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14AFMC Abstract Book BOOK OF ABSTRACTS 14th Australiasian Fluid Mechanics Conference Adelaide University, South Australia December 9-14, 2001 Published by: Causal Productions Pty Ltd www.causal.on.net [email protected] Page Session Name 2 PL Plenary Lectures 2 TR Topical Reviews 3 AA Aero-Acoustics 4 AD Aerodynamics 5 AR Atmospheric Research 6 BL Boundary Layers 8 CO Combustion 9 CF Computational Fluid Dynamics 13 OT Diverse Fluid Mechanics Topics 15 ET Experimental Techniques 17 GD Gas Dynamics 17 GW Groundwater 17 HL Hydraulics 18 HD Hydrodynamics 20 IF Industrial Flows 21 JW Jets and Wakes 25 MF Multiphase Flow 26 NN Non-Newtonian Flows 27 OG Oceanography 27 PF Pipe Flow 28 WE Wind Engineering 1 Plenary Lectures by the interaction of the laminar wakes with the leading edge. Re- gions of elevated background unsteadiness appear on either side The Fluid Mechanics of Natural Ventilation of the peak layer thickness, which share many of the characteristics Paul F. Linden of Klebanoff modes, observed at elevated Free Stream Turbulence Page: 1-8, Paper no. 1001 (FST) levels. However, for the low background disturbance level Abstract: Ventilation of buildings is a topic close to our experience, of the free stream (u /U1 < 0.05%), the layer remains laminar to but knowledge and understanding of the airflow within a building the end of the test section (Rx ≈ 1.4x106) and there is no evi- is usually scanty. Even in buildings with purpose built mechanical dence of bursting or other phenomena associated with breakdown ventilation or air conditioned systems, designers use crude rules to to turbulence. A vibrating ribbon apparatus is used to demonstrate specify the ventilation, and the result is often unsatisfactory. I will that the deformation of the mean flow is responsible for substan- review current understanding and research on ventilation concen- tial phase and amplitude distortion of Tollmien-Schlichting (TS) trating on the details of the air flow. I will establish some general waves. Pseudo-flow visualization of hot-wire data shows that the principles, such as why layered stratification occurs in steady flows breakdown of the distorted waves is more complex and occurs at and why some flows are intrinsically unsteady. a lower Reynolds number than the breakdown of the K-type sec- ondary instability observed when the FSN is not present. New Developments in Large Eddy Simulation of Complex Flows Topical Reviews P. Moin Page: 9-13, Paper no. 1002 Stability of Nonparallel Flows: ’Minimal Composite’ Theories Abstract: Recent developments in large eddy simulation method- Roddam Narasimha, Rama Govindarajan ology are reviewed. This includes advances in filtering for inho- Page: 33-40, Paper no. 2001 mogeneous flows, subgrid scale and wall modeling and numerical methods. In particular, a numerical method designed for unstruc- Abstract: The theory of linear stability of shear flows has been tured grids with arbitrary elements which is being used for com- studied extensively over much of the last century. Most stud- putations in the combustor of a gas turbine jet engine is described. ies have been based on the Orr-Sommerfeld equation for parallel Progress in LES of turbulent combustion at CTR is reviewed. flows, but in recent decades there have been several attempts at more general theories, including the use of parabolized stability Near-Wall Coherent Structure Generation in a Tur- equations. As shear flows tend in general to be nonparallel, the bulent Boundary Layer question has remained about the formulation of a proper theory Wade Schoppa, Fazle Hussain accounting for flow nonparallelism. Introducing the concept of Page: 15-21, Paper no. 1003 minimal composite equations, with the use of similarity coordi- Abstract: We present new insight into the generation of stream- nates, it has been possible during the last ten years to develop a wise vortices near the wall, and an associated drag reduction strat- hierarchy of stability equations ranging from an ordinary differ- egy. Growth of x-dependent spanwise velocity disturbances w(x) ential equation like the Orr-Sommerfeld (but not identical to it) to is shown to occur via two mechanisms: (i) linear transient growth, partial differential equations like the PSE. The approach through which dominates early-time evolution, and (ii) linear normal-mode minimal composite equations has now been extended to include instability, dominant asymptotically at late time (for frozen base effects of wing sweep and compressibility, and we present a re- flow streaks). Approximately 25% of streaks extracted from near- view of these developments and their implications. wall turbulence are shown to be strong enough for linear insta- ’Homogeneous Turbulence’ and its Relation to Real- bility (above a critical vortex line lift angle). However, due