Computational Study of Hydraulic Accumulators
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The scope of this project is to make a CFD model to be used for getting a betterunderstanding of accumulator discharge. To be able to establish the models credibility isthere a need for validation of the models developed. First a model of one accumulator isto be validated by use of an experimental project as well as an analytical approach. Thismodel is then to be adapted to a system of two accumulators in series to be studied andvalidated by a theoretical equation developed.The literature review reveal that the study of accumulator discharge for applicationsfor the oil industry is not a area were many articles is presented, which makes the scope ofthis thesis more interesting.The first case studied is a single bladder-type accumulator, which is discharged throughthree different outlet areas and has an internal volume of 4 l, with a pre-charge pressure of2 bar. The physical model developed is validated by experimental data, and a theoreticalapproach to establish the models credibility. The average discrepancies obtained fromthe results was below 12.56% for all cases modeled. These results shows a high levelof agreement to the various validation points, which leads to significant credibility of thephysical model developed. This model is then to be adapted to the following cases in thisstudy.The second case studies discharge of a set of two 40 l accumulators placed in serieswith different pre-charge pressures, but equal charge pressure. The case studies the effectof changing the ambient temperature, outlet area of the discharge nozzle, and different outletpressures (backpressure). The obtained results shows that the effect of various ambienttemperature will not have a significant impact on the discharge pattern, but by changing therestrictions in the outlet nozzle the profiles obtained showed great deviation from the basecase computation. Where the variation of outlet area of the nozzle had a bigger impacton the discharge than by changing the backpressure in the system. An observation fromthis case shows that the pressure drop in the accumulator with the lowest pre-charge had arapid pressure drop in the first part of the discharge cycle. This pressure drop is caused bythe flow pattern out of the given accumulator.The last case studied is a similar case as the one above, but with accumulator volumesof 10 l each. In this case the effect of changing the pre-charge order, as well asthe backpressure was studied. The results obtained from this study shows that changingthe pre-charge order will provide a more constant pressure delivery without a rapid pressuredrop in the system. This will result in a more stable and predictable flow out of thehydraulic system studied. Even when changing the restrictions in the outlet nozzle, theresults shows a more stable flow out of the system, with similar pressure profiles.