Prediction of the Flow Response of a Turbulent Flame to Acoustic Pertubations Based on Mean Flow Resolvent Analysis

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Thomas Ludwig Kaiser ◽  
Lutz Lesshafft ◽  
Kilian Oberleithner
Keyword(s):  
Turbulent Flame ◽  
Low Rank ◽  
Reacting Flow ◽  
Mean Flow ◽  
Cold Flow ◽  
Flow Response ◽  
Hydrodynamic Response ◽  
Order Of Magnitude ◽  
Acoustic Forcing ◽  
Swirled Jet

Abstract Resolvent analysis is applied to a nonreacting and a reacting swirled jet flow. Time-averaged flows as input for the resolvent analysis and validation for the results of the resolvent analysis are obtained by experiments. We show that in the nonreacting (cold) flow case, the resolvent analysis is capable of predicting the hydrodynamic response to upstream harmonic acoustic forcing if the flow shows low-rank behavior. This is the case for low and moderate acoustic forcing amplitudes. Even for very strong acoustic velocity amplitudes that are of the same order of magnitude as the flow velocity, the resolvent analysis still provides reasonable results. The method also yields very good results for the reacting flow in terms of velocity fluctuation and heat release response to the acoustic forcing. This confirms the idea that the resolvent method could be applied to estimate the flame transfer function (FTF) based on the mean flow and flame.

Prediction of the Flow Response of a Turbulent Flame to Acoustic Pertubations Based on Mean Flow Resolvent Analysis

2019 ◽  
Author(s):  
Thomas Ludwig Kaiser ◽  
Lutz Lesshafft ◽  
Kilian Oberleithner
Keyword(s):  
Turbulent Flame ◽  
Low Rank ◽  
Reacting Flow ◽  
Mean Flow ◽  
Cold Flow ◽  
Flow Response ◽  
Hydrodynamic Response ◽  
Order Of Magnitude ◽  
Acoustic Forcing ◽  
Swirled Jet

Abstract Resolvent analysis is applied to a non-reacting and a reacting swirled jet flow. Time-averaged flows as input for the resolvent analysis and validation for the results of the resolvent analysis are obtained by experiments. We show that in the non-reacting (cold) flow case, the resolvent analysis is capable of predicting the hydrodynamic response to upstream harmonic acoustic forcing if the flow shows low-rank behavior. This is the case for low and moderate acoustic forcing amplitudes. Even for very strong acoustic velocity amplitudes, that are of the same order of magnitude as the flow velocity, the resolvent analysis still provides reasonable results. The method also yields very good results for the reacting flow in terms of velocity fluctuation and heat release response to the acoustic forcing. This confirms the idea that the resolvent method could be applied to estimate the Flame Transfer Function based on the mean flow and flame.

Flow Response of an Industrial Gas Turbine Combustor To Acoustic Forcing Extracted From Unforced Data

2021 ◽  
Author(s):  
Jan Paul Beuth ◽  
Jakob G. R. von Saldern ◽  
Thomas Ludwig Kaiser ◽  
Thoralf G. Reichel ◽  
Christian Oliver Paschereit ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Operating Conditions ◽  
Flow Dynamics ◽  
Low Rank ◽  
Frequency Range ◽  
Flow Response ◽  
Flow Fluctuations ◽  
Flame Dynamics ◽  
Flame Response ◽  
Acoustic Forcing

Abstract Gas turbine combustors are commonly operated with lean premix flames, allowing for high efficiencies and low emissions. These operating conditions are susceptible to thermoacoustic pulsations, originating from acoustic-flame coupling. To reveal this coupling, experiments or simulations of acoustically forced combustion systems are necessary, which are very challenging for real-scale applications. In this work we investigate the possibility to determine the flame response to acoustic forcing from snapshots of the unforced flow. This approach is based on three central hypothesis: first, the flame response is driven by flow fluctuations, second, these flow fluctuations are dominated by coherent structures driven by hydrodynamic instabilities, and third, these instabilities are driven by stochastic forcing of the background turbulence. As a consequence the dynamics in the natural flow should be low-rank and very similar to those of the acoustically forced system. In this work, the methodology is applied to experimental data of an industry-scale swirl combustor. A resolvent analysis is conducted based on the linearized Navier-Stokes equations to assure analytically the low-rank behavior of the flow dynamics. Then, these dynamics are extracted from flow snapshots using spectral proper orthogonal decomposition (SPOD). The extended SPOD is applied to determine the heat release rate fluctuations that are correlated with the flow dynamics. The low-rank flow and flame dynamics determined from the analytic and data-driven approach are then compared to the flow response determined from a classic phase average of the acoustically forced flow, which allow the research hypothesis to be evaluated. It is concluded that for the present combustor, the flow and flame dynamics are low-rank for a wider frequency range and the response to harmonic forcing can be determined quite accurately from unforced snapshots. The methodology further allows to isolate the frequency range where the flame response is predominantly driven by hydrodynamic instabilites.