to vis- ω izable Flows cous cross-diffusion of streak normal vorticity y , normal mode W.K. George, H. Wang, C. Wollblad, T.G. Johansson growth ceases after a factor of two energy growth. In contrast, the Page: 41-48, Paper no. 2002 linear transient disturbance produces a 20-fold amplification, due to its rapid, early-time growth before significant viscous streak de- Abstract: This paper examines in some detail how the decay of cay. Thus, linear transient growth of w(x) is revealed as a new, ap- homogeneous turbulence in the absence of shear is affected by parently dominant, generation mechanism of x-dependent turbu- the constraints of finite boundaries. It demonstrates how the ra- lent energy near the wall. Combined transient growth/instability tio of the wavenumbers of the spectral peak to the lowest resolved of lifted, vortex-free low-speed streaks (above the instability cutoff wavenumber (or tunnel size to integral scale) can influence directly of streak strength) is shown to generate new streamwise vortices, the time dependence of the energy, the integral scale, and even the which dominate near-wall turbulence phenomena. Significantly, rate of decay of the turbulence. If this ratio is not large enough, the 3D features of the (instantaneous) vortices generated by tran- the length scales grow too slowly and the energy decays too fast. sient/instability growth agree well with the coherent structures Criteria are proposed for assessing the validity of the data; but few educed (i.e. ensemble-averaged) from fully turbulent flow, suggest- experiments or simulations satisfy them. ing the prevalence of this mechanism. Results suggest promising Challenges for Innovation in Aerodynamics new strategies for drag and heat transfer control, involving large- A.J. Smits scale (hence more durable) actuators, without requiring wall sen- Page: 49-56, Paper no. 2003 sors or control logic. Abstract: New challenges for innovation in aerodynamics are pre- Laboratory and Computer Experiments on Turbu- sented in the context of transonic, supersonic and hypersonic flight, lent Mixing as currently under consideration in the U.S. Paul E. Dimotakis Page: 23-24, Paper no. 1004 Some Basic Problems of Microfluidics P. Tabeling Abstract: This discussion covers some progress in turbulent mix- Page: 57-62, Paper no. 2004 ing stemming from experimental, modeling, and direct-numerical simulation (DNS) studies. Topics include the mixing transition, Abstract: I present here several phenomena, which (I believe) are results from DNS studies of the Rayleigh-Taylor instability in mis- worth being discussed, because of their practical importance, the cible fluids, experimental investigations in transverse jets and the scientific challenge they convey, or both. The phenomena I discuss assumption of isotropy in turbulence and mixing, and experiments here are : slip of simple liquids over smooth surfaces, gas flows in high-speed shear layers that elucidate some effects of compress- in microchannels, chaotic micromixing, two phase flows in mi- ibility on the mixed-fluid field. crochannels, microelectrohydrodynamics, and bottleneck effect. The descriptions are made in a pedagogical rather than technical Effects of Free-Stream Nonuniformity on Boundary style. The few topics presented here represent a number of mi- Layer Transition crofluidics situations of importance, which raise interesting fun- J.H. Watmuff damental and practical issues. Page: 25-32, Paper no. 1005 Abstract: Experiments are described in which fine wires are posi- tioned upstream of the leading edge of a flat plate to generate well- defined FSN (Free Stream Nonuniformity). Large spanwise thick- ness variations in the downstream boundary layer are generated 2 A Few Examples of Industrial Problems that would Experiments on Natural Convection Boundary Lay- Benefit from Improved Understanding of Fluid Flow ers -the Role of Instabilities Peter Mullinger John C. Patterson Page: 63-69, Paper no. 2005 Page: 87-94, Paper no. 2009 Abstract: Fluid flow plays an enormous, and underrated, role in in- Abstract: In this paper, an experimental investigation of the tran- dustrial processes and its contribution of is become more widely sient behaviour of the flow adjacent to a suddenly heated vertical recognised. Topics such as flow in ducts, air distribution between wall is described. The experiments confirm that the primary devia- burners, conveying of powders, mixing of fluids and powders, etc tion from one dimensional to two dimensional flow at a particular are becoming increasingly recognised as fluid flow problems. Many location occurs at the time at which the fastest traveling wave aris- of these problems are not well understood, yet the cost of failure ing from the perturbation caused at startup reaches that location. caused
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