Numerical Studies of Unsteady Friction in Transient Pipe Flow

In this thesis, unsteady friction in transient pipe flow is given a closer look. The common quasi-steady friction model and two one-dimensional convolution-based models, developed by Zarzycki and Vardy & Brown, are considered. A quasi-two-dimensional approach to the water hammer problem is also derived, where the pipe friction is related to the near-wall behavior of the velocity profile. The models are implemented using Method of Characteristics as a foundation for the one-dimensional water hammer equations and MacCormack’s method for modeling the velocity profile. The computational results are evaluated and verified with respect to experimental data for both laminar and turbulent flow conditions. For laminar flow it is found that the quasi-steady model gives very poor results while the other friction models considered yield results that are near identical to the experimental data. For turbulent flow the quasisteady model yields better conformance than in the laminar simulations in terms of amplitude, while an unsatisfactory prediction of the shape of the pressure waves is still obtained. The Zarzycki and Vardy & Brown models both underestimate the amplitude while providing a good approximation of the wave shape. The quasi-two-dimensional model yields good conformance with the experimental data, and when assuming a dampened eddy viscosity distribution, the results are near identical to the experimental data.