Abstract: In hydraulic fracturing operations for oil and gas extraction, high-speed turbulent flow of sand-laden fracturing fluid in buffer elbows causes severe erosion wear on the pipe wall. The complex mechanisms involved pose significant challenges for optimizing erosion resistance. To elucidate the erosion mechanism, a multi-scale prediction model (CFD-DPM-MD) coupling fluid dynamics, discrete element modeling, and molecular dynamics is developed. Key findings indicate that the primary erosion zone in the buffer elbow occurs at the intersection line. This damage is not related to particle retention but is dominantly driven by multi-angle particle collisions induced by vortices. Microscopic impact analysis reveals that collisions between solid particles and the wall surface trigger dislocation explosions when atomic stresses and kinetic energy exceed critical thresholds, leading to non-phase-transition plastic deformation and material spalling. Furthermore, while a 40° impact angle generates the largest shear strain area, a 65° impact angle creates a specific erosion morphology that increases the particle-wall contact area, ultimately resulting in more severe erosion. Consequently, effective strategies to enhance buffer elbow service life include applying high-shear-resistance erosion-resistant coatings or designing wall surfaces with specific morphologies to mitigate damage from high-impact angles.

Key words: solid-liquid two-phase, fluid dynamics simulation, molecular dynamics simulation, erosion wear