Analysis of condensation and secondary flows at T-junctions using optical visualization techniques and Computational Fluid Dynamics

T-junctions are employed in almost all piping systems, whenever two streams need to be merged into one duct.In some applications, the mixing between streams plays an important role for determining the performance of down-stream elements. The situation is particularly interesting for low pressure EGR junctions featured in piston engines,where warm humid exhaust gases meet cold fresh air, since the mixing of both streams can produce water conden-sation. This condensation deteriorates the integrity and performance of the adjacent compressor wheel. This workexplores the aforementioned flow configuration in a T-junction by means of a specific gas test bench that allows thecharacterization of the transversal section at the T-junction outlet, and 3D CFD simulations. Two optical techniquesare employed: laser particle image velocimetry, which is used to characterize the cross-section secondary flows, andthe planar laser-induced visualization, which is employed to obtain the condensation pattern. The experimental mea-surements are conducted at two different working points and for two different T-junction designs, being in agreementwith 3D CFD simulation embedded with a previously-developed condensation model. The work shows that the T-junction design dictates whether the air-EGR mixing is either located at a narrow interface or is performed across thewhole cross-section, which boosts the produced condensation. The techniques shown can be therefore employed tooptimize the T-junction design, which would entail a reduction ofNOX,CO2and particulate matter emissions duringengine warm-ups.