Unsteady pipe friction : formulation of efficient models and investigation of existing modeling assumptions

Applications that warrant transient flow simulation over a time scale well in excess of the wave travel time include design and analysis of complex pipe systems; identification of leaks and model parameters through the inversion of transient data; and modeling of transient related water quality problems. The reliability of results from transient simulations over a time scale larger than the wave travel time depends on the accuracy of the wall shear stress model for the case of onedimensional (1-D) models and on the validity of turbulence closure relations for the case of two dimensional (2-D) models. Existing unsteady wall shear stress formulas and turbulence closure equations for water hammer applications involve far-reaching assumptions about the turbulence behavior during a transient event. The common assumptions are: (i) the turbulence in the pipe is either quasi-steady, frozen or quasi-laminar; (ii) the turbulent relations that are derived and tested for steady flows remain valid in unsteady pipe flows; and (iii) the unsteady flow is stable and axisymmetric. The validity of existing models and their assumptions are investigated in detail in this thesis using stability theory, dimensional analysis and numerical simulations. In order to reduce the computational time and to ensure that the numerical damping do not overwhelm the physical dissipation, accurate and efficient numerical schemes for 1-D and 2-D water hammer models are also developed