scholarly journals Stability and Blowout Behavior of Jet Flames in Oblique Air Flows

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Jonathan N. Gomes ◽  
James D. Kribs ◽  
Kevin M. Lyons
Keyword(s):  
Stability Limit ◽  
Oblique Angle ◽  
Jet Flames ◽  
Jet Flame ◽  
Flow Configurations ◽  
The Stability ◽  
Burner Nozzle ◽  
Two Parameters ◽  
Stability Limits ◽  
Supply Velocity

The stability limits of a jet flame can play an important role in the design of burners and combustors. This study details an experiment conducted to determine the liftoff and blowout velocities of oblique-angle methane jet flames under various air coflow velocities. A nozzle was mounted on a telescoping boom to allow for an adjustable burner angle relative to a vertical coflow. Twenty-four flow configurations were established using six burner nozzle angles and four coflow velocities. Measurements of the fuel supply velocity during liftoff and blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction. Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed. For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types.

Evaluation of a Turbulent Jet Flame Flashback Correlation Applied to Annular Flow Configurations with and Without Swirl

2020 ◽  
Author(s):  
Elliot Sullivan Lewis ◽  
Vincent McDonell ◽  
Alireza Kalantari ◽  
Priyank Saxena
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
Annular Flow ◽  
Jet Flames ◽  
High Hydrogen ◽  
Jet Flame ◽  
High Hydrogen Content ◽  
Round Jet ◽  
Significant Difference ◽  
Flow Configurations

Abstract The adaptation of high hydrogen content fuels for low emissions gas turbines represents a potential opportunity to reduce the carbon footprint of these devices. The high flame speed of hydrogen air mixtures combined with the small quenching distances poses a challenge for using these fuels in situations where significant premixing is desired. Flashback along the walls (i.e., boundary layer flashback) can be exacerbated with high hydrogen content fuels. In the present work, the ability of a flashback correlation previously developed for round jet flames is evaluated for its ability to predict flashback in an annular flow with and without swirl. Flashback data are obtained for various mixtures of hydrogen and methane and hydrogen and carbon monoxide for all the annular flow configurations. Pressures from 3-8 bar are tested with mixture temperatures up to 750 K. Flashback is induced by slowly increasing the equivalence ratio. The results obtained show that the same form of the correlation developed for round jet flames can be used to correlate flashback behavior for the annular flow case with and without swirl despite the presence of the centerbody. Adjustments to some of the constants in the original model were made to obtain the best fit, but in general, the correlation is quite similar to that developed for the round jet flame. A significant difference with the annular flow configurations is the determination of the appropriate gradient at the wall, which in the present case is determined using a cold flow CFD simulation.

Topology of vortex breakdown bubbles in a cylinder with a rotating bottom and a free surface

2001 ◽  
Vol 428 ◽  
pp. 133-148 ◽  
Author(s):  
MORTEN BRØNS ◽  
LARS K. VOIGT ◽  
JENS N. SØRENSEN
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Hopf Bifurcation ◽  
Numerical Methods ◽  
Aspect Ratio ◽  
Vortex Breakdown ◽  
Stability Limit ◽  
Similarities And Differences ◽  
The Stability ◽  
Two Parameters

The flow patterns in the steady, viscous flow in a cylinder with a rotating bottom and a free surface are investigated by a combination of topological and numerical methods. Assuming the flow is axisymmetric, we derive a list of possible bifurcations of streamline structures on varying two parameters, the Reynolds number and the aspect ratio of the cylinder. Using this theory we systematically perform numerical simulations to obtain the bifurcation diagram. The stability limit for steady flow is found and established as a Hopf bifurcation. We compare with the experiments by Spohn, Mory & Hopfinger (1993) and find both similarities and differences.

A New Method for Identification and Modeling of Process Damping in Machining

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
E. Budak ◽  
L. T. Tunc
Keyword(s):  
Stability Limit ◽  
Damping Coefficient ◽  
Test Results ◽  
Limited Data ◽  
Damping Force ◽  
Process Damping ◽  
Analytical Stability ◽  
Practical Model ◽  
The Stability ◽  
Stability Limits

Although process damping has a strong effect on cutting dynamics and stability, it has been mostly ignored in chatter analysis as there is no practical model for estimation of the damping coefficient and very limited data are available. This is mainly because of the fact that complicated test setups were used in order to measure the damping force in the past. In this study, a practical identification and modeling method for the process damping is presented. In this approach, the process damping is identified directly from the chatter tests using experimental and analytical stability limits. Once the process damping coefficient is identified, it is related to the instantaneous indentation volume by a coefficient which can be used for different cutting conditions and tool geometries. In determining the indentation coefficient, chatter test results, energy, and tool indentation geometry analyses are used. The determined coefficients are then used for the stability limit and process damping prediction in different cases, and verified using time-domain simulations and experimental results. The presented method can be used to determine chatter-free cutting depths under the influence of process damping for increased productivity.

