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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 19 Sep 2021 01:11:46 GMT2021-09-19T01:11:46ZCavitation in a hydraulic system: The influence of the distributor geometry on cavitation inception and study of the interactions between bubbles
http://hdl.handle.net/10985/10566
Cavitation in a hydraulic system: The influence of the distributor geometry on cavitation inception and study of the interactions between bubbles
ADAMA MAIGA, Mahamadou; COUTIER-DELGOSHA, Olivier; BUISINE, Daniel
Hydraulic systems are often subjected to pressure drops, which may lead to cavitation. In systems such as power steering, hoist loads, or ventricular assist devices, distributors are generally used. Significant pressure losses can happen in a distributor due to gap and overlap, which may lead to cavitation development. However, this issue is almost never included in the conception of the distributors. In this study, the multibubble model of the modified Rayleigh–Plesset equation is applied to the rotary distributor of an oil hydraulic system. The influence of the overlap length, the gap, the rotation speed, and distributor inlet pressure on the cavitation and particularly the interactions between bubbles at cavitation inception are studied. The study highlights a critical length of the overlap; over this value, the overlap length influences significantly the cavitation duration and the void fraction. More generally, some geometrical details have a strong influence on cavitation. Optimization of these details in engine parts, taking account the occurrence of cavitation, would be an appropriate solution to reduce its effects. The study also demonstrates that the growth of small bubbles may be delayed by the interactions with the nearby bigger ones, even if the ambient pressure is lower than their theoretical critical pressure. They eventually collapse at the first moments of the cavitation development. However, if the ambient pressure drops further, that is, beyond a critical pressure, a small bubble gains enough inertial energy to overcome these interaction phenomena and thus to grow. The growth of small bubbles increases the interactions between bubbles and slows down the growth of nearby bigger ones. The results show that the interactions between bubbles are of primary importance in the first moments of the cavitation development, which suggests that they should be taken into account in the definition of the critical pressure.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/105662015-01-01T00:00:00ZADAMA MAIGA, MahamadouCOUTIER-DELGOSHA, OlivierBUISINE, DanielHydraulic systems are often subjected to pressure drops, which may lead to cavitation. In systems such as power steering, hoist loads, or ventricular assist devices, distributors are generally used. Significant pressure losses can happen in a distributor due to gap and overlap, which may lead to cavitation development. However, this issue is almost never included in the conception of the distributors. In this study, the multibubble model of the modified Rayleigh–Plesset equation is applied to the rotary distributor of an oil hydraulic system. The influence of the overlap length, the gap, the rotation speed, and distributor inlet pressure on the cavitation and particularly the interactions between bubbles at cavitation inception are studied. The study highlights a critical length of the overlap; over this value, the overlap length influences significantly the cavitation duration and the void fraction. More generally, some geometrical details have a strong influence on cavitation. Optimization of these details in engine parts, taking account the occurrence of cavitation, would be an appropriate solution to reduce its effects. The study also demonstrates that the growth of small bubbles may be delayed by the interactions with the nearby bigger ones, even if the ambient pressure is lower than their theoretical critical pressure. They eventually collapse at the first moments of the cavitation development. However, if the ambient pressure drops further, that is, beyond a critical pressure, a small bubble gains enough inertial energy to overcome these interaction phenomena and thus to grow. The growth of small bubbles increases the interactions between bubbles and slows down the growth of nearby bigger ones. The results show that the interactions between bubbles are of primary importance in the first moments of the cavitation development, which suggests that they should be taken into account in the definition of the critical pressure.A new cavitation model based on bubble-bubble interactions
http://hdl.handle.net/10985/15141
A new cavitation model based on bubble-bubble interactions
ADAMA MAIGA, Mahamadou; COUTIER-DELGOSHA, Olivier; BUISINE, Daniel
In this paper, a new model based on bubble-bubble interactions is proposed for cavitation. Unlike the well-known existing models (Rayleigh-Plesset, Gilmore), which are derived from the local balance equations in the vicinity of a single cavitation bubble, the present approach is based on the mutual interaction between two spherical bubbles of different sizes. The mass and momentum conservation equations, coupled with the local flowdivergence, lead to two equations for the evolution of the bubble radii and one equation for the local pressure. The bubble size variations predicted by the model are found in close agreement with the previous experimental data reported by Ohl [“Cavitation inception following shock wave passage,” Phys. Fluids 14(10), 3512–3521 (2002)]. The distinct radii of bubbles located close to each other, as well as the premature collapse of small bubbles during the initial stage of cavitation inception, are correctly reproduced by the model. The results generally show that bubble/bubble interactions play a primary role in the physics of cavitation inception, which is a preponderant phenomenon in cavitation-induced noise and erosion. The influence of the size of the nuclei on these interactions is discussed. During the expansion phases, the variations in the local flow divergence only slightly affect the growth of the big nuclei, which is mainly governed by their interaction with the neighboring bubbles, while it triggers the expansion of the small nuclei. Conversely, in the compression phase, the behavior of the bubbles is not influenced anymore by the initial size of the nuclei. It is also shown that large amplitude pressure variations resulting from the multiple collapses of small bubbles should be taken into account, in addition to the ambient pressure evolution, to calculate the instantaneous local pressure in the liquid and eventually evaluate the flow aggressiveness and the resulting erosion.
