Analysis of the pressure buildup behind rigid porous media impinged by shock waves in time and frequency domains

2015 ◽  
Vol 779 ◽  
pp. 842-858 ◽  
Author(s):  
O. Ram ◽  
O. Sadot
Keyword(s):  
Porous Medium ◽  
Shock Waves ◽  
Shock Tube ◽  
Pressure Profile ◽  
Air Gap ◽  
Front Face ◽  
Porous Sample ◽  
Rear Face ◽  
Pressure Buildup ◽  
End Wall

The transformation of a time-dependent pressure pulse imposed on the front face of a rigid porous medium sample, mounted in a tunnel, through the sample and a fixed-volume air gap between the rear face of the sample and the end wall of a tunnel is studied both experimentally and analytically. In the experiments, rigid porous samples that are placed at various distances from a shock tube end wall are subjected to the impingement of shock waves. The pressure buildup behind the porous sample is monitored and compared with the pressure imposed at the front face of the porous sample. The shock tube is fitted with a short driver section in order to generate blast-like decaying pressure profiles, which continue to decay after the initial shock impingement. In this scenario, the measured pressure profile at the end wall, which is affected by the properties of the porous medium and the size of the air gap separating its rear face and the shock tube end wall, is significantly different from the pressure profile imposed on the front face of the porous sample. The mechanism governing the pressure transformation provided by the porous medium is attributed to a selective filtration process that attenuates the pressure changes associated with high frequencies. The results of the present study are also analysed in conjunction with previously published analytical and numerical models to achieve a broader understanding of the physical mechanisms affecting the pressure buildup.

A simple constitutive model for predicting the pressure histories developed behind rigid porous media impinged by shock waves

2013 ◽  
Vol 718 ◽  
pp. 507-523 ◽  
Author(s):  
O. Ram ◽  
O. Sadot
Keyword(s):  
Shock Wave ◽  
Porous Medium ◽  
Porous Media ◽  
Shock Waves ◽  
Constitutive Model ◽  
Wave Attenuation ◽  
Front Face ◽  
Viscous Effects ◽  
Pressure History ◽  
Target Wall

AbstractShock wave attenuation by means of rigid porous media is often applied when protective structures are dealt with. The passage of a shock wave through a layer of porous medium is accompanied by diffractions and viscous effects that attenuate and weaken the transmitted shock, thus reducing the load that develops on the target wall that is placed behind the protective layer. In the present study, the parameters governing the pressure build-up on the target wall are experimentally investigated using a shock tube facility. Different porous samples are impinged by normal shock waves of various strengths and the subsequent pressure histories that are developed on the target wall are recorded. In addition, different standoff distances from the target wall are investigated. Assuming that the flow through the porous medium is close to being isentropic enabled us to develop a general constitutive model for predicting the pressure history developed on the target wall. This model can be applied to predict the pressure build-up on the target wall for any pressure history that is imposed on the front face of the porous sample without the need to conduct numerous experiments. Results obtained by other investigators are found to be in very good agreement with the predictions of the presently developed constitutive model.

scholarly journals Shock Loading of Closed Cell Aluminum Foams in the Presence of an Air Cavity

2020 ◽  
Vol 10 (12) ◽  
pp. 4128
Author(s):  
Mahesh Thorat ◽  
Shiba Sahu ◽  
Viren Menezes ◽  
Amol Gokhale ◽  
Hamid Hosano
Keyword(s):  
Shock Waves ◽  
Shock Tube ◽  
Shock Loading ◽  
Pressure Rise ◽  
Incident Shock ◽  
Foam Density ◽  
Aluminum Foams ◽  
Closed Cell ◽  
Rigid Walls ◽  
End Wall

It is important to protect assets located within cavities vulnerable to incident shock waves generated by explosions. The aim of the present work is to explore if closed cell aluminum foams can mediate and attenuate incident shocks experienced by cavities. A small cavity of 9 mm diameter and 2 mm length was created within the steel end-wall of a shock tube and exposed to shocks, directly or after isolating by aluminum foam liners. Shock waves with incident pressure of 9–10 bar travelling at a velocity of 1000–1050 m/s were generated in the shock tube. Compared to the no-foam condition, the pressure induced in the cavity was either equal or lower, depending on whether the foam density was low (0.28 g/cc) or high (0.31 to 0.49 g/cc), respectively. Moreover, the rate of pressure rise, which was very high without and with the low density foam barrier, reduced substantially with increasing foam density. Foams deformed plastically under shock loading, with the extent of deformation decreasing with increasing foam density. Some interesting responses such as perforation of cell walls in the front side and densification in the far side of the foam were observed by a combination of scanning electron microscopy and X-ray microscopy. The present work conclusively shows that shocks in cavities within rigid walls can be attenuated by using foam liners of sufficiently high densities, which resist densification and extrusion into the cavities. Even such relatively high-density foams would be much lighter than fully dense materials capable of protecting cavities from shocks.

