Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D34: Turbulent Non-Premixed Flames |
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Chair: Benedetta Franzelli, Institut National Polytechnique de Toulouse Room: 2024 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D34.00001: High-Speed Tomographic PIV Measurements of Strain Rate Properties in Turbulent Partially-Premixed Jet Flames Bruno Coriton, Jonathan H. Frank The effects of combustion on the strain rate field in turbulent jets were studied using 10 kHz tomographic particle image velocimetry (TPIV). Measurements were performed in a series of turbulent partially-premixed jet flames with increasing jet Reynolds numbers and increasing probabilities of localized extinction. Properties of the strain rate were analyzed including the relative ratios of principal strain rates, the preferential alignment of the principal strain rates with vorticity, and the strain rate clustering and intermittency. Comparisons with measurements in turbulent air jets revealed the effects of heat release on the structure and dynamics of the strain rate field. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D34.00002: Simultaneous PIV/OH-PLIF measurements in the wake of a reacting jet in swirling vitiated crossflow Pratikash Panda, Mario Roa, Yashowardhan Wagh, Robert Lucht A reacting jet issuing into a swirling, vitiated cross flow was investigated as a means of secondary injection of fuel in a distributed combustion system. Rapid mixing and chemical reaction in the near field of the jet injection is desirable in this application. Current study present time resolved planar measurements within the wake of reactive jets using simultaneous 2D-PIV/OH-PLIF at a repetition rate of 10 kHz. Based on our analysis it is hypothesized that the shear layer and wake field vortices play a significant role is stabilizing a steady reaction front within the near wake region of the jet. The reactive jets were injected through an extended nozzle into the crossflow which is located in the downstream of a low swirl burner (LSB) that produced the swirled, vitiated crossflow. PIV measurements and OH--PLIF based flame visualizations were acquired simultaneously at three measurement planes along the cross- section of the jet. The time resolved measurements provided significant information on the evolution of complex flow structures and highly transient features like, local extinction, re-ignition, vortex-flame interaction prevalent in a turbulent reacting flow. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D34.00003: Structure and stabilization of hydrogen-rich transverse jets in a vitiated turbulent flow Sgouria Lyra, Benjamin Wilde, Hemanth Kolla, Jerry Seitzman, Tim Lieuwen, Jacqueline Chen Results are presented from a joint experimental and numerical study of the flow characteristics and flame stabilization of a hydrogen rich jet injected into a turbulent, vitiated crossflow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements are obtained alongside 3D direct numerical simulations of inert and reacting JICF with detailed H$_{2}$/CO chemistry. Under the investigated conditions an autoigniting, burner-attached flame initiates uniformly around the burner edge. Significant asymmetry is observed between the reaction zones located on the windward and leeward sides, due to the substantially different scalar dissipation rates. The unsteady dynamics of the windward shear layer are explored to elucidate the important flow stability implications arising in the reacting JICF. Vorticity spectra extracted from the windward shear layer reveal that the reacting jet is globally unstable and features two high frequency peaks, including a fundamental mode whose Strouhal number of $\sim$ 0.7 agrees well with previous non-reacting JICF stability studies. Chemical explosive mode analysis shows that the entire windward shear layer, and a large region on the leeward side, are highly explosive prior to ignition and are dominated by non-premixed flame structures after ignition. The predominantly mixing limited nature of the flow after ignition is confirmed by the Takeno flame index, showing that $\sim$ 70{\%} of the heat release occurs in non-premixed regions. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D34.00004: Experimental investigation of the velocity field of a laboratory fire whirl Katherine Hartl, Pengfei Wang, Alexander Smits A fire whirl is a swirling diffusion flame that may occur to great destructive effect in urban fires or wildfires. To study fire whirls in the laboratory, we use a burner flame supplied with DME, and induce swirl by entraining air through a split cylinder surrounding the central flame. Stereo Particle Image Velocimetry (PIV) is used to obtain distributions of the three components of velocity inside and outside the fire whirl core. The effects of heat release rate and gap size on whirl height, circulation, and air entrainment are examined, and scaling behavior is discussed. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D34.00005: Models for differential diffusion in turbulent non-premixed combustion Haifeng Wang Models for differential diffusion are developed and are incorporated in the flamelet model for turbulent non-premixed combustion. The models are based on the limiting behavior of differential diffusion in turbulent combustion at zero and infinite Reynolds numbers. The effect of differential diffusion in a finite Reynolds number flame is approximated by the blending of the two limits. A turbulent non-premixed CH4/H2/N2 jet flame is adopted as a validation test case. The modeling results are found to be in excellent agreement with the experimental data, including the level of differential diffusion. