to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

The goal of this survey is to review recent developments in the hydro­ dynamic stability theory of spatially developing flows pertaining to absolute/convective and local/global instability concepts. We wish to dem­ onstrate how these notions can be used effectively to obtain a qualitative and quantitative description of the spatio-temporal dynamics of open shear flows, such as mixing layers, jets, wakes, boundary layers, plane Poiseuille flow, etc. In this review, we only consider open flows where fluid particles do not remain within the physical domain of interest but are advected through downstream flow boundaries. Thus, for the most part, flows in "boxes" (Rayleigh-Benard convection in finite-size cells, Taylor-Couette flow between concentric rotating cylinders, etc.) are not discussed. Further­ more, the implications of local/global and absolute/convective instability concepts for geophysical flows are only alluded to briefly. In many of the flows of interest here, the mean-velocity profile is non-

/pdf/local-and-global-instabilities-in-spatially-developing-flows-ja4x14nrk6.pdf

Local and global instabilities in spatially developing flows

Perturbed Free Shear Layers

▪ Abstract We review the direct numerical simulation (DNS) of turbulent flows. We stress that DNS is a research tool, and not a brute-force solution to the Navier-Stokes equations for engineering problems. The wide range of scales in turbulent flows requires that care be taken in their numerical solution. We discuss related numerical issues such as boundary conditions and spatial and temporal discretization. Significant insight into turbulence physics has been gained from DNS of certain idealized flows that cannot be easily attained in the laboratory. We discuss some examples. Further, we illustrate the complementary nature of experiments and computations in turbulence research. Examples are provided where DNS data has been used to evaluate measurement accuracy. Finally, we consider how DNS has impacted turbulence modeling and provided further insight into the structure of turbulent boundary layers.

/pdf/direct-numerical-simulation-a-tool-in-turbulence-research-2a650vh1lf.pdf

DIRECT NUMERICAL SIMULATION: A Tool in Turbulence Research

Computational Fluid Dynamics: Principles and Applications, Third Edition presents students, engineers, and scientists with all they need to gain a solid understanding of the numerical methods and principles underlying modern computation techniques in fluid dynamics By providing complete coverage of the essential knowledge required in order to write codes or understand commercial codes, the book gives the reader an overview of fundamentals and solution strategies in the early chapters before moving on to cover the details of different solution techniques

	This updated edition includes new worked programming examples, expanded coverage and recent literature regarding incompressible flows, the Discontinuous Galerkin Method, the Lattice Boltzmann Method, higher-order spatial schemes, implicit Runge-Kutta methods and parallelization

	An accompanying companion website contains the sources of 1-D and 2-D Euler and Navier-Stokes flow solvers (structured and unstructured) and grid generators, along with tools for Von Neumann stability analysis of 1-D model equations and examples of various parallelization techniques



	
		Will provide you with the knowledge required to develop and understand modern flow simulation codes
	
		Features new worked programming examples and expanded coverage of incompressible flows, implicit Runge-Kutta methods and code parallelization, among other topics
	
		Includes accompanying companion website that contains the sources of 1-D and 2-D flow solvers as well as grid generators and examples of parallelization techniques

Computational Fluid Dynamics: Principles and Applications Ed. 3

A Computational and Experimental Study of Resonators in Three Dimensions

Supersonic jet noise generated by large scale disturbances

1. Finite difference equations 2. Spatial discretization in wave number space 3. Time discretization 4. Finite difference scheme as dispersive waves 5. Finite difference solution of the Euler equations 6. Radiation, outflow, and wall boundary conditions 7. The short wave component of finite difference schemes 8. Nonlinear acoustic waves and shocks 9. Advanced numerical boundary treatments 10. Time domain impedance boundary condition 11. Extrapolation and interpolation 12. Multi-scales problems 13. Complex geometry 14. Continuation of a near field acoustic solution to the far field 15. CAA code design and applications.

Computational Aeroacoustics: A Wave Number Approach

The κ-e model has no provision to include the effect of the presence of a large-density gradient when used to compute the mean flow and noise of very hot jets. As a result, the model is found to give good predictions only when the jet is cold or moderately hot. Stability consideration indicates that a large density difference across a shear layer would generate strong spatial Kelvin-Helmholtz instabilities. Such instabilities would, invariably, lead to intense mixing in the jet shear layer. This, in turn, gives rise to an increase in turbulence intensity and jet spreading rate. A modification to the κ-e model is proposed to mimic these effects

Christopher K. W. Tam

Papers

A Computational and Experimental Study of Resonators in Three Dimensions

Supersonic jet noise generated by large scale disturbances

Computational Aeroacoustics: A Wave Number Approach

Modified kappa-epsilon Turbulence Model for Calculating Hot Jet Mean Flows and Noise

Broadband shock-associated noise from supersonic jets in flight