Evaluation of blunt body velocity gradient at the shock tube end-wall

2020 ◽  
Vol 170 ◽  
pp. 570-576 ◽  
Author(s):  
Yosheph Yang ◽  
Ikhyun Kim ◽  
Gisu Park
Keyword(s):  
Shock Tube ◽  
Velocity Gradient ◽  
Blunt Body ◽  
Body Velocity ◽  
End Wall

Generation of Cylindrical Converging Shock Waves in a Conventional Shock Tube

2015 ◽  
pp. 1077-1082 ◽  
Author(s):  
L. Biamino ◽  
G. Jourdan ◽  
C. Mariani ◽  
L. Houas ◽  
M. Vandenboomgaerde ◽  
...  
Keyword(s):  
Shock Waves ◽  
Shock Tube ◽  
Converging Shock Waves

The numerical simulation of shock bifurcation near the end wall of a shock tube

1995 ◽  
Vol 7 (10) ◽  
pp. 2475-2488 ◽  
Author(s):  
Y. S. Weber ◽  
E. S. Oran ◽  
J. P. Boris ◽  
J. D. Anderson
Keyword(s):  
Numerical Simulation ◽  
Shock Tube ◽  
End Wall

Shock-initiated exothermic reactions. VI. The oxidation of ethylene oxide and cyclopropane

1969 ◽  
Vol 22 (7) ◽  
pp. 1355 ◽  
Author(s):  
LJ Drummond ◽  
J Kikkert
Keyword(s):  
Shock Waves ◽  
Ethylene Oxide ◽  
Shock Tube ◽  
Induction Period ◽  
Ignition Delay ◽  
Exothermic Reactions ◽  
Induction Periods ◽  
Reflected Shock ◽  
Formaldehyde Oxidation ◽  
Temperature Dependences

Mixtures of ethylene oxide or cyclopropane with oxygen and argon were ignited with reflected shock waves In a shock tube. The temperature dependences of the ignition delay and the growth of light emitted during the induction period to explosion of C2H4O-O2 mixtures indicate that the rate-controlling reaction is that of formaldehyde oxidation. The temperature dependence of induction periods for C3H6-O2 mixtures suggests that a complicated but undetermined mechanism controls the delay to ignition.

End-Wall Effects on Freely Propagating Flames in a Shock Tube

2022 ◽  
Author(s):  
Adam J. Susa ◽  
Lingzhi Zheng ◽  
Zach D. Nygaard ◽  
Ronald K. Hanson
Keyword(s):  
Shock Tube ◽  
Wall Effects ◽  
End Wall

Inverse Problems in Non-Newtonian Electrokinetic Flows in Microchannel Networks

Volume 3 ◽  
2004 ◽  
Author(s):  
William B. Zimmerman ◽  
Julia M. Rees ◽  
Thomas J. Craven
Keyword(s):  
Slip Velocity ◽  
Pressure Profile ◽  
Carreau Fluid ◽  
Boundary Slip ◽  
Electrokinetic Flow ◽  
Nonlinear Viscosity ◽  
Relaxation Time Scale ◽  
Electrokinetic Flows ◽  
Electrokinetic Motion ◽  
End Wall

A model of the electrokinetic flow of a fluid with a nonlinear viscosity of the Carreau type is simulated by finite element methods in a microchannel T-junction. The simulations accelerate the fluid from rest using the model for boundary slip velocity imposed due to a Debye double layer motion proposed by Zimmerman and MacInnes (2003). The simulations demonstrate an interval of the transient evolution of the end wall pressure profile that scales proportionally with the Reynolds number. The shape of the steady state profile is shown to be sensitive to the relaxation time scale characterizing the shear rate dependence of a Carreau fluid. Consequently, this flow regime can be taken as a paradigm viscometric flow for electrokinetic motion.

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