Shape Optimization Design Of Siphon Channel Based On Computational Fluid Dynamics

Siphon is a common flow phenomenon. Having the advantage of convenient acquisition method for power only by altitude difference, the siphon technology is widely used in engineering. It is very meaningful to study the shape optimization design methods of siphon channel. The current researches are mainly focused on the application of siphon without sufficient insight in the theory of unsteady siphon flow. In addition, the research about optimization design on unsteady flow has just started, which is difficult in shape optimization design. Considering the situation mentioned above, this dissertation makes the further studies on the basic theories, and the analysis of flow characteristic and siphon-generate in unsteady siphon based on computational fluid dynamics (CFD), and the method capturing the geometry of flow channel based on reverse engineering (RE), and the shape optimization design and experimental verification of complex siphon channel using performance indexes presented in this dissertation, and the optimization methods of complex siphon using Artificial Neural Network (ANN). The main contents and productions of this dissertation are as follows.1. Study on the CFD model for siphon research and the conditions of siphon-generate.Based on the analysis of the limitation on traditional research methods of siphon, the concept of unsteady siphon was defined, which guiding the selection of CFD models. Furthermore, the qualitative analysis of siphon was performed using Bernoulli equation on the condition of steady hypothesis. Results show that the Bernoulli equation can but used to the qualitative analysis of siphon and the quantitative analysis on unsteady siphon should be carried out using CFD method. It is presented that in the four conditions of siphon-generate (gravitation, pressure, geometry parameter and flow regime), the pressure is the necessary condition. The results also show that the flow regime is the excitation condition generating siphon, which indicates that a closed water column or a local full pipe flow should impel siphon- generate. Finally, the piston effect in siphon was presented. The conclusions above lay a foundation on unsteady siphon research.2. Study on the characteristic of unsteady siphon and siphon-generate.The geometry model and CFD model were constructed to investigate the flow characteristic of unsteady siphon. As an example, the process of siphon-generate on filter which usually used in engineering was studied. The researches have confirmed the three characteristics (flow reime, velocity field, pressure field) of unsteady siphon and indicated that both the max average velocity and pressure drop in unsteady siphon could be effectively controlled by adjusting the length of outlet pipe. It is also confirmed that the closed water column formed in flow is the key of siphon-generate, which could induce piston effect and could impel a globe full pipe flow by pumping out air.3. Study on the method capturing the shape of complex siphon channel and the form feature.The method capturing the shape of complex siphon channel on water closet (WC) was studied. The results show that the reverse engineering (RE) and computer aided design (CAD) can be used to build accurate CAD model for simulation and optimization design. The form feature analysis indicated that the keys of shape optimization design of siphon are diameter of flow channel, angleαandβ, water seal and the contract region. The curvature of siphon channel should be design to be smoothing to reduce the resistance in flow.4. Study on optimization design methods of complex siphon based on CFD.The CFD model verified by Particle Image Velocimetry (PIV) experiments was constructed and applied to predict the velocity field and pressure field in siphon. The predicted value combined with several performance indexes was used to studied the effects of contractive section, elevation angle (α) and the length (L) in outlet on siphonage. The CFD model was proved to be accurate in simulating the flow field in complex siphon. It was found that the siphon could be obviously influenced by contractive section,αand L. The design with smooth shape andαof 39°and L of 227 mm have improved the efficiency of siphon, which reduced the water consumption of WC from 6.0 to 5.0 liter. Results also indicated that the pressure drop could be the best index to assess the unsteady siphon flow.5. Study on optimization design methods of complex siphon based on Artificial Neural Network.Using the samples from CFD, the Artificial Neural Network (ANN) models were constructed with inputs of geometry and output of cumulative pressure drop. Comparing Levengerg-Marquardt ANN (L-M ANN) and Bayesian ANN built after network structure optimization, it is found that the first one is good at fitting training samples and the last one has more capability on generalization performace. The best structure of L-M ANN is proved to be 2-4-1 and in Bayesian ANN the effective number of parameters is 3.67967. Based on the simulation of Bayesian ANN, the best bend radius R and diameter D in outlet were found to be respectively 80 mm and 45 mm. An optimal design framework based on CFD and ANN was constructed to provide reference to optimization design of complex siphon.6. Study on experimental system of optimization design of complex siphon.The experimental system used to verify optimization design was constructed in allusion to optimization design of complex siphon. The PIV technique was used to validate CFD model. An experimental set up which can produce most shape of siphon was developed based on the theory of similarity and used to examine the performance of different siphon channel, provding refference to the experiment researches on abnormity flow channel. Based on modern design methodes, an experimental set up of water closet was designed and proved to be convenient to siphon test and water saving test of WC, avoiding the time consuming and laboursome methods by modifing mould. The water-saving test proved that the optimization design method in this dissertation is effective to shape optimization design and improvging siphon.