Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L01: Rarefied Flows and General Combustion |
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Chair: Suo Yang, University of Minnesota Room: 2A |
Monday, November 25, 2019 1:45PM - 1:58PM |
L01.00001: Solution of the full BGK model of the Boltzmann Transport Equation using Alternating Least Squares Arnout Boelens, Daniele Venturi, Daniel Tartakovsky High-dimensional partial-differential equations (PDEs) arise in a number of fields of science and engineering, where they are used to describe the evolution of joint probability functions. Due to the curse of dimensionality these kind of equations are notoriously hard to solve. We develop a new parallel algorithm to solve high-dimensional PDEs and apply it to the BGK model of the Boltzmann Transport Equation (BGK-BTE). The algorithm uses an implicit time integration scheme and is based on canonical numerical tensor methods combined with a pseudo-spectral method and alternating least squares. We demonstrate the accuracy and efficiency of the proposed new algorithm in computing the numerical solution to the full BGK model of the Boltzmann Transport Equation in six variables plus time. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L01.00002: Transport of gas mixtures in a Knudsen pump with specular and diffuse walls Tobias Baier, Steffen Hardt Gas flow in Knudsen pumps is induced by thermal gradients in channels or pores when the mean free path of the gas molecules is comparable to the geometric feature size. While thermal transpiration is often associated with flow along pores with a net axial temperature gradient, flow can also be induced by imposing a temperature difference across the channel, when suitably structured walls induce a periodic but non-mirror-symmetric temperature profile along the channel. One such arrangement, inspired by the Crookes radiometer, consists of placing an array of plates with different reflection properties on their opposing sides along a channel. By direct simulation Monte Carlo (DSMC) we investigate the transport of gas mixtures along such channels, focusing on the discrimination of individual species in the mixture by molecular size and mass during flow due to temperature, composition and pressure gradients. As Knudsen pumps do not possess any moving parts, they lend themselves for operation in low-maintenance situations such as for feeding gases to sensor surfaces. The observed discrimination of different gas species may thus – adversely or favorably – influence the overall detection characteristic of such a combined device. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L01.00003: Soot chemical pathways under elevated pressures in co-flow ethylene flames. Suo Yang, Dezhi Zhou, Hongyuan Zhang Internal combustion engines and gas turbines are operating under high pressures. One of the major concerns in high pressure combustion is its high soot yield, which was found in many sooting flame experiments. Specifically, the maximum soot volume fraction increases with the increasing pressure, with the dependence of soot on pressure weaker as pressure is further increased. To explain the dependence of soot on pressure, most of the experiments attribute this phenomenon to higher temperature, steeper precursor concentration gradients, and increased gas density. However, an exact and comprehensive mechanism behind this phenomenon, from a chemical kinetics perspective, is still elusive. In this study, a series of pressurized (from 1 to 16 atm) co-flow ethylene diffusion flames are simulated with detailed finite rate chemistry. The soot evolution is described by the bivariate Hybrid Method of Moments (HMOM). The experimental maximum soot volume fraction in the flames are reproduced by the simulations. Most importantly, the Global Pathway Analysis (GPA) is conducted to reveal the dominance and sensitivity of soot chemical pathways under elevated pressures. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L01.00004: Influence of Temperature and Dilution on Final Soot Nanostructure Justin Davis, Igor Novosselov Morphological evolution of nascent to mature combustion-generated particles is of interest due to changes in particle optics, chemical composition, and their effect on human health. In this work, the nanostructure of primary soot particles is investigated using argon dilution in laminar ethylene, ethane, and methane flames. A co-flow reactor oriented downwards allows for precise control on combustion conditions due to increased flame stability brought on by competing buoyant and convective forces. The dilution is varied from 0{\%} to 90{\%} by volume to investigate particle formation in temperature ranges from 1500 to 1950 K. High-resolution TEM displays different levels of particle maturity, from young soot with minimal order to mature particles with a core-shell nanostructure. A novel image processing algorithm helps to quantify differences in soot nanostructure, indicating the molecular weight of PAHs is similar for young and mature soot. However, molecular curvature decreases, suggesting the driving factor of soot maturity is a reduction in steric hindrance due to carbonization kinetics at high flame temperatures. These results can be used for validation of soot modeling approaches and to improve the understanding of structural changes as soot particles traverse the flame front. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L01.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 2:50PM - 3:03PM |
L01.00006: Experimental investigation of solid fuel smoldering using 3D X-ray computed tomography with gas-phase temperature measurements. Emeric Boigne, Matthias Ihme Smoldering is a regime of combustion that is characterized by low temperatures, slow rates of fuel consumption, and the absence of a flame. Recent research investigations on smoldering have focused on applications within confined environments such as peat fires, subsurface wildfires, and remediation of soil contamination. The present work reports on the use of 3D X-ray computed tomography to experimentally investigate smoldering in confined configurations. By temporally resolving the surface recession of solid fuel materials, the local consumption rates are extracted at the submillimeter scale. By diluting the ambient flow with Krypton, an inert X-ray tracer, the X-ray measurements enable simultaneous estimations of the 3D gas-phase temperature field. First, a configuration within an over-ventilated environment is considered for validation. Then, more complex fuel-configurations are examined, exhibiting spatial fuel heterogeneities and different fuel materials. Effects of the spatial heterogeneities on the smoldering process are discussed using the temporally-resolved 3D measurements. The simultaneous measurements of local consumption rate and gas-phase temperature allow further investigations of state-of-the-art models of smoldering. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L01.00007: Experimental Investigation of Combustion in Porous Media Burners with Tailored Matrix-Structure Using Additive Manufacturing Priyanka Muhunthan, Sadaf Sobhani, Emeric Boigne, Danyal Mohaddes, Matthias Ihme Porous Media Burners (PMBs) have been shown to enable enhanced burning velocities, extend flammability limits, and lower emissions. In this study, the viability of 3D printing complex ceramic structures is examined, and the performance of a novel functionally graded PMB design is investigated. Three different alumina matrix foams were designed and printed using lithography-based ceramic manufacturing. The flame stability, temperature profiles, and pressure drop for each burner are examined. X-ray computed tomography is used to characterize the printed matrix structure and to obtain important geometric information about pore diameter and porosity profiles. This work builds upon previous experimental investigations into graded PMBs, and the results demonstrate the feasibility of using additive manufacturing for tailoring PMB topologies to achieve specific system requirements. [Preview Abstract] |
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