Showing papers in "Journal of The American Helicopter Society in 2015"

Numerical Investigation of Three-Dimensional Static and Dynamic Stall on a Finite Wing

Abstract: Three-dimensional numerical computations using ONERA’s structured elsA code and the unstructured DLR-TAU code are compared with the OA209 finite wing experiments in static stall and dynamic stall conditions at a Mach number of 0.16 and a Reynolds number of 1 × 10^6 . The DLR-TAU computations were run with the Spalart–Allmaras and Menter shear stress transport (SST) turbulence models, and the elsA computations were carried out using the Spalart–Allmaras and the k–ω Kok + SST turbulence models. Although comparable grids were used, the static simulations show large discrepancies in the stall region between the structured and unstructured approaches. Large differences for the three-dimensional dynamic stall case are obtained with the computations using the Spalart–Allmaras turbulence model showing trailing edge separation only in contrast to the leading edge stall in the experiment. The three-dimensional dynamic stall computations with the two- equation turbulence models are in good agreement with the unsteady pressure measurements and flow field visualizations of the experiment, but also show a shift in the stall angle compared to the experiment. The analysis of the flow field around the finite wing using the numerical simulations reveals the evolution of the -shaped vortex, generated by the interaction of the blade tip vortex.

Structures perspective for strength and fatigue prognosis in composites with manufacturing irregularities

Abstract: Recent advances in understanding deformation and failure mechanisms of polymermatrix composites used in rotor structures enable accurate and efficient measurement of material stiffness, strength, and fatigue characteristics based on testing small unidirectional laminate specimens. Successful failure predictions increased our confidence in the development of virtual test methods replacing some of the standard tests of multi-directional laminated composite materials with three-dimensional models accurately predicting deformation, damage topography, strength, and cycles to failure. However, the remaining key questions are related to the ability of transitioning the material-scale virtual test information to larger composite structures. This work presents results of the feasibility assessment targeting the scaling of knowledge and methods acquired at the material scale, to larger structural elements.

Experimental Analysis of the Aerodynamics of Long-Shrouded Contrarotating Rotor in Hover

Abstract: This paper aims to quantify the benefits of a shrouded coaxial rotor configuration through experimental comparisons with free (not shrouded) rotors in hover. The experiment shows that both the figure of merit of contrarotating rotors and the system power loading are improved by the shroud inclusion. Improvements are induced by a suction effect at the inlet, which can be optimized by a regulation effect of the mass flow. Compared to free rotors, the strong suction peak formed on the shroud leading edge by a 65% increase in mass flow, allowing the shroud to contribute up to 56% of the total thrust. More uniform pressure distribution in the downstream rotor and less contraction of the slipstream decrease losses and increase the rotor efficiency. The shrouded system efficiency is further improved if the upstream rotor rotates slower than the rear one, for a given total shaft power, because a stronger pressure depression occurs upstream of the rotors to generate more mass flow. On the other hand, the system behavior is insensitive to the interrotor distance.

Segment-wise Measurement of Helicopter Approach Noise with a Reduced Microphone Setup

Abstract: To measure the noise footprint of a helicopter approach procedure, microphones are usually distributed over a large area. In this paper, however, a method is utilized where the measurement of the noise footprint is conducted in parts by distributing the microphones over a limited area and executing the same approach procedure, while the position of the landing point is shifted. The flight tests are conducted with the EC135-ACT/FHS helicopter. Guidance to the pilots is provided by use of a “tunnel-in-the-sky” head down pilot display. Since the same flight procedure is executed multiple times, it is possible to conduct a statistical analysis on the accuracy and reproducibility of the approach procedure in terms of position, velocity, and generated noise. This statistical analysis shows that the geometric accuracy is on the order of 6 m in the horizontal plane and 12 m in the vertical plane. The variations in the measured sound exposure level from one approach to another are on the order of 3–7.5 dB(A). The approach procedure is also executed with excessive cyclic pilot control inputs to identify an upper limit of the extra noise generated by unsteady flight. However, these approaches are indistinguishable, in terms of the sound exposure level or sound pressure level, from the approaches with normal pilot control inputs.

Advanced composite materials technology for rotorcraft through the use of nanoadditives

Abstract: Composite materials are increasingly used in rotorcraft structures to reduce weight and improve efficiency. The rotorcraft industry is constantly in need of higherperformance materials that offer improved mechanical strength and stiffness at a lower weight. In polymer-matrix composite structures, matrix-dominated failures impose severe limitations on structural performance. The objective of this work is to advance composite material technologies for rotorcraft through the use of nanoadditives to improve structural efficiency. Technical challenges and potential solutions for improving matrix-dominated performance of prepreg composites through nanoparticle reinforcement, are discussed. In particular, a promising technology for improving compression and interlaminar strength and fatigue performance, is identified. The advanced materials technology is based on high weight content loading of approximately 100-nm diameter nanosilica particles in low-viscosity resins. Such technology resulted in

Shallow groundwater intrusion to deeper depths caused by construction and drainage of a large underground facility: —Estimation using 3 H, CFCs and SF 6 as trace materials—@@@— 3 H, CFCs, SF 6 トレーサーを用いた評価—

Abstract: This study evaluates a method to estimate shallow groundwater intrusion in and around a large underground research facility(Mizunami Underground Research Laboratory-MIU). Water chemistry, stable isotopes(δD and δ18O), tritium (3H), chlorofluorocarbons(CFCs)and sulfur hexafluoride(SF6)in groundwater were monitored around the facility(from 20 m down to a depth of 500 m), for a period of 5 years. The results show that shallow groundwater inflows into deeper groundwater at depths of between 200–400 m. In addition, the content of shallow groundwater estimated using 3H and CFC-12 concentrations is up to a maximum of about 50%. This is interpreted as the impact on the groundwater environment caused by construction and operation of a large facility over several years. The concomitant use of 3H and CFCs is an effective method to determine the extent of shallow groundwater inflow caused by construction of an underground facility.