Structure- and Fluid-Borne Acoustic Power Sources in 90 Degree Piping Elbows Excited by Turbulent Flow

Abstract

The structure-borne and fluid-borne vibro-acoustic power spectra induced by turbulent fluid flow over the walls of a continuous 90 degree piping elbow are computed. Although the actual power input by the wall pressure fluctuations to the piping is distributed throughout the elbow, equivalent total powers input to various structural wavetypes (bending, torsion, axial) and fluid (plane waves) at the inlet and discharge of the elbow are computed. The powers at the elbow ‘ports’ are suitable inputs to wave-based and statistically-based models of larger piping systems that include the elbow. Calculations for several flow and structural parameters, including pipe wall thickness, flow speed, and flow Reynolds number are shown. The power spectra are scaled on flow and structural-acoustic parameters so that levels for conditions other than those considered in the paper may be estimated, subject to geometric similarity constraints (elbow radius/pipe diameter). The approach for computing the powers, which links Computational Fluid Dynamics, Finite Element and Boundary Element modeling, and efficient random analysis techniques, is general, and may be applied to other piping system components excited by turbulent fluid flow, such as U-bends and T-sections.