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Effect of vent opening area and arrangement on gas flow field as gas propelled cylinder exits a flow tube

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Abstract

The effects of auxiliary flow tube vent opening area and arrangement on the gas flow field as a gas propelled cylinder exits a flow tube were studied numerically. Configurations with a single opening of increasing size and multiple opening arrangements with equivalent opening area were considered for comparison to a baseline no-opening system. The openings are positioned near the end of the flow tube. The intended use of the openings is to reduce the pressures of the gases escaping to the surroundings and thus to reduce the intensity and size of the gas expansion zone in the surroundings. The results indicated that increasing the opening flow area decreased the pressure at the axial end of the flow tube and the radial extent of the end of flow tube exit plume. However, the radially directed flow streams leaving through the side vent openings could increase the overall radial spread of the gas expansion into the surroundings. The single opening arrangement produced as much as a 95% decrease in the pressure at the end of the flow tube and a 37% decrease in the recoil force at a given time with about 95% of the exiting flow leaving through the opening. For the parameters considered, the multiple opening arrangement produced up to a 93% decrease in the pressure at the end of the flow tube and a 90% decrease in the recoil force at a given time with about 93% of the exiting flow leaving through the openings. The results showed larger single openings to be more effective at reducing end of flow tube pressure, while the multiple openings to be more conducive to a reduced recoil force.

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Abbreviations

d :

diameter of flow tube (m) (Fig. 1)

F press :

pressure force (N) (Eq. 5)

F res :

resistance force (N) (Eq. 5)

F viscous :

viscous force (N) (Eq. 5)

F tube :

force acting on the flow tube in the negative x direction

G,Y,S:

turbulence parameters (Eq. 4)

h :

enthalpy (J/kg) (Eq. 3)

k gas :

thermal conductivity of gas (W/mK) (Eq. 3)

m c :

mass of propelled cylinder (kg) (Eq. 5)

ol :

length of opening (m) (Fig. 1)

p :

pressure (Pa) (Eq. 3)

P init :

initial gas pressure acting on moving cylinder (Pa)

t :

time (s)

T :

temperature (K)

T init :

initial gas temperature acting on moving cylinder (K) (Fig. 1)

ν :

fluid velocity vector (m/s) (Eqs. 1–4)

V c :

instantaneous velocity of moving cylinder (m/s) (Eq. 5, Fig. 1)

x,y:

coordinates

α :

angle of flow stream with x (flow tube) axis (Eq. 6)

ε :

turbulence parameter (Eq. 4b)

κ :

turbulence parameter (Eq. 4a)

ρ :

gas density (kg/m3)

τ :

stress tensor (Eq. 2)

τ′:

stress tensor (Eq. 3)

μ :

fluid viscosity

c :

related to moving cylinder (Fig. 1a)

ref :

reference values used for normalizing data presented

Δ:

difference

1,2,3:

reference to the opening number for particular arrangement

e :

reference to end of flow tube

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  1. Technology Branch, Small and Medium Caliber Armaments Division, RDAR-WSW-F, US ARMY ARDEC, Building 65N, Picatinny Arsenal, NJ, 07806, USA

    L. A. Florio

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  1. L. A. Florio
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Florio, L.A. Effect of vent opening area and arrangement on gas flow field as gas propelled cylinder exits a flow tube. Meccanica 45, 475–501 (2010). https://doi.org/10.1007/s11012-009-9266-3

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