scholarly journals Analyzing the Interaction of Vortex and Gas–Liquid Interface Dynamics in Fuel Spray Nozzles by Means of Lagrangian-Coherent Structures (2D)

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2552
Author(s):  
Dauch ◽  
Ates ◽  
Rapp ◽  
Keller ◽  
Chaussonnet ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Fuel Spray ◽  
Nozzle Geometry ◽  
Spray Nozzle ◽  
Sph Method ◽  
Time Resolved ◽  
Fuel Flow ◽  
Finite Time Lyapunov Exponent ◽  
Primary Breakup ◽  
Unique Approach

Predictions of the primary breakup of fuel in realistic fuel spray nozzles for aero-enginecombustors by means of the SPH method are presented. Based on simulations in 2D, novel insightsinto the fundamental effects of primary breakup are established by analyzing the dynamics ofLagrangian-coherent structures (LCSs). An in-house visualization and data exploration platformis used in order to retrieve fields of the finite-time Lyapunov exponent (FTLE) derived from theSPH predictions aiming at the identification of time resolved LCSs. The main focus of this paperis demonstrating the suitability of FTLE fields to capture and visualize the interaction between thegas and the fuel flow leading to liquid disintegration. Aiming for a convenient illustration at a highspatial resolution, the analysis is presented based on 2D datasets. However, the method and theconclusions can analoguosly be transferred to 3D. The FTLE fields of modified nozzle geometriesare compared in order to highlight the influence of the nozzle geometry on primary breakup, whichis a novel and unique approach for this industrial application. Modifications of the geometry areproposed which are capable of suppressing the formation of certain LCSs, leading to less fluctuationof the fuel flow emerging from the spray nozzle.

Computation of Liquid Fuel Atomization and Mixing by Means of the SPH Method: Application to a Jet Engine Fuel Nozzle

2016 ◽  
Author(s):  
T. Dauch ◽  
S. Braun ◽  
L. Wieth ◽  
G. Chaussonnet ◽  
M. Keller ◽  
...  
Keyword(s):  
Fuel Spray ◽  
Nozzle Geometry ◽  
Engine Fuel ◽  
Sph Method ◽  
Flow Problems ◽  
Fuel Atomization ◽  
Particle Hydrodynamics ◽  
Primary Breakup ◽  
Smoothed Particle ◽  
Fuel Nozzle

At the “Institut für Thermische Strömungsmaschinen” (ITS) a numerical method based on the the meshfree “Smoothed Particle Hydrodynamics” (SPH) approach has been developed with the objective of computing primary breakup in the vicinity of fuel spray nozzles [1, 2]. In recent publications the successful application of the code to different flow problems is demonstrated [3, 4]. In this paper we present the first application of the method to investigate a simplified, but applied fuel spray nozzle geometry of the swirl cup design in 2D. The atomization process of Jet-A1 at ambient and at high pressure conditions is compared in terms of film flow development, mixing and spray characteristics. The influence of pressure is pointed out and quantified. The study demonstrates that the SPH method is a suitable toolbox for the analysis and the design of fuel spray nozzles. Unique analysis tools that are not available in grid-based CFD methods are presented and applied. Droplet distributions are extracted, which can be considered as possible input in subsequent Euler-Lagrange computations.

scholarly journals Progress in the Smoothed Particle Hydrodynamics Method to Simulate and Post-process Numerical Simulations of Annular Airblast Atomizers

2020 ◽  
Vol 105 (4) ◽  
pp. 1119-1147
Author(s):  
G. Chaussonnet ◽  
T. Dauch ◽  
M. Keller ◽  
M. Okraschevski ◽  
C. Ates ◽  
...  
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Flux Ratio ◽  
Liquid Sheet ◽  
Sph Method ◽  
Post Process ◽  
Finite Time Lyapunov Exponent ◽  
Fragmentation Spectrum ◽  
Particle Hydrodynamics ◽  
Primary Breakup ◽  
Smoothed Particle

