The paper focuses on the possibilities of adequately simulating complex flow
fields that appear around small-scale propellers of multicopter aircraft.
Such unmanned air vehicles (UAVs) are steadily gaining popularity for their
diverse applications (surveillance, communication, deliveries, etc.) and the
need for a viable (i.e. usable, satisfactory, practical) computational tool
is also surging. From an engineering standpoint, it is important to obtain
sufficiently accurate predictions of flow field variables in a reasonable
amount of time so that the design process can be fast and efficient, in
particular the subsequent structural and flight mechanics analyses. That is
why more or less standard fluid flow models, e.g. Reynolds-averaged
Navier-Stokes (RANS) equations solved by the finite volume method (FVM), are
constantly being employed and validated. On the other hand, special
attention must be given to various flow peculiarities occurring around the
blade segments shaped like airfoils since these flows are characterized by
small chords (length-scales), low speeds and, therefore, low Reynolds
numbers (Re) and pronounced viscous effects. The investigated low-Re flows
include both transitional and turbulent zones, laminar separation bubbles
(LSBs), flow separation, as well as rotating wakes, which require somewhat
specific approaches to flow modeling (advanced turbulence models, fine
spatial and temporal scales, etc). Here, the conducted computations (around
stationary blade segments as well as rotating rotors), closed by different
turbulence models, are presented and explained. Various qualitative and
quantitative results are provided, compared and discussed. The main
possibilities and obstacles of each computational approach are mentioned.
Where possible, numerical results are validated against experimental data.
The correspondence between the two sets of results can be considered
satisfactory (relative differences for the thrust coefficient amount to 15%,
while they are even lower for the torque coefficient). It can be concluded
that the choice of turbulence modeling (and/or resolving) greatly affects
the final output, even in design operating conditions (at medium
angles-of-attack where laminar, attached flow dominates). Distinctive flow
phenomena still exist, and in order to be adequately simulated, a
comprehensive modeling approach should be adopted.