Physical and Technical Background

Measurement of the Flow Field Generated by Multicopter Propellers

“…In the experiments, the DHES (dioctyl sebacate, di(2-ethylhexyl) sebacate) particles were used with a characteristic time of 2 μs. The selected particles followed the investigated flow based on their Stokes parameter value of less than 10 −1 [ 7 , 39 , 40 , 41 ].…”

“…Such a location caused the area to be obscured (covered), e.g., under the engine or (partially) by the propeller itself. At the stage of The experimental data acquisition and evaluation of the particle image recordings were performed according to best practices (i.e., the selection of tracer particles, imaging optics, optimal time between laser pulses, and seeding density listed in Reference [7]). The laser plane lens was located outside the measurement space above the research object.…”

“…If there is a difference in the density of the medium and the particles sent into it, it is necessary to take into account the velocity lag in the constantly accelerating fluid. This situation occurs in the case of gases, where the density of particles is much higher than the density of fluid [ 7 ]. The velocity lag value can then be calculated using the formula: where: u p —velocity of the tracer particles (m/s), u —fluid velocity (m/s), ρ p —density of the tracer particles (kg/m 3 ).…”

“…In the PIV method, Brownian motion plays an important role, which involves the chaotic movements of particles in a fluid caused by the collisions of a suspension with fluid particles. The motion of a spherical particle, which the Stokes law can be applied to, is characterized by the diffusion coefficient introduced by Einstein [ 7 ]: where: d p —particle diameter (m), K —Boltzmann constant (J/K), T a —absolute fluid temperature (K), μ —dynamic viscosity of the fluid (Pa·s). …”

“…The measurements using modern PIV systems are characterized by an increasing frequency and a spatial resolution, thus making it possible to examine complex flow phenomena [16]. The development of PIV systems is a consequence of the progress in laser and computer technologies, which facilitate the implementation of advanced image processing algorithms [7,17,18]. In this work, the PIV technique was used to determine the aerodynamic interference of rotor streams of an innovative multirotor aircraft.…”