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Unsteady Simulations of Rotorcrafts In Ground Effect using a Fast Panel - Fast Vortex Formulation

A. Verna, A. D'Andrea
Since the last past years, there have been several attempts to simulate entire helicopter configurations using lifting surface (or panel) codes coupled with different free-wake vortex models. Results normally exhibit a good level of correlation at least in steady level forward flight conditions out of ground effect (OGE). However, in case of rotorcraft operations very close to the ground (IGE - in ground effect), several phenomena have still remained a challenge to be numerically simulated by rotorcraft potential tools because the strong non-linear effects induced by the ground on the development of rotor wake. At the same time, the usage of Eulerian of Navier-Stokes solvers, seem to be a strong challenge because of the enormous amount of required computational times and allocated computer memory. Experimental and numerical studies led up to now on this subject, have confirmed that as a hovering rotor moves from OGE conditions toward the ground, the wake starts to impinge on it and convents out with a strong radial component. IGE operations in forward flight complicates further more the aerodynamics environment around the helicopter. At very low advance ratios, a small region of "flow recirculation" is formed upstream of the rotor, increasing the inflow through the forward part of the rotor disk. At a bit higher advance ratios, previous recirculation disappeared, and a large vortex ("ground vortex") occurs below the rotor making the flow more uniform. This ground vortex is finally overrun with the increasing of the helicopter advancing speed. Normally, positioning and generation of the ground vortex can happen intermittently in time further increasing flowfield unsteadiness and pilot workload in these transitional flight regimes, which occur as a strong function of advance ratio and of square root of the disk loading. Present paper will present the capability of the tool ADPANEL (AgustaWestland in-house developed) to simulate and predict the unsteady vortical flows generated by a rotorcraft operating on ground, both in Hover and in Forward-Flight. Different rotor configurations will be examined in present work, taking into account a change in rotor solidity and in its disk-loading value. Particular emphasis will be given to the understanding of main characteristics of different regimes occurring in IGE, as well as to the numerical assessment of velocity and vorticity unsteadiness of ground-vortex-structures dominated flows.
35th European Rotorcraft Forum 2009,
Conference Paper
21,0 x 29,7 cm, 15 Seiten
DGLR-Bericht, 2009, 2009-03, 35th European Rotorcraft Forum 2009 - Conference Proceedings; S.1-15; 2009; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn
in getr. Zählung;
Stichworte zum Inhalt:
simulation, ground effect (aerodynamics), rotorcrafts

Dieses Dokument ist Teil einer übergeordneten Publikation044:
35th European Rotorcraft Forum 2009 - Conference Proceedings