Turbulent flow in a 90° pipe junction: Part 1: Decay of fluctuations upstream the flow bifurcation

Abstract A water flow at the inlet and downstream, before the bifurcation, of a 90° tee pipe junction has been investigated. The tee junction bifurcates the flow of Reynolds number 1.26×10 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 of velocity conducted with laser Doppler anemometry compared well in general. However, the fact that the flow bifurcates downstream to 90° causes the converged solution from three models for turbulence k – e , renormalization 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, indicate non-symmetry, whereas the profiles of the streamwise component of velocity 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 separation. In a separate paper the characteristics of the flow at the branch exit of the tee are analysed.