Research On Cavitation In Multi-way Valves Of Construction Machinery

Multi-way valve is one of the key components of construction machinery. Its quality and performance have a great effect on the whole machinery. At present, study on multi-way valve by CFD method is just the simple and intuitive analysis of the theory. Also, the research on cavitation of multi-way valve at home is not much, and almost experiment or simple analysis of flow field. The thesis is based on multi-way valve of excavator as research object, using CFD software to research the cavitation of multi-way valve. The following research work has been done:Analyze the key factors of cavitation. According to the definition of cavitation number, the direct factors are including pressure and velocity. And the pressure and flow rate are influenced by opening area and flow coefficient. Establish different models in Gambit, simulate in FLUENT, and compute opening area in MATLAB to study the problems. Results show that, opening areas mostly influence pressure and flow rate, however, flow coefficient can be regarded as constant.Establish the three-dimensional models of multi-way valve, according to its principle and basic structure. Choose tetrahedral grid (TGrid) to mesh the models, through theoretical analysis and a large number of numerical simulation. Meanwhile, conduct intensive meshing of valve port, in order to save computing time and improve simulation accuracy.Study on pressure factors of cavitation under the condition of constant flow rate. When the valve is in the small opening position, the throttling effect is better, however, the outlet pressure of cavitation is smaller; when in the fixed position, the outlet pressure is smaller, and the minimum pressure of flow field is smaller. A new method to calculate critical outlet pressure of cavitation is presented by calculating σ, σi and Pout-Pmin.Study on velocity factors of cavitation under the condition of constant outlet pressure and fixed position. By calculating σ,σi, Pin—Pmin, Pin—Pout, find the linear relationship between Pin-Pmin and Pin—Pout. A new method to calculate the critical flow rate of cavitation is presented.