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D34.00006: Effects of differential diffusion on the flame structure of oxygen enhanced turbulent non-premixed jet flames Felix Dietzsch, Michael Gauding, Christian Hasse By means of Direct Numerical Simulation we have investigated the influence of differential diffusion for non-premixed oxygen-enhanced turbulent flames. Oxygen-enhanced conversion usually yields higher amounts of H2 as compared to conventional air combustion. It is well known that H2 as a very diffusive species leads to differential diffusion effects. In addition to the diffusive transport mixing processes are also often controlled by turbulent transport. Previous investigations of a turbulent CH4/H2 oxygen-enhanced jet flame have shown that in mixture fraction space it is important to distinguish between regions of equal diffusivities and detailed transport. These findings are of particular interest when performing Large-Eddy simulations applying a flamelet approach. Using this approach a LES study was performed of the aforementioned flame considering differential diffusion. Therefore, flamelet equations including differential diffusion via non-unity constant Lewis numbers were solved. However, this study showed that keeping the non-unity Lewis numbers constant, is not sufficient to capture the diffusion phenomena in this particular flame. Direct Numerical Simulations have been conducted in order to investigate how Lewis numbers are affected in mixture fraction space. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D34.00007: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D34.00008: Validity of the constant non-unity Lewis number assumption in chemically reacting flows Nicholas Burali, Guillaume Blanquart, Yuan Xuan Describing molecular diffusion using constant but non-unity Lewis numbers has been widely used in numerical simulations of chemically reacting flows. These constant Lewis numbers need to be selected carefully, as they should correctly describe the molecular diffusion of different species. However, in practice they are extracted from one-dimensional flame structure calculations. The objective of the current work is to assess the validity of the constant non-unity Lewis number assumption in the description of molecular mixing. Towards this goal, a three-tiered analysis is carried out. First, the sensitivity of key reacting flow characteristics to species Lewis numbers is assessed on both laminar diffusion flames and laminar premixed flames. Second, detailed numerical simulations using the multi-component diffusion model are performed for the same flames, and used as reference data. The validity of different Lewis number extraction criteria is examined by comparing simulation results obtained by using different sets of Lewis numbers to the reference data, and an optimal criterion is proposed. Finally, as a validation, a turbulent flame simulation is performed using Lewis numbers extracted following this optimal criterion, and results are compared to the experimental measurements. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D34.00009: Direct Numerical Simulation Study of Thermochemical Nonequilibrium Effect on Mixing and Combustion Romain Fievet, Stephen Voelkel, Heeseok Koo, Venkat Raman, Philip Varghese Nonequilibrium of internal states of molecules is an important physical phenomenon that could affect flow behavior in supersonic flows. Translational nonequilibrium, where molecular velocities do not conform to the Maxwell distribution could impact dissipation processes in turbulence. Similarly, vibrational and/or rotational nonequilibrium will lead to marked changes in mixing and combustion. In this study, these nonequilibrium effects are explored using direct numerical simulation of a supersonic hydrogen jet issuing into a coflow of air. Nonequilibrium reaction rates derived using detailed computational chemistry methods are used in the flow simulations. It is shown that underpopulation of vibrational states leads to significant change in flame stabilization. Hence, the processing of the incoming air by the bow shocks formed ahead of a scramjet could lead to significant ignition delay. [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D34.00010: Principal Component Transport in Turbulent Combustion Tarek Echekki, Hessam Mirgolbabaei We present a posteriori validation of the solution of a turbulent combustion problem based on the transport of principal components (PCs). The PCs are derived from a priori principal component analysis (PCA) of the same composition space. This analysis is used to construct and tabulate the PCs' chemical source terms and diffusion coefficients in terms of the PCs using artificial neural networks (ANN). The a posteriori validation is implemented on a stand-alone one-dimensional turbulence (ODT) simulation of Sandia flame F resulting in a very good reconstruction of the original thermo-chemical scalars profiles at different downstream distances. [Preview Abstract] |
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