Theoretical And Experimental Researches On Leakage Characteristics Of Water Hydraulic Annular Clearance

In21st century, people must advocate energy saving and emission reduction and use the greenenergy resources to make the environment better and to protect the future of human beingssince the survival of our species is threatened due to the resource scarcity and environmentaldeterioration. Therefore, water hydraulic technology, as a kind of green and clean fluid powertransmission technology, will be wildly used, even take the place of traditional oil hydraulictechnology. However, there is a big gap in design and manufacturing of the components ofwater hydraulic system between our county and foreign counties. The main reason, whichresults in that we lack the theories and the experiments data, so we have to depend on theexperience and oil hydraulic technology when we design and manufacture the components, isthe backwardness of the study of basic theories. This situation restricts the development of ourwater hydraulic technology. The present dissertation investigates the basic theories ofcharacteristics of the leakage of water hydraulic annular clearance by theoretical research andexperiments, and explores the characteristics and the fluxion pattern of annular gap fluid fieldto lay the foundation for solving the problems we encountered in design this kind ofclearance.Firstly, based on the normal working condition of the water hydraulic annular clearance,which is that the pressure ranging from8to14MPa, the piston diameter ranging from20to35mm, the seal length ranging from10to40mm, the clearance height ranging from0.005to0.02mm, the eccentricity, the tilt and the reciprocating (frequency of25Hz) of the piston, thethesis designs the orthogonal test to research the leakage characteristics of this kind clearancein the range of these factors’ variables. Then according to the study of basic theories ofparallel plates clearance flow, the thesis derives the formulas of flowrate under the conditionof concentric, eccentric, tilt, both eccentric and tilt, when the flow is laminar. Meanwhile, themechanism and condition of the transition from laminar flow to turbulent flow in annularclearance fluid field, the critical Reynolds’ number and the method of computing the flowrateof turbulent flow in clearance is discussed.Secondly, considering the complexity of the flow field, the CFD tool, fluent, is used tosimulate the flow field of the orthogonal test. The laminar model and the turbulent model areused for different test sets separately depending on the critical Reynolds’ number. The featherof the flow field and the rules of the flow of the annular clearance are obtained with thevisualization analysis of simulation results.At last, the test rig of the leakage characteristics of water hydraulic annular clearance wasmanufactured and the experiments of orthogonal test were carried out. In order to verify theresults of the CFD simulation and the criterion of the transition of the flow, the results of theexperiments, the CFD simulation and the computing with laminar flow equations are compared in detail. Then the method of orthogonal analysis is used to analyze the results ofCFD stimulations and experiments to obtain the law and tendency of the influence of differentfactors. Furthermore, a formula, which is suitable for calculating the leakage flowrate of theturbulent flow in a water hydraulic annular clearance, was obtained by comparing the resultsof fitting the results of simulations and experiments with the genetic algorithm.