Hydraulic fluid

Summary

A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoes, hydraulic brakes, power steering systems, automatic transmissions, garbage trucks, aircraft flight control systems, lifts, and industrial machinery. Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has zero compressibility. Functions and properties The primary function of a hydraulic fluid is to convey power. In use, however, there are other important functions of hydraulic fluid such as protection of the hydraulic machine components. The table below lists the major functions of a hydraulic fluid and the properties of a fluid that affect its ability to perform that function: Composition Base stock The original hydraulics fluid, dating back to the tim

Official source

https://en.wikipedia.org/wiki/Hydraulic_fluid

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Design optimization of a 2D blade by means of milling tool path

François Avellan, Christophe Tournier, Christian Vessaz

In a conventional design and manufacturing process, turbine blades are modeled based on reverse engineering or on parametric modeling with Computer Fluids Dynamics (CFD) optimization. Then, only raises the question of the manufacturing of the blades. As the design does not take into account machining constraints and especially tool path computation issues in flank milling, the actual performance of the machined blade could not be optimal. In this paper, a new approach is used for the design and manufacture of turbine blades in order to ensure that the simulated machined surface produces the expected hydraulic properties. This consists in the modeling of a continuous tool path based on numerical simulation rather than the blade surface itself. Consequently, this paper aims at defining the steps of the proposed design approach including geometrical modeling, mesh generation, CFD simulation and genetic optimization. The method is applied on an isolated blade profile in a uniform water flow and results are compared to the conventional design process.

2013

Hydraulic performance evaluation of a micro-turbine with counter rotating runners by experimental investigation and numerical simulation

Loïc Andolfatto, François Avellan, Cécile Münch-Alligné, Elena Vagnoni

The development of energy recovery systems on existing water utility networks is a new challenge for increasing the sustainability of electricity generation mix. The concept of the new micro-turbine with counter rotating runners braces this goal by allowing the recovery of the energy which is spoiled in pressure reducing valves in many water supply networks. The hydraulic performances of the micro-turbine are evaluated through an analysis on the angular momentum balance applied to the investigated cross-sections of the machine. For this analysis, an experimental campaign involving 2D Laser Doppler Velocimetry (LDV) is performed to measure the velocity field of the flow at the inlet and outlet sections of the machine. Since the optical access to perform LDV measurements is blocked close to the hub of the runners, a further analysis on the mass balance and numerical simulations are performed to complete the velocity profiles and to evaluate the machine performance. The combination of numerical and experimental methods grants a full study on the operating condition of the micro-turbine and strengthens the results achieved. The results back up the best operating condition of the machine for different discharges and support further improvements of the runner blades shape.

2018

Cavitation surge modelling in Francis turbine draft tube

Sébastien Alligné, François Avellan, Christophe Nicolet

Francis turbines may experience cavitation surge phenomenon in the draft tube inducing large pressure fluctuations which can jeopardize the hydraulic system integrity. To predict this phenomenon, a one-dimensional draft tube model is derived from flow momentum and continuity equations including the convective terms that are not considered in the existing models. A parametric analysis of the draft tube model is carried out to investigate the influence of parameters on the cavitation surge onset identified by the hydraulic system stability. It is shown that convective terms have a stabilizing influence modifying stability limit prediction driven by the divergent geometry modelling of the draft tube.

Taylor & Francis Ltd2014