Computational Fluid Dynamics and Aerodynamics

Two-equation eddy-viscosity turbulence models for engineering applications

Two new two-equation eddy-viscosity turbulence models will be presented.They combine different elements of existing models that are considered superior to their alternatives.The first model, referred to as the baseline (BSL) model, utilizes the original k-u model of Wilcox in the inner region of the boundary layer and switches to the standard A>e model in the outer region and in free shear flows.It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity.The second model results from a modification to the definition of the eddy-viscosity in the BSL model, which accounts for the effect of the transport of the principal turbulent shear stress.The new model is called the shear-stress transport-model and leads to major improvements in the prediction of adverse pressure gradient flows.

Modeling of swirl in turbulent flow systems

Flame Extinction Dynamics of Lean Premixed Bluff-Body Stabilized Flames

There is a crucial need to improve energy conversion efficiencies and minimize the environmental impact of turbulent combustion systems for energy production. Lean premixed turbulent combustion operation will significantly reduce efficiency-based thermal losses and combustion emissions. However, the performance of lean turbulent combustion technology is inevitably limited by the effects of flame extinction. Flames operating at lean conditions are susceptible to stabilization dynamics caused by local reaction extinction; this leads to global flame blowout and termination of the combustion energy production process. An improved understanding and prediction of flame extinction and stability will guide strategies to enhance efficiency, reduce emissions and improve performance of turbulent combustion systems. This research is focused on understanding the physical mechanisms of flame extinction using a newly-developed physics-based model. The novelty of this model is that it interactively couples the physics of the turbulent flow through a dynamic Lagrangian vortex method and the strained flame reaction kinetics using a one-dimensional opposed-jet flame. This innovative modeling strategy effectively captures the dynamic flame stability and extinction for turbulent premixed combustion.

Development and validation of the multicopter modelling code: a physics-based tool for multicopter analysis

Purpose This study aims to present details of the development and validation of the multicopter modelling code (MMC), a tool for the analysis of small-scale multicopters based on flight physics. Design/methodology/approach The development effort involved the study of aircraft dynamics and translating the equations of motion into MATLAB code. The authors also developed several auxiliary functions, so that the tool could trim the aircraft about a steady state, linearize the dynamic equations to produce a model that could be used for control systems design and carry out flight simulation. Findings MMC proved to be of good accuracy, producing results similar to those of other software such as AcuSolve, Overflow and the Rensselaer Multicopter Analysis Code (RMAC), which served as the motivation for this study. Originality/value The tool presented here provides an alternative to the aforementioned software, which are not freely available, programmed in MATLAB, a language well known to engineers and scientists.