Hi Mr Rob The inlet of the pipe is split into upper and lower halves (the upper for oil, the lower for water). For both, i use the Vortex Method for Fluctuating velocity algorithm, and i put number of vortices as number of faces at the face divided by 4 (as suggested).

Actually, i was trying to run a case again, this time i switched transient formulation to 1st order implicit (instead of bounded 2nd order implicit), but still i get pressure bursts as seen in the below pic
The residuals are also seen below: (Before 30,000 iterations i was using K-Omega SST, then i switched to LES (WALE) as suggested)