Visualization and measurement of helicopter rotor flow with swept back tip shapes at hover flight using the “flow visualization gun” time line technique

Abstract

The Flow Visualization Gun (FVG), a novel time line visualization technique, has been used to investigate the flow field of a helicopter rotor with swept back tip shape in hover flight condition. After introducing the FVG-technique, the paper presents some visualization photographs of the rotor blade tip vortices and the rotor downwash. Using orthogonal sets of flow photographs and digital image analysis, the 3-dimensional time line displacement within the flow and the tip vortex structure are determined. The data of 16 time line experiments are interpolated in space and time to obtain velocity data on an evenly spaced 3-dimensional grid. Vorticity contour plots of the flow field show the complex arrangement of the tip vortices of the blade itself and of the preceding blade and some additional vorticity in the direct wake which may form a secondary vortex. Understanding and control of this vorticity distribution is important for the design of new efficient tip shapes. While the FVG technique has been used so far for qualitative investigation of complex flow patterns at local velocities of up to 20 m/s, a good comparison to laser velocimetry data validates the technique as an interesting tool for both qualitative and quantitative investigation.

Adaptive BEM for Low Noise Propeller Design

“…Numerical studies have focused on the main factors affecting the performance of propellers in various configurations [8][9][10][11][12][13][14] and models have been developed which allow the prediction of propeller aerodynamics at relatively low computational cost, in particular using time domain panel methods *Address correspondence to this author at the Dipartimento di Tecnologie ed Infrastrutture Aeronautiche, Università di Palermo, Italy; E-mail: romario@unipa.it [15,16] which allow for the inclusion of unsteadiness effects due to oscillation and blade deflection. Comparison with measurements on rotors in hover [17] have shown that quasisteady models give good results for unsteady aerodynamics. This justifies the use of hybrid methods using free wake analysis (FWA) and boundary element methods (BEM) for the aerodynamics of propellers [18,19].…”

“…on the wake at the M nodes along the trailing edge. There, one has, via the trailing edge condition, i.e., Eq (17). and j are the potential values at the upper and lower trailing edge of the j-station taken along the blade radial sections distribution, respectively.…”