Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session G02: Turbulent Combustion III: Combustors |
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Chair: Paul Palies, CFD Research Corporation Room: Georgia World Congress Center B203 |
Monday, November 19, 2018 10:35AM - 10:48AM |
G02.00001: Numerical study of swirl boundary layer flashback using LES-based tabulation method based on premixed and diffusion flamelet Yihao Tang, Malik Hassanaly, Venkatramanan Raman Swirl boundary layer flashback is an important issue in practical swirl combustor design that may lead to severe device damages and deserves more attention. Here, a numerical study is performed to simulate partially-premixed methane/air flashback in a complex geometry of high-swirl combustor with a center body. The flashback mechanism is believed to be subject to the combined effect of large scale swirling flame front and small scale bulges of reverse flow, and is further complicated by the effects of fuel stratification and wall quenching. To account for the physicals, a large-eddy-simulation(LES)-based flamelet tabulation method is developed, and two types of combustion model, i.e. tabulation based on premixed flamelet and diffusion flamelet are incorporated and tested. Non-adiabatic effects are also introduced into the combustion model to account for wall heat loss. The performance of both models are first compared against each other under multiple levels of global equivalence ratio in terms of the initiation of flashback. Results are then compared with experimental data in terms of the flame front behavior and the speed of flashback. |
Monday, November 19, 2018 10:48AM - 11:01AM |
G02.00002: A flamelet tabulation method for the CFD simulation of supercritical CO2 reacting flows R V Manikantachari Kancherla, Martin Scott, Jose Bobren-Diaz, Subith Vasu Supercritical CO2 (sCO2) power cycles are gaining the attention of industry and academia due to their attractive features such as efficiency, eco-friendliness, compactness, and cost. However, the development of a combustor for direct-fired sCO2 cycles is challenging due to very high operating pressures. Therefore, accurate CFD simulations play a major role in the initial design and development of this combustor. In the current study, the applicability of various flamelet assumptions for supercritical CO2 combustion is discussed and variation of important non-premixed combustion characteristics with dilution and pressure are discussed. Here, chemistry is tabulated using the opposed jet diffusion flame flamelet approach with real-gas corrections. |
Monday, November 19, 2018 11:01AM - 11:14AM |
G02.00003: Physical Insights into the Flameless Combustion of Methane under MILD combustion conditions Efstathios-Al. Tingas, Dimitris M. Manias, Yuki Minamoto, Hong G Im Moderate or intense low-oxygen dilution (MILD) combustion is a promising technology for energy efficient industrial combustors. Many experimental studies have been carried out on the parameters that characterize the dynamics of this type of combustion, which is associated with intense preheating and dilution. Yet, there is limited understanding about the physical processes that characterize this mode of combustion, which makes it difficult to maintain and to model MILD combustion at different operating conditions. To this end, the mathematical tools provided by the computational singular perturbation (CSP) method can be applied to systematically analyze the relevant physics, by identifying the important dynamical characteristics driven by the key processes. In the current work, CSP tools are used to analyze the dynamics of an EGR-type methane/air premixed flame under MILD combustion conditions that was previously generated in the context of DNS and compare it with a conventional turbulent methane flame. In addition, the topological characteristics of these two flames are identified and compared. |
Monday, November 19, 2018 11:14AM - 11:27AM |
G02.00004: Large-eddy simulations of turbulent combustion fields generated by a Submerged Combustion Vaporizer (SCV) burner - Effect of water spray injection on combustion behavior - Takafumi Honzawa, Reo Kai, Makoto Seino, Takayuki Nishiie, Kenichi Wazaki, Yoshiharu Suzuki, Ryoichi Kurose Submerged Combustion Vaporizers (SCVs) are often used as LNG vaporizers, and those burners are designed to reduce the maximum flame temperature, which causes the reduction of NOx emission. In order to reduce the maximum flame temperature, it is useful to equip the water spray system for the burners. In this study, large-eddy simulations of the turbulent combustion fields generated by a SCV burner are conducted, and the effect of the water spray injection on the combustion behavior is investigated. As the combustion model, a non-adiabatic flamelet approach, which can take into account the effects of heat losses due to water evaporation and cooling wall, is employed. The results show that the water spray injection effectively causes the reductions of maximum gas temperature and then the NOx emissions. |
Monday, November 19, 2018 11:27AM - 11:40AM |
G02.00005: A numerical study on NO emission in bluff-body stabilized swirl diffusion flames Nafiseh Jalalatian, Babak Kashir The combustion characteristics of the methane blended bluff-body stabilized swirl diffusion flames within the turbulent regime are studied numerically with a coupled flamelet/radiation approach along with a modified k-ε turbulence model to determine the effect of swirl number on the flame dynamics and NO emission. The selected flames are controlled by changing the bulk tangential velocity of the swirl annulus whilst they possess the same operating conditions. Two different structures are observed by changing the swirl intensity. Flames with low swirl number (Sg=0.3) showed a radially converged shape in downstream. With increasing the swirl number a downstream recirculation zone is appeared due to vortex breakdown formation which provides an hourglass shape with open tails. However, the flame length is inversely related to the swirl number. Furthermore, results show that NO emission profiles are strongly analogous to the temperature distribution which demonstrates the thermal NO formation. The NO mass fraction values in the near-field and far-field regions are investigated with fuel enrichment. It is found that increasing the H/C atoms at the inflow diminishes the NO level. |