AbstractThis paper illustrates recent progresses in the development of the smoothed particle hydrodynamics (SPH) method to simulate and post-process liquid spray generation. The simulation of a generic annular airblast atomizer is presented, in which a liquid sheet is fragmented by two concentric counter swirling air streams. The accent is put on how the SPH method can bridge the gap between the CAD geometry of a nozzle and its characterization, in terms of spray characteristics and dynamics. In addition, the Lagrangian nature of the SPH method allows to extract additional data to give further insight in the spraying process. First, the sequential breakup events can be tracked from one large liquid blob to very fine stable droplets. This is herein called the tree of fragmentation. From this tree of fragmentation, abstract quantities can be drawn such as the breakup activity and the fragmentation spectrum. Second, the Lagrangian coherent structures in the turbulent flow can be determined easily with the finite-time Lyapunov exponent (FTLE). The extraction of the FTLE is particularly feasible in the SPH framework. Finally, it is pointed out that there is no universal and ultimate non-dimensional number that can characterize airblast primary breakup. Depending on the field of interest, a non-dimensional number (e.g. Weber number) might be more appropriate than another one (e.g. momentum flux ratio) to characterize the regime, and vice versa.

Part 2: Design Optimisation Strategies for a Fuel Spray Nozzle

2021 ◽  
Author(s):  
Thomas Andreou ◽  
Craig White ◽  
Konstantinos Kontis ◽  
Shahrokh Shahpar ◽  
Nicholas Brown
Keyword(s):  
Fuel Spray ◽  
Spray Nozzle ◽  
Design Optimisation

Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame

2017 ◽  
Author(s):  
Ramgopal Sampath ◽  
S. R. Chakravarthy
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Pressure Oscillation ◽  
Velocity Fields ◽  
Premixed Flame ◽  
Time Resolved ◽  
Acoustic Feedback ◽  
Acoustic Characterization ◽  
Partially Premixed ◽  
Partially Premixed Flame

The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.

Transport and Mixing in Patient Specific Abdominal Aortic Aneurysms With Lagrangian Coherent Structures

2012 ◽  
Author(s):  
Amirhossein Arzani ◽  
Shawn C. Shadden
Keyword(s):  
Coherent Structures ◽  
Abdominal Aortic Aneurysms ◽  
Aortic Aneurysms ◽  
Lagrangian Coherent Structures ◽  
Patient Specific ◽  
Complex Flow ◽  
Flow Topology ◽  
Finite Time Lyapunov Exponent ◽  
Abdominal Aortic ◽  
High Gradients

Abdominal aortic aneurysms (AAA) are characterized by disturbed flow patterns, low and oscillatory wall shear stress with high gradients, increased particle residence time, and mild turbulence. Diameter is the most common metric for rupture prediction, although this metric can be unreliable. We hypothesize that understanding the flow topology and mixing inside AAA could provide useful insight into mechanisms of aneurysm growth. AAA morphology has high variability, as with AAA hemodynamics, and therefore we consider patient-specific analyses over several small to medium sized AAAs. Vortical patterns dominate AAA hemodynamics and traditional analyses based on the Eulerian fields (e.g. velocity) fail to convey the complex flow structures. The computation of finite-time Lyapunov exponent (FTLE) fields and underlying Lagrangian coherent structures (LCS) help reveal a Lagrangian template for quantifying the flow [1].

scholarly journals Sparse reduced-order modelling: sensor-based dynamics to full-state estimation

2018 ◽  
Vol 844 ◽  
pp. 459-490 ◽  
Author(s):  
Jean-Christophe Loiseau ◽  
Bernd R. Noack ◽  
Steven L. Brunton
Keyword(s):  
Coherent Structures ◽  
Feature Space ◽  
Black Box ◽  
Box Model ◽  
Sensor Data ◽  
Dynamic Feature ◽  
Time Resolved ◽  
Reduced Order ◽  
Reduced Order Modelling ◽  
Full State

