scholarly journals Numerical Simulations of DDT Limits in Hydrogen-Air Mixtures in Obstacle Laden Channel

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 24
Author(s):  
Wojciech Rudy ◽  
Andrzej Teodorczyk
Keyword(s):  
Numerical Simulations ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Transition Process ◽  
Numerical Results ◽  
Flame Acceleration ◽  
Detonation Transition ◽  
Run Up ◽  
Experimental Values ◽  
Concentration Limits

The main aim of this study was to perform numerical simulations of deflagration to detonation transition process (DDT) in hydrogen–air mixtures and assess the capabilities of freeware open-source ddtFoam code to simulate and capture DDT limits. The numerical geometry was based on the real 0.08 × 0.11 × 4 m (H × W × L), rectangular cross-section detonation channel previously used to experimentally investigate DDT limits in obstacle-filled channel. The constant blockage ratio (BR) equal to 0.5 was kept for three obstacle spacing configurations: S = H, 2H, 3H. The results showed that hydrogen concentration limits for successful DDT from simulations are close to the experimental values, however, the simulated DDT limits range is wider than the experimental one and depends on the obstacles spacing. The numerical results were analyzed by means of propagation velocities, overpressures, and run-up distances. The best match between numerical and experimental DDT limits was observed for obstacles spacing L = 3H and the lowest match for spacing L = H. The comparison between experimental and numerical results points at the possible application of ddtFoam in geometry with a relatively low level of congestion. This work results proved that simulations in such geometry provide numerical flame acceleration velocity profiles, run-up distance, and recorded overpressures very close to experimentally measured.

Analysis of Twisting Stiffness for a Multifiber Composite Layer

1974 ◽  
Vol 41 (3) ◽  
pp. 658-662 ◽  
Author(s):  
C. W. Bert ◽  
S. Chang
Keyword(s):  
Cross Section ◽  
Least Squares Method ◽  
Rectangular Cross Section ◽  
Torsional Rigidity ◽  
Composite Layer ◽  
Circular Cross Section ◽  
Relaxation Method ◽  
Fiber Composites ◽  
Numerical Results ◽  
Torsion Problem

The twisting stiffness of a rectangular cross section consisting of a single row of solid circular cross-section fibers embedded in a matrix is analyzed. The problem is formulated as a Dirichlet torsion problem of a multielement region and solved by the boundary-point least-squares method. Numerical results for a single-fiber square cross section compare favorably with previous relaxation-method results. New numerical results for three and five-fiber composites suggest that the torsional rigidity of a multifiber composite can be approximated from the torsional rigidities of single and three-fiber models.

Flame acceleration and deflagration-to-detonation transition in narrow channels with thin obstacles

2018 ◽  
Vol 32 (29) ◽  
pp. 1850354 ◽  
Author(s):  
Jin Huang ◽  
Xiangyu Gao ◽  
Cheng Wang
Keyword(s):  
Turbulent Flame ◽  
Narrow Channels ◽  
Flame Acceleration ◽  
Deflagration To Detonation Transition ◽  
Smooth Channel ◽  
Detonation Transition ◽  
Run Up ◽  
Thin Obstacle ◽  
Strong Confinement ◽  
Small Spacing

The entire process of deflagration-to-detonation transition (DDT) in narrow channels with thin obstacle configurations is studied through high-resolution simulations. The results show that the confinement and disturbance of obstacles promote considerably the flame acceleration and DDT. There exist two modes of DDT associating with obstacle spacing S. For small spacing S, the flame acceleration depends on strong confinement and jet flow between obstacles; eventually DDT occurs due to early burning amplified by shocks in front of the flame. However, for large spacing S, the flame acceleration is mainly attributed to turbulence; DDT results from the interaction of reflection shock with turbulent flame. It is found that the run-up distance of DDT in the obstructed channels shortens significantly, as compared with that in the smooth channel.

Influence of Impact Location on the Plastic Response and Failure of Rectangular Cross Section Tubes Struck Transversely by a Hemispherical Indenter1

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Bin Liu ◽  
C. Guedes Soares
Keyword(s):  
Numerical Simulations ◽  
Cross Section ◽  
Failure Modes ◽  
Rectangular Cross Section ◽  
Plastic Behavior ◽  
Collapse Mechanism ◽  
Transverse Loads ◽  
Impact Location ◽  
The Impact ◽  
Rectangular Tubes

Drop weight impact tests and numerical simulations have been performed to examine the plastic behavior and failure of clamped rectangular cross section tubes subjected to transverse loads. The selected indenter is a hemisphere with diameter of 20 mm. The tube lengths are 125 and 250 mm, and they are struck at the midspan and the quarter-span. The impact point along the width direction is located at the central position and displaced 10 mm from the center, respectively. The results show that the impact location affects strongly the plastic behavior and failure of the tubes. The impact location displaced along the width increases the energy absorbing capability of the tubes accompanied with an asymmetrical deformation mode. The experimentally recorded force–displacement responses and failure modes show good agreement with the numerical simulations, performed by the LS-DYNA finite-element code. The numerical results show the process of crack initiation and propagation and provide the details to analyze the structural plastic deformation and failure of the tubular specimens under transverse loads. The impact characteristics of the rectangular tubes are well presented based on the relevant failure modes observed in beams, plates, and circular tubes. Moreover, the influence of the impact location on the strength of tube specimens is characterized, and the collapse mechanism of rectangular tubes is described.

