Ahmad Reza Estakhr Number, (Fluid Dynamics)

The Estakhr Number is a dimensionless number defined as: $E_n=\frac{\lambda}{\eta}$ where $\lambda$ denotes mean free path and $\eta$ denotes Kolmogorov length scale. The Mach and Estakhr Numbers are therefore related by: $E_n=Ma\sqrt{\frac{\gamma\pi}{2}}$ where the $Ma$ denotes Mach number, $\gamma$ denotes the ratio of specific heats and is dimension less. At high Reynolds number the Knudsen, Estakhr and Reynolds Numbers are therefore related by: $E_n=K_nR_e$ where the $K_n$ denotes Knudsen number and $R_e$ denotes Reynolds number.