Experimental Study of the Velocity Characteristics of an Elbow under a Pulsating Turbulent Flow

Abstract

An experimental study was conducted on the velocity characteristics of a pulsating turbulent flow in a strongly curved 90° elbow with a curvature radius ratio of R_c=2 and a circular cross-section. Experiments were conducted under the following conditions: Womersley number of α=20, mean Reynolds number of Re_ta=20000, and flow rate ratio of η=0.5. LDV (laser Doppler velocimetry) measurements were performed on the instantaneous axial and outward velocities, and the phase-averaged velocities and turbulence intensities were obtained. The primary flow fluctuated significantly, with a large bias toward the inner wall, just behind the elbow inlet, and an abrupt deviation toward the outer wall near the elbow exit. Such changes along the elbow axis were greater than those for steady flow and became evident in the latter half of the acceleration phase. In addition, the secondary flow in the section of deviation between the inner and outer wall sides increased rapidly, compared with the steady flow. Moreover, the turbulence intensities increased. The influence of the pulsation on the elbow persists downstream.