نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی مکانیک، دانشکده مهندسی مکانیک، دانشگاه جندی شاپور دزفول، دزفول، ایران
2 گروه مهندسی مکانیک دانشکده مهندسی مکانیک دانشگاه جندی شاپور دزفول، دزفول، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
High-response proportional directional control valves play a crucial role in improving the efficiency of hydrostatic power transmission systems in agricultural machinery. However, the rapid switching of these valves can generate undesirable transient phenomena in hydrostatic power transmission systems, thereby compromising overall system stability and energy efficiency. In this study, a comprehensive numerical analysis was performed to investigate the influence of spool displacement speed (2 and 20ms) and the curvature radius of spool lands (0, 2, 4 and 6µm) on the performance characteristics of a high-response proportional directional control valve under both steady-state and transient operating conditions. A three-dimensional computational fluid dynamics model was developed using a moving-mesh approach coupled with the k"-" ε turbulence model to capture the transient flow behavior accurately. To validate the numerical results, a hydraulic power transmission test bench was designed and fabricated to experimentally measure the valve's performance parameters. The comparison revealed that deviations between the numerical and experimental results were less than 5% under steady conditions and less than 6% under transient conditions. Furthermore, reducing the valve switching time from 20 to 2ms resulted in a 19.8% decrease in the average flow rate and a 29.8% increase in the required actuation force. Moreover, introducing a 2µm curvature radius at the spool edges improved the steady-state flow rate by 7.3% and reduced the actuation force by 9.2%. Under transient conditions, this geometric modification further enhanced the flow rate by 15.3% and reduced the required actuation force by 13.4%.
کلیدواژهها [English]
The enhancement of performance and response speed in modern agricultural machinery relies heavily on the implementation of fast-acting proportional directional control valves in hydrostatic power transmission systems. However, the rapid switching of these valves induces detrimental transient phenomena, such as water hammer and cavitation, which compromise system efficiency, stability, and longevity. While prior research has extensively analyzed the steady-state performance of such valves, a significant research gap persists in the comprehensive understanding of their transient behavior under real-world operating conditions. This study addresses this critical necessity by investigating the performance of a novel spool design featuring curved lands, aiming to mitigate adverse transient effects. The primary objective is to compare this innovative design against a conventional spool under both steady-state and two distinct transient operating speeds. Through a combined numerical and experimental approach, key performance indicators, including flow capacity and required actuation force, are meticulously evaluated. The findings of this research are expected to provide crucial insights for optimizing valve design, ultimately leading to enhanced stability, reduced energy losses, and improved reliability of hydrostatic systems in agricultural applications.
This study employs a combined numerical and experimental approach to investigate the valve's performance. The numerical analysis is based on solving the three-dimensional, incompressible Reynolds-Averaged Navier-Stokes (RANS) equations using the standard k-ε turbulence model and standard wall functions to accurately capture the complex turbulent flow and near-wall behavior. A detailed 3D model of the valve was created in ANSYS Fluent, incorporating a dynamic mesh to simulate the spool's movement during transient operation. The computational domain was discretized using polyhedral cells with significant refinement in the orifice regions and prism layers near the walls to ensure a y+ value between 30 and 300. The pressure-based solver utilized the PISO algorithm for enhanced stability, with a second-order upwind scheme for momentum. A time step of 10⁻⁵ s was employed for the transient simulations, and convergence was monitored through residual values and spool axial force stability. A comprehensive mesh independence study confirmed that a mesh of 9.8 million cells yielded grid-independent results. To validate the numerical findings, an experimental hydrostatic power transmission test rig was designed and constructed. The system incorporated a fast-acting proportional directional control valve, with high-precision sensors to measure the inlet/outlet pressures, flow rate, and the axial force exerted on the spool. Data was acquired via a dedicated data acquisition card for real-time analysis and comparison with the simulation results. The study systematically compared a conventional spool with a novel design featuring a 2μm edge curvature. Analyses were conducted under both steady-state and transient conditions, with the spool actuated at two distinct speeds (2ms and 20ms). Furthermore, the effect of varying the curvature radius (2, 4, and 6μm) on key performance metrics-flow capacity and required actuation force-was thoroughly evaluated.
This study presents a comprehensive numerical and experimental analysis of the dynamic behavior of a proportional directional control valve featuring a spool-type moving element. The investigation focused on two critical performance parameters—oil flow rate and the axial force required for valve actuation—under a constant pressure drop of 30 bar. The valve's performance was evaluated in both steady-state and transient conditions, with switching times of 2 ms (fast) and 20 ms (slow) to simulate rapid and gradual operations. Furthermore, the research explored the impact of geometric optimization by introducing a radius of curvature to the spool's edges. The results revealed a significant discrepancy between the valve's steady-state and transient performance. For the baseline spool with sharp-edged geometries, the transient flow rate was consistently lower than its steady-state counterpart, with average reductions of 19.77% and 9.92% for the 2 and 20ms switching times, respectively. This phenomenon is attributed to transient flow effects, including flow instability, sudden pressure drops, increased risk of cavitation, fluid inertia, and water hammer. Conversely, the required axial force during transient states was substantially higher than in steady-state, increasing by 29.8% and 20.7% for the respective switching times. This force escalation is primarily caused by inertial forces from the accelerating fluid, pressure waves, and the formation of vortices due to the rapid spool movement. The numerical model demonstrated strong validation against experimental data. In steady-state conditions, the average discrepancy between simulated and measured values for both flow rate and force was less than 5%. This difference slightly increased in transient conditions (to approximately 5-6%), which is expected given the inherent complexity of accurately modeling transient phenomena such as internal leakage and instantaneous fluctuations in the discharge coefficient. To mitigate these adverse transient effects, the study investigated optimizing the spool geometry by introducing a radius of curvature to its edges. This modification proved highly effective. The rounded edges reduced local flow resistance and suppressed vortex formation, leading to an increased discharge coefficient and a higher flow rate (up to 23% in steady-state). Crucially, this geometric change also significantly reduced the performance gap between steady and transient states. For instance, the 19.77% flow rate deficit for the sharp-edged spool at 2ms was reduced to 15.4% with a 2μm radius. Furthermore, the rounded edges substantially lowered the required actuation force and reduced the difference between steady-state and transient force requirements by up to 71%, resulting in more balanced pressure distribution on the spool. While a radius of 4μm was identified as a point of diminishing returns for further improvements, the findings conclusively demonstrate that optimizing the spool geometry is a viable and effective strategy for designing hydraulic valves with superior dynamic performance, reduced energy consumption, and higher operational stability. These results align with previous research and offer valuable insights for the design of advanced fluid power systems.
The findings demonstrate a significant performance gap between the valve's steady-state and transient conditions. This study concludes that geometric optimization of the spool, specifically by introducing a radius of curvature to its edges, is an effective strategy to mitigate this discrepancy. This modification minimizes the performance gap by enhancing the flow rate and reducing the required actuation force. Consequently, it also increases the accuracy of numerical modeling. These results provide practical and reliable guidelines for designing hydraulic valves with superior dynamic performance and optimal energy efficiency.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
Data available on request from the authors.
The study was approved by the Ethics Committee of the University of ABCD (Ethical code: IR.UT.RES.2024.500). The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare no conflict of interest.
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