Unsteady flamelet / progress variable approach for non-premixed turbulent lifted flames

The unsteady flamelet/progress variable approach has been developed for the prediction of a lifted flame to capture the extinction and re-ignition physics. In this work inclusion of the time variant behavior in the flamelet generation embedded in the large eddy simulation technique, allows better understanding of partially premixed flame dynamics. In the process sufficient simulations to generate unsteady laminar flamelets are performed, which are a function of time. These flamelets are used for the generation of the look-up table and the flamelet library is produced. This library is used for the calculation of temperature and other species in the computational domain as the solution progresses. The library constitutes filtered quantities of all the scalars as a function of mean mixture fraction, mixture fraction variance and mean progress variable. Mixture fraction and progress variable distributions are assumed to be -PDF and d-PDF respectively. The technique used here is known as the unsteady flamelet progress variable (UFPV) approach. One of the well known lifted flames is considered for the present modeling which shows flame lift-off. The results are compared with the experimental data for the mixture fraction and temperature. Lift off height is predicted from the numerical calculations and compared with the experimentally given value. Comparisons show a reasonably good agreement and the UFPV combustion model appear to be a promising technique for the prediction of lifted and partially premixed flames

Large eddy simulation of turbulent unconfined swirling flows

Swirl stabilized flames are common in many engineering applications and modeling of such flames is particularly difficult due to their recirculation and vortex characteristics. Most standard approaches such as k-e and Reynolds Stress models based Reynolds averaged Navier-Stokes (RANS) equations which work very well in other situations fail to perform well in high swirl recirculating flows. In this study a recently developed large eddy simulation (LES) code has been applied for the prediction of non reacting swirling flows experimentally tested by Al-Abdeli and Masri [1]. For the sub-grid scale closure, the localized dynamic Smagorinsky eddy viscosity model is used. Predicted results are compared with experimentally measured mean velocities, rms fluctuations and Reynolds shear stresses. The agreement between predictions and experiments are very good at most axial and radial locations, although some discrepancies exist at certain locations downstream from the burner exit plane. It is observed that great care has to be taken over the boundary conditions specification for the LES simulation of high swirl intensity recirculation flows

A modified boundary condition of velocity for continuity equation with non-uniform density distribution at outlet boundary plane

Boundary conditions in computational fluid dynamics significantly affect the prediction of flow field. However, the outlet boundary conditions for the continuity equation have been rarely investigated. In addition, the velocities at the outlet boundary might not be accurately predicted with the conventional outlet boundary conditions when a flow that has non-uniform density distribution on the outlet boundary is simulated. In the present study, we modified a boundary condition for the continuity equation in consideration of the non-uniform density distribution on the outlet boundary plane, comparing the numerical results of combustion between the conventional and modified boundary conditions. As a result, the proposed boundary condition can resist the generation of an unrealistic temperature field better than the conventional methods

Improvement of the prediction accuracy of NO emissions in counter-flow diffusion flames on using NO mass fraction as a progress variable

Computational fluid dynamics has been widely used to predict the production of nitrogen oxide (NO). Flamelet approach is commonly used as a modelling technique to perform turbulent combustion simulations. As the prediction of NO emissions with the flamelet approach is not reliable, when predicting the NO emission, the NO emissions are calculated with the conservation equation of NO mass fraction, and the NO production rate is predicted with the flamelet approach. In this study, we used the mixture fraction and NO mass fraction to predict the NO production rate in the conservation equation of the NO mass fraction, comparing the numerical results calculated with proposed method with those with the conventional methods and detailed chemistry model. Numerical simulations of counter-flow diffusion flames where NO was not supplied, that was supplied with fuel, and that was supplied with oxidizer indicated that the distribution of NO mole fraction calculated with the proposed method was in better agreement with that of the detailed chemistry model than that of the conventional methods

Inflammatory arthritis in HIV positive patients: A practical guide

Background: Musculoskeletal manifestations of the human immunodeficiency virus (HIV) have been described since the outset of the global HIV epidemic. Articular syndromes that have been described in association with HIV include HIV-associated arthropathy, seronegative spondyloarthropathies (SPA) (reactive arthritis, psoriatic arthritis (PsA) and undifferentiated SPA), rheumatoid arthritis (RA) and painful articular syndrome. Methods: We carried out a computer-assisted search of PubMed for the medical literature from January 1981 to January 2015 using the keywords HIV, acquired immune-deficiency syndrome, rheumatic manifestations, arthritis, spondyloarthropathy, anti-TNF and disease modifying antirheumatic drugs. Only English language literature was included and only studies involving adult human subjects were assessed. Results: There are challenges in the management of inflammatory arthritis in patients who are HIV-positive, including difficulties in the assessment of disease activity and limited information on the safety of immunosuppressive drugs in these individuals. Conclusions: This review focuses on the clinical characteristics of the inflammatory articular syndromes that have been described in association with HIV infection and discusses the therapeutic options for these patients

Co-constructing cultural ecosystem services and wellbeing through a place-based approach

Reductive practices in fisheries management have tended to focus on ecological and economic dimensions that have rendered the social and cultural importance of fishing largely invisible, at least in the context of governance and policy making. This chapter builds on 5 years’ research in the English Channel and Southern North Sea in which the authors adopted a sense of place perspective as a framework for understanding the social and cultural value of small-scale fisheries. Through a number of case studies, the chapter describes how small-scale fisheries result in a series of ‘transformations’ as the marine environment is translated into cultural ecosystem services in coastal settings giving rise to socio-cultural value. This perspective is further developed by considering the value of the social wellbeing ‘lens’ to broaden the sense of place / cultural ecosystem services framework. In pursuing ‘values’ through sense of place, cultural ecosystem services and social wellbeing we discuss how the dualistic treatment of nature and society is problematic. We conclude that a relational co-constructionist approach, although challenging, offers a way of making visible an array of social and cultural values that emerge from the activity of small-scale fisheries

A Note on some Sanskrit Words in the Japaneese Language

A Note on some Sanskrit Words in the Japaneese Languag

A Brief Review on How to Make a Database for Flamelet Approach

The simulation of turbulent combustion has been of more importance to develop practical combustors. The flamelet (or tabulated chemistry) approach is one of the techniques to estimate combustion reaction rate and to describe turbulent combustion field. This approach can reduce computational cost in comparison with the reduced reaction schemes because the combustion reaction rate is just looked up from the pre-calculated database. The difficulty of the flamelet approach comes from the variety of how to make this pre-calculated database. In the present study, we reviewed previous researches in terms of the flamelet approach and summarized the ideas to make the database for the flamelet approach. First, the fundamental combustion reaction models such as the detailed reaction model and skeletal model were introduced. And then, how to generate the dataset for the database in flamelet, flamelet progress variable, and flamelet generated manifolds models were mentioned. Moreover, how to process the dataset into the database for the turbulent combustion simulation was pointed out. Finally, apart from making the database, the treatment of the database in the computational fluid dynamics was described briefly

Turbulent combustion simulation based on flamelet model

Turbulent combustion simulation based on flamelet mode