The Effect of Intrinsic Instabilities on Effective Flame Speeds in Under-Resolved Simulations of Lean Hydrogen–Air Flames

2017 ◽  
Vol 3 (4) ◽  
Author(s):  
Peter Katzy ◽  
Josef Hasslberger ◽  
Lorenz R. Boeck ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Front ◽  
Optical Measurement ◽  
Initial Conditions ◽  
Measurement Techniques ◽  
Evaluation Methods ◽  
Line Of Sight ◽  
Flame Surface ◽  
Validation Data ◽  
Time Resolved ◽  
The Impact

The presented work aims to improve computational fluid dynamics (CFD) explosion modeling for lean hydrogen–air mixtures on under-resolved grids. Validation data are obtained from an entirely closed laboratory-scale explosion channel (GraVent facility). Investigated hydrogen–air concentrations range from 6 to 19 vol %. Initial conditions are p = 0.1 MPa and T = 293 K. Two highly time-resolved optical measurement techniques are applied simultaneously: (1) 10 kHz shadowgraphy captures line-of-sight integrated macroscopic flame propagation and (2) 20 kHz planar laser-induced fluorescence of the OH radical (OH-PLIF) resolves microscopic flame topology without line-of-sight integration. This paper presents the experiment, measurement techniques, data evaluation methods, and simulation results. The evaluation methods encompass the determination of flame tip velocity over distance and a detailed time-resolved quantification of the flame topology based on OH-PLIF images. One parameter is the length of wrinkled flame fronts in the OH-PLIF plane obtained through automated postprocessing. It reveals the expected enlargement of flame surface area by instabilities on a microscopic level. A strong effect of mixture composition is observed. Simulations based on the new model formulation, incorporating the microscopic enlargement of the flame front, show a promising behavior, where the impact of the augmented flame front on the observed flame front velocities can be detected.

Application of High-Speed OH-PLIF Technique for Improvement of Lean Hydrogen-Air Combustion Modeling

2016 ◽  
Author(s):  
Peter Katzy ◽  
Lorenz R. Boeck ◽  
Josef Hasslberger ◽  
Thomas Sattelmayer
Keyword(s):  
High Speed ◽  
Optical Measurement ◽  
Initial Conditions ◽  
Measurement Techniques ◽  
Evaluation Methods ◽  
Line Of Sight ◽  
Flame Surface ◽  
Validation Data ◽  
Time Resolved ◽  
Wrinkled Flame

The presented work aims to improve CFD explosion modeling for lean hydrogen-air mixtures on under-resolved grids. Validation data is obtained from an entirely closed laboratory scale explosion channel (GraVent facility). Investigated hydrogen-air concentrations range from 6 to 19 vol.-%. Initial conditions are p = 1 atm and T = 293 K. Two highly time-resolved optical measurement techniques are applied simultaneously: (1) 10 kHz shadowgraphy captures line-of-sight integrated macroscopic flame propagation; and (2) 20 kHz OH-PLIF (planar laser-induced fluorescence of the OH radical) resolves microscopic flame topology without line-of-sight integration. This paper presents the experiment, measurement techniques, data evaluation methods and initial results. The evaluation methods encompass the determination of flame tip velocity over distance and a detailed time-resolved quantification of flame topology based on OH-PLIF images. One parameter is the length of wrinkled flame fronts in the OH-PLIF plane obtained through automated post-processing. It reveals the expected enlargement of flame surface area by instabilities on microscopic level. A strong effect of mixture composition is observed.

