Role of bulk viscosity and acoustic parameters in tribological problems

The bulk viscosity of the medium, which is closely and substantially connected with the acoustic characteristics, can be an important factor in determining the course of hydromechanic processes; however, in modern hydromechanics it is usually, and traditionally, disregarded. The same situation can be observed in many other fields of science and technology. Using examples of the theory of lubrication, and those of the simplest flows it is shown that this assumption is not always justifiable. On the basis of ultrasonic measurement data, numerical evaluation of the influence of the bulk viscosity and compressibility on the characteristics of the flows and processes taking place between contacting rubbing surfaces has been performed. Theoretical data are illustrated by experiments on rubbing-friction regime test machines. It is shown that the acoustic parameters of lubricants have a certain practical importance.