Monday, November 19, 2018 11:40AM - 11:53AM |
G02.00006: Large Eddy Simulations of the Vortex-Flame Interaction in a Turbulent Swirl Burner Zhen Lu, Ayman Elbaz, William L. Roberts, Hong G Im, Francisco E. Hernandez Perez A series of swirl-stabilized flames are simulated using large eddy simulation along with the flamelet based model for combustion. The target burner has separate and concentric methane and air streams, with methane in the center and the air flow swirled through the tangential inlets. By fixing the swirl number and air flow rate, the fuel jet velocity is reduced to study flame stability as the flame approaches towards the lean blow-off limit. Simulation results are compared against measured data, yielding a generally good agreement on the velocity, temperature, and species mass fraction distributions. The proper orthogonal decomposition method is applied on the velocity and progress variable fields to analyze the dominant unsteady flow structure, indicating a coupling between the vortex and the flame. The effects of vortex-flame interactions on the stabilization of the lifted swirling flame are also investigated. For the stabilization of the lifted swirling flame, the effects of convection, enhanced mixing, and flame stretching introduced by the vortex structure are assessed based on the numerical results. |
Monday, November 19, 2018 11:53AM - 12:06PM |
G02.00007: Effects of hydrogen enrichment ratio and turbulence on the structures of methane/hydrogen/air turbulent swirling premixed flames in a cuboid combustor Joonhwi Park, Yuki Minamoto, Masayasu Shimura, Mamoru Tanahashi Direct numerical simulations of stoichiometric CH4/H2/air turbulent swirling flames in a cuboid combustor have been conducted to clarify the effects of hydrogen enrichment ratio and turbulence on the flame structures. The dimension of combustor, Lx x Ly x Lz is 15 mm x 10 mm x 10 mm and swirl number S is 1.2. The fuel mixture and wall temperature is 700 K and pressure is 0.1 MPa. In this study two cases of fuel composition, of which volumetric ratio of CH4:H2 equals 1:1 (M05H05) and 4:1 (M08H02) are simulated by using a reduced chemical mechanism consists of 25 species and 111 reactions. For M08H02, the concentrations of hydrogen molecules remain high and production reaction prevails in the boundary of shear layers. Quantitative evaluation in phase space suggests that the hydrogen mass fraction profile is almost flat for M08H02, whereas decreases similarly to unstrained laminar flame for M05H05. The rates of elementary reactions related to the hydrogen are suppressed compared to the laminar flames. Finally, the effects of turbulence on the reactions and heat release rates will be discussed. |
Monday, November 19, 2018 12:06PM - 12:19PM |
G02.00008: Mechanisms of premixed turbulent swirling flame stabilization Paul Palies The presentation focus on the mechanisms of flame stabilization for premixed swirling flames on a laboratory scale experiment. A set of local contributors responsible of flame stabilization are identified from literature review. These local explicit (temperature, velocity,… ) or implicit (flame stretch, equivalence ratio, flame surface speed) local contributors are further investigated with numerical simulation of a premixed swirling flame. They are computed on flame surfaces and their distributions are obtained. Theoretical expressions are derived which focus on the flame surface, flame speed and velocity budget to guide the analysis. It indicates that the flame stabilization can be described with instantaneous, steady-state and fluctuating budgets respectively. Selected budgets’ terms are computed with the numerical simulations and indicate that the flame is stabilized by flow effect including low velocity region and turbulence/acoustic fluctuation region. The thermal diffusion term of the flame speed originating from the burnt gas of the recirculation zone and the combustion reaction effects are studied as part of the mechanisms of stabilization. |
Monday, November 19, 2018 12:19PM - 12:32PM |
G02.00009: Exploration of turbulent swirling flows with high-speed dual-plane stereo-PIV Tongxun Yi, Naibo Jiang, Christopher Fugger, Paul Hsu, Josef Felver, Sukesh Roy, Ianko Chterev, Matthew Sirignano, Benjamin Emerson, James R. Gord Turbulent swirling flows are highly three dimensional and spatially developing, including the mean flow, the large coherent structures and small-scale turbulence. Single-plane particle-image-velocimetry (PIV)/planar-laser-induced-fluorescence (PLIF) measurements, commonly used in laboratorial research on turbulent combustion, only allow determination of the six in-plane velocity gradients upstream of the flame front. In the reported study, high-speed (10 kHz) dual-plane stereoscopic particle image velocimetry (PIV) measurements are conducted on a turbulent swirling jet to spatially, temporally and fully resolve the nine-component velocity-gradient tensor, which is critical for accurate determination of the flame-stretch rate in turbulent combustion. Three key issues facing dual-plane PIV measurements are addressed, namely precise alignments of the two parallel PIV planes, refinements of the PIV-plane separation and optimal procedures for determination of the velocity gradients. Successful high-speed dual-plane stereoscopic PIV measurements as well as complete and accurate determination of the nine-component velocity-gradient tensor are demonstrated. |
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