where: k {\displaystyle k} = specific heat ratio ( c p / c v {\displaystyle c_{p}/c_{v}} ), dimensionless q v , 1 {\displaystyle q_{v,1}} = volume flow rate under upstream conditions, m³/s ρ 1 {\displaystyle \rho _{1}} = real gas density under upstream conditions, kg/m³ and other symbols are as above