16th Australasian Fluid Mechanics Conference
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Hydraulic Jumps: Bubbles and Bores
Professor Hubert Chanson
Abstract: The hydraulic jump is the sudden transition from a high-velocity open channel flow regime to a subcritical flow motion. The flow properties may be solved using continuity and momentum considerations. In this plenary lecture, recent advances in turbulent hydraulic jumps are reviewed: the non-breaking undular hydraulic jump, the positive surge and tidal bore, and the air bubble entrainment in hydraulic jumps with roller. This keynote lecture demonstrates that the hydraulic jump is a fascinating turbulent flow motion that remains poorly understood.
Microscale Combustion: Progress and Challenges
Professor SK Chou
Abstract: Microcombustion-related research was mainly motivated by the development of micro heat engines to meet the demand for a new generation of micro power sources. Unlike conventional combustion, which takes place in macro-sized combustion chambers (centimeter scale and above), the flame stability in microcombustion is significantly influenced by intensive heat loss (thermal quenching) and destruction of active species (chemical quenching) at the gas-solid interface. To overcome the negative effects associated with the reduced combustor size (down to sub-millimeter scale), a better understanding of the heat transport in the microcombustion process is particularly important. This paper reviews recent developments in this area, focusing on the fundamental studies on the characteristics of microcombustion using analytical, numerical and experimental approaches. In particular, the progress made at the Department of Mechanical Engineering at NUS is more fully described. Employing a one-dimensional flame model, we investigate the flame temperature and entropy generation in the microscale combustion process. Based on this model and analysis, a set of “microcombustion rules” is proposed. Furthermore, the slip-wall boundary effects (velocity-slip and temperature-jump), which are typical in microfluidic devices, have been implemented in a numerical model to investigate their influence on the microscale combustion regime. The results show that the effects are negligible over the generic range of sizes of most microcombustors. Despite the difficulty of measuring the key parameters in the small confined space, the effects of operational conditions (fuel-air equivalence ratio and flow velocity) and structural parameters (combustor diameter, step height, wall thickness and combustor length) have been experimentally studied in a series of cylindrical combustors. The expansion-step design has been shown to be able to stabilize the flame across a wider range of velocities. Finally, we highlight opportunities for future work that might help to extend the application of microcombustion.
The mechanics of yield stress fluids: similarities, specificities and open questions
Professor Philippe Coussot
Abstract: A wide range of materials encountered in our everyday life, such as clay suspensions, foams, concentrated emulsions, cement pastes, paints, glues, purees, creams, can flow like simple liquids under certain conditions and behave like solids under other conditions. This is the specificity of yield stress fluids which makes them so useful in various applications. In their liquid regime these materials exhibit typical flow properties of simple fluids such as a transition to turbulence, the roll wave instability, the hydraulic jump, etc. The specific properties occur when the solid regime is involved, either in a part of the material or as a whole. In that case one may for example observe plug flow, flow stoppage over steep slopes, no sedimentation of dense particles, cylindrical drips, Saffman-Taylor instability at vanishing velocity, etc. In addition yield stress fluids are often thixotropic, i.e. their viscosity may vary in time. The physical origin of this phenomenon and the mechanical model appropriate for describing it remain the most challenging aspects of these fluids.
A Perspective on Computational Aerothermodynamics at NASA
Dr. Peter A. Gnoffo
Abstract: The evolving role of computational aerothermodynamics (CA) within NASA over the past 20 years is reviewed. The paper highlights contributions to understanding the Space Shuttle pitching moment anomaly observed in the first shuttle flight, prediction of a static instability for Mars Pathfinder, and the use of CA for damage assessment in post-Columbia mission- support. In the view forward, several current challenges in computational fluid dynamics and aerothermodynamics for hypersonic vehicle applications are discussed. Example simulations are presented to illustrate capabilities and limitations. Opportunities to advance the state-of-art in algorithms, grid generation and adaptation, and code validation are identified.
G. K. Batchelor Lecture - Particle Methods: Past, Present and Future
Professor J Monaghan
Abstract: In this talk I will explain how the particle method Smoothed Particle Hydrodynamics (SPH) was developed and describe many of its applications. The key ideas are based on a method of interpolation using particles in disordered positions. The equations of motion can then be found directly using this interpolation, or by using a Lagrangian. Because of the simple formulation it is usually easy to include complex physics. For example, thermal processes, fracture, non-Newtonian rheology, multi-phase flow and the motion of solids in fluids can all be treated easily using SPH. I will illustrate these ideas with examples drawn from wave breaking and wave making, the fragmentation of asteroids, Rayleigh Taylor instabilities and the application of SPH to special effects in movies. I will conclude the talk with a description of new work involving the swimming of linked bodies.
Hypersonic Flight and Ground Testing Activities in India
Professor K. P. J. Reddy
Abstract: India has undertaken many hypersonic technology development programmes to meet the goals of future missions in space as well as missile development. While large scale ground based tests facilities are under construction, existing test facilities are being used to develop the preliminary design data needed for flight tests as well as for CFD code validation. A brief review of the hypersonic flight vehicle development programmes and the existing test facilities in the country along with some sample results from our laboratory for these programs is presented here.
Studying Complex Fluid Dynamics – From Direct Numerical Simulations to Tomographic Digital Holographic Particle Image Velocimetry
Professor Julio Soria
Abstract: Fluid Mechanics is an example of a complex dynamical system with uncountable applications in industry, transportation, manufacturing, medicine, atmospheric sciences, oceanography, hydrology, ionised gases or plasma, the earth's interior and space plasma turbulence. The scales of the fluid flows in these applications vary widely in the range from microns, as seen in the blood flow of living organisms, micro electro-mechanical system and micro-reactors to thousands of km in atmospheric, oceanographic and astrophysical flows. There are basically two approaches to the study of the three-dimensional spatio-temporal dynamics of complex fluid flows: experimental and numerical – with both relying heavily on theory to interpret and explain the results. The main and more recent techniques in numerical and experimental techniques are reviewed and by drawing on examples from research in our laboratory and that of others the specific and complementary nature of these two approaches is presented.