Numerical and experimental study on the churning losses of 2D high-speed piston pumps

Abstract

This paper first introduces the structure and working principle of a 2D piston pump invented by the research team that the authors are involved with. Afterward, the mechanism of the churning losses caused by the pump's moving parts, which are rotating in oil, is carefully studied by building up mathematical models and using CFD simulations. A test rig is set up to estimate the churning losses of the moving parts by monitoring the torque at different rotational speeds. The analytical results indicated that the torque of the churning losses increased with the increase of the rotational speed. In addition, the experimental data of the churning losses were consistent with the solutions from both the conducted mathematical models and CFD simulations before the rotational speed reached 8000 rpm. However, when the rotational speed exceeded 8000 rpm, the experimental data showed an apparent difference from the calculated ones. Based on the changes in the oil temperature and noise, this difference might be due to cavitation or turbulence. As a result, the churning losses that took place in the 2D high-speed piston pump need to be further studied, especially when the pump is driven by a high-speed motor.

Investigation of the Churning Loss Reduction in 2D Motion-Converting Mechanisms

“…The churning loss situation in a 2D motion-converting mechanism in Huang's previous research was quite different from that of axial piston pumps, and it was mainly caused by the stirring of the active parts in the oil [15]. When the rotational speed was high, the active parts were acting like four blades or impellers.…”

“…The reciprocating stroke of the 2D piston keeps the same as well as the pump's displacement for every stroke. Since the same working principle was introduced in references [10,15], the distribution function was still provided through the windows and the rotating slots on the rotating 2D piston, whereas the opposite reciprocation motion from the 2D piston and piston rings provides the discharging and sucking functions. The driving rail is inside the balancing rail, and they keep a simultaneous rotational speed due to the fork.…”

“…Due to the consideration of time tern in the N-S equation, the simulation uses the SIMPLE scheme to carry out instantaneous calculations. In particular, due to the consideration of time tern in equation 1, the unstructured tetrahedral mesh was used through the commercial software ICEM-CFD, an integrated grid, which is set without an interface [15], was applied to guarantee good continuity, and the smoothing method was adopted to simulate the rotation with various rotational speeds by writing UDFs in the commercial software Fluent. Since the axial motion of the rotator was not considered in the last research, the authors attempted to consider the influence of the axial relative motion of the two rails on the churning loss.…”

“…He also applied his accurate model for predicting the steady temperature of EHA pumps [32]. Huang started to use CFD simulations to evaluate the churning losses in a 2D motion-converting mechanism in a high-speed 2D piston pump [15]. In his research, the rotating parts, two supports, and four cone rollers were simplified into a cross-like structure, as shown in Figure 2, to save the calculation time.…”

“…However, because the 2D motion-converting mechanism not only converted motions but also transferred power and bear load pressures, the strength requirement and the mounting dimensions of the standard parts, such as bearings, make it hard to optimize the structures of supports and cone rollers. Therefore, a new 2D motion-converting mechanism structure was proposed in this paper with the same pump displacement and installation parameters of the older mechanism [15]. Subsequently, a series of CFD simulations were carried out to specifically obtain the churning loss and theoretically compare it with that of the former mechanism, and they additionally included the axial motion of the active parts in oil.…”