Research on the mechanism and application of crystal deposition in corrugated drainage pipes

LYU Jianbing; CHEN Zuru; LI Jia; FENG LI; DONG Qinxi; WANG Hui; ZHANG Guocai

doi:10.11932/karst20250101

Abstract：The frequent clogging of drainage pipes of tunnel engineering in the limestone regions has significantly impacted the long-term operation and maintenance of tunnels.To better solve this problem,in this study,a multi-field coupled numerical model was constructed to thoroughly analyze the formation mechanisms and key influencing factors of drainage pipe clogging. In recent days,fluid simulation has become an important tool for solving such problems,thanks to the rapid development of computational power.At present,numerous simulation models have been developed to simulate pipeline scaling;however,the conditions they simulate are often far cry from the actual working conditions of tunnel drainage pipes.To be specific,most simulations of pipeline scaling are conducted under full-pipe flow conditions,while the actual tunnel drainage pipes are rarely operated under full-pipe conditions.Considering this situation,this study integrated Fick's law of mass transfer with the Navier-Stokes equations,thereby coupling fluid dynamics with chemical reaction kinetics through flow velocity.This coupling was achieved by incorporating mass transfer processes,which allowed for the determination of flow velocity and the distribution of calcium carbonate content within the pipe.Subsequently,a computational and simulation model was established for the curved boundaries of corrugated pipe by integrating an equation for calculating deposition thickness.To further enhance the model's accuracy,a combination of the phase-field method and dynamic mesh technology was employed.The phase-field method simulated the movement of the gas-liquid interface,while dynamic mesh technology simulated flow channel contraction changes due to deposition.Moreover,changes in flow channel contraction may alter the flow velocity and the distribution of calcium carbonate content within the pipe,which in turn affected the contraction of the flow channel.Additionally,to ensure smooth mesh movement,mesh smoothing conditions were set,and functions were applied at the inlet and outlet to transition the movement rate from zero displacement to a specified velocity.In terms of boundary conditions,this model adopted a turbulence model.The inner wall friction coefficient of the pipe was calculated by formulas from hydraulic design manuals.Subsequently,the inner wall friction coefficient obtained from experiments was converted into an equivalent sand-grain roughness height using the Nikuradse formula,which was then used to represent various wall conditions in the model.Given that the model involves corrugated pipes,further adjustments to the Nikuradse formula are required.From the perspective of energy conservation,the energy loss caused by corrugated pipe grooves in water flow can be divided into two parts:firstly,the energy dissipation caused by imparting rotation to the stagnant water within the grooves;secondly,similar to a smooth pipe,energy loss caused by friction along the pipe wall.This portion of energy loss is related to the length of the wall.In this model,the equivalent length of the corrugated pipe is 1.2 times that of a smooth pipe with the same length.In condition of energy dissipation,and based on a series of trial calculations,the logarithmic function with base 10 was adjusted to a logarithmic function with base 11.3.The dynamic impact of crystal formation on flow field changes under free surface conditions was successfully simulated using this method. Simulation results indicate that the model developed in this study exhibits high predictive accuracy when the inner wall friction coefficient is within the range of 0.2 to 0.3,with an overall deviation between 10％and 20％.However,when the friction coefficient is below 0.2,significant deviations occur in the simulation results,which are higher than the actual deposition results.This may be due to the need for further optimization of the coefficients in the wall functions and deposition formulas under low-friction wall conditions.Moreover,when the friction coefficient exceeds 0.3,this model becomes inapplicable due to the failure of the boundary layer,which is caused by excessively high height of equivalent sand-grain roughness. In conclusion,based on the above research findings,this study has further applied the model to simulate the actual working conditions of drainage pipes in a tunnel in northern Guangdong.By predicting the clogging time and formulating corresponding treatment plans,this study provides scientific basis and technical support for the optimal design and clogging prevention of tunnel drainage systems.