Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E31: Experimental Techniques - Reactive Flows |
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Chair: Douglas Kelley, University of Rochester Room: F152 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E31.00001: Front tracking for characterizing and quantifying reactive mixing Douglas Kelley, Thomas Nevins Mixing in industrial chemical reactors involves complicated interactions between advection, reaction, and diffusion that are difficult to simulate or measure in detail. However, in large-Damk\"ohler-number systems which show sharp fronts between reacted and unreacted regions, reactor dynamics might be more simply and usefully characterized in terms of the reaction fronts themselves. In fact, prior work has already shown that the reaction rate and material diffusivity can be calculated directly if front speed and front thickness are known. We have developed methods to optically track reaction fronts, measuring their speed and thickness throughout space and time. We will present such measurements in both simulation and experiment, consider their statistics, and discuss future efforts to characterize and quantify mixing in chemical reactors. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E31.00002: Spontaneous Raman Scattering Measurements of Vibrational Non-Equilibrium in High-Speed Jets Heath Reising, Timothy Haller, Noel Clemens, Philip Varghese Vibrational non-equilibrium is detected and quantified in a high-speed jet using spontaneous Raman scattering. The non-equilibrium is induced by rapid mixing of the different temperature streams of the jet and coflow which are approximately 500 K and 1000 K, respectively. Simultaneous measurements of vibrational and rotational temperatures are made using fits of time-averaged high-resolution Stokes spectra of both N$_{2}$ and O$_{2}$ to high fidelity models of the spectrum. Independent measurements of these two species temperatures show good agreement in rotational temperature while the vibrational temperatures show only N$_{2}$ to have a strong non-equilibrium. This suggests that vibrational energy transfer between these two molecules is very inefficient at these conditions. Work is being conducted to extend the technique to single-shot measurements by employing a multiple-pass cell to increase the incident laser fluence in the measurement volume. This new capability will allow for statistics of vibrational temperature to be quantified. The instantaneous nature of the measurements will also allow the technique to be applied in regions of large temperature fluctuations, such as the base of a lifted turbulent jet flame, where time-average measurements are not valid. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E31.00003: Application of computer vision in studying fire plume behavior of tilting flames AmirHessam Aminfar, Jeanette Cobian IƱiguez, Stephanie Pham, Joey Chong, Gloria Burke, David Weise, Marko Princevac With the development in computer sciences especially in the field of computer vision, image processing has become an inevitable part of flow visualization. Computer vision can be used to visualize flow structure and to quantify its properties. We used a computer vision algorithm to study fire plume tilting when the fire is interacting with a solid wall. As the fire propagates to the wall the amount of air available for the fire to consume will decrease on the wall side. Therefore, the fire will start tilting towards the wall. Aspen wood was used for the fuel source and various configurations of the fuel were investigated. The plume behavior was captured using a digital camera. In the post processing, the flames were isolated from the image by using edge detection technics, making it possible to develop an algorithm to calculate flame height and flame orientation. Moreover, by using an optical flow algorithm we were able to calculate the speed associated with the edges of the flame which is related to the flame propagation speed and effective vertical velocity of the flame. The results demonstrated that as the size of the flame was increasing, the flames started tilting towards the wall. Leading to the conclusion that there should be a critical area of fire in which the flames start to tilt. Also, the algorithm made it possible to calculate a critical distance in which the flame will start orienting towards the wall [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E31.00004: Flame structure and chemiluminescence in premixed flames. Jose Grana-Otero, Siamak Mahmoudi The quantitative use of chemiluminescence requires the knowledge of the relationship between the concentration of excited species with flame properties such as the equivalency ratio, the burning rate or the heat release rate. With the aim of rigorously finding from first principles these relations we have analyzed, numerically and analytically, the distribution of the excited species OH$^*$ and CH$^*$ in steady hydrogen and methane planar premixed flames. Their mass fractions turn out to be extremely small; thus, a kinetic mechanism describing their dynamics in the flame can be obtained by simply adding the kinetic mechanism describing the excitation and de-excitation to the mechanism of the base flame. Due also to their small concentrations, the excited species are in steady state, facilitating a simple analytical description. The analyses show that OH$^*$, both in hydrogen and methane flames, can be found broadly distributed downstream the preheat region, in a three-layer structure that is analytically described. The distribution of CH$^*$ is much simpler, being always in equilibrium with CH, whose concentration is in turn proportional to that of CH$_4$. As a result, CH$^*$ is confined to the methane consumption layer in lean flames, but broadly distributed in rich flames. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E31.00005: Composition Independent Thermometry in Gaseous Combustion Using Spectral Lineshape Information Dominic Zelenak Temperature is an important thermochemical property that holds the key to revealing several combustion phenomena such as pollutant formation, flame extinction, and heat release. In a practical combusting environment, the local composition is unknown, hindering the effectiveness of established non-intrusive thermometry techniques. This study aims to offset this limitation by developing laser thermometry techniques that do not require prior knowledge of the local composition. Multiple methods for obtaining temperature are demonstrated, which make use of the spectral line broadening of an absorbing species (Kr) seeded into the flow. These techniques involve extracting the Doppler broadening from the Voight profile and utilizing compositional scaling of collisional broadening and shift to determine temperature. Doppler broadening-temperature scaling of two photon Kr-PLIF is provided. Lean-premixed and diffusion jet flames of CH4 will serve as the test bed for experimentation, and validation of the two methods will be made using the corresponding temperature determined from Rayleigh scattering imaging with adiabatic mixing and unity Lewis number assumptions. A ratiometric dual lineshape thermometry method for turbulent flames will also be introduced. [Preview Abstract] |
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