Numerical analysis for force at embedded end of sand barrier under wind loads

Abstract: Inserted depth is an important parameter in sand fence engineering. In order to provide a theoretical support for inserted depth of sand fence, the sand fence with different porosity was studied by using LES method. Five kinds of sand fence were selected as the research objects with the porosity of 0, 20%, 40%, 60% and 80%. The height of sand fence was 50 mm. Boundary condition was of great importance to the simulation of the flow structure around the sand fence, the large eddy model (LES) was employed as the turbulence model. The gas phase had been simplified with the influence of sand particles ignored. It was treated as incompressible gas, and its flow was assumed to be in transition state. The velocity at inlet of calculation domain followed the logarithm distribution and the friction velocity was 0.5 m/s. The SIMPLIC method was employed for flow field prediction. Ten layers were arranged near wall and the height of the first layer was 0.01 mm, and yplus was less than 1. The top boundary of calculation domain was slip wall boundary, and the bottom was nonslip wall boundary. The turbulence numerical results for sand fence with the porosity 0 were compared with the experimental results of a similar study that was conducted in a blowing sand wind tunnel at the Key Laboratory of Desert and Desertification of Chinese Academy of Sciences. The particle image velocimetry (PIV) was employed to determine mean velocity and the turbulence fields were calculated by the velocity. The numerical model was well verified. Then, the variation of bending moment and shear force with porosity and the flow structure around the fence were analyzed. The results showed that the bending moment and shear force on the embedded end of sand fence without pores was much higher than that for the sand fence with pores under the sudden air flow with same velocity, and its maximum bending moment and shear force on the embedded end were 2 and 1.5 times of that with 40% porosity, and were 16.5 and 14.45 times of that with 80% porosity. The maximum bending moment and shear force on the embedded end decreased with increasing porosity. The bending moment and shear force decreased greatly under continuous wind forces. When the porosity of sand fence was 0, its maximum bending moment and shear force on the embedded end was about 9.4 and 6.9 times of the mean under the continuous wind forces. When the porosity of sand fence was 80%, its maximum bending moment and shear force on the embedded end was about 2.3 and 2.5 times of the mean under the continuous wind forces. The size of the main vortex behind the sand fence decreased with the increase of the porosity. Large eddy had a stronger resistance to its movement change, causing the lager bending moment and shear force at the embedded end of sand fence with 0 porosity compared to the sand fence which has porosity. When the porosity was less than 50%, there was no obvious main vortex structure in the rear of the sand fence and its flow structure was similar to that for the single plate. The flow structure around the sand barrier with closed porosity had similar appearance, and it could be divided into 2 groups by the porosity of 50%, and the stress in each of the group had the similar varying characteristics.