Abstract:The demand for new propeller designs has increased alongside the development of new technology, such as urban aircraft and large unmanned aerial vehicles. In order to experimentally identify the performance of a propeller, a wind tunnel that provides the operating flow is essential. However, in the case of a meter class or larger propeller, a large wind tunnel is required and the related equipment becomes heavy; therefore, it is difficult to implement in reality. For this reason, propeller studies have been co… Show more
Wall-modeled large-eddy simulation (WMLES) is an advanced mathematical model
for turbulent flows which solves for the low-pass filtered numerical
solution. A subgrid-scale (SGS) model is used to account for the effects of
unresolved small-scale turbulent structures on the resolved scales (i.e. for
the dissipation of the smaller scales), while the flow behavior near the
walls is modeled by wall functions (thus reducing the requirements for mesh
fineness/ quality). This paper investigates the possibilities of applying
WMLES in the estimation of aerodynamic performance of small-scale
propellers, as well as in the analysis of the wake forming downstream.
Induced flows around two propellers designed for unmanned air vehicles
(approximately 25 cm and 75 cm in diameter) in hover are considered unsteady
and turbulent (incompressible or compressible, respectively). Difficulties
in computing such flows mainly originate from the relatively low values of
Reynolds numbers (several tens to several hundreds of thousands) when
transition and other flow phenomena may be present. The choice of the
employed numerical model is substantiated by comparisons of resulting
numerical with available experimental data. Whereas global quantities, such
as thrust and power (coefficients), can be predicted with satisfactory
accuracy (up-to several percents), distinguishing the predominant flow
features remains challenging (and requires additional computational effort).
Here, wakes forming aft of the propeller rotors are visualized and analyzed.
These two benchmark examples provide useful guidelines for further numerical
and experimental studies of small-scale propellers.
Using the unsteady vortex lattice method based on the potential flow theory, a rapid modeling approach is developed for the aerodynamic computation of multi-lifting surfaces. Multiple lifting surfaces with different geometric parameters and grid divisions can be quickly integrated and meshed with the object-oriented data structure. The physical influence between different lifting surfaces was modeled, and the wake–surface interaction was also considered by using different built-in vortex core models. The trajectory data were used to replace the pre-calculated downwash superposition for boundary condition integration, and the instantaneous boundary condition was generated directly from the kinematic states and mesh messages of the model concerned. Considering the direct coupling effect between aerodynamics and rigid body dynamics, the function for free flight was built for medium-fidelity dynamic simulations and aerodynamic data identifications. The proposed high-efficiency modeling and simulation process can be easily applied to models with any number of different lifting surfaces and arbitrary motion modes.
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