The role of flow instability in combustion resonance

The main objective of this work was to investigate a possible two step hydrodynamic mechanism for the production of combustion resonance in fully premixed gas burners. This two step mechanism was modelled numerically using a two stage procedure. In the first stage, the stability of a low Reynolds number, impinging shear layer to acoustic forcing, similar to that in a burner at resonance, was investigated. This was carried out using an unsteady, higher order, incompressible, finite volume Navier-Stokes solver specifically developed for this purpose. Simulation of the isothermal entry flow for a range of parametric forcing conditions was carried out. Results indicate quite strongly that at Reynolds numbers where the unforced flow is steady, acoustic forcing may result in the roll up of the shear layer into coherent vortices by a convective instability mechanism. Flow visualisation was carried out, primarily using vorticity contours and quantitative measurements were made of the vortex characteristics.;In the second stage of the work, the interaction of vortices (representative of those formed at the entry of the burner and simulated in the first stage of this work) with a laminar flame front were calculated using a simple, inviscid, Lagrangian flame model. The flame was represented as a discontinuity across which cold unburnt reactants were transformed into hot combustion products. Preliminary results from this study indicate the usefulness of this method for investigating flame-vortex interaction of the type thought to occur in these burners, though further refinement of the model is required.;The results of this study would therefore indicate that flow instability may be the primary mechanism by which resonance occurs in fully premixed gas burners of a design investigated in this work, though at very low Reynolds numbers this would become increasingly difficult

Visualisation of Results from LES of Combustion

We examine the role of visualisation in the context of LES simulations of premixed turbulent combustion. The physical processes involved in premixed turbulent combustion are extremely complex, and the modelling of both the turbulence (via LES) and the combustion (via ame-wrinkling models) is diÆcult. Appropriate visualisation is required to understand the behaviour of the models, and ultimately to understand better the ow processes which are important in many industrial applications. We examine visualisations of two specic cases; simple ame kernel growth in a box of turbulence, and combustion behind a backward-facing step. Finally we discuss the role of the WWW in the continuing development of scientic visualisation techniques. 1 Introduction Although the governing equations of uid dynamics, the Navier-Stokes equations (NSE) have been known for more than 150 years, they are strongly non-linear, and so typically cannot be solved analytically. The increasing power of computers p..

NaHCO3 treatment potentiates the nutritional qualities and androgenic capabilities of bambara (Vigna subterranean L. Verdc) groundnut seeds

Bambara groundnut (Vigna subterranean L. Verdc) is a legume crop cultivated by few indigenous subsistence farmers in sub-Saharan Africa. Using established procedures, we investigated the effects of alkaline treatment towards improving the nutritional qualities of these groundnut seeds, and also in enhance the hematological and androgenic capabilities in 6 groups of male Wistar rats fed for 28 days with varied proportions at 0, 10, 30, 50, 70, and 90% of NaHCO3 -treated seeds mixed with basal diet. There were significant increases in several micro- and macro- nutrients and hematological (hemoglobin, packed cell volume, red blood cells, white blood cells, and platelets) and androgenic (testosterone, luteinizing hormone and follicle-stimulating hormone) indicators, when compared to the control group (0%). More importantly, the 70 and 90% fed groups showed significant reduction in the number of abnormal/dead sperm cells with improved sperm cell qualities, in terms of pH, minerals and vitamins. NaHCO3 treatment of Bambara groundnut seeds may therefore provide additional enhancement of the nutritional values, and the consumption could improve vitality and virility. Thus, it will be imperative if this is applied towards formulation of functional foods that can be useful in addressing the associated health challenges and/or malnutrition in developing countries