Browse Topic: Emissions
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Time-resolved background-oriented schlieren (BOS) data are used to calculate the two-dimensional velocity field in the wake of free-flying full-scale helicopters in ground effect. The calculation is performed based on the density gradient pattern of the helicopter engine exhaust gas passing the BOS field of view. A classical BOS evaluation allows the visualization of density gradients such as vortices and the exhaust plume. The result is the BOS displacement field. Applying the two-dimensional divergence to this data results in a pattern that is constant in shape across multiple BOS images, but convects downstream with the outwash velocity of the helicopter. Using this data as input to a second, timeresolved evaluation, quantitative two-dimensional velocity fields are calculated. Choosing an appropriate strategy for preparing and evaluating the data is critical to reliable velocity estimation. Another important aspect is to distinguish between reliable velocity data and erroneous results in areas of reduced signal intensity due to a lack of thermal structures. The velocity data obtained are compared with an analytical outwash model and constant temperature anemometry data acquired simultaneously with the BOS images. The data show good quantitative agreement in areas of sufficient thermal structures within the field of view.
Installation effects of the Volocopter 2-X beam structures are studied by performing high-fidelity CFD simulations of a single and three-rotor configurations in hover. The studied cases are compared with simulations without airframe to investigate the installation effects. In addition, the noise emission of the configurations is simulated by using a Ffowcs Williams-Hawkings based CAA code. Scattering effects are also included by using a BEM code. The rotors are simulated at an identical RPM and are placed in their mounting position. Furthermore, an additional setup with individual rotor RPMs is simulated for the three-rotor configuration. The installation mainly affects the rotor wake, thrust and pressure fluctuations on the rotor, while the integral aerodynamic quantities remain almost unchanged. This resulted in additional oscillations in the acoustic pressure signal. Overall, the installation increases the OSPL by about 1.5 dB, but has a greater effect on the 3-20 harmonics. The simulation data were compared with the Volocopter measurements and showed good agreement. For the three-rotor configurations, the rotor-rotor interactions were found to be dominant for the aerodynamic and acoustic performance, while the installation effects only locally influenced the noise emission by 3-4dB.
ABSTRACT This paper introduces the Shape Adaptive Blades for Rotorcraft Efficiency (SABRE) Horizon 2020 research program and presents initial comprehensive analysis results on the efficacy of adapting blade shapes as a means of reducing rotorcraft power requirements and emissions. The aims of the research program are introduced, followed by discussion of the six different morphing concepts that will be explored. The morphing mechanisms are based on active camber, chord extension, twist, and active tendon morphing technologies. SABRE will explore the use of these concepts individually and in combination, for rotor quasi-steady configuration-type morphing and up to 2/rev actuation of some of the mechanisms, with the objective being to find the best balance between emissions reductions versus complexity and added weight. Initial investigations into the potential power reductions compared to the baseline full-scale BO-105 main rotor achievable with the morphing concepts were performed using Blade Element Momentum Theory and a comprehensive analysis model that was developed using CAMRAD II. The analytical model was validated by full-scale rotor wind tunnel measurements. A combination of active twist and active chord extension achieved up to 11% performance gain in hover. Active camber morphing performance was very sensitive to the combination of deflection, morphing section radial length and placement on the blade, as well as the actuation phasing and blade loading coefficient. The active camber morphing showed power reductions of up to 5.5% in hover and 5% at an advance ratio of 0.313 with a 2/rev actuation, while the active tendon concept showed the capability to change the dynamic response of the rotor blade.
In the emerging market of Advanced Air Mobility (AAM), aerospace companies have been designing and prototyping electric and hybrid vehicles to revolutionize travel. These vehicles must have low noise and particulate emissions while also having enough propulsive efficiency to complete the mission. This paper presents the relationship between noise and propulsive efficiency as related to any aircraft equipped with an electric motor and a variable pitch rotor/propeller. The combination of the electric motor with the variable pitch propeller/rotor allows for a decoupled rotational speed and torque generation, meaning that the electric motor can generate the same amount of torque while operating at different rotational speeds. This feature allows the rotor/propeller to hold constant thrust at different combinations of rotational speeds and torque, by adjusting the collective pitch of the blades. Therefore, for a rotor at constant thrust, the minimum noise (from loading and thickness contributions) and minimum power operating points in terms of rotor RPM and collective blade pitch, are not the same thus leading to the fact that it takes increased energy to decrease noise. A MATLAB code is developed to investigate the power and noise relationship by employing several functions to integrate XFOIL and Blade Element Momentum Theory for the rotor performance calculations and WOPWOP for thickness and loading noise analysis.
This slash document collects general reference material related to gaseous oxygen system flow requirements and sizing calculations. This document will assist oxygen system equipment designers and operators to establish systems and equipment requirements. The document consists of charts, tables, system schematics, system requirements, and sample calculations for system sizing.
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