scholarly journals Laboratory sample stability. Is it possible to define a consensus stability function? An example of five blood magnitudes

2018 ◽  
Vol 56 (11) ◽  
pp. 1806-1818 ◽  
Author(s):  
Rubén Gómez Rioja ◽  
Débora Martínez Espartosa ◽  
Marta Segovia ◽  
Mercedes Ibarz ◽  
María Antonia Llopis ◽  
...  
Keyword(s):  
Specific Antigen ◽  
Stability Limit ◽  
Medical Laboratory ◽  
Stability Function ◽  
Measured Property ◽  
Bibliographic Search ◽  
The Stability ◽  
Conditions Of Stability ◽  
Time Required ◽  
Stability Limits

Abstract Background: The stability limit of an analyte in a biological sample can be defined as the time required until a measured property acquires a bias higher than a defined specification. Many studies assessing stability and presenting recommendations of stability limits are available, but differences among them are frequent. The aim of this study was to classify and to grade a set of bibliographic studies on the stability of five common blood measurands and subsequently generate a consensus stability function. Methods: First, a bibliographic search was made for stability studies for five analytes in blood: alanine aminotransferase (ALT), glucose, phosphorus, potassium and prostate specific antigen (PSA). The quality of every study was evaluated using an in-house grading tool. Second, the different conditions of stability were uniformly defined and the percent deviation (PD%) over time for each analyte and condition were scattered while unifying studies with similar conditions. Results: From the 37 articles considered as valid, up to 130 experiments were evaluated and 629 PD% data were included (106 for ALT, 180 for glucose, 113 for phosphorus, 145 for potassium and 85 for PSA). Consensus stability equations were established for glucose, potassium, phosphorus and PSA, but not for ALT. Conclusions: Time is the main variable affecting stability in medical laboratory samples. Bibliographic studies differ in recommedations of stability limits mainly because of different specifications for maximum allowable error. Definition of a consensus stability function in specific conditions can help laboratories define stability limits using their own quality specifications.

Evaluation of a Turbulent Jet Flame Flashback Correlation Applied to Annular Flow Configurations With and Without Swirl

2020 ◽  
Author(s):  
E. Sullivan Lewis ◽  
Vincent G. McDonell ◽  
Alireza Kalantari ◽  
Priyank Saxena
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
Annular Flow ◽  
Jet Flames ◽  
High Hydrogen ◽  
Jet Flame ◽  
High Hydrogen Content ◽  
Round Jet ◽  
Significant Difference ◽  
Flow Configurations

Abstract The adaptation of high hydrogen content fuels for low emissions gas turbines represents a potential opportunity to reduce the carbon footprint of these devices. The high flame speed of hydrogen air mixtures combined with the small quenching distances poses a challenge for using these fuels in situations where significant premixing is desired. In particular flashback in either the core flow or along the walls (i.e., boundary layer flashback) can be exacerbated with high hydrogen content fuels. In the present work, the ability of a flashback correlation previously developed for round jet flames is evaluated for its ability to predict flashback in an annular flow. As a first step, an annular flow is generated with a centerbody located at the centerline of the original round jet flame. Next, various levels of axial swirl is added to that annular flow. Additional flashback data are obtained for various mixtures of hydrogen and methane and hydrogen and carbon monoxide for all-the annular flow configurations. Pressures from 3–8 bar are tested with mixture temperatures up to 750 K. Flashback is induced by slowly increasing the equivalence ratio. The results obtained show that the same form of the correlation developed for round jet flames can be used to correlate flashback behavior for the annular flow case with and without swirl despite the presence of the centerbody. Adjustments to some of the constants in the original model were made to obtain the best fit, but in general, the correlation is quite similar to that developed for the round jet flame. A significant difference with the annular flow configurations is the determination of the appropriate gradient at the wall, which in the present case is determined using a cold flow CFD simulation.

Stability, Accuracy, and Efficiency of Sequential Methods for Coupled Flow and Geomechanics

SPE Journal ◽  
2011 ◽  
Vol 16 (02) ◽  
pp. 249-262 ◽  
Author(s):  
J.. Kim ◽  
H.A.. A. Tchelepi ◽  
R.. Juanes
Keyword(s):  
Numerical Solutions ◽  
Stability Limit ◽  
Stability And Convergence ◽  
Coupled Flow ◽  
Unconditionally Stable ◽  
Von Neumann ◽  
Solution Strategies ◽  
Solution Methods ◽  
The Stability ◽  
Stability Limits

