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RESEARCH PAPERS: Interior Ballistics

Understanding Interior Ballistic Processes in a Flash Tube

[+] Author and Article Information
Ryan W. Houim

Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802rwh162@psu.edu

Kenneth K. Kuo2

Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802kenkuo@psu.edu

2

Corresponding author.

J. Appl. Mech 77(5), 051403 (May 17, 2010) (9 pages) doi:10.1115/1.4001285 History: Received July 22, 2009; Revised September 25, 2009; Published May 17, 2010; Online May 17, 2010

Vented flash tubes have often been used in the ignition train of medium and large caliber weapon systems. Despite their long history of ballistic usage, there are undesirable features associated with uneven venting of the combustion products. Pressure measurements at various locations from the flash tube have shown severe variations with time, which is associated with spatially nonuniform mass discharging rate from the vent holes. Measured pressure profiles in the flash tube show counterintuitive, nonmonotonic pressure distributions with the lowest pressure in the middle of the venting section of the flash tube. A model of the flash tube venting process was developed to explain these phenomena using modern, high-order numerical schemes. Source terms accounting for mass addition from the black powder pellets, mass loss through the vent holes, wall friction, differential area changes, and volume changes from surface regression of black powder pellets were fully coupled in the model. The numerical results of this model reproduced the severe pressure variations and nonmonotonic pressure profiles observed in experiments. In general, they are caused by gas dynamic effects from a slowly moving normal shock wave in the middle portion of the venting section of the flash tube. As the driving pressure from the burning black powder pellets changes, the location of the normal shock wave jumps from one vent hole set to another, producing pressure variations observed in experiments. The physical understanding gained from this model solution has provided guidance for achieving more uniform mass discharging rate by varying the vent hole sizes as a function of distance along the flash tube.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 4

Superposition of 12 measured pt traces at the p5 location with statistical averaged trace and standard deviations

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Figure 5

Generic control volume for ith computational cell

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Figure 6

Geometry of a computational cell partially contained by black powder

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Figure 7

Verification results of (a) the shock tube problem at a time of 0.5 ms and (b) the steady transonic flow test

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Figure 8

Calculated p3 pressure-time traces under grid refinement

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Figure 9

Comparison between the calculated and measured average pressure-time trace at the p5 location along with the minimum and maximum envelopes of the experimental data

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Figure 10

Comparison between the calculated and measured average pressure-time trace data at p1 through p4 locations; the maximum and minimum envelopes of the experimental data are also shown

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Figure 11

Effect of the Mylar tape bursting pressure on the early portion of the pt trace at the p5 location

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Figure 12

Calculated pressure-time traces at all five measurement stations

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Figure 13

Calculated density distribution on x-t diagram

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Figure 14

Calculated pressure and Mach number profile at a time of 1.5 ms

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Figure 15

Qualitative analogy between the quasi-steady flow in the flash tube and steady transonic flow in a diverging nozzle

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Figure 16

Computed mass flow rates for each set of vent holes (a) baseline case: uniform hole size; (b) modified case: nonuniform hole size distribution

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Figure 3

Typical pt trace measured by Moore (1-2)

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Figure 2

Schematic diagram of the detailed geometry of the flash tube modeled in this study

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Figure 1

Schematic diagram of a flash tube used to ignite a granular propellant bed

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