Craig Meskell

The effect that a splitter plate placed in the wake behind a bluff body has on the vortex-induced vibrations (VIV) is well recognised in the literature. This study explores whether similar effects are caused by long cantilevered extensions found on some bridge decks. The analysis employs two-dimensional Reynolds-averaged Navier–Stokes equations, prescribed motion computational fluid dynamics simulations coupled with the energy balance approach to investigate the VIV response of a set of bridge decks with varying overhang lengths. It was found that with increasing overhang length, the displacement amplitude due to vortex shedding drastically decreased. The studied deck sections exhibited a reduction of 75% in the maximum displacement amplitude when compared to the section without the overhang. A similar decrease was observed in the lock-in region width. For the sections with longer overhangs, oscillations in the wake characteristic of motion-induced vortices have been observed. These oscillations occurred at larger displacement amplitudes than those related to Karman vortex shedding by a factor of 4.5 and occurred only after an initial sustained perturbation in the displacement amplitude. Finally, the sections with longer overhangs displayed higher susceptibility to the changing Scruton number, highlighting the importance of modelling the correct damping level when committing to wind tunnel tests.

Wind tunnel tests are still the state-of-the-art method for evaluating the aerodynamic behaviour of new and existing bridges. However, these tests can significantly increase the cost of the design stage of a project. While computational fluid dynamics (CFD) has been used in bridge engineering in the past decade, it is not routinely used in design. Most of the published work analyses streamlined deck sections, while bluff (aerodynamically more complex) sections are neglected. This paper explores the accuracy and practical applicability of CFD models when applied in bridge design industry for a typical bluff bridge deck. The models were of such size that a desktop workstation could provide sufficient computational power while delivering results sufficiently fast. It was found that two-dimensional Reynolds-averaged Navier–Stokes (2D RANS) models can deliver the static force coefficients and the vortex-induced vibration response. Three-dimensional models did not provide improved results; however, including a representation of the deck barrier is essential, although it can be simplified if the gross blockage is comparable to the target geometry. The fluid–structure interaction model predicted the vortex-induced vibration lock-in range, but the oscillation amplitude was overestimated by approximately 40%. For a parametric study of the structural damping, a prescribed motion model provided results in a computationally lighter manner.

A promising class of devices for ocean wave energy conversion is called the oscillating water column in which the wave power is transferred to an airflow that rotates a turbine. A closed cycle power takeoff (CCPTO), in which air is forced through two valves and a turbine, has two main benefits for such a system: it allows a unidirectional turbine, and it smooths the large variations in pressure due to irregular (i.e., polychromatic) seas. This paper presents the design of a CCPTO for a shore-based installation, with particular attention paid to the turbine. The entire system is simulated with a reduced order model for a range of sea states to estimate the operating conditions of the turbine. It is found that the pressure drop range is modest but strongly dependent on the tide and sea chamber geometry. The geometry of the turbine is initially developed with a 1D preliminary design of the blades and then the turbine performance is analysed and the design is refined using Reynolds Averaged Navier–Stokes simulations. The design process is conducted based on the geometry and the sea climate of a real-life wave energy installation located in Mutriku (Spain). A turbine that displays efficient performance over a wide range of sea states is obtained. The overall performance of this turbine as part of the entire CCPTO system is assessed and leads to an energy output of ∼1500 kWh for one month in sea conditions at Mutriku wave power plant in Spain. It is concluded that the CCPTO deserves further development in any fixed oscillating wave column system.

The effect of the axial gap on the energy consumption of a single-blade wastewater pump (Sulzer XFP PE-2 150E CB1.1) is assessed using unsteady Reynolds-averaged Navier–Stokes simulations with ANSYS Fluent. The numerical model was compared to experimental data with a nominal design configuration (i.e. gap size) to provide confidence in the modeling approach. The global performance of the pump was evaluated in terms of pressure-discharge, torque, and efficiency for a range of volumetric flow rates (110 m³ċh⁻¹ to 254 m³ċh⁻¹) and gap sizes (0.3 mm to 1.15 mm). While it is found that the power consumption at a given flow rate is reduced with increased gap, this is at the expense of a drop in outlet pressure, and hence the efficiency of the pump drops significantly. At the largest volumetric flow rate considered (254 m³ċh⁻¹), the sensitivity of the efficiency to the gap size is −13.5%ċmm⁻¹ and the sensitivity of the reduction in mechanical power consumption to gap size is 0.58 kWċmm⁻¹. These results emphasize the importance of active maintenance during the lifetime of a wastewater pump to avoid a reduction in the energy performance caused by increased gap size.

A study of the surface pressure distribution of a cylinder in a deformed rotated triangular tube array with pitch-to-diameter ratio of 1.375 has been performed. This work was motivated by the failure of steam generators in San Onofre Nuclear Generating Station (SONGS) in Southern California, which occurred as a result of fluidelastic instability in the streamwise direction. This particular failure occurred in the U-bend region of the steam generators. The presence of anti-vibration bars (AVB) in this region prevent the tubes from experiencing fluidelastic insatiably (FEI) in the transverse direction but offer little support in the streamwise direction. This study analyses the streamwise direction vibration of the tubes in the U-bend region using experimental data and a simplified quasi-steady model. Surface pressure data was gathered in a draw down wind tunnel for a range of flow velocities using an instrumented cylinder with 36 pressure taps around the circumference of the cylinder at midplane. The instrumented cylinder was mounted in the 4^th and 6^th rows of the tube array. The effect of streamwise displacement of up to ±10% of the instrumented tube and its neighbours was investigated. Although bi-stable flow was detected, only the forces in the lift direction were substantially affected. The displacement dependent drag forces acting on the instrumented cylinder were determined by integrating the pressure distributions with respect to angle. Hence the coupled fluid stiffness matrix could be assembled for each flow velocity studied. The effect of Reynolds number was also investigated for a number of scenarios.