Aerospace

This paper presents the results of experimental investigation of unsteady flows in a concentric circular annulus. The flow is generated by the controlled motion of a piston. A range of Reynolds number and boundary layer thickness is obtained by changing the piston velocity and piston displacement. Velocity profiles during deceleration of the flow are with reverse flow near the wall and are highly unstable due to their inflectional nature. The unstable flow ends in periodic vortices at walls of inner and outer pipes. Any arbitrary piston motion is expressed in terms of Fourier series and the generalized analytical solution is obtained for an arbitrary unsteady volume flow rate through the concentric pipe annulus. The velocity profiles for the experimental cases are obtained from the analytical solution. These mean velocity profiles are used for quasi-steady 3D linear stability analysis. The quasi-steady 3D linear stability analysis is used to explain the observed instability and tran...

The present study highlights the capability of a newly developed chimera grid methodolgy to analyze complex fluid flows. The developed chimera methodology incorporates high accuracy compact schemes on orthogonal body-fitted grids which guarantees Dispersion Relation Preservation and fourth-order Lagrange interpolation for minimization of interpolation error. Navier-Stokes equation formulated using streamfunction-vorticity variables is adopted for reasons of ac-curacy. Current analysis looks at a 2D incompressible flow past two-side-by-side cylinders at Reynolds number 100 and gap ratio 2.5. Computed results show excellent agreement with experiments and other computational results.

The Generation and propagation of the human voice is studied in two-dimensions using a full-body domain, using direct numerical simulation. The fluid/air in the vocal tract is modeled as a compressible and viscous fluid interacting with the non-linear, viscoelastic vocal folds (VF). The VF tissue material properties are multi-layered, with varying stiffness, and a finite-strain model is utilized and implemented in a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. The full-body domain includes the near VF region, the vocal tract, a simplified model of the soft palate and mouth, and extends out into the acoustic far-field. A new kind of inflow boundary condition based upon a quasi-one-dimensional formulation with constant sub-glottal volume velocity, which is linked to the VF movement, has been adopted. The sound pressure levels (SPL) measured are realistic and we analy...

This review aims to summarize state-of-the-art knowledge on silicon manufacturing using an ultra precision manufacturing process known as single point diamond machining. After highlighting the many contributions that molecular dynamics (MD) simulation has made in aiding the study of silicon manufacturing, this review provides critical insight into some of the analytical theories concerning high pressure phase transformation mechanisms underlying the so called brittle-ductile transition. This review is aimed at providing a particular focus on understanding of the process rather than the process parameters (i.e. rather than suggesting an optimum mix of machining variables, the importance of each machining variable namely, maximum undeformed chip thickness, cutting edge radius, cutting tool rake and clearance angle, crystal structure of the material, anisotropy of the material and tool wear, all of which are essential for efficient silicon manufacturing is highlighted).

For centuries, scratch testing has been used to characterize the hardness of materials, yet a quantitative measure of hardness through scratch testing is not known. In this paper, a new measure “cutting hardness” is proposed as a novel indicator for evaluation of hardness of the material from orthogonal scratch testing. The new measure is applied to nanocrystalline silicon and iron, along with their carbon alloys via molecular dynamics (MD) simulation. It is shown that various simulation based studies concerning material removal can be easily validated by using the cutting hardness measure without recourse to a tailor made experiment.