Andrew P. Wandel

Testing multiple mapping conditioning mixing for Monte Carlo probability density function simulations

Mitarai [Phys. Fluids 17, 047101 (2005)] compared turbulent combustion models against homogeneous direct numerical simulations with extinction/recognition phenomena. The recently suggested multiple mapping conditioning (MMC) was not considered and is simulated here for the same case with favorable results. Implementation issues crucial for successful MMC simulations are also discussed.

Hybrid binomial Langevin-multiple mapping conditioning modeling of a reacting mixing layer

A novel, stochastic, hybrid binomial Langevin-multiple mapping conditioning (MMC) model—that utilizes the strengths of each component—has been developed for inhomogeneous flows. The implementation has the advantage of naturally incorporating velocity-scalar interactions through the binomial Langevin model and using this joint probability density function (PDF) to define a reference variable for the MMC part of the model. The approach has the advantage that the difficulties encountered with the binomial Langevin model in modeling scalars with nonelementary bounds are removed. The formulation of the closure leads to locality in scalar space and permits the use of simple approaches (e.g., the modified Curl’s model) for transport in the reference space. The overall closure was evaluated through application to a chemically reacting mixing layer. The results show encouraging comparisons with experimental data for the first two moments of the PDF and plausible results for higher moments at a relatively modest computational cost.

Modelling of Non-Premixed Turbulent Combustion of Hydrogen using Conditional Moment Closure Method

Most of the electricity generation and energy for transport is still generated by the conversion of chemical to mechanical energy by burning the fuels in the combustion chamber. Regulation for pollution and the demand for more fuel economy had driven worldwide researcher to focus on combustion efficiency. In order to reduce experimental cost, accurate modelling and simulation is very critical step. Taylor series expansion was utilised to reduce the error term for the discretization. FORTRAN code was used to execute the discretized partial differential equation. Hydrogen combustion was simulated using Conditional Moment Closure (CMC) model. Combustion of hydrogen with oxygen was successfully simulated and reported in this paper.

Work in progress — Performance evaluation of online learning tools

Remote Access Laboratories (RAL) are tools that provide off-campus students with video supported access to practical activities on campus. A key success factor of any online activity is the quality of the student experience. As these systems use the Internet, quality depends not only on the learning activity design but also on access speed, geographical location and network traffic. Currently only anecdotal evidence exists regarding the relationship of technical performance parameters and the quality of user experience. This project proposes a systematic evaluation of the Quality of Experience of students using online learning tools. It will collect technical data as well as the subjective user experience of students using RAL systems. This paper introduces a framework and methodology that are used to evaluate the quality of the student learning experience.

The Effect of the Width and Number of Gaps on the Characteristics of Swirl Flow Induced Naturally inside Split Channel Using Hot Air Inlet

Split channels are commonly employed in research laboratories to generate fire whirls. The purpose of this computational study is to investigate the effects of the width and number of side gaps on the performance of the split channel when hot air enters at the base of the channel instead of using a fire. Three cylindrical channels are modeled. The first channel includes two identical slots, the second channel has only one gap with a width double that of the first channel, and the third channel comprises one gap identical to that of the first channel. Comparisons between the results of the first and the second channel provide the assessment of the impacts of the number of gaps on the performance of the split channel. Moreover, the comparison between the results of the second and third channels shows the effect of changing the width of the gap. The combined (overall) effects of the number and the width of the gaps on the characteristics of the flow within the channel are also evaluated by comparing the results of the first and the third channel. The results show that increasing the number of the slots without increasing the total area of the gaps leads to an increase in centerline vorticity within the channel. In addition, the inlet velocity of hot air from the base and entrainment ratio decreases with the increase of the number of the side slots. Increasing the width of the gap without changing the number of the slots reduces the entrainment velocity, the inlet velocity, but the entrainment mass flow rate and centerline vorticity increase. The entrainment mass flow rate centerline vorticity and entrainment ratio increases by the increase in the number of identical gaps and the increase of gap width whereas the entrainment velocity and the inlet velocity decrease.

Conditional dissipation of scalars in homogeneous turbulence: Closure for MMC modelling

While the mean and unconditional variance are to be predicted well by any reasonable turbulent combustion model, these are generally not sufficient for the accurate modelling of complex phenomena such as extinction/reignition. An additional criterion has been recently introduced: accurate modelling of the dissipation timescales associated with fluctuations of scalars about their conditional mean (conditional dissipation timescales). Analysis of Direct Numerical Simulation (DNS) results for a passive scalar shows that the conditional dissipation timescale is of the order of the integral timescale and smaller than the unconditional dissipation timescale. A model is proposed: the conditional dissipation timescale is proportional to the integral timescale. This model is used in Multiple Mapping Conditioning (MMC) modelling for a passive scalar case and a reactive scalar case, comparing to DNS results for both. The results show that this model improves the accuracy of MMC predictions so as to match the DNS results more closely using a relatively-coarse spatial resolution compared to other turbulent combustion models.

Implementation of multiple mapping conditioning for single conserved scalar

The Multiple Mapping Conditioning (MMC) model is a combination of probability density function (pdf) modelling and Conditional Moment Closure (CMC) and applicable to a wide range of turbulent flow and combustion situations. We are the first to implement the model and favourably compare the mixture fraction probability density function at various locations for an inhomogeneous mixing layer with those observed in experiments. The extension to multiple scalar flows will be future work.