Mahesh Athavale

Plastic In-Line Chaotic Micromixer for Biological Applications

A plastic 3D “L-shaped” serpentine micromixer is developed to enhance mixing of biological samples. Both numerical simulation and experiments show such a device has high mixing efficiency and low shear strain field.

Accuracy of 1D microvascular flow models in the limit of low Reynolds numbers

We describe results of numerical simulations of steady flows in tubes with branch bifurcations using fully 3D and reduced 1D geometries. The intent is to delineate the range of validity of reduced models used for simulations of flows in microcapillary networks, as a function of the flow Reynolds number Re. Results from model problems indicate that for Re less than 1 and possibly as high as 10, vasculatures may be represented by strictly 1D Poiseuille flow geometries with flow variation in the axial dimensions only. In that range flow rate predictions in the different branches generated by 1D and 3D models differ by a constant factor, independent of Re. When the cross-sectional areas of the branches are constant these differences are generally small and appear to stem from an uncertainty of how the individual branch lengths are defined. This uncertainty can be accounted for by a simple geometrical correction. For non-constant cross-sections the differences can be much more significant. If additional corrections for the presence of branch junctions and flow area variations are not taken into account in 1D models of complex vasculatures, the resultant flow predictions should be interpreted with caution.

Computational design of membrane pumps with active/passive valves for microfluidic MEMS

Modern microsystems use integrated sensors, controllers and actuators, and involve multi-physics phenomena. Detailed and accurate multi-physics based simulations are a key to device optimization and successful designs. In recent years, CFD- ACE+, a fluid flow solver has been validated and demonstrated on different MEMS devices involving coupled fluid flow, heat transfer, structural mechanics and electrostatics. Presented here are results of dynamic devices such as micropumps with dynamic valves and membrane micropumps as well as priming of a capillary pump and novel valves that use fluid surface tension for operation. Comparisons with experimental and other data are also presented to demonstrate the accuracy of multi-physics simulations. The capabilities of this state-of-the-art software and its usefulness in MEMS design environment is demonstrated.

Experimental and numerical investigation of flow through an oscillated acoustic resonator

An acoustic resonator was oscillated experimentally at the fundamental gas resonant frequency to develop standing pressure waves. The conical shaped resonator contained openings that provided an air passage from a pressurized cavity through the resonator to the ambient environment. For several pressure differentials applied across the resonator, the rate of air flow is reported for no resonator oscillation, and for on‐resonant and near‐resonant frequency oscillations. When compared to no oscillation and near‐resonant frequency oscillation at all pressure differentials, the standing waves within the resonator reduced the flow of air through the system when oscillated on‐resonance. A two‐dimensional numerical model was developed using a commercial CFD package to simulate the gas flow within the system. The mass flow of air through the oscillating resonator was matched using the numerical simulations. For a low value of differential pressure, the simulations showed the reversal of gas flow into the high pres...

Coupled, Transient Simulations of the Interaction Between Power and Secondary Flowpaths in Gas Turbines

This paper presents a coupled analysis of the interaction between mainpath and secondary flowpaths in gas turbines using transient simulations. Some of the topics include: 1) Need for Coupled Analysis; 2) Primary-Secondary Coupling Schematic; 3) Secondary Flow Requirement; 4) Objectives of Present Methodology; 5) Current Methodologies Recap; 6) Proposed Coupled Code Methodology; 7) Description of SCISEAL Code; 8) Description of Turbo Code; 9) Code Coupling/Interface Issues; and 10) Current Interface Strategy. This paper is presented in viewgraph form.