Turbulent transport modelling of separating and reattaching shear flows

The improvement of capabilities for computer simulation of turbulent recirculating flows was investigated. Attention has been limited to two dimensional flows and principally to statistically stationary motion. Improvement of turbulence modeling explored the treatment of the near wall sublayer and of the exterior fully turbulent region, working within the framework of turbulence closures requiring the solution of transport equations for the turbulence energy and its dissipation rate. The work on the numerical procedure, based on the Gosman-Pun program TEACH, addressed the problems of incorporating the turbulence model as well as the extension to time dependent flows, the incorporation of a third order approximation of convective transport, and the treatment of non-orthogonal boundaries

Effect of width and temperature of a vertical parallel plate channel on the transition of the developing thermal boundary layer

Numerical simulations are performed to study the transition of the development of the thermal boundary layer of air along an isothermal heated plate in a large channel which is bounded by an adiabatic plate. In particular, the aim is to investigate the effects of the channel width (b) on the transition of the flow under various plate temperatures. Three different RANS based turbulent k–ε models namely standard, RNG and Realizable with an enhanced wall function are employed in the simulations. The channel width was varied from 0.04 m to 0.45 m and the numerical results of the maximum values of the flow velocity, turbulent kinetic energy were recorded along the vertical axis to examine the critical distance of the developing flow. The results show that the transition delays when the width is increased from 0.04 m to 0.08 m and particularly, the critical distance at b = 0.08 m reaches its maximum with the Grashof number of 2.8 × 1010. However, the critical distance drops when b is increased further from 0.08 m to 0.45 m, indicating an early transition of the flow. The transition remains unaffected by the adiabatic plate when b is greater than 0.45 m. Comparisons of selected numerical results are made with available experimental data of turbulent flow and a satisfied agreement is received

Osborne Reynolds: the Turbulent Years

The paper summarizes aspects in the life of Osborne Reynolds, FRS, with particular attention to: his appointment to the newly established Chair of Civil & Mechanical Engineering at Owens College Manchester in 1868; hitherto unreported aspects of his personal life concerning his second marriage; and the period from 1883 to 1895 during which his pioneering and much cited papers on turbulent flow were published, despite in one case strong criticisms from the referees. The paper also examines Reynolds’ unsuccessful applications in 1884 for professorships in London and Cambridge. The former was for a position requiring a major organizational role which, had his application succeeded, may well have prevented his Reynolds-decomposition analysis from being written

Microbiological indicators of water quality in submerged karst caves of Wakulla Springs

22 slides in Powerpoint presentation

Nonlinear softening as a predictive precursor to climate tipping

Approaching a dangerous bifurcation, from which a dynamical system such as the Earth's climate will jump (tip) to a different state, the current stable state lies within a shrinking basin of attraction. Persistence of the state becomes increasingly precarious in the presence of noisy disturbances. We consider an underlying potential, as defined theoretically for a saddle-node fold and (via averaging) for a Hopf bifurcation. Close to a stable state, this potential has a parabolic form; but approaching a jump it becomes increasingly dominated by softening nonlinearities. If we have already detected a decrease in the linear decay rate, nonlinear information allows us to estimate the propensity for early tipping due to noise. We argue that one needs to extract information about the nonlinear features (a "softening") of the underlying potential from the time series to judge the probability and timing of tipping. This analysis is the logical next step if one has detected a decrease of the linear decay rate. If there is no discernable trend in the linear analysis, nonlinear softening is even more important in showing the proximity to tipping. After extensive normal form calibration studies, we check two geological time series from paleo-climate tipping events for softening of the underlying well. For the ending of the last ice age, where we find no convincing linear precursor, we identify a statistically significant nonlinear softening towards increasing temperature. The analysis has thus successfully detected a warning of the imminent tipping event.Comment: 22 pages, 11 figures, changed title back, corrected smaller mistakes, updated reference

"How Is My Child Doing?": Selected Case Studies of How Childcare Centres Meet the DoPs Requirement to Discuss Children's Progress with Parents

The 1989 New Zealand educational reforms heralded major changes in all sectors of education. These changes included the introduction of a charter, which is essentially a contract, between the Crown and each individual education service. The Early Childhood Charter Guidelines: A Statement of Desirable Objectives and Practices, promulgated by the Minister of Education in December 1990, became the basis for the contract document required of early childhood centres which sought to become chartered centres in receipt of government finding. The Early Childhood Charter Guidelines, commonly referred to as the `DoPs', include over 60 requirements and objectives which early childhood services must meet as part of their contractual obligations (Meade and Dalli, 1991). Included in these is a requirement that centre personnel make provision at all times 'for parents and families to discuss their child's progress and be informed about their child's daily programme' (Ministry of Education 1990, p.3). The meaning and intent of the above requirement was investigated in a study carried out in the second half of 1994 in which government agency, parent, and centre personnel understanding of the requirement was investigated. The study was carried out as part of the requirements of the Master of Education programme in which the first author was enrolled. This paper focuses on data from interviews with parents and teachers which show how teachers in eleven childcare centres translated the requirement into manageable systems within their centres. The paper also illuminates the practices that developed in the centres from these systems and the extent to which the requirement became a tool for the development of parent-teacher partnerships in the education and care of children

Combustion of hydrogen-air jets in local chemical equilibrium: A guide to the CHARNAL computer program

A guide to a computer program, written in FORTRAN 4, for predicting the flow properties of turbulent mixing with combustion of a circular jet of hydrogen into a co-flowing stream of air is presented. The program, which is based upon the Imperial College group's PASSA series, solves differential equations for diffusion and dissipation of turbulent kinetic energy and also of the R.M.S. fluctuation of hydrogen concentration. The effective turbulent viscosity for use in the shear stress equation is computed. Chemical equilibrium is assumed throughout the flow

Two-fluid model of the truncated Euler Equations

A phenomenological two-fluid model of the (time-reversible) spectrally-truncated 3D Euler equation is proposed. The thermalized small scales are first shown to be quasi-normal. The effective viscosity and thermal diffusion are then determined, using EDQNM closure and Monte-Carlo numerical computations. Finally, the model is validated by comparing its dynamics with that of the original truncated Euler equation

Turbulence Closure Models for Computational Fluid Dynamics

The formulation of analytical turbulence closure models for use in computational fluid mechanics is described. The subject of this chapter is the types of models that are used to predict the statistically averaged flow field – commonly known as Reynolds‐averaged Navier–Stokes equations (RANS) modeling. A variety of models are reviewed: these include two‐equation, eddy viscosity transport, and second moment closures. How they are formulated is not the main theme; it enters the discussion but the models are presented largely at an operational level. Several issues related to numerical implementation are discussed. Relative merits of the various formulations are commented on