A method is proposed for computations of rotordynamic coefficients of deliberately roughened stator gas annular seals using computational fluid dynamics. The method is based on a transient analysis with deforming mesh. Frequency-dependent direct and cross-coupled rotordynamic coefficients are determined as a response to an assigned rotor surface periodic motion. The obtained numerical results are found to be in good agreement with the available test data and one-dimensional tool predictions. The method can be used as a research tool or as a virtual annular seal test rig for seal design and optimization.

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Many natural and industrial applications involve non‐Newtonian fluids w­ith high effective viscosity ratios flowing between surfaces with spatial variations in aperture. In particular, hydraulic fracturing operations often require pumping sequences of non‐Newtonian fluids with yield‐stress into a variable‐aperture fracture that initially contains water. Numerical methods for this class of problem must deal robustly with the high aspect ratio of the flow domain and large contrasts in effective viscosity while maintaining interfaces between immiscible phases. We avoid the computational burden of a fully three‐dimensional approach by introducing an aperture‐averaged analytic solution for flow of a Hershel‐Bulkley fluid between two plates. We discuss the incorporation of this analytic solution within a simulator of flow within a fracture with spatial variations in aperture. We minimize numerical diffusion through use of a hybrid Lagrangian‐Eulerian approach that naturally tracks the multiple fluid phases. We demonstrate effectiveness of the numerical method through comparison with analytic results and one‐dimensional finite difference numerical solutions. Benchmarking of the 2‐D model against a 3‐D model reveals both advantages and shortcomings of a through‐aperture averaged method. The two simulations agree on the bulk behaviour of the phases while the 2‐D model is two orders of magnitude more efficient. Comparison between predictions of the models after water injection behind the pad reveals that the 3‐D model predicts non‐uniformity across the fracture aperture. This suggests that while bulk behaviour may be well captured by the 2‐D model, improved accuracy could be obtained by introducing multiple fluid layers within each cell of the model.

Throttle valves in steam turbines often operate at very small lift positions during turbine startup. The large pressure differentials across these valves, combined with the very small openings at the valve seat, result in large pressure drops across these valves and high local steam Mach numbers. A steam turbine throttle valve operated under these conditions was found to be undergoing self-excited vibration. Stress and structural dynamic finite element analyses (FEA) were performed to identify the structural mode for the valve oscillations. A three-dimensional transient computational fluid dynamics (CFD) analysis of the valve revealed an unsteady fluid dynamics phenomenon in the pressure balancing arrangement that served as a forcing function for this vibration. Valve modifications were implemented as a result of these analyses. The improved valve has performed successfully, and the design modifications have been incorporated in other production valves.