An Experimental-Numerical Investigation of the Wake Structure of a Hovering Rotor by PIV Combined with a Γ 2 Vortex Detection Criterion

Fabrizio De Gregorio, Antonio Visingardi and Gaetano Iuso
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Fabrizio De Gregorio: Fluid Mechanics Laboratory, Italian Aerospace Research Centre—CIRA, 81043 Capua, Italy
Antonio Visingardi: Aerodynamic Measurement Methodologies Laboratory, Italian Aerospace Research Centre—CIRA, 81043 Capua, Italy
Gaetano Iuso: Mechanical and Aerospace Engineering Department, Politecnico di Torino, 10129 Turin, Italy

Energies, 2021, vol. 14, issue 9, 1-19

Abstract: The rotor wake aerodynamic characterization is a fundamental aspect for the development and optimization of future rotary-wing aircraft. The paper is aimed at experimentally and numerically characterizing the blade tip vortices of a small-scale four-bladed isolated rotor in hover conditions. The investigation of the vortex decay process during the downstream convection of the wake is addressed. Two-component PIV measurements were carried out below the rotor disk down to a distance of one rotor radius. The numerical simulations were aimed at assessing the modelling capabilities and the accuracy of a free-wake Boundary Element Methodology (BEM). The experimental and numerical results were investigated by the Γ 2 criterion to detect the vortex location. The rotor wake mean velocity field and the instantaneous vortex characteristics were investigated. The experimental/numerical comparisons show a reasonable agreement in the estimation of the mean velocity inside the rotor wake, whereas the BEM predictions underestimate the diffusion effects. The numerical simulations provide a clear picture of the filament vortex trajectory interested in complex interactions starting at about a distance of z/R = −0.5. The time evolution of the tip vortices was investigated in terms of net circulation and swirl velocity. The PIV tip vortex characteristics show a linear mild decay up to the region interested by vortex pairing and coalescence, where a sudden decrease, characterised by a large data scattering, occurs. The numerical modelling predicts a hyperbolic decay of the swirl velocity down to z/R = −0.4 followed by an almost constant decay. Instead, the calculated net circulation shows a gradual decrease throughout the whole wake development. The comparisons show discrepancies in the region immediately downstream the rotor disk but significant similarities beyond z/R = −0.5.

Keywords: rotary-wing aerodynamics; vortex detection criterion; BEM method; tip vortex interactions (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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