The state-of-art technical devices - from the aircraft and missile equipment to mobile machines in sphere of construction and agriculture -widely use hydraulic drives based on adjustable axial-piston hydraulic machines. During operation of such hydraulic drives, pressure fluctuations and power fluid flow rate occur, and it results in vibrations of hydraulic machine housing and its components and acoustic radiation of units. Such processes arise from the wave transients that may appear when a mode of operation is changed, or are available when the hydraulic machine separate units are in operation. Origination specificities of these processes and their development are not well studied. So implementation of such hydraulic machines in hydraulic drives of equipment with a wide variety of dynamic loads requires additional experimental and theoretical investigations.

The objectives of this paper is to develop a hydraulic drive model based on adjustable axial-piston hydraulic machines and to investigate transients that are available in the operational cycle of a hydraulic drive.

To study transients a method of mathematical modeling was used. For hydraulic drive mechanism with rotational displacement, a model with lumped parameters was developed. The model takes into consideration the kinematic and physical features of hydraulic drive components structure, peripheral devices and physical and mechanical properties of power fluid, thereby partially solving the task of investigating transients.

There is no possibility to describe all aspects of transients within the framework of a mathematical model with lumped parameters. Difficulties spring up when modeling the wave processes that occur at transient of pumping unit hydraulic cylinders between the suction and discharge zones.

For modeling the power fluid transient from pumping unit into discharge line, was developed a two-dimensional turbulent model with distributed parameters. An equation of state for two-phase power fluid in baratropic approximation was obtained.

Based on the computational experiment results, it is found that unloading pressure fluctuations, which occur at transients in a pumping unit, considerably change the power fluid pressure distribution along a discharge line, and must be taken into consideration when modeling the dynamic processes in hydraulic drives based on adjustable axial-piston hydraulic machines.