Impact of Swirl Flow on the Penetration Behaviour and Cooling Performance of a Starter Cooling Film in Modern Lean Operating Combustion Chambers

2014 ◽  
Author(s):  
B. Wurm ◽  
A. Schulz ◽  
H.-J. Bauer ◽  
M. Gerendas
Keyword(s):  
Optical Measurement ◽  
Measurement Techniques ◽  
Swirl Flow ◽  
Main Flow ◽  
Heat Shield ◽  
Fuel Injector ◽  
Combustion Chambers ◽  
Cooling Performance ◽  
The Impact ◽  
Penetration Behaviour

An experimental and numerical study is presented that deals with the impact of the swirled hot gas main flow on the penetration behaviour and cooling performance of a starter cooling film. Within modern combustion chambers designed for lean combustion the whole fuel/air mixing process is done by the fuel injectors without any additional mixing ports. Typically swirl stabilization is used within this kind of combustion chambers. The swirl flow interacts in a particular way with near wall cooling flows like starter cooling films which assure a proper wall cooling near the fuel injector. Experiments without combustion show the impact of the swirled main flow on the stability of the starter cooling film. Thermal analyses reveal a reduced cooling performance of the starter film near the stagnation area of the swirl flow. Laser optical measurement techniques reveal a significant reduced penetration of the starter cooling film close to the stagnation area. Numerical simulations show the reason for the reduced starter film performance in areas which cannot be accessed by optical measurement techniques. Based on experimental and numerical data different adaptive hole geometries where tested in combination with heat shield ribs in order to improve the starter film cooling performance. Results show that the combined application of heat shield ribs and adaptive cooling holes stabilize the starter cooling film and lead to a homogenous cooling performance.

Error Estimations in Digital Image Correlation Technique

2007 ◽  
Vol 7-8 ◽  
pp. 265-270 ◽  
Author(s):  
Thorsten Siebert ◽  
Thomas Becker ◽  
Karsten Spiltthof ◽  
Isabell Neumann ◽  
Rene Krupka
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Image Correlation ◽  
Field Analysis ◽  
Correlation Technique ◽  
Full Field ◽  
Wide Range ◽  
The Impact

The reliability for each measurement technique depends on the knowledge of it’s uncertainty and the sources of errors of the results. Among the different techniques for optical measurement techniques for full field analysis of displacements and strains, digital image correlation (DIC) has been proven to be very flexible, robust and easy to use, covering a wide range of different applications. Nevertheless the measurement results are influenced by statistical and systematical errors. We discuss a 3D digital image correlation system which provides online error information and the propagation of errors through the calculation chain to the resulting contours, displacement and strains. Performance tests for studying the impact of calibration errors on the resulting data are shown for static and dynamic applications.

TRANSIENT EXPERIMENTS IN ZED-2 TO INVESTIGATE THE IMPACT OF LEAKAGE ON REACTOR PHYSICS PHENOMENA

2015 ◽  
Vol 4 (1) ◽  
pp. 67-73
Author(s):  
M.B. Zeller ◽  
J.E. Atfield
Keyword(s):  
Neutron Transport ◽  
Measurement Techniques ◽  
Critical Conditions ◽  
Reactor Physics ◽  
Validation Data ◽  
Reactor Kinetics ◽  
Static Measurement ◽  
Transient Experiments ◽  
Point Kinetics ◽  
The Impact

This paper describes an experimental approach where reactor kinetics experiments are used to study reactor physics phenomena that are normally investigated using static-measurement techniques. This approach provides validation data relating to these phenomena for a range of core reactivities, rather than only providing data at critical conditions. Sub-critical and super-critical transient measurements were performed in the ZED-2 reactor. The transients were analyzed using a point kinetics model to derive the reactivity states that induced the transients. The reactor physics phenomenon of interest for the current study is Coolant Density Induced Reactivity. Initial measurements were performed using an air-cooled (i.e., voided) ZED-2 lattice; the measurements were then repeated using the same lattice cooled with light water. These measurements yielded reactivity values for both coolant conditions in the lattice for a range of super-critical and sub-critical states. This investigation avoids the inherent assumption of static-measurement analyses that the bias in predicting criticality for the two coolant conditions is identical to the bias in predicting the phenomenon of Coolant Density Induced Reactivity itself. The measured reactivity values are compared with calculations employing the 3-D stochastic neutron transport reactor code MCNP.

