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.

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.

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.

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.

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.