to model the behaviors of fluid flow, heat transfer, volume shrinkage, residual stress as well as the moving immiscible interface. The extrusion of the polymer is modeled by using a volume source inside a rigid body with an open outlet, which is moving along a specific path. A temperature and shear-rate depend viscosity and a modified neo-Hooke stress model are applied for the polymer to describe its viscoelastic behavior and find the solid stress. The model is computed by an implicit projection scheme with second-order accuracy both for time integration and space derivation. The accuracy and convergence properties are tested by grid refinement studies for a simple setup involving two short filaments, one on top of the other. The effect of the various injection parameters, such as nozzle speed, cooling condition, depositing and bridging space are briefly examined and the applicability of the approach to simulate the construction of simple multilayer objects is shown. The fully resolved model can be helpful to understand the physical mechanism, predict the process, model the other relevant novel processes, and provide “ground truth” results for the simplified/reduced order model that is suitable for the part-scale simulations.

4:25 pm Presentation (New Time)

Experimental Investigation of Compliant Wall Surface Deformation in Turbulent Boundary Layer

 Presented by JIN WANG (Adviser: Prof. Katz)

In our previous work, correlations between a compliant wall surface deformation and turbulent channel flow are studied by Tomographic PIV (TPIV) and Mach-zehnder Interferometer (MZI). In the ongoing experiment, a softer compliant surface with Young’s modulus reduced from 1 MPa to around 100 KPa is used. The material is a mixture of 88% Dow Corning Sylgard 527 and 12% Sylgard 184 by weight. The Young’s modulus is chosen to increase the amplitude of deformation so that a two-way coupling instead of one-way coupling in the stiffer surface experiment is expected. The coating thickness (l0=5mm) is tuned to guarantee that large amplitude surface deformation with a length scale of 3l0 predicted by the Chase model can be captured in our limited FOV.  Corresponding shear wave speed for the softer compliant surface, calculated from ct=(G/ρc)1/2 is around 5.37 m/s. Thus, a designed flow speed around 6 m/s is capable of trigger the static divergence wave. MZI and TPIV will be used to measure the surface deformation and the 3D velocity, volume pressure is calculated from the TPIV data via a GPU-based, parallel-line, omni-directional integration method. Measurement of large field of view (>50x50mm2) deformation will be implemented using MZI to study the large scale deformation, followed by a simultaneous measurement of velocity by TPIV and deformation by MZI in a small field of view (<20×20 mm2).  In this talk, the large field of view MZI experiment results will be presented and discussed.

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