Manfred Hajek

Stick-slip motion of turbine blade dampers

Turbine blade dampers are small elements of a parabolic configuration usually fabricated from sheet steel. They are positioned loosely between the roots of turbine blades improving the damping of blade vibrations by generating dry friction from the relative motion of blades and damper. This paper presents a theoretical approach to these stick-slip vibrations and compares theory with measurements. Additionally, some design aspects of such dampers are discussed by considering the damping behaviour in relation to important design parameters.

Aeromechanics Analysis of a Coaxial Rotor System in Hover and High-Advance-Ratio Forward Flight

The aerodynamics and dynamics of a sub-scale coaxial rotor model designed for high-advance-ratio forward flight were investigated by means of a comprehensive analysis. Hover measurements were used to calibrate and validate the numerical predictions. The dynamics of the rotor system were analyzed with a focus on the interactional aerodynamics responsible for in-creased hub loads, blade loads, and blade deflections. A numerical aeromechanics model with reduced-order aerodynamics modeling using a free vortex wake method was used to ensure computational efficiency. Performance predictions as well as predicted blade flap deflections showed good correlation with the measurements. Predicted hub loads correlated well with the measurements in terms of the average loads. Vibratory loads showed similar trends compared to the measurements, although the peak loads were underpredicted. The effects of varying lift offset on the harmonic hub loads were different depending on the specific harmonics and advance ratios. Furthermore, strong rotor–rotor interactions were seen, and local excursions in the flap bending moments could be correlated to blade–vortex interactions on the advancing side of the rotors even at relatively high advance ratios, and to the unsteady aerodynamic effects of the reverse flow regions on the respective retreating sides of the rotor disks. The improved comprehensive analysis modeling capabilities will be helpful to quickly assess the dynamics and their aerodynamic sources, including the effects of lift offset and rotor–rotor interactions, and so they will prove instrumental in the understanding of the investigated test rig as well as future coaxial rotor designs.

Requirements and Design Challenges in Rotorcraft Flight Simulations for Research Applications

Research flight simulators often differ in requirements and design parameters compared to flight simulation training devices due to their broad field of applications. Flexibility and extensibility are the key factors to be able to use the simulation environment for numerous projects to save budget and to increase simulation fidelity over time. With design and implementation examples of the Rotorcraft Simulation Environment (ROSIE) at the Institute of Helicopter Technology at the Technische Universitaet Muenchen, compliance with these requirements shall be demonstrated. After a discussion of the challenges in high fidelity real-time flight simulation, e. g. time delays and resolution of visual cue information, current research projects performed with ROSIE are illustrated.

Comprehensive Analysis of a Coaxial Ultralight Rotorcraft and Validation with Full-Scale Flight-Test Data

The results of full-scale flight testing in combination with comprehensive analysis of an ultralight counterrotating coaxial rotorcraft are presented. The CoAX 2D was developed and manufactured by edm aerotec in Geisleden, Germany. The helicopter features two-bladed, 6.5-m-diameter upper and lower rotors in teeter configuration with uniform airfoil sections and linearly twisted blades. The focus was on the development of a comprehensive analysis model using CAMRAD II, its validation with measured flight-test data, and results evaluation from both measurements and analysis. The CoAX 2Ds power consumption, tail loads, hub loads, teeter angles, and blade-tip clearance were evaluated for both hover and forward flight. Performance and thrust correlated well between the analysis and the measurements. Effects from rotor-fuselage interference dominated the measured 2/rev hub load and 1/rev teeter angle harmonics. The numerical model also matched well with the measured vibrations during forward flight in terms of hub loads, teeter angles, and resulting blade-tip clearance. Minimal rotor-rotor blade-tip clearance occurred at low flight speeds because of dominating effects from rotor-rotor interference.

Bilinear approach to tensile properties of flax composites in finite element analyses

Flax fibers show potential in bio-efficiency compared to conventional composite fibers with good mechanical properties. The tensile behavior of flax fibers shows a nonlinear stress–strain relation. Within this work, a bilinear elastic–plastic approach is described, which is based on the generalized Hill potential theory and easily applicable in ANSYS. The method was used to model the nonlinear stress–strain behavior under quasi-static tensile loading of flax fiber-reinforced laminates. Hashin failure mechanisms using the stress–strain data of the bilinear model are applied as well. The results were compared to experimental data, carried out using pre-impregnated flax fibers in three types of tensile test specimens. The layups of investigation were

Dynamic Rotor Blade Displacement Tracking with Fiber-Optical Sensors for a Health and Usage Monitoring System

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Investigation of Centrifugal Pumping Rotor Blades in Hover Using CFD

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