Pressure losses at bends and junctions

Abstract

A series of computational fluid dynamics (CFD) simulations and experiments were performed to study the flow in bends and junctions, to determine whether the CFD simulations could yield accurate pressure loss data for input into a one-dimensional engine simulation code. The experiments were carried out on a steady flow rig, and three bends with varying degrees of curvature, a T-junction, and a Y-junction were tested. The experiments covered Reynolds numbers from approximately 19800 to 126200, and the pressure loss data was presented in two forms: equivalent length, le/d, and loss coefficients. The loss coefficient data showed a good correlation with reliable published data, but was prone to scatter, as has been reported in the literature. However, the le/d analysis produced consistent data, which showed clear trends. An empirical equation
has been developed to calculate the pressure drop due to the separation of the flow in an elbow bend. The addition of this equation to an existing equation, used to calculate the pressure drop due to friction, gives the total pressure drop in an elbow bend.

The experimental pressure measurements were used to provide boundary conditions for the CFD simulations. The k −, realizable k −, k −ω and Reynolds stress turbulence models were studied. The simulations predicted accurate pressure loss data for the bends with a moderate radius of curvature, where no flow separation occurred, and the combining flow configurations of the junctions, where favourable pressure gradients were present. However, for the bend with the tightest radius of curvature and for the dividing flow junction configurations, flow separation and strong adverse pressure gradients conspired to have a detrimental effect on the accuracy of the predicted pressure losses. The Reynolds stress turbulence model (RSM) yielded the most accurate
correlation with the experimental pressure loss data.

Date of Award	2005
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Geoff Cunningham (Supervisor)