Being widely ubiquitous in fluidic mediums from aquatic environments to bodies, for the sake of their mobility, microorganisms, such as bacteria and motile cells, make use of particular swimming strategies that are counter-intuitive to that of our daily life experience, given that the physics governing micrometer is different from that of macroscale physics. Living in this particular realm of supposedly zero Reynolds number, these microscopic creatures are constrained such that their methods of swimming as well as their sequence of strokes need to utterly satisfy the so-called scallop theorem. Considering the importance of motility for both microrobots and living creatures, this study aims to propose a model swimmer for artificial swimmers that might also be a prospective model explaining a mode of swimming for existing self-propelled natural living matters that can move forward by changing the shape of their body. The proposed swimmer is made up of three equal spheres, arranged in a triangular configuration by placing the center of each of them at the vertices of a triangle. The active links form a T-shape frame, such that the first link serves to connect two spheres, and the second link originates from the other sphere to connect it to the middle of the first link. Considering only two degrees of freedom for each link, this swimmer can translate along a straight path, by expanding or contracting its links consecutively in proper order. Obtaining the velocity of the swimmer, we study the effects of geometrical parameters of the triangle on the mean velocity of the swimmer over each cycle of motion. Finally, it will be shown that the velocity obtained here, which linearly depends on its characteristic parameters, resembles perfectly its well-known rectilinearly configured spheres counterpart, initially proposed by Najafi and Golestanian (Phys. Rev. E 69, 062901 (2004)), and its properties have been extensively studied over past years.

This study presents a numerical analysis of a UAV propeller's aeroacoustic behavior under hovering conditions. The Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations for incompressible flow were solved using ANSYS Fluent, with turbulence modeled using the k-ω SST approach. Far-field noise prediction was performed employing the Ffowcs Williams-Hawkings (FW-H) acoustic equation. Static pressure contours revealed extensive low-pressure regions on the blade's upper surface, particularly near the leading edge at the tip, significantly contributing to both thrust generation and loading noise. Surface pressure fluctuations were most pronounced along the leading edge, diminishing toward the trailing edge, suggesting the leading edge as the primary broadband noise source due to turbulent interaction with preceding blades. Far-field analysis showed dominant tonal noise at 100 Hz and its harmonics, with higher-order blade passing frequencies exhibiting near-linear attenuation. Directivity patterns indicated negligible tonal noise at 0° and 15° (suction side) and 165° and 180° (wake side) polar angles, while broadband noise decreased and tonal noise intensified at 90°.

Paulhausen integral techniques together with Johnson, Redford and Jungho correlations are used in predicting transition onset, separation point position and penetration of free stream turbulence into transitional boundary layer in a diffusing flow. Free stream turbulence intensities are set to variety of values covering both linear and non-linear disturbances. In addition, diffuser half angle opening is assumed to vary in ranges not more than that bringing separation point into transitional zone. Results show that the free stream turbulence intensity and positive pressure gradient have both direct effects to bring transition onset closer to indifference stability point. Separation point, however, moves closest towards diffuser's inlet point as pressure gradient increases and moves away as FSTI increase. FSTI effects on near wall turbulence intensity, primarily causing its increase to a maximum and later approaching to a limit for the rest of boundary layer length.

In this paper, 2-D numerical solution scheme is used to study the performance of semi-passive flapping foil flow energy harvester at Reynolds numbers ranging from 5000 to 50, 000. The energy harvester comprises of NACA0015 airfoil which is supported on a translational spring and damper. An external sinosoidal pitch excitation is provided to the airfoil. Energy is extracted from the flow induced vibration of airfoil in translational mode. Movement of airfoil is accommodated in fluid domain by using a hybrid meshfree-Cartesian fluid grid. A body conformal meshfree nodal cloud forms the near field domain, encompassing the airfoil. During the simulation, the solid boundary causes the motion of the meshfree nodal cloud, without necessitating re-meshing. In the far field, the static Cartesian grid encloses and partly overlaps the meshfree nodal cloud. A coupled mesh based and meshfree solution scheme is utilized to solve laminar flow, viscous, incompressible equations, in Arbitrary-Lagrangian-Eulerian (ALE) formulation, over a hybrid grid. Spatial discretization of flow equations is carried out using radial basis function in finite difference mode (RBF-FD) over meshfree nodes and conventional finite differencing over Cartesian grid. Stabilized flow momentum equations are used to avoid spurious fluctuations at high Reynolds numbers. A closely coupled, partitioned, sub iteration method is used for fluid structure interaction. The study is focused to analyse the behaviour of flow energy harvesters at various Reynolds numbers. Effects of changing the translational spring stiffness and pitch activation frequency are also investigated. Instantaneous flow structures around the airfoil have been compared at different Reynolds numbers and pitch amplitudes. It is found that net power extracted by the system increases at high Reynolds numbers. Moreover, re-attachment of leading edge separation vortex plays an important role in ther overall system performance.

In the current study, three airfoils—PSU94-097, SD6060, and S2055—were analyzed for their aerodynamic performance across Reynolds numbers (Re) ranging from 50,000 to 500,000, typical for Small Wind Turbine (SWT) blade airfoils. Results indicated that as Re increased, the aerodynamic efficiency of all modified airfoils improved. Optimal thickness-to-camber ratios (t/c) of 1.50-2.25, 2.25-3, and 0.60-1.50 for SD6060, S2055, and PSU94-097 airfoils, respectively, contributed to enhanced efficiency. PSU94-097-modified airfoil demonstrated the highest lift-to-drag ratio (CL/CD) of 151.60 at Re of 500,000. Peak CL/CD values for SD6060-modified and S2055-modified airfoils were 109.87 and 97.13, respectively. PSU94-097-modified, SD6060-modified, and S2055-modified airfoils attained peak lift coefficients (CL) of 1.534, 1.219, and 1.174, respectively. PSU94-097-modified airfoil also showed the highest peak CL across Re ranging from 50,000 to 500,000. Percentage increase in peak CL/CD across Re range of 50,000 to 500,000 was 15.8%, 16.08%, 24.43%, 17.12%, 17.30%, 17.98%, and 20.22% for PSU94-097-modified airfoil; 27.87%, 2.03%, 13.77%, 15.83%, 15.14%, 17.95%, and 17.73% for SD6060-modified airfoil; and 16.70%, 7.11%, 5.77%, 7.25%, 11.40%, 9.99%, and 6.04% for S2055-modified airfoil. In addition to enhancing the aerodynamic efficiency of airfoils and consequently increasing electricity production in wind turbines, optimizing the t/c reduces the material needed for wind turbine construction. This not only lowers the cost but also minimizes environmental impact by using fewer resources. Thus, these modifications are environmentally beneficial, contributing to sustainable development alongside improving wind turbine efficiency.