Study on Blade Property Measurement and Its Influence on Air/Structural Loads

Abstract

In this study, the structural properties of Second Higher-Harmonic Aeroacoustic Rotor Test blades are determined using state-of-the-art test techniques. The measurement includes bending and torsion stiffnesses, section geometric offsets, and mass and inertia properties. Several Second Higher-Harmonic Aeroacoustic Rotor Test blades, including the original instrumented blade used for the wind-tunnel test campaign in 2001, as stated by Yu et al. ) are used for the activity. A finite element-based cross-section analysis combined with an x-ray computer tomography technique is employed for the cases where no mechanical measurement is available or attempted. The resulting structural properties are correlated against the earlier estimated values, which have extensively been used in the literature for the validation of the Second Higher-Harmonic Aeroacoustic Rotor Test rotor. A substantial deviation is observed between the present measurement and the earlier property result. The comprehensive rotor dynamics analysis is performed to quantify the impact of the measured blade properties on the aeromechanics behavior of the rotor. The location of the center of gravity is demonstrated to be the most influential factor affecting the deviation and the sensitivity of the aeroelastic response of the rotor. Nomenclature C T = thrust coefficient; T∕ρRΩ 2 πR 2 c = chord, m EA = axial stiffness, N EI β = flap-bending stiffness, N · m 2 EI ζ = chord-bending stiffness, N · m 2 GJ = torsion stiffness, N · m 2 I θ = polar mass moment of inertia per length, kg · m M = hover tip Mach number R = rotor radius, m T = applied torque, N · m α s = shaft tilt angle, deg μ = advance ratio ρ = air density, kg∕m 3 Ω = rotor nominal speed, rad∕s

Modelling and analysis of coupled flap-lag-torsion vibration characteristics helicopter rotor blades

“…To carry out this comparison, a resonant chart is calculated for the small scale hingeless HART II rotor described in Ref. 21. Additionally, the dominant mode shapes are calculated and compared at its nominal rotational speed.…”

“…The averaged relative errors across the rotorspeed range are of the order of 3%, 2%, 3%, 2%, 4%, 4%, and 5% for the first 7 natural frequencies. The larger deviations from CAMRAD calculations can be Calculated resonance charts for the HART II rotor described in Ref 21 . comparison with CAMRAD calculation from Ref.…”

X-ray Computed Tomography Method for Macroscopic Structural Property Evaluation of Active Twist Composite Blades

“…KSEC2D II is an expanded version of the earlier KSEC2D [21], and is suitable for analyzing generic beams and blades with arbitrary cross-sectional geometries. The code has been successfully applied to the Korean Helicopter Program development and measurement campaign of HART II blade properties, working jointly with NASA Ames, German DLR, and Konkuk University [15,16]. KSEC2D is equivalent to the Euler-Bernoulli formulation for bending and to the St. Venant level for torsion, which leads to 4 × 4 stiffness constants.…”

“…A mechanical (non-destructive) measurement technique was employed to evaluate some of the blade structural properties, confirm the fidelity of the constructed analytical model, and assess the correlation with the predicted results. The test rig used for HART II blades [16] was updated and used in the present study. Figure 11 shows the measurement setup for a STAR II (epsilon) blade.…”

“…The basic principle behind the exploitation of CT in identifying the material distributions over the structure is that each voxel (volume element) image has a discrete CT number (called Hounsfield unit in the medical field) according to the physical density of the material domain [14]. This method was successfully used by Jung et al [15] to determine the structural properties of the HART II blades [16,17]. CT images were available for limited portions of the blade in an earlier study [15] that focused only on the blade root region.…”