Turbulent flow in a 90 degrees pipe junction Part 1. Decay of fluctuationsupstream the flow bifurcation

A water flow at the inlet and downstream, before the bifurcation, of a 90 d egrees tee pipe junction has been investigated. The tee junction bifurcates the flow of Reynolds number 1.26 x 10(5), based on the inlet bulk velocity and a pipe diameter of 50 mm, into a branch exit-to-inlet mass flow ratio Q(1)/Q(3) = 0.5. Predictions and measurements of the streamwise component o f velocity conducted with laser Doppler anemometry compared well in general . However, the fact that the flow bifurcates downstream to 90 degrees cause s the converged solution from three models for turbulence k-epsilon, renorm alization group theory (RNG) and Reynolds stress model (RSM) to differ from each other. At the inlet the second moment normalised with respect to both the outer and inner scales of velocity, u(x) and u*, respectively, indicat e non-symmetry, whereas the profiles of the streamwise component of velocit y indicate symmetry. Downstream, close to the onset of flow bifurcation at the chamfer of the tee junction, the measured turbulence fluctuations damp down drastically within the inner and outer layers. The RSM model performs the best in reproducing the experimental data. Decay of turbulence has been observed also in U bends where measurements show typical behaviour of sepa ration. In a separate paper the characteristics of the how at the branch ex it of the tee are analysed. (C) 2000 Elsevier Science Ltd. All rights reser ved.