We propose a general dynamic reduced-order modelling framework for typical experimental data: time-resolved sensor data and optional non-time-resolved particle image velocimetry (PIV) snapshots. This framework can be decomposed into four building blocks. First, the sensor signals are lifted to a dynamic feature space without false neighbours. Second, we identify a sparse human-interpretable nonlinear dynamical system for the feature state based on the sparse identification of nonlinear dynamics (SINDy). Third, if PIV snapshots are available, a local linear mapping from the feature state to the velocity field is performed to reconstruct the full state of the system. Fourth, a generalized feature-based modal decomposition identifies coherent structures that are most dynamically correlated with the linear and nonlinear interaction terms in the sparse model, adding interpretability. Steps 1 and 2 define a black-box model. Optional steps 3 and 4 lift the black-box dynamics to a grey-box model in terms of the identified coherent structures, if non-time-resolved full-state data are available. This grey-box modelling strategy is successfully applied to the transient and post-transient laminar cylinder wake, and compares favourably with a proper orthogonal decomposition model. We foresee numerous applications of this highly flexible modelling strategy, including estimation, prediction and control. Moreover, the feature space may be based on intrinsic coordinates, which are unaffected by a key challenge of modal expansion: the slow change of low-dimensional coherent structures with changing geometry and varying parameters.

Modal Analysis of Breakup Mechanisms for a Liquid Jet in Crossflow

2021 ◽  
pp. 1-36
Author(s):  
Sheikh Salauddin ◽  
Wilmer Flores ◽  
Michelle Otero ◽  
Bernhard Stiehl ◽  
Kareem Ahmed
Keyword(s):  
Coherent Structures ◽  
Liquid Fuel ◽  
Hydrodynamic Instability ◽  
Aviation Industry ◽  
Dynamic Mode ◽  
Capillary Breakup ◽  
Breakup Mechanism ◽  
Jet In Crossflow ◽  
Fuel Jet ◽  
Primary Breakup

Abstract Liquid fuel jet in Crossflow (LJIC) is a vital atomization technique significant to the aviation industry. The hydrodynamic instability mechanisms that drive a primary breakup of a transverse jet are investigated using modal and traveling wavelength analysis. This study highlights the primary breakup mechanisms for aviation fuel Jet-A, utilizing a method that could be applied to any liquid fuel. Mathematical decomposition techniques known as POD (Proper Orthogonal Decomposition) and Robust MrDMD (Multi-Resolution Dynamic Mode Decomposition) are used together to identify dominant instability flow dynamics associated with the primary breakup mechanism. Implementation of the Robust MrDMD method deconstructs the nonlinear dynamical systems into multiresolution time-scaled components to capture the intermittent coherent structures. The Robust MrDMD, in conjunction with the POD method, is applied to data points taken across the entire spray breakup regimes: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The dominant frequencies of breakup mechanisms are extracted and identified. These coherent structures are classified with an associated time scale and Strouhal number. Three primary breakup mechanisms, namely ligament shedding, bag breakup, and shear breakup, were identified and associated with the four breakup regimes outlined above. Further investigation portrays these breakup mechanisms to occur in conjunction with each other in each breakup regime, excluding the low Weber number Enhanced Capillary Breakup regime. Spectral analysis of the Robust MrDMD modes' entire temporal window reveals that while multiple breakup mechanisms are convolved, there is a dominant breakup route for each breakup regime. An associated particular traveling wavelength analysis further investigates each breakup mechanism. Lastly, this study explores the effects of an increased momentum flux ratio on each breakup mechanism associated with a breakup regime.

