Time-Resolved PIV Measurements of Non-Reacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control

2014 ◽  
Author(s):  
Joseph Meadows ◽  
Ajay K. Agrawal
Keyword(s):  
Flow Field ◽  
Direct Injection ◽  
Combustion Noise ◽  
Reacting Flow ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Turbulence Structures ◽  
Precessing Vortex Core ◽  
Acoustic Control ◽  
Acoustic Instabilities

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry to measure the turbulent flow field in a non-reacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the Proper Orthogonal Decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core, which would ultimately affect the acoustic behavior in a favorable manner.

Time-Resolved Particle Image Velocimetry Measurements of Nonreacting Flow Field in a Swirl-Stabilized Combustor Without and With Porous Inserts for Acoustic Control

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
Joseph Meadows ◽  
Ajay K. Agrawal
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Direct Injection ◽  
Combustion Noise ◽  
Turbulent Structures ◽  
Time Resolved ◽  
Turbulence Structures ◽  
Image Velocimetry ◽  
Acoustic Instabilities

Combustion noise and thermo-acoustic instabilities are of primary importance in highly critical applications such as rocket propulsion systems, power generation, and jet propulsion engines. Mechanisms for combustion instabilities are extremely complex because they often involve interactions among several different physical phenomena such as unsteady flame propagation leading to unsteady flow field, acoustic wave propagation, natural and forced hydrodynamic instabilities, etc. In the past, we have utilized porous inert media (PIM) to mitigate combustion noise and thermo-acoustic instabilities in both lean premixed (LPM) and lean direct injection (LDI) combustion systems. While these studies demonstrated the efficacy of the PIM concept to mitigate noise and thermo-acoustic instabilities, the actual mechanisms involved have not been understood. The present study utilizes time-resolved particle image velocimetry (PIV) to measure the turbulent flow field in a nonreacting swirl-stabilized combustor without and with PIM. Although the flow field inside the annulus of the PIM cannot be observed, measurements immediately downstream of the PIM provide insight into the turbulent structures. Results are analyzed using the proper orthogonal decomposition (POD) method and show that the PIM alters the flow field in an advantageous manner by modifying the turbulence structures and eliminating the corner recirculation zones and precessing vortex core (PVC), which would ultimately affect the acoustic behavior in a favorable manner.

Study of the steady flow produced by direct injection diesel engine intake ports

2001 ◽  
Vol 215 (2) ◽  
pp. 285-298 ◽  
Author(s):  
J M Desantes ◽  
J V Pastor ◽  
A Doudou
Keyword(s):  
Spectral Analysis ◽  
Diesel Engine ◽  
Flow Field ◽  
Steady Flow ◽  
Cylinder Head ◽  
Laser Doppler Anemometry ◽  
Direct Injection ◽  
Valve Lift ◽  
Turbulent Structures ◽  
Direct Injection Diesel Engine

In this paper laser Doppler anemometry is used to characterize the steady flow field inside the cylinder generated by the two intake ports of a four-valve diesel head over the whole valve lift range and to compare the patterns at two different sections commonly used for global characterization in order to decide which is more appropriate for cylinder head evaluation. A more detailed investigation is performed for two valve lifts where the change in the flow patterns is more evident by applying a spectral analysis with the local normalized slotting technique to study the turbulent structures accompanying the in-cylinder swirl development.

Global and Local Hydrodynamic Stability Analysis as a Tool for Combustor Dynamics Modeling

2015 ◽  
Author(s):  
Pedro Paredes ◽  
Vassilis Theofilis ◽  
Steffen Terhaar ◽  
Kilian Oberleithner ◽  
Christian Oliver Paschereit
Keyword(s):  
Stability Analysis ◽  
Flow Field ◽  
Prediction Models ◽  
Global Analysis ◽  
Local Analysis ◽  
Reacting Flow ◽  
Dynamics Modeling ◽  
Mean Flow ◽  
Global Mode ◽  
Precessing Vortex Core

