scholarly journals Instability of Strong Regular Reflection and Counterexamples to the Detachment Criterion

2009 ◽  
Vol 70 (4) ◽  
pp. 1330-1340 ◽  
Author(s):  
Volker Elling
Keyword(s):  
Regular Reflection ◽  
Detachment Criterion

Gaseous detonation propagation in a bifurcated tube

2008 ◽  
Vol 599 ◽  
pp. 81-110 ◽  
Author(s):  
C. J. WANG ◽  
S. L. XU ◽  
C. M. GUO
Keyword(s):  
Numerical Simulation ◽  
Detonation Wave ◽  
Mach Reflection ◽  
Initial Pressure ◽  
Gaseous Detonation ◽  
Recirculation Region ◽  
Horizontal Branch ◽  
Regular Reflection ◽  
Detonation Propagation ◽  
Wall Geometry

Gaseous detonation propagation in a bifurcated tube was experimentally and numerically studied for stoichiometric hydrogen and oxygen mixtures diluted with argon. Pressure detection, smoked foil recording and schlieren visualization were used in the experiments. Numerical simulation was carried out at low initial pressure (8.00kPa), based on the reactive Navier–Stokes equations in conjunction with a detailed chemical reaction model. The results show that the detonation wave is strongly disturbed by the wall geometry of the bifurcated tube and undergoes a successive process of attenuation, failure, re-initiation and the transition from regular reflection to Mach reflection. Detonation failure is attributed to the rarefaction waves from the left-hand corner by decoupling leading shock and reaction zones. Re-initiation is induced by the inert leading shock reflection on the right-hand wall in the vertical branch. The branched wall geometry has only a local effect on the detonation propagation. In the horizontal branch, the disturbed detonation wave recovers to a self-sustaining one earlier than that in the vertical branch. A critical case was found in the experiments where the disturbed detonation wave can be recovered to be self-sustaining downstream of the horizontal branch, but fails in the vertical branch, as the initial pressure drops to 2.00kPa. Numerical simulation also shows that complex vortex structures can be observed during detonation diffraction. The reflected shock breaks the vortices into pieces and its interaction with the unreacted recirculation region induces an embedded jet. In the vertical branch, owing to the strength difference at any point and the effect of chemical reactions, the Mach stem cannot be approximated as an arc. This is different from the case in non-reactive steady flow. Generally, numerical simulation qualitatively reproduces detonation attenuation, failure, re-initiation and the transition from regular reflection to Mach reflection observed in experiments.

scholarly journals SIMULATION OF FRACTURE USING A MESH-DEPENDENT FRACTURE CRITERION IN THE DISCRETE ELEMENT METHOD

2018 ◽  
Vol 16 (1) ◽  
pp. 41 ◽  
Author(s):  
Andrey Dimaki ◽  
Evgeny Shilko ◽  
Sergey Psakhie ◽  
Valentin Popov
Keyword(s):  
Particle Size ◽  
Discrete Element Method ◽  
Mechanical Behavior ◽  
Fracture Criterion ◽  
Discrete Element ◽  
Macroscopic Behavior ◽  
Detachment Criterion ◽  
Discrete Element Methods ◽  
Adhesive Contacts ◽  
Fracture Processes

Recently, Pohrt and Popov have shown that for simulation of adhesive contacts a mesh dependent detachment criterion must be used to obtain the mesh-independent macroscopic behavior of the system. The same principle should be also applicable for the simulation of fracture processes in any method using finite discretization. In particular, in the Discrete Element Methods (DEM) the detachment criterion of particles should depend on the particle size. In the present paper, we analyze how the mesh dependent detachment criterion has to be introduced to guarantee the macroscopic invariance of mechanical behavior of a material. We find that it is possible to formulate the criterion which describes fracture both in tensile and shear experiments correctly.

scholarly journals Interaction between Shock Waves Travelling in the Same Direction

Fluids ◽  
2021 ◽  
Vol 6 (9) ◽  
pp. 315
Author(s):  
Pavel Bulat ◽  
Konstantin Volkov ◽  
Igor Volobuev
Keyword(s):  
Shock Waves ◽  
Contact Discontinuity ◽  
Jet Engines ◽  
Mach Stem ◽  
Regular Reflection ◽  
Reflected Shock ◽  
Different Types ◽  
Irregular Reflection

In this paper, we study the intersection (interaction) between several steady shocks traveling in the same direction. The interaction between overtaking shocks may be regular or irregular. In the case of regular reflection, the intersection of overtaking shocks leads to the formation of a resulting shock, contact discontinuity, and some reflected discontinuities. The type of discontinuity depends on the parameters of incoming shocks. At the irregular reflection, a Mach shock forms between incoming overtaking shocks. Reflected discontinuities come from the points of intersection of the Mach stem with the incoming shocks. We also consider the possible types of shockwave configurations that form both at regular and irregular interactions of several overtaking shocks. The regions of existence of overtaking shock waves with different types of reflected shock and the intensity of reflected shocks are defined. The results obtained in the study can potentially be useful for designing supersonic intakes and advanced jet engines.

scholarly journals Theoretical study on regular reflection of shock wave–boundary layer interactions

2020 ◽  
Vol 899 ◽  
Author(s):  
Longsheng Xue ◽  
Ferry F. J. Schrijer ◽  
Bas W. van Oudheusden ◽  
Chengpeng Wang ◽  
Zhiwei Shi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Theoretical Study ◽  
Regular Reflection ◽  
Wave Boundary Layer ◽  
Image Position ◽  
Wave Boundary

Abstract

scholarly journals Mobile extracorporeal membrane oxygenation service for severe acute respiratory failure – A review of five years of experience

2019 ◽  
Vol 21 (2) ◽  
pp. 134-139 ◽  
Author(s):  
Ada M Krzak ◽  
Jo-Anne Fowles ◽  
Alain Vuylsteke
Keyword(s):  
Intensive Care Unit ◽  
Intensive Care ◽  
Respiratory Failure ◽  
Qualitative Study ◽  
Extracorporeal Membrane Oxygenation ◽  
Acute Respiratory Failure ◽  
Equipment Failure ◽  
Quality And Safety ◽  
Regular Reflection ◽  
Membrane Oxygenation

Provision of extracorporeal membrane oxygenation as part of support escalation in severe refractory acute respiratory failure in England is provided by five specialist centres that operate within a well-defined quality and safety framework. We conducted a qualitative study of the extracorporeal membrane oxygenation retrieval service provided by one of the five centres. We analysed 176 consecutive debrief reports written between October 2013 and April 2018 by the consultant. Main identified issues were short delays in retrieval predominantly due to insufficient communication or equipment failure. All issues were addressed in subsequent practice. Our results suggest a need for improved communication between the referring intensive care unit and retrieving team. Our findings highlight the value of regular reflection-based evaluation to ensure continued provision of safe and efficient service.

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