The wake of a square cylinder is investigated for Reynolds number Re < 107. Two-dimensional (2D) laminar simulation and three-dimensional (3D) large-eddy are conducted at ≤ 1.0 × 103, while experiments hotwire, particle image velocimetry, force measurements carried out higher range 103 4.5 104. Furthermore, data covering wide range, from 100 to 107, in the literature comprehensively collected discussion comparison purposes. dependence on recirculation bubble size or vortex formation...

A turbulent boundary layer developed over a herringbone patterned riblet surface is investigated using stereoscopic particle image velocimetry in the cross-stream plane at $Re_{\unicode[STIX]{x1D70F}}\approx 3900$ . The three velocity components resulting from this experiment reveal pronounced spanwise periodicity all single-point statistics. Consistent with previous hot-wire studies similar-type riblets, we observe weak time-average secondary flow form of $\unicode[STIX]{x1D6FF}$ -filling...

Abstract Active control of a turbulent boundary layer has been experimentally investigated with view to reducing the skin-friction drag and gaining some insight into mechanism that leads reduction. A spanwise-aligned array piezo-ceramic actuators was employed generate transverse travelling wave along wall surface, specified phase shift between adjacent actuators. Local exhibits strong dependence on parameters, including wavelength, amplitude frequency oscillation. maximum reduction 50 %...

This work aims to provide a systematic experimental study of the wake behind two staggered square cylinders at Reynolds number $Re=1.3\times 10^{4}$ . Four distinct flow regimes, i.e. single-street modes S-I and S-II double-street T-I T-II, are identified based on extensive data, including Strouhal numbers $(St)$ , structures their downstream evolution. S-I, T-II each further subdivided into types. The characteristics in regime presented terms shear layer reattachment impingement, vortex gap...

This work aims to investigate, based on the measured/reported Strouhal number (St) and flow structure, Reynolds (Re) effect wake of two identical cylinders with a diameter d over P∗=P/d=1.2–4.0 α=0°–90°, where P is center-to-center spacing between α angle incident respect line through cylinder centers. The Re range examined from 1.5×103 2.0×104. Two hotwires were used measure St simultaneously behind each cylinders. St-Re relationship classified into four distinct types, i.e., types 1–4....

Turbulence modifications over a rough wall with spanwise-varying roughness are investigated at moderate Reynolds number Reτ ≈ 2000 (or Reθ 6400), using particle image velocimetry (PIV) and hotwire anemometry. The is comprised of spanwise-alternating longitudinal sandpaper strips two different heights. ratio high- low-roughness heights 8, the strip width 0.5. PIV measurements conducted in wall-parallel plane located logarithmic region, while made throughout entire boundary layer cross-stream...

The sinusoidal wavy cylinder of circular cross section is able to substantially reduce the fluid forces by effectively stabilizing near wake in subcritical flow regime. Based on anechoic wind tunnel measurements and large eddy simulations (LESs), we investigate capability aeroacoustic noise as well underlying physics. studied this work covers a range spanwise wavelength λz = 1.8–6.0Dm wave amplitude 0.15–0.25Dm, where Dm mean diameter cylinder. are conducted at Reynolds number ReDm 2.9–8.0 ×...

Effects of the spanwise wavelength ( λ ) a sinusoidal wavy cylinder with elliptic cross-section on wake structures and fluid forces are numerically investigated at Reynolds number Re = 100. A wide range wavelength, $0.43 \le \lambda /{D_m} 8.59$ , is considered wave amplitude / D m 0.048, where hydraulic diameter cylinder. Based vortical structures, Strouhal St closure length L c ), forces, streamline topologies spatio-temporal evolutions near wake, five distinct flow patterns (I–V)...

Aiming to uncover the propulsion mechanisms underlying a cruising crocodile, we conduct computational fluid dynamics (CFD) simulations on flow around simplified three-dimensional model of Crocodylus siamensis. The locomotion crocodile is realized through undulating its body and tail, mimicking crocodile-like swimming pattern. At speed U∞ = 0.5 m/s (corresponding Reynolds number Re 9.95 × 105 based length L), hydrodynamics are investigated, taking into account effects undulation parameters...

Shear layers separating from opposite sides of a bluff body are inherently connected with near wake flow structures; interfering one the shear may lead to dramatic changes in and fluid forces on body. Being motivated by this, we investigate square cylinder disturbed synthetic jet at leading edge cylinder. Large-eddy simulations conducted Reynolds number Re = 5.0 × 103. The is driven sine function frequency fj 0–1.65 fo magnitude Vj,o 0–1.0 Uo (corresponding momentum coefficient Cμ 0–1.01%),...

Evolutionary based Genetic Algorithms (GAs) were employed to optimize the blade shape of a Savonius-type vertical-axis wind turbine (S-VAWT) as well and location one doubly-curved deflector placed upstream returning an S-VAWT. To this end, GAs incorporated into computational fluid dynamics (CFD) simulations. Significant improvement in performance was observed for S-VAWT with optimal blades that deflector. The time-averaged power coefficient can be increased by up 34% over semi-circular...

The performance of multiple vertical-axis wind turbines (VAWTs) can be greatly enhanced when they are placed close in some configurations where positive interaction or coupling occurs. Based on a systematic study using computational fluid dynamics (CFD) simulations, we investigate the two co-rotating Savonius-type VAWTs. A wide range covered, i.e., P/D = 1.2−3.0 and α -90°−90°, P is distance between turbines' centres, D diameter turbine rotation, incident angle line connecting centres...

While considerable research has addressed flow around stationary sinusoidal wavy cylinders, studies on vortex-induced vibration (VIV) of elastic-supported cylinders still remain limited. This study aims to address this gap through a series water tunnel experiments, focusing the effects cylinder's spanwise wavelength. Three typical wavelengths (λ* = 1.8, 3.6, and 6.0) are considered, with first third identified as optimal for reducing fluid forces (lift by over 90%) in previous cylinder...

VAWTs benefit from constructive coupling effect that significantly improves efficiency. This work aims at optimizing the configuration of turbine clusters with three Savonius turbines. To maximize aggregate power output a cluster, two-dimensional (2D) computational fluid dynamics (CFD) is utilized, along an evolutionary based Genetic Algorithm (GA). Four scenarios are investigated considering different combinations rotational directions. For optimal cluster obtained, highest 37% increase in...