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Vortex-induced vibrations (VIV) of an elastically supported circular cylinder (of diameter D) undergoing a wall interference are investigated for a mass-damping ratio 0.31, Reynolds numbers 1.77 × 103–1.24 × 104, and wall-cylinder gap height ratios e* = e / D = 0.1–1.6. Measurements of vibration responses and vortex shedding frequencies are done using a laser vibrometer and a hotwire anemometer, respectively, while particle image velocimetry techniques are employed to capture flow fields. This investigation aims to assimilate the effect of e* on vibration response, frequency response, VIV range, quality factor of VIV, added mass, added damping, lift force, and flow structure. A smaller e* is observed to increase the added mass, reduce the maximum vibration amplitude, and shorten the VIV range while enhancing the quality factor of VIV. The increase in added mass and the decrease in the maximum vibration amplitude in the VIV range are dramatic when e* is decreased from 0.6. Decreasing e* significantly impacts the flow structures and vortex shedding modes, resulting in intensified asymmetry in pressure distributions. The interference between the wall and the cylinder is further reflected by increasing time-mean lift forces and decreasing fluctuating lift forces with decreasing e* < 0.6. • Vortex-induced vibrations of a circular cylinder undergoing wall interference are investigated. • A smaller gap spacing ratio increases the flow-induced added mass and quality factor. • Interference between the cylinder and the wall is strong when the gap spacing ratio is less than 0.6. • A smaller gap spacing ratio reduces the time-mean stagnation pressure. [ABSTRACT FROM AUTHOR]

Abstract: Numerically simulated results are presented for a family of rectangular cylinders (placed parallel to a wall and subjected to a uniform shear flow) with aspect ratios r ( with height a and width b) ranging from 0.1 to 1.0 (square cylinder) to gain a better insight into the dependency of the aerodynamic characteristics on the operational dimensionless parameters, namely aspect ratio r, gap height L and Reynolds number Re. The governing unsteady Navier–Stokes equations are solved numerically through SIMPLE algorithm with the QUICK scheme for convective terms. The critical Reynolds numbers at which an alternating vortex shedding commences from each of the rectangular cylinder are specified for different gap heights. A special attention is paid to search a rectangular cylinder of suitable thickness to produce the stronger vortices in the wake. The present numerical results are certified with some previous numerical and experimental findings. [Copyright &y& Elsevier]

There is a strong gap flow exists between the pump rotor tip and the inside of the duct of the pump jet propulsor. To predict the hydrodynamic performance of a pump jet propulsor more accurately, considering the influence of fluid viscosity in the gap area, a gap flow model suitable for a pump jet propulsor is proposed. Through an analysis of the hydrodynamic performance of the pump jet propulsor, it is determined that it is optimal for the gap height to be 0.98–1.0 times of the complete gap height, Additionally, it is verified that the flux coefficient (C Q) range of 0.8–0.84, which can accurately simulate the energy loss of the fluid at the gap flow, is reasonable. Moreover, through a comparative analysis of the hydrodynamic performance, pressure, and circulation distribution of the pump jet propulsor, it is found that, when the influence of the gap flow model is considered, the wall pressure and circulation distribution of the rotor blade and duct are more consistent with the calculation results of viscous flow. In addition, the introduction of the gap flow model only improves the prediction accuracy of the hydrodynamic performance of the pump jet propulsor. • The gap flow model can improve the prediction accuracy of the hydrodynamic performance of pump jet propulsion, especially the greatest impact on the improvement of duct performance. • This article showed that when the gap flow model height was within the range of 0.98–1.0 times the full height, the calculation result converged. • The calculation result of the selection of the flux coefficient indicated that the flux coefficient selection range of 0.8–0.84 was reasonable and could truly reflect the energy attenuation at the gap flow of the pump jet propulsion. • The gap flow model truly reflects the circulation and pressure distribution of the rotor blade as well as the pressure differential force distribution between the blade surface and back of the blade. [ABSTRACT FROM AUTHOR]