CFD and Experimental Investigations of Drag Force on Spherical Leak Detector in Pipe Flows at High Reynolds Number

Spherical leak detectors can detect very tiny leakage in pipelines and have low risk of blockage. In this paper the passing ability of the detector in the vertical segment of a pipe was studied using CFD simulations and experiments. The Reynolds number for the sphere exceeds 104 at the economical velocity range for oil pipelines, and there were few researches related to the hydrodynamic force on the sphere by the pipe flow at high Reynolds number. For sphere with different sizes and density, and at different flow rates, more than 100 3-D steady numerical simulations were carried out. The simulation data was verified by comparing the experimental critical velocity with that of the simulation, the results shows that they agree well with each other. The drag on the sphere is related to the flow velocity V and the diameter ratio λ. The effect of flow velocity was more significant at λ > 0.65. An empirical formula for the drag with λ and V is established for 0.2 ≤ λ ≤ 0.9, 4000 ≤ Res ≤ 54000. The passing ability of the sample detector in 8-28 inch pipelines is predicted; it shows that the detector could go through the vertical pipe under normal economical flow velocity (0.7m/s-1.5m/s) in 8 or 10-inch pipelines. A passing ability test of the sample detector was carried out in an 8-inch pipe loop The optimal range for λ (0.7~0.8) is given based on the analysis results.