MAT_POWDER_BURN
Material properties
Beta command
This command is in the beta stage and the format may change over time.
"Optional title"
mid, $\rho$, $E$, $\nu$, did
$C_v$, $\gamma$, $e_0$, $b$, fid, $T_i$, $p_i$, $t_i$
local, $A$, $B$, $n$
Parameter definition
Description
This material command is used to model unburned propellant as rigid or elasto-plastic grains and its combustion products as gas lumped into an overlapping CFD grid. The grains are assumed rigid, unless $E \gt 0$.
If $E \gt 0$ then the flow stress is defined as:
$\displaystyle{ \sigma_y = A + B(\varepsilon_{eff}^p)^n }$
The pressure of the generated gases is defined as:
$\displaystyle{ p = \frac{\gamma-1}{1 - \rho b} e}$
where $\rho$ is the current gas density and $e$ is the current specific internal energy. Note that $b$ has the units $m^3/kg$.
By default (local=0) the burn rate is uniform for each grain. That is, the average pressure and temperature is calculated and used for all element faces on the grain. If local=1, then the local pressure and temperature define the local burn rate for each individual element face.
A grain ignites if the local gas pressure $p_{CFD} \geq p_i$ and the grain surface temperature $T_g \geq T_i$. The grain temperature evolves according to:
$\displaystyle{ \dot T_g = \frac{T_{CFD} - T_g}{t_i} }$
The command POWDER_BURN_IGNITE can also be used to ignite grains inside a specific region.
Example
Propellant burning inside a small cylinderical space
Idealized rings of propellant burning inside a cylindrical container. The inner ring is ignited by depositing hot gases at time zero, using CFD_GAS.
