Airfoil blades can experience a significant change of angle of attack during operation cycles, which may lead to static or dynamic stall in various applications. It is unclear how elements distributed at the leading edge would affect the aerodynamic performance and stall behaviors. In the present study, a distributed dimples configuration was investigated and compared to a baseline smooth NACA0015 airfoil at low Reynolds numbers. Two- and four-camera, tomographic particle image velocimetry (PIV), and temperature sensitive paint (TSP) techniques were set up to gather flow and surface information near the curved leading-edge surface and to study flow separation. Results suggest that distributed dimples configuration create abrupt separation leading to stall and induce a similar stall compared to the smooth model. However, the stall is induced more abruptly and with different flow patterns. Results show that patterns of separated shear layer at stalled conditions were enhanced by the current configuration. Effect of these structures on the boundary layer transition were also analyzed based on combined tomographic PIV and TSP measurement techniques.

An experimental investigation regarding the dynamic stall of various swept wing models with pitching motion was performed to analyze the effect of sweep on the dynamic stall. The experiments were performed on a wing with a NACA0012 airfoil section with an aspect ratio of AR = 4. The experimental study was conducted for chord-based Reynolds number Re_c$=2\times {10}^5$ and freestream Mach number $Ma=0.1$. First, a ‘particle image velocimetry’ (PIV) experiment was performed on the wing with three sweep angles, $\mathsf{\Lambda }=0^{\mathrm{o}}, {15}^{\mathrm{o}}, \mathrm{and} {30}^{\mathrm{o}}$, to obtain the flow structure at several wing spans. The results obtained at a reduced frequency showed that a laminar separation bubble forms at the leading edge of the wing during upward motion. As the upward pitching motion continues, a separation burst occurs and shifts towards the wing trailing edge. As the wing starts to pitch downward, the growing dynamic stall vortex (DSV) vortex sheds from the wing’s trailing edge. With the increasing sweep angle of the wing, the stall angle is delayed during the dynamic motion of the wing, and the presence of DSV shifts toward the wingtip. During the second stage, a ‘turbo pressure-sensitive paint’ (PSP) technique was deployed to obtain the phase average of the surface pressure patterns of the DSV at a reduced frequency, $k=0.1$. The phase average of pressure shows a distinct pressure map for two sweep angles, $\mathsf{\Lambda }=0^{\mathrm{o}}, {30}^{\mathrm{o}}$, and demonstrates a similar trend to that presented in the published computational studies and the experimental data obtained from the current PIV campaign.

Camber deflection concepts for a VR-12 rotorcraft airfoil were studied for the optimization of unsteady aerodynamics, including dynamic stall conditions and wing–wing interactions during pitching. The designs are based on deflections of the leading edge and trailing edge sections of the airfoil. The deflection parameters were initially established using Computational Fluid Dynamics (CFD). Results from CFD and Particle Image Velocimetry (PIV) were generated for various leading and trailing edge deflection combinations for comparison of their performances. The conditions of this study are for a Reynolds number of 250,000 and pitching reduced frequency of 0.04, representing a medium regime of rotorcraft operations. Linear tandem tests were performed to simulate unsteady wing–wing interactions. The effects of the deflections are discussed and compared to the baseline. Significant benefits are observed, notably dynamic stall mitigation from the leading edge (LE) deflected wing for certain angles of attack and decrease in the separation regions. Overall, from the numerical simulations and the experimental data fields, the LE deflection provides about 10% improvement, followed by the combined LE&TE deflections (8%). It is also found that combining various deflections can provide a performance increase over drastically different areas of the range of angle of attack.

An experimental study is conducted to analyze a streamwise-oriented vortex and investigate the unsteady interaction with a finite-aspect-ratio wing. A pressurized vortex tube is used to generate streamwise vortices in a wind tunnel and the resulting flow behavior is analyzed. The vortex tube, operated at various pressures, yields flows that evolve downstream under several freestream wind tunnel speeds. Flow measurements are performed using two- and three- dimensional (2D and 3D) particle image velocimetry to observe vortices and their freestream interactions from which velocity and vorticity data are comparatively analyzed. Results indicate that vortex velocity greater than freestream flow velocity is a primary factor in maintaining vortex structures further downstream, while increased supply pressure and reduced freestream velocity also reduce vortex dissipation rate. The generated streamwise-oriented vortex is also impinged on a finite-aspect-ratio airfoil wing with a cross-section of standard NACA0012 airfoil. The wingtip-aligned vortex is shown to investigate the interaction of the streamwise vortex and the wingtip vortex region. The results indicate that the vorticity at the high vortex-tube pressure has a significant effect on the boundary layer of airfoil.

Hydrolysis is essential for converting biomass into biofuels and value-added materials within a sustainable circular economy. However, the high viscosity, non-Newtonian rheology, and high-solids loading of biomass slurries pose significant challenges to reactor design, optimization, and scale-up, making experimental investigations costly and time-consuming. This study employs computational fluid dynamics (CFD) to investigate flow patterns and mixing characteristics in a baffled, mechanically stirred tank designed for high-solids suspensions. A single pitched-blade axial impeller is first validated against published experimental velocity data for a Newtonian fluid using ANSYS Fluent, the multiple-reference-frame (MRF) approach, and the steady Reynolds-averaged Navier–Stokes (RANS) k–ε turbulence model. Several dual-stage impeller configurations are subsequently evaluated under Newtonian conditions to optimize bulk mixing while maintaining realistic tank hydrodynamics. Two identical impellers positioned equidistantly from the tank top, bottom, and each other increase average turbulence intensity by 24% compared with a single impeller in a 100 L tank. Extending the validated model and optimized configuration to non-Newtonian slurry conditions increases turbulence intensity from 8.40% to 10.42%. The results demonstrate that shear-dependent rheology causes flow damping and high-viscosity stagnant zones that cannot be adequately captured using a Newtonian model. Axial positioning of dual-stage impellers emerges as the most influential design parameter for minimizing these zones, with a greater impact than modifying blade size or blade number. These findings provide a foundation for improved biomass slurry mixing and future integration with a thermo-electrocatalytic biomass-to-hydrogen reactor.