Numerical simulation of hydraulic characteristics of cyclical slit flow with moving boundary of tube-contained raw materials pipelines hydraulic transportation

Abstract: In order to solve effectively the problems of lower transport efficiency and higher utilization cost during the process of the long-distance transportation for the agricultural products, a kind of agricultural mechanical transport mode having a wide and great application prospect is proposed and known as the technique of tube-contained raw materials pipelines hydraulic transportation. The technique of tube-contained raw materials pipelines hydraulic transportation is the freight transportation mode that uses a fluid to suspend (float) and pull (drive) the pipe vehicle filled with the agricultural products from one location to another through a pressurized pipeline. According to the kinetic mechanism of the pipe vehicle, the mathematical models of the cyclical slit flow with the moving boundary under the different cyclical slit widths in the technique of tube-contained raw materials pipelines hydraulic transportation were established in this paper. The mathematical models were solved by adopting the RNG k-ε turbulent model, the 6DoF coupling model and the PISO algorithm of the commercial software Fluent. The effects of the cyclical slit width on the internal hydraulic characteristics of the flow velocity and the pressure in the cyclical slit flow with the moving boundary were obtained. At the same time, through a wide of experimental investigations, the cyclical slit flow with 4 widths of 0.025, 0.02, 0.015, 0.01 m respectively were studied by using the Laser Doppler velocimeter (LDV) when the pipe vehicle moved within the pipelines. The experiment was carried out in the parallel straight pipe section of the test piping system, whose the control flow was 50 m3/h, carrying the loading of 800 g. The flow field characteristics such as the instantaneous velocity of the pipe vehicle with the moving boundary, the average axial velocity of the cyclical slit flow, the pressure distributions through the static wall of the pipeline and the velocity distributions of several typical sections were obtained. Comparing with the numerical results and experimental results, it was shown that the simulated results and the experimental results on the instantaneous velocity of the pipe vehicle with the moving boundary, the pressure distributions and the velocity distributions of the cyclical slit flow in the technique of the tube-contained raw materials pipelines hydraulic transportation were in substantial agreement, and the maximum relative error did not exceed 5.3%, which further indicated that using the commercial software Fluent was feasible for solving the hydraulic characteristics of the cyclical slit flow with the moving boundary in the technique of tube-contained raw materials pipelines hydraulic transportation; The overall pressure of the cyclical slit flow with the moving boundary within the pipelines showed a decreasing trend at the inlet of the cyclical slit areas, an increasing trend in the central location of the cyclical slit areas and a precipitous decline trend again at the outlet of the cyclical slit areas along the static boundary of the pipeline. The near-wall pressure of the moving boundary of the pipe vehicle was slightly higher than that of the static boundary of the pipeline. With the increasing of the cyclical slit width, the range in distributions of the low-velocity areas formed by the near-wall of the moving boundary at the inlet of the cyclical slit space increased gradually. As the cyclical slit width increased, the pressure drop increased gradually at the inlet of the cyclical slit areas while the pressure drop at the central location of the cyclical slit areas decreased significantly. The hydraulic characteristics of the cyclical slit flow with the moving boundary was affected not only by the structural parameters of the pipe vehicle, but also by the flow field of the upstream and the downstream of the pipe vehicle with the moving boundary within the pipelines. The study of this paper not only improved the relevant theories of the cyclical slit flow with the moving boundary, but also provided a feasible method for further study on the hydraulic characteristics of the cyclical slit flow with the moving boundary in the technique of tube-contained raw materials pipelines hydraulic transportation.