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Research activities
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Hybrid mobile hydraulics for excavators
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0D models of axial piston pumps/motors
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CFD studies on conical poppet valves
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CFD analysis of gerotor pumps
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Lumped parameter models of crescent pumps
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Lumped parameter models of vane pumps
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Lumped parameter models of gerotor pumps
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Coupled simulation of telehandler hydraulics
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Modelling of brake booster vacuum pumps
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Absorbed energy in ICE lubricating pumps
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Multi-body simulation of axial piston pumps
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Development of variable flow lubricating pumps
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Optimization of ICE lubrication gerotor pumps
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Publications
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Research projects
CFD studies on conical poppet valves (2015-2017)
The study deals with the 3D and 0D simulation of a conical poppet pressure relief valve with flow force compensation.
In a hydraulic valve the steady-state performances are strongly affected by the flow forces, which are generated by the change of fluid momentum inside the valve. In particular, in a pressure relief valve the undesired effect is the increment of the regulated pressure as the flow rate discharged by the valve increases.
Some techniques exist for the compensation of the flow forces, most of them are applied to spool valves. A method of compensation in conical poppet valves consists in deflecting the outgoing flow in order to reduce the change in the axial momentum. The difficulty during the design phase is due to the fact that the jet angle does not coincide with the trailing edge angle of the deflector. Moreover the intensity of the force is also function of the fluid velocity where the jet leaves the deflector, hence it depends on how much the jet spreads. In addition if the angle tends to 180°, the jet is partially reflected inwards by the seat of the poppet and a vortex is generated. Therefore to predict with a good accuracy the valve behaviour a CFD simulation is mandatory.
A dynamic model of the valve in ANSYS Fluent® and Simerics PumpLinx® was created and the interaction between the poppet dynamics and pressure field was taken into account. In particular PumpLinx has been used for the first time for this type of studies and a proper subdivision of the fluid domain has been conceived to identify the regions with fixed, deformable and sliding meshes.
The models are able to determine the opening force generated on the deflector by the jet deviation and therefore the equilibrium position of the poppet as function of the flow rate, which determines the regulated pressure. The steady-state flow-pressure characteristic of the valve was validated at three different cracking pressures on a specific test bench.
Once validated, the CFD codes were used to study the influence of the deflector geometry on the opening force. Moreover it was also used for determining some proper data to be supplied as input to a lumped parameter model of the valve. In conclusion, the 3D transient model has been proved to be an effective tool in the pre-design stage and also a valid substitute of the experimental tests for tuning a lumped parameters model.
In figure 1 the pressure field in the valve is shown. The flow is from left to right. The location of the pressure tranducers P1 for the inlet port P and P2 for the outlet port T is also indicated. An increment of the pressure up to 10 bar is observed on the left surface of the flow deflector due to the impact of the jet shown in figure 2.
Figure 1
Figure 2
In figure 3 the comparison between the simulated and the experimental steady-state characteristics is shown for three different cracking pressures. The dashed blue lines are obtained without the flow deflector.
Figure 3
More analyses and details are available in:
ALTARE G, RUNDO M, OLIVETTI M, 2016: 3D Dynamic Simulation of a Flow Force Compensated ...
FINESSO R, RUNDO M, 2017: Numerical and experimental investigation on a conical poppet ...
RUNDO M, ALTARE G, 2017: Comparison of Analytical and Numerical Methods ...