• International Journal of Fluid Machinery and Systems
• /
• 제10권1호
• /
• pp.76-85
• /
• 2017

Wall pressure measurements and flow visualization were conducted for a 90 degree elbow with an axis curvature radius the same as its inner diameter (125 mm). Reynolds numbers 320,000 and 500,000, based on the inner diameter and bulk velocity, were examined. A deflected inflow, having an almost constant velocity slope and a faster velocity at the inside, was introduced. Ensemble averaged pressure distributions showed that no difference of normalized pressure could be found in both the Reynolds number cases. Power spectral density functions of pressures exhibited that the fluctuation having the Strouhal number (based on the inner diameter and bulk velocity) of 0.6 existed in the downstream region of the elbow, which was 0.1 larger than that of the uniform inflow case [1]. Results of numerical calculations qualitatively coincided with the experimental ones.

• Wind and Structures
• /
• 제17권4호
• /
• pp.379-397
• /
• 2013

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제13권1호
• /
• pp.163-177
• /
• 2021

Numerical simulations of the Vortex-Induced Vibration (VIV) about a large-scale flexible pipe subject to shear flow were carried out in this paper. Efficiency verification was performed firstly, validating that the proposed fluid-structure interaction solution strategy is competent in predicting the VIV response. Then, the VIV characteristics related to multi-mode and spanwise hybrid waveform about the flexible pipe attributed to shear flow were investigated. When inflow velocity rises, higher vibration modes are apt to be excited, and the spanwise waveform easily convertes from a standing-wave-dominated status to a hybrid standing-traveling wave status. The multi-mode or even multiple-dominant-mode is prone to occur, that is, the dominant mode is often followed by several apparent subordinate modes with considerable vibration energy. Hence, the shedding frequencies no longer obey Strouhal law, and vibration trajectories become intricate. According to the motion analysis concerning the coupled cross-flow and in-line vibrations, as well as the corresponding wake patterns, a tight coupling interaction exists between the structural deformation and the wake flow behind the flexible pipe. In addition, the evolution of the vortex tube along the pipe span and a strong 3D effect are observed due to the slenderness of the flexible pipe and the variability of the vortex shedding attributed to the shear flow.