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°.

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.

Introduction: Photocatalytic oxidation of gaseous pollutants in differential reactors is simulated using computational fluid dynamics. Materials and methods: The momentum equation and pollutant transport are solved by using ANSYS Fluent. The SIMPLE algorithm is used to treat the pressure-velocity coupling. The laminar flow and low Reynolds k− ε models are used to describe turbulence. Results: Velocity field distribution and degradation efficiency of different models at various flow rates were obtained and compared with the experimental data. The simulation results of degradation efficiency under different models are basically consistent. Conclusion: Although low Reynolds k-ε models have better simulation results for high inlet flow rates, in terms of computation complexity, laminar flow is recommended for simulation.

The study of corrugated wings has become acquainted in the field of insect flight in recent times. Recent studies on the aerodynamic effects of a corrugated wing are based on insects like the Dragonfly, whereas the likes of Fruitfly (Drosophila Melanogaster) usually go unobserved due to their smaller size. Consequently, the behaviour of these corrugations is found to be anomalous especially in the low and ultra-low Reynolds number region. Therefore, the main aim of this study is to understand the aerodynamic effects of the corrugated airfoil present in the wing of a Fruitfly, by conducting a geometric parametric study during a static non-flapping flight at 1000 Re. In this computational study, a 2-D section of the corrugated wing along the chord is considered. The parametric study helps in understanding the effects of varying number of corrugations, angle of corrugations and the presence of a hump at the trailing edge. The dimensions were scaled to a suitable reference value to additionally compare the corrugated airfoil of Fruitfly to that of a Dragonfly. The present study shows that the aerodynamic performance of the corrugated wing in terms of cl and cd are predominantly governed by the subtle geometric variations that can largely impact the formation of bubbles, vortex zones, and their mutual interaction. The reduction in the number of leading edge corrugations improved the cl/cd ratio and reduction in the corrugation angle helped produce higher lift. The presence of a trailing edge hump also improved the stall angle with a better flow re-attachment. The presence of corrugation at the trailing edge proved to be more beneficial compared to the model with corrugations at the leading edge. This also helped in understanding, the aerodynamic superiority of the trailing edge corrugations present in the Dragonfly's wing when compared to the Fruitfly's.

In this paper, the performance of three turbulence models, zonal k-ε , linear low-Reynolds k-ε and nonlinear low-Reynolds k-ε in the prediction of flow and heat transfer through a dimpled channel is investigated. Furthermore, the effect of YAP term replacement with NYP length scale correction term is studied. Dimples are heat transfer devices which are employed in gas turbine blades to increase the heat transfer levels. These devices do not act as an obstacle for flow, and thus they produce low pressure losses. In this study, the governing equations on flow and energy are solved using the finite volume method together with the SIMPLE algorithm. The results obtained with YAP term indicate that the nonlinear model predicts larger recirculation flow inside the dimple than zonal and linear models. Also, the intensity of impingement and upwash flow in this model is greater than other models. Heat transfer results show that the zonal model predicts the heat transfer levels lower than experimental measurement. Using the linear model leads to a better prediction of heat transfer inside the dimples and their back rim. Compared to these models, the nonlinear model yields a better prediction not only for the smooth area between the dimples, but in the back rim of the dimple. The replacement of the YAP term with the NYP term in linear and nonlinear models leads to more accurate results for heat transfer in dimple span-wise direction and back rim.

One of the reasons for the increase in induced drag is the vortices created at the wing tip, which has a significant effect on reducing aerodynamic efficiency. Therefore, in order to reduce vortices and the induced drag as well as to improve the aerodynamic performance, the use of wing grid is recommended. Wing grids perform better at low Reynolds numbers, and combination of parameters such as taper ratio, aspect ratio, and twist has a better effect on wing performance and reducing turbulence intensity and induced drag. The purpose of this paper is to improve the aerodynamic performance of compound wing using the wing grids. In this study, the numerical and experimental approaches have been used to investigate the effect of these parameters and also, two key parameters: the grid dihedral angle and sweep angle. Also, a force balance test has been performed for force analysis and numerical solution validation. Wing grid dihedral angle decreases induced drag by increasing the space between separated tip vortices and prevents reinforcing effects due to superposition. On the other hand, dihedral angle should be arranged to increase the aerodynamic efficiency. In other words, increase in dihedral angle may defect the overall performance of the wing. The optimum configuration is found to be symmetric, where the dihedral distribution with a 40° angle for the first grid is reduced gradually to a value of -20° for the last one. In addition, sweep angle distribution for the obtained optimized dihedral angle is also investigated. Initially, each grid span is decreased from the first grid to the last at a constant rate. This increases the sweep angle and enhances the aerodynamic efficiency by 15%. Furthermore, the span of the side grids is reduced from the middle grid and marching the wing leading and trailing edges. Elliptical wing configuration has also been shown to increase aerodynamic efficiency by approximately 50%.

This paper presents a comparative assessment of low Reynolds number k- models against standard k- model in an Eulerian framework. Three different low-Re number k- models: Launder-Sharma (LS), YangShih (YS) and AbeKondoh-Nagano (AKN) have been used for the description of bubble plume behaviour in stratified water. The contribution of the gas phase movement into the liquid phase turbulence has been achieved by using the Dispersed with Bubble Induced Turbulence approach (DIS+BIT). The results reveal that the oscillation frequency of gas-liquid flow are correctly reproduced by standard k- and LS models. In fact, we found for standard K- and LS a clear dominant peak at a frequency equal to 0. 1 Hz. On the other hand, YS and AKN models have predicted chaotic oscillations. The oscillation amplitude of the bubble plume predicted from LS model seems to be in good agreement with the PIV measurements of Besbes et al. (2015). However, for the standard K- model the oscillation amplitude is low. The air-water interface shows that the bubble plume mixing with the stratified water is predicted to be stronger compared to standard k- model.