Combining Flow Losses at Circular T-Junctions Representative of Intake Plenum and Primary Runner Interface

The interface between a plenum and primary runner in log-style intake manifolds is one of the dominant sources of flow losses in the breathing system of Internal Combustion Engines (ICE). A right-angled T-junction is one such interface between the plenum (main duct) and the primary runner (sidebranch) normal to the plenum's axis. The present study investigates losses associated with the combining flow through these junctions, where fluid from both sides of the plenum enters the primary runner. Steady, incompressible-flow experiments for junctions with circular cross-sections were conducted to determine the effect of (1) runner interface radius of 0, 10, and 20% of the plenum diameter, (2) plenum-to-runner area ratio of 1, 2.124, and 3.117, and (3) runner taper area ratio of 2.124 and 3.117. Mass flow rate in each branch was varied to obtain a distribution of flow ratios, while keeping the total flow rate constant. The total flow rate was also varied to examine the effect of Reynolds number on the flow losses. All three parameters, including the interface radius, the runner area ratio, and the taper area ratio, were found to significantly affect the magnitude of flow losses through the junction. Loss coefficients were found to be relatively insensitive to Reynolds number. A subset of the results was also compared with the earlier research.