scholarly journals Control of a Lifted H2/N2 Flame by Axial and Flapping Forcing: A Numerical Study

2021 ◽  
Author(s):  
Artur Tyliszczak ◽  
Agnieszka Wawrzak
Keyword(s):  
Numerical Study ◽  
Temperature Fluctuations ◽  
Mixing Process ◽  
Stochastic Field ◽  
Field Approach ◽  
Eddy Simulation ◽  
Fuel Jet ◽  
Large Eddy ◽  
Lift Off ◽  
The Impact

Abstract The large eddy simulation (LES) method combined with the Eulerian stochastic field approach has been used to study excited lifted hydrogen flames in a stream of hot co-flow air in a configuration closely corresponding to the so-called Cabra flame. The excitation is obtained by adding to an inlet velocity profile three types of forcing ((i) axial; (ii) flapping; (iii) combination of both) with amplitude of 15% of the fuel jet velocity and frequency corresponding to the Strouhal numbers St=0.30, 0.45, 0.60 and 0.75. It is shown that such a type of forcing significantly changes the lift-off height Lh of the flame and its global shape, resulting in a flame occupying large volume or the flame, which downstream the nozzle transforms from the circular one into a quasi-planar flame. Both the Lh and their spreading angles of the flames were found to be a function of the type of the forcing and its frequency. The minimum value of Lh has been found for the case with the combination of axial and flapping forcing at the frequency close to the preferred one in the unexcited configuration. The impact of the flapping forcing manifested through a widening of the flame in the flapping direction. It was shown that the excitation can significantly increase the level of the velocity and temperature fluctuations intensifying the mixing process. The computational results are validated based on the solutions obtained for a non-excited flame for which experimental data are available.

Numerical Study of the Wave Impact on a Square Column Using Large Eddy Simulation

2007 ◽  
Author(s):  
H. T. C. Pedro ◽  
K.-W. Leung ◽  
M. H. Kobayashi ◽  
H. R. Riggs
Keyword(s):  
Numerical Study ◽  
Turbulence Models ◽  
Simple Algorithm ◽  
Navier Stokes ◽  
Wave Impact ◽  
Eddy Simulation ◽  
Subgrid Model ◽  
Large Eddy ◽  
Volume Approximation ◽  
The Impact

This work concerns the numerical investigation of the impact of a wave on a square column. The wave is generated by a dam break in a wave tank. Two turbulence models were used: Large Eddy Simulations (LES) and Unsteady Reynolds Averaged Navier-Stokes (URANS). The numerical simulations were carried out using a finite volume approximation and the SIMPLE algorithm for the solution of the governing equations. Turbulence was modeled with the standard Smagorinsky-Lilly subgrid-model for the LES and the standard κ-ε model for the URANS. The results are validated against experimental data for the wave impact on a square column facing the flow. The results, especially for LES, show very good agreement between the predictions and experimental results. The overall accuracy of the LES, as expected, is superior to the URANS. However, if computational resources are limited, URANS can still provide satisfactory results for structural design.

Large eddy simulation of a double-injection cycle and the impact of the needle motion on the sac-volume flow characteristics of a single-orifice diesel injector

2020 ◽  
pp. 146808742095132
Author(s):  
Mohamed Chouak ◽  
Louis Dufresne ◽  
Patrice Seers
Keyword(s):  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
High Energy ◽  
Volume Flow ◽  
Hysteresis Effect ◽  
Double Injection ◽  
Eddy Simulation ◽  
Fuel Jet ◽  
Large Eddy ◽  
The Impact

Study of the flow within diesel injector has gained in importance over the years as several authors have reported that the injector flow in the sac volume highly influenced the nozzle-flow characteristics at low lifts. Few studies have, however, characterized the sac volume and its dynamics. Thus, this paper reports on a numerical characterization of the needle displacement effects (static vs dynamic) on the internal flow of a sac-volume, single-hole diesel injector. To this end, a transient double-injection “closing-opening-closing-opening” cycle was simulated with a monophasic incompressible CFD model in combination with a moving mesh strategy to capture axial needle displacement. A large eddy simulation (LES) approach was chosen to gain better insight into the complexity of this unsteady turbulent flow. The emphasis of the paper is on the dynamic effects of needle movement on the sac flow, while static needle LES results are also shown to illustrate differences. The main findings reported herein are that the dynamic model shows a hysteresis effect associated with the needle motion between opening/closing phases. Quantitatively, the transient needle movement caused a difference in mass flow rate between the sac entrance and exit that was found to reach a maximum of [Formula: see text]. The hysteresis effect was found to be more pronounced at low needle lifts; both static and dynamic models seem to have performed similarly at very high needle lifts. Qualitatively, the LES sac-volume flow representations revealed a fuel jet attachment/detachment with needle movement, while static partial-lift simulations always predict an attached fuel jet. Further analysis of sac vortex dynamics revealed a high-energy vortex-structure breakdown just before the nozzle entrance that could help explain the higher turbulence production reported in the literature, both experimentally and numerically, at low needle lifts.

