Experimental validation of RANS and DES modelling of pipe flow mixing

Velocity and concentration profiles in a pipe flow was measured downstream of injection of a tracer gas at the pipe centerline. The pipe had diameter D = 0.2 m and two Reynolds numbers, Re = 50000 and Re = 100000, were used. The profiles were measured at positions 5 D and 10 D downstream of the injection point. Three different industrial relevant geometrical configurations were used upstream of the injection point: a 10 D straight pipe, two 10 D pipes connected with a 90° bend or a straight 10 D pipe with a mixer plate mounted 2 D upstream the injection point. In all cases, air entered the pipe from the surroundings through a sharp-edged inlet. This represents many practical flow applications and is also a well-defined inlet condition that generates turbulence in the vena contracta in the inlet. The measurements were compared to predictions from three different computational models: two with Reynolds Averaged Navier-Stokes (RANS) and one with high-resolution Detached Eddy Simulation (DES). For RANS, the k- ω SST model had difficulty in predicting the turbulence created by the vena contracta . The k- ε model performed better, but gave completely wrong results for the inlet with a pipe bend. The DES was successful for all cases with only minor deviations from measurements.