Document Type dissertation Author Name Chamberlin, Ryan Earl URN etd-032907-092912 Title A Three-dimensional Direct Simulation Monte Carlo Methodology on Unstructured Delaunay Grids with Applications to Micro and Nanoflows Degree PhD Department Mechanical Engineering Advisors Professor Nikolaos Gatsonis, Advisor Professor John Blandino, Committee Member Professor David Olinger, Committee Member Professor George Karniadakis, Committee Member Professor Mark Richman, Graduate Committee Rep Keywords Nanoflow Microflow Unstructured DSMC Date of Presentation/Defense 2007-03-12 Availability unrestricted
The focus of this work is to present in detail the implementation of a three dimensional direct simulation Monte Carlo methodology on unstructured Delaunay meshes (U-DSMC). The validation and verification of the implementation are shown using a series of fundamental flow cases. The numerical error associated with the implementation is also studied using a fundamental flow configuration.
Gas expansion from microtubes is studied using the U-DSMC code for tube diameters ranging from 100ƒÝm down to 100nm. Simulations are carried out for a range of inlet Knudsen numbers and the effect of aspect ratio and inlet Reynolds number on the plume structure is investigated. The effect of scaling the geometry is also examined.
Gas expansion from a conical nozzle is studied using the U-DSMC code for throat diameters ranging from 250 ƒÝm down to 250 nm. Simulations are carried out for a range of inlet Knudsen numbers and the effect of inlet speed ratio and inlet Reynolds number on the plume structure is investigated. The effect of scaling the geometry is examined.
Results of a numerical study using the U-DSMC code are employed to guide the design of a micropitot probe intended for use in analyzing rarefied gaseous microjet flow. The flow conditions considered correspond to anticipated experimental test cases for a probe that is currently under development. The expansion of nitrogen from an orifice with a diameter of 100ƒÝm is modeled using U-DSMC. From these results, local ¡¥free stream¡¦ conditions are obtained for use in U-DSMC simulations of the flow in the vicinity of the micropitot probe. Predictions of the pressure within the probe are made for a number of locations in the orifice plume. The predictions from the U-DSMC simulations are used for evaluating the geometrical design of the probe as well as aiding in pressure sensor selection.
The effect of scale on the statistical fluctuation of the U-DSMC data is studied using Poiseuille flow. The error in the predicted velocity profile is calculated with respect to both first and second-order slip formulations. Simulations are carried out for a range of channel heights and the error between the U-DSMC predictions and theory are calculated for each case. From this error, a functional dependence is shown between the scale-induced statistical fluctuations and the decreasing channel height.
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