Towards Primary Breakup Simulation of a Complete Aircraft Nozzle at Realistic Aircraft Conditions

2020 ◽  
Author(s):  
Katharina Warncke ◽  
Amsini Sadiki ◽  
Max Staufer ◽  
Christian Hasse ◽  
Johannes Janicka
Keyword(s):  
Numerical Simulations ◽  
Liquid Fuel ◽  
Fuel Injection ◽  
Operating Conditions ◽  
Nozzle Geometry ◽  
Nozzle Flow ◽  
Spray Characteristics ◽  
Wide Range ◽  
Primary Breakup ◽  
Turbulent Scales

Abstract Predicting details of aircraft engine combustion by means of numerical simulations requires reliable information about spray characteristics from liquid fuel injection. However, details of liquid fuel injection are not well documented. Indeed, standard droplet distributions are usually utilized in Euler-Lagrange simulations of combustion. Typically, airblast injectors are employed to atomize the liquid fuel by feeding a thin liquid film in the shear zone between two swirled air flows. Unfortunately, droplet data for the wide range of operating conditions during a flight is not available. Focusing on numerical simulations, Direct Numerical simulations (DNS) of full nozzle designs are nowadays out of scope. Reducing numerical costs, but still considering the full nozzle flow, the embedded DNS methodology (eDNS) has been introduced within a Volume of Fluid framework (Sauer et al., Atomization and Sprays, vol. 26, pp. 187–215, 2016). Thereby, DNS domain is kept as small as possible by reducing it to the primary breakup zone. It is then embedded in a Large Eddy Simulation (LES) of the turbulent nozzle flow. This way, realistic turbulent scales of the nozzle flow are included, when simulating primary breakup. Previous studies of a generic atomizer configuration proved that turbulence in the gaseous flow has significant impact on liquid disintegration and should be included in primary breakup simulations (Warncke et al., ILASS Europe, Paris, 2019). In this contribution, an industrial airblast atomizer is numerically investigated for the first time using the eDNS approach. The complete nozzle geometry is simulated, considering all relevant features of the flow. Three steps are necessary: 1. LES of the gaseous nozzle flow until a statistically stationary flow is reached. 2. Position and refinement of the DNS domain. Due to the annular nozzle design the DNS domain is chosen as a ring. It comprises the atomizing edge, where the liquid is brought between inner and outer air flow, and the downstream primary breakup zone. 3. Start of liquid fuel injection and primary breakup simulation. Since the simulation of the two-phase DNS and the LES of the surrounding nozzle flow are conducted at the same time, turbulent scales of the gas flow are directly transferred to the DNS domain. The applicability of eDNS to full nozzle designs is demonstrated and details of primary breakup at the nozzle outlet are presented. In particular a discussion of the phenomenological breakup process and spray characteristics is provided.

Unveiling the Flow Behavior Inside GDI Engine Cylinder Using High-Speed Time-Resolved Particle Image Velocimetry and CFD Simulation

2021 ◽  
Author(s):  
Mohammed El Adawy ◽  
Morgan Heikal ◽  
bin Abd. Aziz Abd. Rashid
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
Cfd Simulation ◽  
Injection Pressure ◽  
Valve Lift ◽  
Fuel Spray ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Spray Plume

Abstract RICARDO-VECTIS CFD simulation of the in-cylinder air flow was first validated with those of the experimental results from high-speed particle image velocimetry (PIV) measurements taking cognisant of the mid-cylinder tumble plane. Furthermore, high-speed fuel spray measurements were carried out simultaneously with the intake-generated tumble motion at high valve lift using high-speed time-resolved PIV to chronicle the spatial and time-based development of air/fuel mixture. The effect of injection pressure(32.5 and 35.0 MPa) and pressure variation across the air intake valves(150, 300 and 450 mmH2O) on the interaction process were investigated at valve lift 10 mm where the tumble vortex was fully developed and filled the whole cylinder under steady-state conditions. The PIV results illustrated that the intake generated-tumble motion had a substantial impact on the fuel spray distortion and dispersion inside the cylinder. During the onset of the injection process the tumble motion diverted the spray plume slightly towards the exhaust side before it followed completely the tumble vortex. The fuel spray plume required 7.2 ms, 6.2 ms and 5.9 ms to totally follow the in-cylinder air motion for pressure differences 150, 300 and 450 mmH2O, respectively. Despite, the spray momentum was the same for the same injection pressure, the magnitude of kinetic energy was different for different cases of pressure differences and subsequently the in-cylinder motion strength.

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