NUMERICAL STUDY OF DETONATION PROPAGATION IN VISCOUS TURBULENT FLOW IN A DUCT

2020 ◽  
Author(s):  
V. A. SABELNIKOV ◽  
◽  
V. V. VLASENKO ◽  
S. BAKHNE ◽  
S. S. MOLEV ◽  
...  
Keyword(s):  
Complex Geometry ◽  
Numerical Study ◽  
Navier Stokes ◽  
Detonation Waves ◽  
Detonation Propagation ◽  
Eddy Simulation ◽  
Detonation Structure ◽  
Classical Studies ◽  
Large Eddy ◽  
Physical Effects

Gasdynamics of detonation waves was widely studied within last hundred years - analytically, experimentally, and numerically. The majority of classical studies of the XX century were concentrated on inviscid aspects of detonation structure and propagation. There was a widespread opinion that detonation is such a fast phenomenon that viscous e¨ects should have insigni¦cant in§uence on its propagation. When the era of calculations based on the Reynolds-averaged Navier- Stokes (RANS) and large eddy simulation approaches came into effect, researchers pounced on practical problems with complex geometry and with the interaction of many physical effects. There is only a limited number of works studying the in§uence of viscosity on detonation propagation in supersonic §ows in ducts (i. e., in the presence of boundary layers).

Large Eddy Simulation of a Supercritical Fuel Jet in Cross Flow using GPU-Acceleration

2016 ◽  
Author(s):  
Kalyana C. Gottiparthi ◽  
Ramanan Sankaran ◽  
Anthony M. Ruiz ◽  
Guilhem Lacaze ◽  
Joseph C. Oefelein
Keyword(s):  
Large Eddy Simulation ◽  
Cross Flow ◽  
Gpu Acceleration ◽  
Eddy Simulation ◽  
Jet In Cross Flow ◽  
Fuel Jet ◽  
Large Eddy

Large Eddy Simulation of the fuel transport and mixing process in a scramjet combustor with rearwall-expansion cavity

2016 ◽  
Vol 126 ◽  
pp. 375-381 ◽  
Author(s):  
Zun Cai ◽  
Xiao Liu ◽  
Cheng Gong ◽  
Mingbo Sun ◽  
Zhenguo Wang ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Mixing Process ◽  
Eddy Simulation ◽  
Scramjet Combustor ◽  
Large Eddy ◽  
Transport And Mixing

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

Numerical Study on Air-Reed Instruments With LES

2011 ◽  
Author(s):  
Kin’ya Takahashi ◽  
Masataka Miyamoto ◽  
Yasunori Ito ◽  
Toshiya Takami ◽  
Taizo Kobayashi ◽  
...  
Keyword(s):  
Numerical Study ◽  
Sound Field ◽  
Acoustic Analogy ◽  
Empirical Theory ◽  
Sound Sources ◽  
Aerodynamic Sound ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Semi Empirical ◽  
2D And 3D

The acoustic mechanisms of 2D and 3D edge tones and a 2D small air-reed instrument have been studied numerically with compressible Large Eddy Simulation (LES). Sound frequencies of the 2D and 3D edge tones obtained numerically change with the jet velocity well following Brown’s semi-empirical equation, while that of the 2D air-reed instrument behaves in a different manner and obeys the semi-empirical theory, so called Cremer-Ising-Coltman theory. We have also calculated aerodynamic sound sources for the 2D edge tone and the 2D air-reed instrument relying on Ligthhill’s acoustic analogy and have discussed similarities and differences between them. The sound source of the air-reed instrument is more localized around the open mouth compared with that of the edge tone due to the effect of the strong sound field excited in the resonator.

Large Eddy Simulation of Cross Flow in Pipe Junction

2018 ◽  
Author(s):  
Jiajun Chen ◽  
Yue Sun ◽  
Hang Zhang ◽  
Dakui Feng ◽  
Zhiguo Zhang
Keyword(s):  
Large Eddy Simulation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Cross Flow ◽  
Exciting Force ◽  
Navier Stokes ◽  
Pipe Network ◽  
Eddy Simulation ◽  
Large Eddy

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.

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