Experimental Studies Of Multilayer Glass Structures On Compression, Compression With Bending And Simple Bending

2019 ◽  
pp. 22-30
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Applied Load ◽  
Experimental Studies ◽  
Strength Properties ◽  
Research Topic ◽  
Normative Values ◽  
Laminated Glass ◽  
The Cross ◽  
Experimental Values

The work of multilayer glass structures for central and eccentric compression and bending are considered. The substantiation of the chosen research topic is made. The description and features of laminated glass for the structures investigated, their characteristics are presented. The analysis of the results obtained when testing for compression, compression with bending, simple bending of models of columns, beams, samples of laminated glass was made. Overview of the types and nature of destruction of the models are presented, diagrams of material operation are constructed, average values of the resistance of the cross-sections of samples are obtained, the table of destructive loads is generated. The need for development of a set of rules and guidelines for the design of glass structures, including laminated glass, for bearing elements, as well as standards for testing, rules for assessing the strength, stiffness, crack resistance and methods for determining the strength of control samples is emphasized. It is established that the strength properties of glass depend on the type of applied load and vary widely, and significantly lower than the corresponding normative values of the strength of heat-strengthened glass. The effect of the connecting polymeric material and manufacturing technology of laminated glass on the strength of the structure is also shown. The experimental values of the elastic modulus are different in different directions of the cross section and in the direction perpendicular to the glass layers are two times less than along the glass layers.

DETONABILITY OF FUEL-AIR MIXTURES IN TERMS OF DEFLAGRATION-TO-DETONATION TRANSITION

2020 ◽  
Author(s):  
S. M. FROLOV ◽  
◽  
V. I. ZVEGINTSEV ◽  
I. O. SHAMSHIN ◽  
M. V. KAZACHENKO ◽  
...  
Keyword(s):  
Natural Gas ◽  
Experimental Method ◽  
Pyrolysis Products ◽  
Ethylene Propylene ◽  
Pulse Detonation ◽  
Detonation Tube ◽  
Standard Pulse ◽  
Detonation Transition ◽  
Run Up ◽  
Propane Butane

A new experimental method for evaluating the detonability of fuel-air mixtures (FAMs) based on measuring the deflagration-to-detonation (DDT) run-up distance and/or time in a standard pulse detonation tube is used to rank gaseous premixed and nonpremixed FAMs by their detonability under substantially identical thermodynamic and gasdynamic conditions. In the experiments, FAMs based on hydrogen, acetylene, ethylene, propylene, propane-butane, n-pentane, and natural gas of various compositions, as well as FAMs based on the gaseous pyrolysis products of polyethylene (PE) and polypropylene (PP) are used: from extremely fuel-lean to extremely fuel-rich at normal temperatures and pressures.

DEFLAGRATION-TO-DETONATION TRANSITION IN A STRATIFIED SYSTEM “GASEOUS OXYGEN-LIQUID FILM OF N-DECANE”

2020 ◽  
Author(s):  
S. M. FROLOV ◽  
◽  
V. S. AKSENOV ◽  
I. O. SHAMSHIN ◽  
◽  
...  
Keyword(s):  
Liquid Film ◽  
Ignition Source ◽  
Gaseous Oxygen ◽  
Deflagration To Detonation Transition ◽  
Operation Process ◽  
Continuous Detonation ◽  
Smooth Channel ◽  
Detonation Transition ◽  
Run Up ◽  
X 24

Deflagration-to-detonation transition (DDT) in the system “gaseous oxygen- liquid film of n-decane” ' with a weak ignition source was obtained experimentally. In a series of experiments with ignition by an exploding wire that generates a weak primary shock wave (SW) with a Mach number ranging from 1.03 to 1.4, the DDT with the detonation run-up distances 1 to 4 m from the ignition source and run-up time 3 ms to 1.7 s after ignition was observed in a straight smooth channel of rectangular 54 x 24-millimeter cross section, 3 and 6 m in length with one open end. The DDT is obtained for relatively thick films with a thickness of 0. 3-0.5 mm, which corresponds to very high values of the overall fuel-to-oxygen equivalence ratios of 20-40. The registered velocity of the detonation wave (DW) was 1400-1700 m/s. In a number of experiments, a high-velocity quasi-stationary detonation-like combustion front was recorded running at an average velocity of 700-1100 m/s. Its structure includes the leading SW followed by the reaction zone with a time delay of 90 to 190 s. The obtained results are important for the organization of the operation process in advanced continuous-detonation and pulsed-detonation combustors of rocket and air-breathing engines with the supply of liquid fuel in the form of a wall film.

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