Comparison of Two Methods for Sensitivity Analysis of Compressor Blades

2016 ◽  
Author(s):  
Robin Schmidt ◽  
Matthias Voigt ◽  
Konrad Vogeler ◽  
Marcus Meyer
Keyword(s):  
Sensitivity Analysis ◽  
Monte Carlo ◽  
Polynomial Regression ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Sampling Strategy ◽  
Compressor Blades ◽  
Initial Flow ◽  
Efficient Sampling ◽  
The Impact

This paper will compare two approaches of sensitivity analysis, namely (i) the adjoint method which is used to obtain an initial estimate of the geometric sensitivity of the gas-washed surfaces to aerodynamic quantities of interest and (ii) a Monte Carlo-type simulation with an efficient sampling strategy. For both approaches the geometry is parameterized using a modified NACA parameterization. First the sensitivity of those parameters is calculated using the linear (first order) adjoint model. Since the effort of the adjoint CFD solution is comparable to that of the initial flow CFD solution and the sensitivity calculation is simply a postprocessing step, this approach yields fast results. However, it relies on a linear model which may not be adequate to describe the relationship between relevant aerodynamic quantities and actual geometric shape variations for the derived amplitudes of shape variations. In order to better capture nonlinear and interaction effects, secondly a Monte Carlo-type simulation with an efficient sampling strategy is used to carry out the sensitivity analysis. The sensitivities are expressed by means of the Coefficient of Importance, which is calculated based on modified polynomial regression and therefore able to describe relationships of higher order. The methods are applied to a typical high pressure compressor stage. The impact of a variable rotor geometry is calculated by 3D CFD simulations using a steady RANS model. The geometric variability of the rotor is based on the analysis of a set of 400 blades which have been measured using high-precision 3D optical measurement techniques.

Time-Resolved Ellipsometry and Reflectivity Measurements of the Optical Properties of Silicon During Pulsed Excimer Laser Irradiation

1984 ◽  
Vol 35 ◽  
Author(s):  
G. E. Jellison ◽  
D. H. Lowndes
Keyword(s):  
Optical Properties ◽  
Laser Irradiation ◽  
Crystalline Silicon ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Time Resolved ◽  
High Reflectivity ◽  
Use Of Time ◽  
Before And After ◽  
Melting Threshold

ABSTRACTSeveral advances in time-resolved optical measurement techniques have been made, which allow a more detailed determination of the optical properties of silicon immediately before, during, and after pulsed laser irradiation. It is now possible to follow in detail the time-resolved reflectivity signal near the melting threshold; measurements indicate that melting occurs in a spatially inhomogeneous way. The use of time-resolved ellipsometry allowed us to accurately measure the optical properties of the high reflectivity (molten) phase, and of the hot, solid silicon before and after the laser pulse. We obtain n = 3.8, k = 5.2 (±10.1) at λ = 632.8 nm for the high reflectivity phase, in minor disagreement with the published values of Shvarev et al. for liquid silicon. Before and after the high reflectivity phase, the time-resolved ellipsometry measurements are entirely consistent with the known optical properties of crystalline silicon at temperatures up to its melting point.

Analysis of High Pressure Turbine Nozzle Guide Vanes Considering Geometric Variations

2016 ◽  
Author(s):  
Lars Högner ◽  
Alkin Nasuf ◽  
Paul Voigt ◽  
Matthias Voigt ◽  
Konrad Vogeler ◽  
...  
Keyword(s):  
High Pressure ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Initial Assessment ◽  
High Pressure Turbine ◽  
Guide Vanes ◽  
Capacity Change ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
The Impact

