Loss Coefficient of Screw Elbows in Pulsatile Flow

Abstract

Loss coefficients of the commercial 90 deg. screw elbow of Japanese Industrial Standards (JIS B 2301) whose nominal size is 11/4 in, are measured under the steady and pulsatile flow conditions. Effects of the cross-sectional area ratio of elbow to pipe and of the axial velocity distribution at the entrance of the elbow on loss coefficient are investigated in steady flows, and the appicability of Ito's estimation for elbow losses is discussed. The instantaneous and time-averaged loss coefficients are defined and evaluated experimentally in pulsatile flows. A frequency range where the turbulent quasi-steady relation for loss coefficient holds is determined on the basis of the present experimental results.