Study On Solution Of The Clamping Wall Duct To Adaptation Of Civil Engineering Factors Of Baihetan Hydropower Station

Energy is the material resource on which human society depends,and its supply and security play a desicive role in the overall development of China’s modernization.There are abundant hydropower resources in China,which have advantages of clean-liness and renewability.Therefore,hydropower construction in China has entered a period of rapid development in recent years.Hydropower plants often use underground type,which has the advantages of high structural stability,safety and reliability.The function of the ventilation and air-conditioning system is to ensure safe and efficient operation environment of the personnel in the plant and the healthy and comfortable working environment.The clamping wall duct is an important part of the ventilation and airconditioning system of the underground cavern group.It is distributed in the main undeground workshop and the main transformer room where large amount of residual heat and humidity should be eliminated.Due to the speciality of its installation position,the clamping wall duct is easily affected by the civil engineering factors such as the uneven rock wall and anchor cable,which have adverse effects on ventilation,that the actual air volume can not meet the design requirements according to the previous engineering experience,thus affecting the air quality in the plants.Therefore,it is necessary to study the flow characteristics of the clamping wall duct and the solution to adapting the civil conditions,which could provide basis for the construction of this project and reference for similar projects in the future.This paper takes the design of ventilation and air conditioning system of Baihetan Hydropower Station as an example,and summarizes the information such as the form and size of the clamping wall duct.Combined with the information provided by the civil engineering profession,the three projection position relationships of the anchor cable and the clamping wall duct are summarized as follows: the anchor cable is projected in the duct;the anchor cable is projected on the boundary of the duct and the anchor cable is projected outside the duct.In view of the duct affected by the uneven rock wall and anchor cable,two solutions are proposed innovatively: the flattening scheme to reduce the thickness of the duct in derection b1 and the hollowing scheme to "perforate" the part where the clamping wall duct and the anchor cable coincide.According to the similarity theory and the Reynolds model law,two typical sizes of ducts are selected for the similar model experiment.The feasibility of the flattening scheme is explored through model experiments and computer numerical simulation.At the same time,the installation position of fans in the clamping wall duct in the main underground workshop is also studied.In the model experiments,the duct of the original design in the main underground workshop with a maximum aspect ratio of 8 is tested with a similar scale of 1/2.The fans are installed in the original design position,in the extended straight pipe section 2de from the original design position,and in the extension straight pipe section 7.2de from the original design position.The fans are selected five operating conditions to open 4 sets of 220 V,open 3 sets of 220 V,open 2 sets of 220 V,open 4 sets of 160 V and 4 sets of 125 V.The test contents are mainly the section velocity and static pressure,so as to calculate the system air volume and the local resistance coefficient of the elbow in each fans working condition respectively.Using the flattening scheme,the b1 direction is flattened by 20%,30% and 40% respectively.The same method is used to test and calculate the system air volume and the local resistance coefficient of the elbow under various fans working conditions.Meanwhile,a model test with a similar scale of 1/2 is applied to the original design with the most used width to height ratio in the main transformer room,and the duct after 40% flattening in the b1 direction is tested.Then the model experiments results are compared with the CFD numerical simulation results to verify the reliability of the numerical calculation model,and then the simulation of the other sizes of the ducts without the model test is carried out.The results show that after the flattening scheme,resistance values of the clamping wall ducts do not change much.In most cases,the air volume coefficient can be maintained between 0.9 and 1.1,and the flattening scheme is feasible.The fans of the wall clamping wall duct in the main underground workshop are designed and installed near the outlet bend of the duct.Compared with the fans installed on the extended straight pipe section from the outlet and 2de and 7.2de from the original design position,the difference in system air volume is small and the designed installation position is feasible.In brief,this paper proposes a solution to flatten the b1 direction of the clamping wall duct to adapt to the influence of civil engineering factors such as the uneven rock wall and anchor cable in the underground power station.Through the similar model tests and CFD numerical simulation,the feasible reasons of flattening scheme are analyzed,which can provide guidance for the future design of clamping wall duct.