Coherent flow structures in shear flows are generated by instabilities intrinsic to the hydrodynamic field. In a combustion environment, these structures may interact with the flame and cause unsteady heat release rate fluctuations. Prediction and modeling of these structures is thereby highly wanted for thermo-acoustic prediction models. In this work we apply hydrodynamic linear stability analysis to the time-averaged flow field of swirl-stabilized combustors obtained from experiments. Recent fundamental investigations have shown that the linear eigenmodes of the mean flow accurately represent the growth and saturation of the coherent structures. In this work biglobal and local stability analysis is applied to the reacting flow in an industry-relevant combustion system. Both the local and the biglobal analysis accurately predicts the onset and structure of a self-excited global instability that is known in the combustion community as a precessing vortex core (PVC). However, only the global analysis accurately predicts a globally stable flow field for the case without the oscillation, while the local analysis wrongly predicts an unstable global growth rate. The predicted spatial distribution of the amplitude functions using both analysis agree very well to the experimentally identified global mode. The presented tools are considered as very promising for the understanding of the PVC and physics based flow control.

scholarly journals Impact of a Centrebody on the Unsteady Flow Dynamics of A Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Hemchandra ◽  
Masayasu Shimura ◽  
Santosh Shanbhogue ◽  
Ahmed Ghoniem
Keyword(s):  
Nozzle Exit ◽  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Reacting Flow ◽  
Exit Plane ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centrebody diameter (Dc) on the PVC in a non-reacting flow in a single nozzle swirl combustor. Time resolved high speed stereoscopic PIV (sPIV) measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re ∼ 20,000). The centrebody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition (POD) provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centrebody, a coherent PVC is present in the flow as expected. The introduction of a centrebody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the vortex breakdown bubble (VBB) and centrebody wake recirculation zone (CWRZ) regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the de-stabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centrebody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.

Global and Local Hydrodynamic Stability Analysis as a Tool for Combustor Dynamics Modeling

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Pedro Paredes ◽  
Steffen Terhaar ◽  
Kilian Oberleithner ◽  
Vassilis Theofilis ◽  
Christian Oliver Paschereit
Keyword(s):  
Stability Analysis ◽  
Flow Field ◽  
Prediction Models ◽  
Global Analysis ◽  
Local Analysis ◽  
Reacting Flow ◽  
Dynamics Modeling ◽  
Mean Flow ◽  
Global Mode ◽  
Precessing Vortex Core

Coherent flow structures in shear flows are generated by instabilities intrinsic to the hydrodynamic field. In a combustion environment, these structures may interact with the flame and cause unsteady heat release rate fluctuations. Prediction and modeling of these structures are thereby highly wanted for thermo-acoustic prediction models. In this work, we apply hydrodynamic linear stability analysis to the time-averaged flow field of swirl-stabilized combustors obtained from experiments. Recent fundamental investigations have shown that the linear eigenmodes of the mean flow accurately represent the growth and saturation of the coherent structures. In this work, biglobal and local stability analyses are applied to the reacting flow in an industry-relevant combustion system. Both the local and the biglobal analyses accurately predict the onset and structure of a self-excited global instability that is known in the combustion community as a precessing vortex core (PVC). However, only the global analysis accurately predicts a globally stable flow field for the case without the oscillation, while the local analysis wrongly predicts an unstable global growth rate. The predicted spatial distribution of the amplitude functions using both analyses agrees very well to the experimentally identified global mode. The presented tools are considered as very promising for the understanding of the PVC and physics based flow control.

Dynamic Mode Decomposition for Extracting Cycle-to-Cycle Variation of SIDI Engine In-Cylinder Flow Under Motoring Condition

2020 ◽  
Author(s):  
Mengqi Liu ◽  
Fengnian Zhao ◽  
Xuesong Li ◽  
Min Xu ◽  
David L. S. Hung
Keyword(s):  
Flow Field ◽  
Direct Injection ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Field Variation ◽  
Dynamic Features ◽  
Time Resolved ◽  
Cycle Variation ◽  
Mode Decomposition ◽  
Cylinder Flow

Abstract Cycle-to-cycle variation (CCV) of in-cylinder flow strongly affects the performance and efficiency of spark ignition direct injection (SIDI) engines. In order to achieve a precise flow control inside the engine, the underlying dynamic features of flow field CCV must be thoroughly investigated. In this work, large-eddy simulations (LES) with 50 consecutive cycles are employed for high fidelity numerical realizations of engine flow under motoring condition. To supplement the numerical analysis, time-resolved particle image velocimetry (PIV) measurements are also conducted in several cutting planes. Although the velocity root mean square (RMS) is calculated to quantify the cyclic variation intensity of simulation and experiment results, some important dynamic characteristics cannot be observed directly from velocity data. Therefore, dynamic mode decompositions (DMD), which is a widely used modal decomposition algorithm on fluid study, is used to decompose flow fields into modes with specific frequencies and provide growth rates of corresponding flow structures. This spectral information of in-cylinder flow field is ponderable for uncovering dynamic features of engine CCV. In this study, DMD algorithm is applied on both LES and PIV datasets. The frequency and growth rate differences are employed to elucidate the CCV feature deviations captured by LES and PIV. This research provides a guideline for extracting engine flow field cyclic variability feature using DMD algorithm. Based on the discussion for spectral features and potential sources of flow field variation, the capability of LES to capture CCV features is evaluated. The DMD spectrum differences between PIV and LES can guide the boundary condition perturbations used for simulation fidelity improvements.

Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

2011 ◽  
Author(s):  
Dipanjay Dewanji ◽  
Arvind G. Rao ◽  
Mathieu Pourquie ◽  
Jos P. van Buijtenen
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Numerical Study ◽  
Reverse Flow ◽  
Direct Injection ◽  
Flow Characteristics ◽  
Droplet Breakup ◽  
Reacting Flow ◽  
Lean Direct Injection ◽  
Wide Range

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.

Numerical Investigations of a Swirl-Stabilized Premixed Flame at Ultra-Wet Conditions

2011 ◽  
Author(s):  
Oliver Kru¨ger ◽  
Katharina Go¨ckeler ◽  
Sebastian Go¨ke ◽  
Christian Oliver Paschereit ◽  
Christophe Duwig ◽  
...  
Keyword(s):  
Flow Field ◽  
Turbulent Energy ◽  
Dominant Frequency ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Reacting Flow ◽  
Steam Content ◽  
Precessing Vortex Core ◽  
Reduced Mechanism ◽  
Flow Features

The present study focuses on the numerical investigation of a generic swirl-stabilized burner operated with methane at ultra-wet conditions. The burner is fed with a preheated homogeneous mixture formed by steam and air. As a set of operating conditions atmospheric pressure, inlet temperature of 673K, equivalence ratio of 0.85 and a steam content of 30% is applied. Large eddy simulations have been performed to investigate the flow features. In a first step the non-reacting flow field was investigated with water as working medium. Comparison with Particle Image Velocimetry (PIV) and Laser-Doppler Velocimetry (LDV) measurements conducted in a water tunnel facility showed that an excellent agreement within the experimental uncertainty is obtained for the flow field. A dominant frequency in the turbulent energy spectrum was identified, which corresponds to the motion associated with a precessing vortex core (PVC). In order to investigate the reactive flow in a second step, a customized solver for handling low Mach number reacting flows based on an implicit LES approach was developed. As reaction mechanism a reduced 4 steps / 7 species global scheme was used. To compare the simulations qualitatively with a wet flame, OH chemiluminescence pictures serve as a reference. The simulations showed a more compact flame compared to the OH pictures. Nevertheless, the prolongation and position of the flame were found to be reasonable. The reduced mechanism captures the main effects, such as the reduction of the peak and mean temperatures. Furthermore, the presence of a PVC in the reacting flow could be determined and was not suppressed by heat-release.

scholarly journals Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Shanbhogue ◽  
Masayasu Shimura ◽  
Ahmed F. Ghoniem ◽  
Santosh Hemchandra
Keyword(s):  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Axial Position ◽  
Intermittent Flow ◽  
Reacting Flow ◽  
Hydrodynamic Mode ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. We examine the impact of a centrebody on PVC dynamics in a non-reacting flow in a swirl nozzle combustor. Time resolved high speed stereoscopic PIV measurements are performed for two swirl numbers, S=0.67 and 1.17 and three centrebody diameters, 9.5mm, 4.73mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit is kept constant as Ub=8m/s for all cases (Re~20,000). The data is analyzed using a new modal decomposition technique that combines the wavelet transform and proper orthogonal decomposition (WPOD). This gives insight into globally intermittent flow dynamics. A coherent PVC is present in the flow when there is no centrebody. Introducing a centrebody makes the PVC oscillations intermittent. The WPOD results show two qualitatively different intermittent behaviours at S=0.67 and 1.17. For S=0.67, the axial position of the VBB suggests that turbulence destabilizes the PVC mode by causing intermittent separation of the VBB and centrebody wake, resulting in PVC oscillations. For S=1.17, the VBB engulfs the centrebody and stabilizes the PVC mode. Therefore, in this case, PVC oscillations appear to be the flow response to broadband stochastic forcing of the time averaged flow by turbulence.

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