Joon W. Lim

Rotor Wake Vortex Definition-Evaluation of 3-C PIV Results of the HART-II Study:

An evaluation is made of extensive three-component (3-C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a center-of-vorticity criterion and a vorticity “disk” integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.

Helios Prediction of Blade-Vortex Interaction and Wake of the HART II Rotor

In this paper, we present the validation of the multi-disciplinary rotorcraft simulation code Helios for its ability to predict the blade-vortex interactions(BVI) and the rotor wake in the descending flight. Helios uses a dual-mesh paradigm with unstructured mesh near the body and Cartesian mesh in the o-body. The trim of the rotorcraft and the elastic blade deformations are modeled using the loose-coupling with RCAS comprehensive model. Three test conditions baseline, minimum noise and minimum vibration are used for the validation. Helios predictions for the baseline case which has strong BVI on both the advancing and retreating side are compared to the measured data, OVERFLOW 2/CAMRAD II and FUN3D/CAMRAD II predictions. The minimum noise and minimum vibration case predictions are compared to the measured data. Helios predictions compare favorably with the current state-of-the art codes. Cartesian-based unsteady adaptive mesh refinement (AMR) is applied in the o-body flow field to understand the eect of AMR on the prediction of the wake field.