Summary We perform detailed stability and convergence analyses of sequential-implicit solution methods for coupled fluid flow and reservoir geomechanics. We analyze four different sequential-implicit solution strategies, where each subproblem (flow and mechanics) is solved implicitly: two schemes in which the mechanical problem is solved first—namely, the drained and undrained splits—and two schemes in which the flow problem is solved first—namely, the fixed-strain and fixed-stress splits. The von Neumann method is used to obtain the linear-stability criteria of the four sequential schemes, and numerical simulations are used to test the validity and sharpness of these criteria for representative problems. The analysis indicates that the drained and fixed-strain splits, which are commonly used, are conditionally stable and that the stability limits depend only on the strength of coupling between flow and mechanics and are independent of the timestep size. Therefore, the drained and fixed-strain schemes cannot be used when the coupling between flow and mechanics is strong. Moreover, numerical solutions obtained using the drained and fixed-strain sequential schemes suffer from oscillations, even when the stability limit is honored. For problems where the deformation may be plastic (nonlinear) in nature, the drained and fixed-strain sequential schemes become unstable when the system enters the plastic regime. On the other hand, the undrained and fixed-stress sequential schemes are unconditionally stable regardless of the coupling strength, and they do not suffer from oscillations. While both the undrained and fixed-stress schemes are unconditionally stable, for the cases investigated we found that the fixed-stress split converges more rapidly than the undrained split. On the basis of these findings, we strongly recommend the fixed-stress sequential-implicit method for modeling coupled flow and geomechanics in reservoirs.

High Speed Hydrogen Jets: Stability and Instability (Keynote Paper)

2003 ◽  
Author(s):  
A. Koichi Hayashi
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Hydrogen Diffusion ◽  
Jet Flames ◽  
Jet Flame ◽  
Jet Instability ◽  
Keynote Paper ◽  
Stability And Instability ◽  
The Stability ◽  
Pressure Hydrogen

High speed hydrogen jets have been used in many technological fields such as chemical industries, automotive industries, etc. and gradually become important recently since fuel cell technology will become popular and its safety problem such as high pressure hydrogen tank leakage must be cleared and solved by the time of its use. In this paper the stability and instability of high speed hydrogen jet flames and their control are focused on. First of all nature of high speed hydrogen diffusion jet flames are shown experimentally to discuss their instability problems. Secondly numerical analysis of high speed jet flame is shown to explain the details of jet instability with heat releases. Then thirdly as an application a control of high speed hydrogen lifted jet flame is discussed experimentally and numerically.

On the stability limit of charged droplets

1989 ◽  
Vol 422 (1863) ◽  
pp. 319-328 ◽  
Keyword(s):  
Surface Tension ◽  
Particle Size ◽  
Light Scattering ◽  
Stability Limit ◽  
Prolate Spheroid ◽  
Charged Droplets ◽  
Electric Stress ◽  
The Stability ◽  
Stability Limits

Single, highly charged droplets of dioctylphthalate and sulphuric acid of radius between 1 and 10 μm are suspended in vacuum in a quadrupol trap. As the droplets evaporate their radius is monitored continuously by light scattering and their charge is determined periodically by weight balancing. The droplets break when the electric stress exceeds that of surface tension. The largest fragment remains trapped allowing a determination of the change in volume and charge. The fraction of volume and charge lost is found to be independent of particle size and sign of charge and is variable. The oil drops lose (15.0 ± 3.9)% of their charge on breakup and (2.25 ± 0.96)% of their mass. The acid droplets lose (49.4 ± 8.3)% of their charge and less than 0.1% of their mass. The acid results are compared with those from a model of field emission based upon prolate spheroid deformation and the formation of Taylor cones. For both oil and acid droplets the stability limits are in agreement with those predicted by Lord Rayleigh.

scholarly journals Experimental Aerodynamic and Aeroelastic Investigation of a Transonic Compressor Rotor with Reduced Blade Count

2021 ◽  
Vol 6 (2) ◽  
pp. 19
Author(s):  
Daniel Franke ◽  
Daniel Möller ◽  
Maximilian Jüngst ◽  
Heinz-Peter Schiffer ◽  
Thomas Giersch ◽  
...  
Keyword(s):  
Measurement Data ◽  
Axial Compressor ◽  
Stability Limit ◽  
Performance Measurements ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Compressor Map ◽  
The Stability ◽  
Stability Limits ◽  
Transient Measurements

This study investigates the aerodynamic and aeroelastic characteristics of a transonic axial compressor, focusing on blade count reduced rotor behavior. The analysis is based on experiments, conducted at the Transonic Compressor Darmstadt test rig at Technical University of Darmstadt and compulsory simulations. In order to obtain measurement data for the detailed aerodynamic and aeroelastic investigation, extensive steady and unsteady instrumentation was applied. Besides transient measurements at the stability limit to determine the operating range and limiting phenomena, performance measurements were performed, presenting promising results with respect to the capabilities of blade count reduced rotors. Close to the stability limit, aerodynamic disturbances like radial vortices were detected for both rotors, varying in size, count, speed and trajectory. Comparing the rotor configurations results in different stability limits along the compressor map as well as varying aeromechanical behavior. Those effects can partially be traced to the variation in blade pitch and associated aerodynamics.

Sign in / Sign up

Export Citation Format

Share Document