Research Of All-purpose Calculating Model For Tunnel Flow Quality Of Underground Hydroelectric Power Station

Underground hydropower station generally introduce into fresh air through ventilation tunnel, traffic tunnel or other underground tunnel from outside. Owing to the thermal storage effect of the rock mass, the air would exchange heat and humidity with the rock mass of the tunnel wall. The temperature of the fresh air would go down in the summer and go up in the winter. If the exchange effect of the rock mass be properly used, the initial cost of the project and the management fee could be cut down. Nowadays, as the country promoting the energy saving projects, the deep-going research of underground tunnel thermal engineering calculation could be of much more practical significance.In this paper, carried out the following several aspects of research:①On the basis of analysis and evaluation of existing various engineering calculations and research methods, the idea of the establishment of universal model and calculation is proposed . The current engineering calculations and research methods have engineering calculations, diagrams, model experiment, CFD simulation. Although the engineering calculation methods correctly reflect the influence and basic laws to flow parameters of the physical characteristics overall,they still have some inadequacies: 1) They regard wind parameters as the harmonic changes or constant, which does not match with the actual situation. 2) They only consider the ventilation system as some intermittent ventilation work shift or a constant value, which does not match with the complexity of the actual ventilation working conditions. 3) Air condensation releases latent heat ,which has a greater impact to the flow parameters. In the calculation of condensation section of the flow parameters, Engineering calculation methods think that the tunnel wind parameters is constant, and the surface temperature is mean annual ground temperature, which does not match with the actual situation. 4) Engineering calculation methods introduce in a number of special functions, and use the way of searching chart to get through the results. However, the scope of these charts is limited, and it is easy to introduce error and reduce the accuracy of the results. Graphic method is based on the measured data, to get a experience method by analyzing and summarizing ,which is limited to the length of the duct and the wall structure when it is applied. And the method is a simplified method to summer air temperature drop, which does not reflect the changes of flow parameters of different times of the year. Experimental model have the disadvantages of a large investment and long experimental period. In order to ensure the accuracy and stability of computational, CFD simulation often use a smaller model grid spacing and time step ,which cause a long calculate time. And this kind of problem usually requires continuous calculation of several years, resulting in that the software will continuous operation several days to complete the calculation, which is clearly not in accordance with the needs of technicians. CFD simulation still have the disadvantages of tedious preparatory work, high requirements of expertise to engineering and technical personnel.Therefore, in this context, the basic idea of this project to solve the problem is that, first, to establish a all-purpose mathematical calculating model, which can conform to the actual situation of the project, and can comprehensively reflect the three conditions of the outdoor meteorological parameters, tunnel geometry and physical conditions, the ventilation condition. Then using of advanced calculation method to establish the calculation procedure for solving all-purpose mathematical model ,to avoid excessive simplification and increase the accuracy of the results and information richness. Then provide for the calculation software and the underlying database ,which are convenient to engineering and technical personnel .②To establish the all-purpose calculation model and solution of underground tunnel. The air duct will be reduced to "equivalent cylinder model", which can reduce the computational difficulty. Proposed three kinds of simplification ways, such as equivalent perimeters, equivalent area, and equivalent boundary heat convection, according to the principle of closest heat transfer with the actual air flue, to analysis and compare, get the conclusion that the"equivalent perimeters"is the most superior simplification method. Based on heat transfer theory, engineering thermodynamics's fundamental equation, using the circular cylindrical coordinate system, has established the all-purpose mathematical computation model of underground air flue flow quality of hydroelectric power station..According to the"thought of discrete solves", carries on the discrete in the time and the space, has established the complete discrete computation model, uses the dynamic algorithm which the space, the time domain carry on alternately, advance gradually to carry on the computation. The discrete of longitudinal direction is that according to the actual situation, the tunnel is divided into a number of air control unit as a distance of 10m. The discrete process uses the display array of difference. Through judging the stability of the model to get the relationship of the grid spacing△r and time step△t:△r>0.0017(△t)^0.5.To improve accuracy, the△r and△t should be reduced, but when△t is small, the unit cell can not guarantee the stability of the region, and the calculation time is long. Considering that we take△t = 300s, then,△r> 0.03m, take△r = 0.05m, which meet the requirements of stability, and calculate speed.③Dynamic computer program and application software of flow parameters of hydropower station underground tunnel have been Developed. Uses the C language to program. The program has considered fully the actual project operating condition, the air condensation phenomenon, the wall surface lining work structure and so on. Has developed the application software, this software can output in the random time flow quality and the wall surface temperature in the computing time scope, input operation simple convenient, the output data use the method which the writing, the data form, the graph unify, supplies the information to be rich. Software bring foundation database, and permission user voluntarily to perfect database information.④Using the four tunnels'measured data of Dongfeng, Nanya- river Yele, the Ming Tombs,and Ertan hydroelectric power stations to carries on the examination to the software computed result. In the time of high inlet air temperature, the error is relatively large, as about 1.8℃, which is mainly caused by measurement error, and the remaining time can guarantee error within 1℃, the results confirmed the reasonableness and accuracy of the software.⑤Analysis of the influence rule to flow quality of the outdoor air temperature, tunnel structure dimension and velocity, physical parameters of the thermal mass, ventilation working condition etc. Based on a great quantity of software calculation data, a general summer temperature drop simplified formula is obtained. And the equation was compared to the software calculation result with the relative error be controlled in 6%,which confirm the usability of this simplified formula.