Numerical Studies on Trapped-Vortex Concepts for Stable Combustion

1998 ◽  
Vol 120 (1) ◽  
pp. 60-68 ◽  
Author(s):  
V. R. Katta ◽  
W. M. Roquemore
Keyword(s):  
Drag Coefficient ◽  
Reacting Flow ◽  
Flow Conditions ◽  
Third Order ◽  
Cold Flow ◽  
Flow Simulations ◽  
Numerical Studies ◽  
Dynamic Flows ◽  
Experimental Findings ◽  
Trapped Vortex

Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.

scholarly journals Turbulent Flame Shape Switching at Conditions Relevant for Gas Turbines

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Ivan Langella ◽  
Johannes Heinze ◽  
Thomas Behrendt ◽  
Lena Voigt ◽  
Nedunchezhian Swaminathan ◽  
...  
Keyword(s):  
Turbulent Combustion ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Interaction Model ◽  
Numerical Approach ◽  
Reacting Flow ◽  
Combustion Chambers ◽  
Lean Burn ◽  
Large Eddy ◽  
Flame Behavior

Abstract A numerical investigation is conducted to shed light on the reasons leading to different flame configurations in gas turbine (GT) combustion chambers of aeronautical interest. Large eddy simulations (LES) with a flamelet-based combustion closure are employed for this purpose to simulate the DLR-AT big optical single sector (BOSS) rig fitted with a Rolls-Royce developmental lean burn injector. The reacting flow field downstream this injector is sensitive to the intricate turbulent–combustion interaction and exhibits two different configurations: (i) a penetrating central jet leading to an M-shape lifted flame; or (ii) a diverging jet leading to a V-shaped flame. The LES results are validated using available BOSS rig measurements, and comparisons show the numerical approach used is consistent and works well. The turbulent–combustion interaction model terms and parameters are then varied systematically to assess the flame behavior. The influences observed are discussed from physical and modeling perspectives to develop physical understanding on the flame behavior in practical combustors for both scientific and design purposes.

scholarly journals A Comparison of the Transfer Functions and Flow Fields of Flames With Increasing Swirl Number

2018 ◽  
Author(s):  
M. Gatti ◽  
R. Gaudron ◽  
C. Mirat ◽  
L. Zimmer ◽  
T. Schuller
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Flow Fields ◽  
Phase Lag ◽  
Swirl Number ◽  
Gain Curve ◽  
Cold Flow ◽  
Flow Response ◽  
Swirled Flames

The frequency response of premixed swirled flames is investigated by comparing their Transfer Function (FTF) between velocity and heat release rate fluctuations. The equivalence ratio and flow velocity are kept constant and four different swirling injectors are tested with increasing swirl numbers. The first injector features a vanishing low swirl number S = 0.20 and produces a flame anchored by the recirculating flow in the wake of a central bluff body. The three other swirling injectors produce highly swirled flows (S > 0.6) leading to a much larger internal recirculation region, which size increases with the swirl level. When operating the burner at S = 0.20, the FTF gain curve smoothly increases to reach a maximum and then smoothly decreases towards zero. For the highly swirled flames (S > 0.6), the FTF gain curve shows a succession of valleys and peaks attributed to interferences between axial and azimuthal velocity fluctuations at the injector outlet. The FTF phase-lag curves from the vanishing low and highly swirled flames are the same at low frequencies despite their large differences in flame length and flame aspect ratio. Deviations between the FTF phase lag curves of the different swirled flames start above the frequency corresponding to the first valley in the FTF gain of the highly swirled flames. Phase averaged images of the axial flow fields and of the flame chemiluminescence are used to interpret these features. At forcing frequencies corresponding to peak FTF gain values, the cold flow response of all flames investigated is dominated by large coherent vortical structures shed from the injector lip. At forcing frequencies corresponding to a valley in the FTF gain curve of the highly swirled flames, the formation of large coherent structures is strongly hindered in the cold flow response. These observations contrast with previous interpretations of the mechanisms associated to the low FTF response of swirled flames. It is finally found that for flames stabilized with a large swirl number, heat release rate fluctuations result both from large flame luminosity oscillations and large flame volume oscillations. For conditions leading to a small FTF gain value, both the flame luminosity and flame volume fluctuations are suppressed confirming the absence of strong perturbations within the flow at these frequencies. The experiments made in this work reveal a purely hydrodynamic mechanism at the origin of the low response of swirling flames at certain specific frequencies.

