In the modeling of transient one-dimensional, two-phase combustion of granular propellants in gun interior ballistics, the boundary conditions at both the breech end and the base of the projectile must be specified adequately. The form and the total number of the boundary conditions required depend upon the relative velocities of the gases and solid particles with respect to the solid boundary and the condition of fluidization. In the study of a simulated gun system, the flow properties at the boundary are obtained by considering 1) the local balances of mass, momentum, and energy over a small control volume adjacent to the boundary; 2) the compatibility relationships along the characteristic lines; and 3) the number of algebraic relationships according to the instantaneous flow conditions. These considerations are necessary to provide the extraneous boundary conditions required for solving the partial differential equations with a second-order numerical scheme. Numerical results were compared and found in agreement with test-firing data.
Nomenclature
A= cross-sectional area of cylindrical combustion chamber A s = specific surface area of granular propellants, the surface exposed to fluid per unit volume C = speed of sound in particle phase C L = combustion chamber length C v = specific heat at constant volume C p = specific heat at constant pressure dx/dt = slope of characteristic equations D p = drag force due to porosity gradient D t = total drag force between gas and particle phases,=drag force acting on gases by particles per unit wetted area of particles (evaluated from KuoNydegger correlation) D/Dt -Lagrangian time derivative when observer follows motion of the bullet, (d/dt) +u B (d/dx) E = total stored energy (internal plus kinetic energy) per unit mass h c = average convection heat-transfer coefficient over pelletŝ chem = enthalpy of propellant gas at flame temperature /z ign = enthalpy of igniter gas h ( = total heat transfer coefficient, the unit-surface conductance k -thermal conductivity of gases k p = thermal conductivity of particles K = coefficient of characteristic equations M ign = igniter mass flow rate P = pressure (? wg -wetter perimeter between chamber wall and gas phase ($> wp = wetter perimeter between chamber wall and particle phase q = rate of conduction heat transfer per unit area Q w = rate of heat loss to chamber wall per unit spatial volume of gas-particle system r b -burning rate of solid propellant r p -radius of pellets R = gas constant t = time T = temperature T abl = ablation temperature of solid propellant Tf = adiabatic flame temperature of pellets r hg = temperature of hot igniter gas T ps -particle surface temperature r ign = ignition temperature of solid propellant U = velocity with respect to laboratory coordinates U B = projectile velocity with respect to laboratory coordinateŝ feign ~ igniter gas velocity x = distance from beginning of granular propellant bed X B = instantaneous location of base of projectile X L =left boundary of partial-differential-equation solution ...