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10985/151412018-01-01T00:00:00ZADAMA MAIGA, MahamadouCOUTIER-DELGOSHA, OlivierBUISINE, DanielIn this paper, a new model based on bubble-bubble interactions is proposed for cavitation. Unlike the well-known existing models (Rayleigh-Plesset, Gilmore), which are derived from the local balance equations in the vicinity of a single cavitation bubble, the present approach is based on the mutual interaction between two spherical bubbles of different sizes. The mass and momentum conservation equations, coupled with the local flowdivergence, lead to two equations for the evolution of the bubble radii and one equation for the local pressure. The bubble size variations predicted by the model are found in close agreement with the previous experimental data reported by Ohl [“Cavitation inception following shock wave passage,” Phys. Fluids 14(10), 3512–3521 (2002)]. The distinct radii of bubbles located close to each other, as well as the premature collapse of small bubbles during the initial stage of cavitation inception, are correctly reproduced by the model. The results generally show that bubble/bubble interactions play a primary role in the physics of cavitation inception, which is a preponderant phenomenon in cavitation-induced noise and erosion. The influence of the size of the nuclei on these interactions is discussed. During the expansion phases, the variations in the local flow divergence only slightly affect the growth of the big nuclei, which is mainly governed by their interaction with the neighboring bubbles, while it triggers the expansion of the small nuclei. Conversely, in the compression phase, the behavior of the bubbles is not influenced anymore by the initial size of the nuclei. It is also shown that large amplitude pressure variations resulting from the multiple collapses of small bubbles should be taken into account, in addition to the ambient pressure evolution, to calculate the instantaneous local pressure in the liquid and eventually evaluate the flow aggressiveness and the resulting erosion.Interactions by exchange of volume between two spherical bubbles
http://hdl.handle.net/10985/10568
Interactions by exchange of volume between two spherical bubbles
ADAMA MAIGA, Mahamadou; COUTIER-DELGOSHA, Olivier; BUISINE, Daniel
In this paper, by using the system potential of two bubbles and with a special interest in the interaction by exchange of volume and without exchange of mass, a system of equations governing the evolution of two bubbles is proposed. This two-bubble model shows terms that do not appear in the models of interaction between bubbles. The twobubble model is compared with the modified Rayleigh–Plesset equation and a validation with the experimental study of Ohl [2002] is presented. The numerical results show that, on one hand, the development of small nearby bubbles can slow down the evolution of the biggest local one, while their disappearance can favor its growing. Furthermore, in the case of two bubbles in particular, the small bubble exchanges volume with the big one during their evolutions. On the other hand, contrary to the modified Rayleigh–Plesset model, the two-bubble model predicts appearance and disappearance of small bubbles in the neighborhood of the big bubble as it is observed in the experimental study of Ohl [2002]. The present findings show in particular that the interaction by exchange of volume can be very important in the cavitation born phase and it is necessary to take into account the interaction between bubbles as well as the disappearance of small ones on the evolution of the biggest local bubble. Also, this two-bubble model predicts an exchange of volume between both bubbles equal to zero when they are perfectly identical.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/105682014-01-01T00:00:00ZADAMA MAIGA, MahamadouCOUTIER-DELGOSHA, OlivierBUISINE, DanielIn this paper, by using the system potential of two bubbles and with a special interest in the interaction by exchange of volume and without exchange of mass, a system of equations governing the evolution of two bubbles is proposed. This two-bubble model shows terms that do not appear in the models of interaction between bubbles. The twobubble model is compared with the modified Rayleigh–Plesset equation and a validation with the experimental study of Ohl [2002] is presented. The numerical results show that, on one hand, the development of small nearby bubbles can slow down the evolution of the biggest local one, while their disappearance can favor its growing. Furthermore, in the case of two bubbles in particular, the small bubble exchanges volume with the big one during their evolutions. On the other hand, contrary to the modified Rayleigh–Plesset model, the two-bubble model predicts appearance and disappearance of small bubbles in the neighborhood of the big bubble as it is observed in the experimental study of Ohl [2002]. The present findings show in particular that the interaction by exchange of volume can be very important in the cavitation born phase and it is necessary to take into account the interaction between bubbles as well as the disappearance of small ones on the evolution of the biggest local bubble. Also, this two-bubble model predicts an exchange of volume between both bubbles equal to zero when they are perfectly identical.