Polytropic enthalpy
= Polytropic enthalpy
{title2=$Q=(n+1)p/\rho$}
For $p=K\rho^{1+1/n}$ with $K,n>0$, the specific <enthalpy> relative to vacuum is $Q=(n+1)K\rho^{1/n}=(n+1)p/\rho$. It obeys $\nabla Q=\nabla p/\rho$ and $nD_tQ=-Q\nabla\cdot\mathbf u$. The vacuum reference is fixed when these equations are combined with the <polytropic equation of state>.