Bubble Dynamics and Cavitation Inception in Cavitation Susceptibility Meters

1986 ◽  
Vol 108 (4) ◽  
pp. 444-452 ◽  
Author(s):  
G. L. Chahine ◽  
Y. T. Shen
Keyword(s):  
Bubble Dynamics ◽  
Scaling Effects ◽  
Mean Flow ◽  
Cavitation Inception ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
Tentative Explanation ◽  
Bursting Events ◽  
Acoustic Device ◽  
The Relationship

To improve the understanding of the scaling effects of nuclei on cavitation inception, bubble dynamics, multibubble interaction effects, and bubble-mean flow interaction in a venturi Cavitation Susceptibility Meter are considered theoretically. The results are compared with classical bubble static equilibrium predictions. In a parallel effort, cavitation susceptibility measurements of ocean and laboratory water were carried out using a venturi device. The measured cavitation inception indices were found to relate to the measured microbubble concentration. The relationship between the measured cavitation inception and bubble concentration and distribution can be explained by using the theoretical predictions. A tentative explanation is given for the observation that the number of cavitation bursting events measured by an acoustic device is sometimes an order of magnitude lower than the number of microbubbles measured by the light scattering detector. The questions addressed here add to the fundamental knowledge needed if the cavitation susceptibility meter is to be used effectively for the measurement of microbubble size distributions.

Combustion Efficiency of a Premixed Continuous Flow Combustor

1985 ◽  
Vol 107 (3) ◽  
pp. 695-705 ◽  
Author(s):  
M. S. Anand ◽  
F. C. Gouldin
Keyword(s):  
Recirculation Zone ◽  
Thin Sheet ◽  
Turbulent Flame ◽  
Combustion Efficiency ◽  
Combustion Mechanism ◽  
Mean Flow ◽  
Outer Flow ◽  
Flow Swirl ◽  
Air Jet ◽  
Radial Profiles

Experimental data in the form of radial profiles of mean temperature, gas composition and velocity at the combustor exit and combustion efficiency are reported and discussed for a swirling flow, continuous combustor. The combustor is composed of two confined, concentric independently swirling jets: an outer, annular air jet and a central premixed fuel-air jet, the fuel being propane or methane. Combustion is stabilized by a swirl-generated central recirculation zone. The primary objective of this research is to determine the effect of fuel substitution and of changes in outer flow swirl conditions on combustor performance. Results are very similar for both methane and propane. Changes in outer flow swirl cause significant changes in exit profiles, but, surprisingly, combustion efficiency is relatively unchanged. A combustion mechanism is proposed which qualitatively explains the results and identifies important flow characteristics and physical processes determining combustion efficiency. It is hypothesized that combustion occurs in a thin sheet, similar in structure to a premixed turbulent flame, anchored on the combustor centerline just upstream of the recirculation zone and swept downstream with the flow. Combustion efficiency depends on the extent of the radial propagation, across mean flow streamtubes, of this reaction sheet. It is concluded that, in general, this propagation and hence efficiency are extremely sensitive to flow conditions.

