= Interfacial power model for entrainment
{title2=$P_I=S\tau u_I=c_D\rho_lS u_I^3$}
An interfacial stress $\tau=c_D\rho_lu_I^2$ supplies local stress power $P_I=S\tau u_I$. Assuming a fixed fraction $C_W$ becomes global <potential energy> gives $\dot E_P=C_WP_I$. Together with <potential energy of two-layer entrainment>, this gives $\dot h=2C_Wc_Du_I^3/(g'h)$. This is an additional local power-transfer closure. The shaft power of a rotating lid is its torque times its prescribed angular speed and need not equal $P_I$. Geometric factors and a constant transfer fraction may be absorbed into the empirical coefficients only when explicitly assumed time-independent.
Back to article page
