LDA measurements of Reynolds stresses in a swirling turbulent pipe flow

Abstract

This study concentrates on turbulent swirling flows, which are constrained in a stationary and straight circular pipe. Aim was to determine the sole effect of swirl component and its decay on a developing turbulent pipe flow. For this purpose, velocity statistics of a pipe flow with a Reynolds number of ${\mathop{\rm Re}\nolimits} _D = U_m D/v \cong 30.000$ were measured at several downstream positions up to z/D = 17.3. The strength of inlet swirl was adjusted to the desired swirl numbers of N = 0.3 (weak) and N = 1.0 (strong). Emphasis was put on generating a solid-body rotation type of swirl while maintaining axisymmetric inlet conditions. Consequently, the determined mean velocity and Reynolds stress profiles showed almost no deviation from axisymmetry. Furthermore, non-zero Reynolds shear stresses were determined. Both findings contradict some results in the literature. Subtle increase in the magnitude of Reynolds stresses was observed as the swirl component decayed partially.