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Research Papers: Fundamental Issues and Canonical Flows

Numerical Investigation of Shock Wave Attenuation by Geometrical Means: Double Barrier Configuration

[+] Author and Article Information
Shahar Berger

Faculty of Engineering Studies,
Department of Mechanical Engineering,
Protective Technologies R&D Center,
Pearlstone Center for Aeronautical
Engineering Studies,
Ben-Gurion University of the Negev,
Beer Sheva 84105, Israel
e-mail: bergersh@bgu.ac.il

Gabi Ben-Dor

Professor
Faculty of Engineering Studies,
Department of Mechanical Engineering,
Protective Technologies R&D Center,
Pearlstone Center for Aeronautical
Engineering Studies,
Ben-Gurion University of the Negev,
Beer Sheva 84105, Israel
e-mail: bendorg@bgu.ac.il

Oren Sadot

Associate Professor
Faculty of Engineering Studies,
Department of Mechanical Engineering,
Protective Technologies R&D Center,
Pearlstone Center for Aeronautical
Engineering Studies,
Ben-Gurion University of the Negev,
Beer Sheva 84105, Israel
e-mail: sorens@bgu.ac.il

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 26, 2014; final manuscript received October 17, 2014; published online December 18, 2014. Editor: Malcolm J. Andrews.

J. Fluids Eng 137(4), 041203 (Apr 01, 2015) (11 pages) Paper No: FE-14-1098; doi: 10.1115/1.4028875 History: Received February 26, 2014; Revised October 17, 2014; Online December 18, 2014

Due to the increase in global terror threats, many resources are being invested in efforts to find and utilize efficient protective means and technologies against blast waves induced by conventional and nonconventional weapons. Bombs exploding in the entrance of military underground bunkers initiate a blast wave that propagates in a corridor-type structure causing injuries to human and damage both to the structures and the equipment. Rigid barriers of different geometries inside a tunnel can cause the blast wave to diffract and attenuate, leaving behind it a complex flow field that changes the impact on the target downstream of the barrier. In our earlier phase of the research that dealt with a single barrier configuration, it was shown that the opening ratio (i.e., the cross section that is open to the flow divided by the total cross section of the tunnel) is the most dominant parameter in attenuating the shock wave. Additionally, it was found that when the opening ratio was fixed at 0.375, the barrier inclination angle was significantly more effective than the barrier width in attenuating the shock wave. The present phase of the research focuses on the dependence of the shock wave attenuation on a double barrier configuration, while keeping the opening ratio fixed at 0.375. The methodology is a numerical approach that has been validated by experimental results. The experiments were conducted in a shock tube using a high-speed camera. The numerical simulations were carried out using a commercial code based on an MSC-DYTRAN solver under initial conditions similar to those in the experiments. A wide span of the barrier geometrical parameters was used to map in a continues manner the effect of the barrier geometry on the shock wave attenuation. By analyzing the geometrical parameters characterizing the double barrier configuration, better understanding of the physical mechanisms of shock wave attenuation is achieved. It was shown that for a double barrier configuration, the first barrier inclination angle was very dominant in attenuating the shock wave, as expected, while the efficiency of the second barrier inclination angle depended on the distance between the two barriers. Only when the distance between the two barriers was increased and the second barrier was far enough from the first barrier, it affected the attenuation regardless of the first barrier.

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References

Figures

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Fig. 1

Schematic illustration of the experimental setup: (a) The shock-tube, the laser beam path, the mirrors, and the high-speed camera arrangement. (b) The barrier and the pressure transducers arrangement inside the test section.

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Fig. 2

Comparison between the numerical simulations (upper half of the picture) and the experimental results (lower half of the picture) of a shock wave at Ms = 1.2 interacting with a 45 deg single barrier having an opening ratio of 0.375. The time interval between consecutive images is ∼50 μs.

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Fig. 3

Comparison between the numerical simulations (upper half of the picture) and the experimental results (lower half of the picture) of a reflected shock wave at Ms = 1.2 heading upstream toward a 45 deg single barrier. The time interval between consecutive images is ∼50 μs.

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Fig. 4

Validation of the pressure histories recorded at a test section with a double barrier configuration (α1 = 135 deg, α2 = 45 deg, distance between barriers = 1.6). Experiment: solid line, viscous calculation: dotted line and inviscid calculation: dash-dot line.

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Fig. 5

Long test section configurations: configuration 1 (a) and configuration 2 (b) stand for a single and a double barrier arrangement, respectively

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Fig. 6

Numerical simulation of a shock wave attenuation surface for a single barrier configuration as a function of the barrier normalized width and the inclination angle. The opening ratio is 0.375 and the incident shock wave Mach number is 1.2.

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Fig. 7

Attenuation surface of a double barrier configuration, as a function of first barrier inclination angle (α1) and second barrier inclination angle (α2), the normalized distance between the two barriers was set to 0.4.

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Fig. 8

Different barrier arrangements: (a)–(f), when the first barrier inclination angle is set to 75 deg and the second barrier inclination angle is set to 15 deg, 45 deg, 75 deg, 105 deg, 135 deg, and 165 deg, respectively

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Fig. 9

Computed density-Schlieren maps for a double barrier configuration. The first barrier inclination angle is set to 165 deg, the second barrier inclination angle is set to 15 deg, 90 deg, and 165 deg, respectively. The distance between barriers is 0.4.

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Fig. 10

The attenuation surfaces of a double barrier configuration, as a function of first barrier inclination angle (α1) and second barrier inclination angle (α2). Subplots (a)–(d) are for different normalized distances between the two barriers (2, 4, 8, and 12, respectively).

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Fig. 11

The attenuation factor of a double barrier configuration, as a function of the first barrier inclination angle (α1) and the second barrier inclination angle (α2). The distance between the barriers is fixed at eight.

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Fig. 12

Critical normalized distance for the flow expansion and the corresponding attenuation factor when the normalized distance between the barriers is set to eight

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Fig. 13

The attenuation surface of a double barrier configuration as a function of normalized distance between the two barriers and the second barrier inclination angle (α2). The first barrier inclination angle (α1) was set to 165 deg.

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Fig. 14

The attenuation factor of a double barrier configuration inclined at 165 deg, as a function of the normalized distance between the two barriers

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