Flow around a Rectangular Cylinder Placed in a Channel with a High Blockage Ratio under a Subcritical Reynolds Number

Abstract

With the depletion of fossil energy sources, clean energy has become a growing concern for scholars. Vortex-Induced Vibration Aquatic Clean Energy (VIVACE), a device that uses water flow energy to generate electricity, has attracted much attention for its broad applicability and other advantages. Particle Image Velocimetry (PIV) experiments were conducted to improve the efficiency of the VIVACE device in low-velocity areas. The present study investigated the effects of the Blockage ratio (Br), Reynolds number (Re = ρU0D/μ), and Aspect ratio (Ar = B/D, width-to-height) of rectangular cylinders on flow characteristics. The influence of the Ar, Br, and Re on the flow field structure was systematically analyzed in terms of the time-averaged flow field, Reynolds shear stress, space–time correlation, vorticity field, and water pressure characteristics. The vorticity field was deconstructed by Proper Orthogonal Decomposition (POD). The results show that the first two orders of POD modal energy accounted for 75% of the total energy, indicating that the first two modes can be used to identify the large-scale vortex structure. The main water pressure frequency and vortex shedding frequency (f) had a high degree of consistency. Thus, vortex shedding was the main cause of wall water pressure fluctuations. Given the blockage effect, the shear layer’s development spanwise was restricted. Moreover, the blockage effect increased the local flow velocity and accelerated the vortex shedding. The dimensionless time-averaged flow velocity U/U0 increased to 1.5, and the frequency of vortex shedding increased by approximately 25% when the Br increased from 0.067 to 0.25. The frequency increased by 25% when the Ar decreased from 0.5 to 0.2. The experimental results also provide a new idea for optimizing the VIVACE device.

Study of Hydrokinetic Energy Harvesting of Two Tandem Three Rigidly Connected Cylinder Oscillators Driven by Fluid-Induced Vibration

“…Given that significant portions of ocean and river flows are below 1.5 m/s, the hydrodynamic characteristics of standard rotating underwater turbines may not be suitable for such low flow ranges [9][10][11]. Large areas of the world's ocean flows are less than 1.5 m/s, and river flows are usually less than 1.0 m/s, and the hydrodynamic performance and characteristics of ordinary rotating underwater turbines are not necessarily suitable for such a low flow range [12,13]. In the past decade, scholars have proposed low-speed ocean current power generation devices driven by vorticity vibration, which can realize the development of low-speed current energy through alternating lift equipment.…”

Advances in Numerical Data Visualization of Flow around a Square Cylinder

“…Flow around square cylinders at a Reynolds number (Re) of around 10 4 is widely studied given its relevance to characterize fluid performance in the subcritical range, and its adaptability to industrial and energy problems. Its main applications relate to ocean engineering-energy production [1,2], drag reduction [1,3,4], and the aerodynamic optimization of squared-rectangular vehicles [5][6][7].…”