Geometric variations caused by manufacturing scatter can influence the aerodynamic performance of turbomachinery components. In case of nozzle guide vanes (NGVs), the capacity is of particular importance due to its influence on the entire engine behaviour, since often the narrowest cross section of the turbine, which limits the capacity, is found in the first NGV stage. Within this scope, the present paper illustrates different methods in order to quantify the impact of geometric variations of high pressure turbine (HPT) NGVs with respect to capacity change during the development process. At first, in the design phase, a parametric CAD model of the NGV can be used to perform an initial assessment of the effect caused by different geometric variations onto capacity. The results of this study can for example be used to set the tolerances for the subsequent manufacturing process. As soon as the first real hardware components become available, their geometry can nowadays be accurately captured using optical measurement techniques. Consequently, reverse engineering (RE) methods can be used to enable numerical assessment of geometric variability since manufacturing scatter is determined and incorporated into the subsequent CFD analysis. The process to perform this assessment is described in the second part of the paper and its results are compared to the initial CAD-based study. The investigation is conducted using an example of a state-of-the-art NGV stage provided by Rolls-Royce.

Optical Insights into the Internal Electronic and Thermal Behavior of 4H-SiC Bipolar Devices

2010 ◽  
Vol 645-648 ◽  
pp. 1041-1044 ◽  
Author(s):  
Dorothea Werber ◽  
Martin Aigner ◽  
Gerhard Wachutka
Keyword(s):  
Thermal Behavior ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Free Carrier Absorption ◽  
Time Resolved ◽  
Bipolar Devices ◽  
Carrier Absorption ◽  
Optical Probing ◽  
Stationary Conditions ◽  
Yield Time

Two different optical measurement techniques have been combined in one single experimental platform to provide detailed insight into the interior of 4H-SiC bipolar devices with respect to their coupled electronic and thermal behavior: First, free carrier absorption (FCA) measurements yield time-resolved electron and hole densities profiles during turn-on and under stationary conditions; and second, light deflection measurements provide information about the gradients of the electron and hole densities as well as that of the temperature gradient. The full measurement process is also simulated on the computer as “virtual experiment” on the basis of high-fidelity physical device models. Investigations on high-blocking 4H-SiC bipolar diodes exemplify the optical probing methodology and the numerical simulation.

Comparison of Two Methods for Sensitivity Analysis of Compressor Blades

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Robin Schmidt ◽  
Matthias Voigt ◽  
Konrad Vogeler ◽  
Marcus Meyer
Keyword(s):  
Sensitivity Analysis ◽  
Monte Carlo ◽  
Polynomial Regression ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Sampling Strategy ◽  
Initial Flow ◽  
Efficient Sampling ◽  
The Impact

This paper will compare two approaches of sensitivity analysis, namely (i) the adjoint method which is used to obtain an initial estimate of the geometric sensitivity of the gas-washed surfaces to aerodynamic quantities of interest and (ii) a Monte Carlo type simulation with an efficient sampling strategy. For both approaches, the geometry is parameterized using a modified NACA parameterization. First, the sensitivity of those parameters is calculated using the linear (first-order) adjoint model. Since the effort of the adjoint computational fluid dynamics (CFD) solution is comparable to that of the initial flow CFD solution and the sensitivity calculation is simply a postprocessing step, this approach yields fast results. However, it relies on a linear model which may not be adequate to describe the relationship between relevant aerodynamic quantities and actual geometric shape variations for the derived amplitudes of shape variations. Second, in order to better capture nonlinear and interaction effects, a Monte Carlo type simulation with an efficient sampling strategy is used to carry out the sensitivity analysis. The sensitivities are expressed by means of the coefficient of importance (CoI), which is calculated based on modified polynomial regression and therefore able to describe relationships of higher order. The methods are applied to a typical high-pressure compressor (HPC) stage. The impact of a variable rotor geometry is calculated by three-dimensional (3D) CFD simulations using a steady Reynolds-averaged Navier–Stokes model. The geometric variability of the rotor is based on the analysis of a set of 400 blades which have been measured using high-precision 3D optical measurement techniques.

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