Quantifying the spatiotemporal evolution of the turbulent horseshoe vortex in front of a vertical cylinder

Abstract

The spatiotemporal evolution of the turbulent horseshoe vortex (THV) in front of a cylinder vertically mounted on a hydraulically smooth flat-bed was physically modeled in a large water flume. A particle image velocimetry (PIV) system with upward-illumination was, in particular, employed for the junction flow visualization. The examined Reynolds number was varied from 1.28 × 104 to 1.08 × 105, which is above the threshold of turbulent transition for a junction flow. Based on the PIV measurements, the characteristic features were presented for both the time-averaged and the instantaneous flow fields in a sheet flow at the upstream wall-cylinder junction. Statistical analyses on the experimental data are performed to characterize the spatial-temporal evolution of THV strength. The normalized THV strength in the time-averaged flow field increases first and then approaches a constant value with increasing the ratio of cylinder diameter to water depth. Two alternating patterns, i.e., the regular oscillation and the random wandering, are identified for the quasi-periodic oscillating behaviors of the instantaneous THV. It is found that the cumulative distribution curves for the normalized instantaneous THV strength can be described by the Weibul distribution. The present results provide a physical insight and quantitative characterization for the spatiotemporal evolution of THV, which is critical for predicting the associated wall shear stresses.

Wave‐Current Coupling Effects on the Variation Modes of Pore Pressure Response in a Sandy Seabed: Physical Modeling and Explicit Approximations

“…The general experimental procedures are similar to Qi et al (2019), but with different details as follows: the PPTs for the present experiment were installed at 0, 6, 9, and 15 cm below the seabed surface, and the water depth of flume varied among 0.4/0.5/0.6 m. In addition, a LDV was used to monitor the flow velocity instead of the The present test conditions for waves and currents are summarized in Table 1, where h 0 is the original water depth, H 0 is the measured wave height of wave-only conditions (i.e., pre-interaction wave height), H is the measured wave height in the wave-current field, T is the wave period, L is the measured wavelength in the wave-current field, and U c is the measured current-only velocity (pre-interaction) at the level of 0.15 m above the sandy seabed. Based on the value of U c , the mean bulk velocity of the current-only field (U 0 ) can be obtained from the logarithmic velocity distribution along the water depth (Qi et al, 2022). Current velocities between −0.2 and 0.2 m/s were considered.…”

“…The present test conditions for waves and currents are summarized in Table 1, where h 0 is the original water depth, H 0 is the measured wave height of wave‐only conditions (i.e., pre‐interaction wave height), H is the measured wave height in the wave‐current field, T is the wave period, L is the measured wavelength in the wave‐current field, and U c is the measured current‐only velocity (pre‐interaction) at the level of 0.15 m above the sandy seabed. Based on the value of U c , the mean bulk velocity of the current‐only field ( U 0 ) can be obtained from the logarithmic velocity distribution along the water depth (Qi et al., 2022). Current velocities between −0.2 and 0.2 m/s were considered.…”

Lateral Bearing Capacity of a Hybrid Monopile: Combined Effects of Wing Configuration and Local Scour

“…As a consequence, local scour would reduce the effective embedment of monopiles and, in turn, the lateral bearing capacity [21,22]. For winged monopiles, local scour may still exist and expose the wings out of the seabed, since the wings embedded near the mudline have no impact on the large-scale coherent flow structures (e.g., horseshoe vortex) for initiating the scour process [23]. Li et al's [24] scour tests in a water flume revealed that wings near the mudline can significantly enlarge the range of the scour hole and even the scour depth, which impedes the effectiveness of the wings.…”

Junction flow inside and around three-row cylindrical group on rigid flat surface

“…The interaction of the separation flow and the downflow generates a system of horseshoe vortices that envelope the base of the obstacle. Horseshoe vortex structures are unstable, change their shape, number, circulation and location, interact with each other and the streamlined surface, pair and break under the action of Reynolds and viscous stresses ( Rona et al., 2020 ; Robison et al., 2021 ; Qi et al., 2022 ; Lin and Wu, 2022 ). On the lateral sides of the bluff body, separated shear layers are formed.…”