Showing papers by "William J. Rider published in 2005"

The design and construction of implicit LES models

Abstract: We offer preliminary thoughts on the design of a modified equation and the construction of a corresponding numerical algorithm, which may be intended for use in an implicit large eddy simulation. The principle of design here is based on ensuring a form for the energy dissipation that is not significantly dissipative on the resolved scales of the numerical mesh, but is strongly dissipative when the solution is unresolved and so provides strong nonlinear stability in the simulation. The construction process is modelled on the composition (hybridization) of two flux approximations by means of a nonlinear, flow-dependent switch

Combining high‐order accuracy with non‐oscillatory methods through monotonicity preservation

Abstract: We have extended the usual notions used in high-resolution methods. Rather than applying a single principle such as monotonicity or essentially non-oscillatory stencil selection, we hybridize multiple principles applying them where they are most effective. We define methods that blend high-order accuracy with essentially non-oscillatory methods when monotonicity conditions are violated. The methods can be defined with a number of variants leading to results with differing properties. We also focus on the impact of the selection of the high-order accurate stencil on the overall method. Published in 2005 by John Wiley & Sons, Ltd.

Planar velocity and scalar concentration measurements in shock-accelerated unstable fluid interfaces

Abstract: We report applications of several high-speed photographic techniques to diagnose fluid instability and the onset of turbulence in an ongoing experimental study of the evolution of shock-accelerated, heavy-gas cylinders. Results are at Reynolds numbers well above that associated with the turbulent and mixing transitions. Recent developments in diagnostics enable high-resolution, planar (2D) measurements of velocity fields (using particle image velocimetry, or PIV) and scalar concentration (using planar laser-induced fluorescence, or PLIF). The purpose of this work is to understand the basic science of complex, shock-driven flows and to provide high-quality data for code validation and development. The combination of these high-speed optical methods, PIV and PLIF, is setting a new standard in validating large codes for fluid simulations. The PIV velocity measurements provide quantitative evidence of transition to turbulence. In the PIV technique, a frame transfer camera with a 1 ms separation is used to image flows illuminated by two 10 ns laser pulses. Individual particles in a seeded flow are tracked from frame to frame to produce a velocity field. Dynamic PLIF measurements of the concentration field are high-resolution, quantitative dynamic data that reveal finely detailed structure at several instances after shock passage. These structures include those associated with the incipient secondary instability and late-time transition. Multiple instances of the flow are captured using a single frame Apogee camera and laser pulses with 140 ?s spacing. We describe tradeoffs of diagnostic instrumentation to provide PLIF images.