Bulk viscosity: Past to present

A review of the concept of a hulk viscosity coefficient beta is presented, involving a discussion of theoretical approaches and a summary of existing experimental data. Two independent viscosity coefficients mu and lambda are obtained in the viscous stress tensor as a result of the isotropic Newtoni an assumption. Hence, all solutions of the Navier-Stokes equations must mak e an assumption regarding the functional form of lambda. With beta = lambda +(2)(3)mu by definition, the assumption is often arbitrarily made that the two viscosity coefficients are not independent, with beta = 0. This assumpt ion has been shown to be valid only for dilute monatomic gases and is equiv alent to stating that dilatational flowfield effects are not significant. T heoretical approaches for quantifying beta are classified according to whet her the subject fluid is dilute or dense. Experimental methods used to esti mate bulk viscosity are described. Existing experimental data are summarize d for each fluid classification, and issues related to using these data for dilatational flows in local thermodynamic equilibrium are addressed.