Study of the Boundary Layer in the Inboard Sections of a Tilt-Rotor Blade by Embedded LDV Measurements
Abstract
This report focuses on the boundary layer (BL) velocity distribution in the inboard region of a tiltrotor blade. The instrumentation consists of a Laser Doppler Velocimeter embedded in the inboard region of the blade. This set up allows measuring the chordwise and spanwise component of the boundary layer velocity from a distance of 0.3 mm to 20 mm along a direction normal to the blade surface. The experiments were carried out on a two-bladed rotor with a blade geometry close to the one of CAMRAD II model of TRAM. The blade section located at r/R=0.3 was explored in three abscissa x/C=0.10; 0.33; 0.54, and for 3 pitch angles, two of them at values lower than the static stall angle of incidence, the third at a higher value. During the tests the tip Mach number was maintained constant at M(sub tip)=0.22. Results obtained on the velocity components have allowed characterizing the different aspects of the BL. At low incidences, chordwise velocity profiles exhibit a turbulent behavior (power law in 1/n) for x/C=0.33 and 0.54. At the chord station x/C=0.10, the BL is very thin with a laminar velocity profile. At the incidence higher than the static stall one, it is worthy to note that the chordwise velocity profile at x/C=0.3 shows an attached turbulent BL, while at x/C=0.54 the velocity profile begins to deviate from a turbulent shape to a separated one that produces the thickening of the BL and an evolution of the profile to a velocity distribution with an inflexion point. This result confirms the delay of the BL separation due to rotation, already observed. At the leading edge (x/C=0.1), and for the present low rotational speed OMEGA, the velocity distribution in the BL seems to point out a transitional zone inside of which the randomness of the velocity intensity attests to a high vorticity that may be due to a leading edge vortex or a bubble formation sustaining during the rotation the reattachment of the BL as observed at x/C=0.33.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2003
- Accession Number
- ADA420100
Entities
People
- Charlie Barla
- Christian Maresca
- Daniel Favier
- Eric Berton
- Marcellin Nsi Mba