Computation of 3D Turbulent Not-Premixed Reacting Flows Using an Implicit Unstructured Solver

2000 ◽  
Author(s):  
P. Adami ◽  
F. Martelli
Keyword(s):  
Bluff Body ◽  
Cfd Simulation ◽  
Turbulent Flame ◽  
Steady State Solution ◽  
Reacting Flows ◽  
Tvd Scheme ◽  
Reacting Flow ◽  
Riemann Solver ◽  
Turbulent Reactive Flows ◽  
Volume Method

A 3D CFD simulation of turbulent reactive flows is discussed. The original compressible version of the solver HybFlow designed for turbine rows investigation is here applied for low speed burning flow. A conserved scalar approach is considered to simulate the turbulent reacting flow field of non-premixed flames. The spatial discretization is based on an upwind finite volume method for unstructured grids using the Roe’s Riemann solver with a non-linear TVD scheme. The steady state solution is computed by means of an implicit relaxed Newton method. The linear solver is GMRES coupled with an ILU(0) preconditioning scheme. The turbulence chemistry interaction is described using a presumed β-PDF Flamelet approach. Two test applications are here presented to verify the methodology characteristics for a pilot-jet turbulent flame and a bluff-body stabilized flame both using CH4. A model combustor supplied with propane is also briefly shown as an example of application to a more realistic configuration.

Response Dynamics of Recirculation Structures in Coaxial Nonpremixed Swirl-Stabilized Flames Subjected to Acoustic Forcing

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Uyi Idahosa ◽  
R. Santhosh ◽  
Ankur Miglani ◽  
Saptarshi Basu
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Fluid Dynamic ◽  
High Energy ◽  
Reacting Flow ◽  
Flow State ◽  
Response Dynamics ◽  
Jet Flame ◽  
Flame Response ◽  
Acoustic Forcing

This paper reports the time-mean and phase-locked response of nonreacting as well as reacting flow field in a coaxial swirling jet/flame (nonpremixed). Two distinct swirl intensities plus two different central pipe flow rates at each swirl setting are investigated. The maximum response is observed at the 105 Hz mode in the range of excitation frequencies (0–315 Hz). The flow/flame exhibited minimal response beyond 300 Hz. It is seen that the aspect ratio change of inner recirculation zone (IRZ) under nonreacting conditions (at responsive modes) manifests as a corresponding increase in the time-mean flame aspect ratio. This is corroborated by ∼25% decrease in the IRZ transverse width in both flame and cold flow states. In addition, 105 Hz excited states are found to shed high energy regions (eddies) asymmetrically when compared to dormant 315 Hz pulsing frequency. The kinetic energy (KE) of the flow field is subsequently reduced due to acoustic excitation and a corresponding increase (∼O (1)) in fluctuation intensity is witnessed. The lower swirl intensity case is found to be more responsive than the high swirl case as in the former flow state the resistance offered by IRZ to incoming acoustic perturbations is lower due to inherently low inertia. Next, the phase-locked analysis of flow and flame structure is employed to further investigate the phase dependence of flow/flame response. It is found that the asymmetric shifting of IRZ mainly results at 270 deg acoustic forcing. The 90 deg phase angle forcing is observed to convect the IRZ farther downstream in both swirl cases as compared to other phase angles. The present work aims primarily at providing a fluid dynamic view point to the observed nonpremixed flame response without considering the confinement effects.

Numerical Investigations of the Gas Flow Inside the Bassoon

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Andreas Richter
Keyword(s):  
Gas Flow ◽  
Three Dimensional ◽  
Musical Instrument ◽  
Mean Flow ◽  
Steady State Flow ◽  
Plane Wave Solution ◽  
Pressure Time ◽  
Flow Features ◽  
Order Of Magnitude ◽  
Three Dimensional Simulations

This work is devoted to the numerical investigation of the gas flow inside a bassoon while it is played. The digitized geometry for the simulations is taken from measurements using laser scan techniques in combination with image processing. Pressure time series measured at the bell and reed were used to define adequate boundaries. Additional pressure measurements inside the musical instrument helped to validate the calculations. With this approach, it was possible to model the characteristics of a bassoon which plays the lowest note. The results of the three-dimensional simulations showed that the acoustic velocities and the underlying mean flow exhibit the same order of magnitude. The calculations indicate that the flow in curved sections such as the crook and the 180 deg bend is considerably different from a steady-state flow. For example, in bends the time-averaged flow features chains of small, alternating vortex pairs, and the pressure distribution differs significantly from a plane wave solution.

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