Khaoula Qaissi

The growing demand for urban air mobility (UAM) has accelerated the development of hybrid/electric vertical takeoff and landing (H-/eVTOL) aircraft, which use distributed propulsion systems that generate complex aerodynamic interactions during forward and transition flight. This study investigates the aerodynamic interactions between two propellers arranged in a one-after-another (OAA) configuration, using unsteady Reynolds-averaged Navier–Stokes (URANS) simulations coupled with the [ ] shear stress transport (SST) turbulence model. The numerical setup was validated against experimental data for the isolated propeller across all investigated advance ratios, showing good agreement. Results reveal that, in forward flight, the rear propeller experiences up to 24% thrust and 20% power loss due to the disturbed airflow created by the wake of the front propeller. This is accompanied by only a 21% increase in axial velocity at the rear propeller location, indicating less effective energy transfer and lower thrust. Pressure coefficient analysis at the rear propeller midspan within the overlap region indicates increased flow separation and lower local loading. During transition, the overlap decreases with tilt, yet at 30° and 60°, the rear propeller still loses up to 11% thrust and 10% power due to slipstream deflection. As the propeller tilt angle increases, the thrust in the propeller axis direction also increases; however, this requires more power and generates a more complex slipstream. These findings provide valuable insights into wake interactions and their influence on rear propeller performance, offering practical design guidelines to improve the efficiency and reliability of UAM vehicles.

The rapid growth of urbanization and increasing road traffic congestion are straining ground transportation infrastructure for both conventional and emergency purposes, driving the need for alternative mobility solutions. urban air mobility (UAM) offers a promising pathway by deploying electric vertical takeoff and landing (eVTOL) aircraft to enable efficient and flexible aerial transport in dense urban environments. However, the successful integration of UAM into city airspace faces critical technical challenges, both at the vehicle and operational levels. In particular, complex aerodynamic and aeroacoustic interactions between closely spaced propellers significantly influence vehicle performance, energy efficiency, and public acceptance. This work presents a review of experimental and computational studies on propeller–propeller and propeller–wing interactions, highlighting the state-of-the-art methodologies and their application to multirotor eVTOL designs. Results indicate that distributed electric propulsion systems arranged in side-by-side configurations exhibit minimal thrust degradation, typically less than 3% compared to an isolated propeller. However, reductions in propeller spacing can induce unsteady blade loading and increase tonal noise levels by up to 10 dB. In contrast, one-after-another configurations may suffer thrust losses of up to 80%, due to slipstream ingestion by the rear propeller, with a lateral separation of at least twice the propeller radius required to recover performance within 4% of the isolated case. The review also addresses propeller–wing interactions that modify local pressure distributions and spanwise lift, particularly in wing-mounted distributed propulsion configurations. The insights provided establish a foundation for developing efficient, low-noise multirotor architectures for future UAM integration.

For the rotor, achieving relatively high aerodynamic performance in specific wind conditions is a long-term goal. Inspired by the remarkable flight characteristics of owls, an optimal trailing edge serration design is investigated and proposed for a wind turbine rotor blade. Fluid flow interaction with the proposed serrations is explored for different wind conditions. The result is supported by subsequent validation with three-dimensional numerical tools. The present work employs a statistical-numerical method to predict and optimize the shape of the serrations for maximum aerodynamic improvement. The optimal combination is found using the Taguchi method with three factors: Amplitude, wavelength, and serration thickness. The viability of the solution on an application is assessed using the Weibull distribution of wind in three selected regions. Results show that the presence of serration is capable of improving the annual power generation in all the investigated cities by up to 12%. The rated speed is also shifted from 10 m/s to 8 m/s for most configurations. Additionally, all configurations show similar trends for the instantaneous torque, where an increase is observed in pre-rated speed, whereas a decrease is noticed in the post-rated speed region. A look at the flow field pattern for the optimal design in comparison with the clean blade shows that the modified blade is able to generate more lift in the pre-stall region, while for the post-stall region, early separation and increased wake dominate the flow.

For the rotor, achieving relatively high aerodynamic performance in specific wind conditions is a long-term goal. Inspired by the remarkable flight characteristics of owls, an optimal trailing edge serration design is investigated and proposed for a wind turbine rotor blade. On wind turbine blades, trailing-edge (TE) serration is a common tool for noise reduction. The underlying scientific theory for noise reduction has already been established and the majority of earlier research on TE serrations focused on reducing noise. The knowledge about how these serrations affect wind turbine aerodynamics is limited. A horizontal axis wind turbine rotor performance is improved by serrated leading edges and tested for different wind conditions. The result is supported by subsequent validation with three-dimensional numerical tools. The present work employs a statistical-numerical method to predict and optimize the shape of the serrations for maximum aerodynamic improvement. The optimal combination is found using the Taguchi method with three factors: Amplitude, wavelength, and serration thickness. The viability of the solution on an application is assessed using the Weibull distribution of wind in three selected regions. Results show that the presence of serration improves the annual power generation in all the investigated cities by up to 12%. The rated speed is also shifted from 10 m/s to 8m/s for most configurations. Additionally, all configurations show similar trends for the instantaneous torque where an increase is observed in pre-rated speed whereas a decrease is noticed in the post-rated speed region. A look at the flow field pattern for the optimal design in comparison with the clean blade shows an improvement of the wake in specific radial positions near the tip.

A wind turbine blade has the particularity of containing twisted and tapered thick airfoils. The challenge with this configuration is the highly separated flow in the region of high twist. This research presents a numerical investigation of the effectiveness of a vortex trapping cavity (VTC) on the aerodynamics of the National Renewable Energy Laboratory phase VI wind turbine. First, simulations are conducted on the S809 profile to study the fluid flow compared to the airfoil with the redesigned VTC. Second, the blade is simulated with and without VTC to assess its effect on the torque and the flow patterns. The results show that for high angles of incidence at Rec = 106, the lift coefficient increases by 10% and the wake region appears smaller for the case with VTC. For wind speeds larger than 10 m/s, the VTC improves the torque by 3.9%. This is due to the separation that takes place in the vicinity of the VTC and leads to trapping early separation eddies inside the cell. These eddies roll up forming a coherent laminar vortex structure, which in turn sheds periodically out of the cell. This phenomenon favorably reshapes excessive flow separation, reenergizes the boundary layer, and globally improves blade torque.