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Unsteadiness of the rotor slipstream in the ground effect and its impact on helipad loads
Get PDFThe concept of elevated (rooftop) heliport is known and developed for decades. However due to the significant noise and other drawbacks of helicopters, their application in practice is currently limited mostly to emergency cases, like the lifesaving. Secondly, in recent years the idea of autonomic, light and quiet air taxies flying to cities gains in interests. Such vehicles would need some amount of free space to land and take-off safely; the rooftop heliports seem to be perfectly suitable. A drawback of the elevated heliports may be vibrations of the whole building, caused primarily by the unsteadiness of the rotor slipstream impinging on the heliport surface during take-off and landing. It is especially awkward in case of medical heliports, due to strict vibration requirements. On the other hand, oscillations of loads caused by a helicopter rotor slipstream are quite unappreciated issue. To investigate this topic, an experimental investigation focused on a remotely controlled, 450-class helicopter, has been performed. Measurement of pressure acting on the simulated heliport plate showed a level of pressure oscillations for different test cases, as a function of radial position. The Fourier analysis has also been performed to show dominant frequency of the oscillation. Moreover, the velocity field in the rotor slipstream was captured using PIV method to capture the tip vortices position, to explain the low-frequency component of the oscillation
Full electric helicopter anti-torque
Get PDFOn the way to complete electric flight, the electrification of helicopter subsystems is an essential milestone. This paper discusses the design of an electric helicopter anti-torque system, which uses Kopter’s AW09 helicopter as a platform and shall be tested in ground tests. Analysis of state of the art anti-torque devices for helicopters has helped to identify concepts, which are suitable to be combined with electric propulsion and actuation. Engineering models are used to estimate the power benefits of varied tail rotor RPM, enlarged and steerable vertical stabilizers and drag reducing devices, which cover the rotor in forward flight. In connection with operational benefits viewed from the OEMs perspective, an architecture is proposed which consists of an electric driven shrouded tail rotor, an electric pitch actuation system and additional aerodynamic surfaces, like a steerable vertical stabilizer and a drag optimized tail rotor cover. The systems were developed according to the results of a safety analysis to meet the requirements of CS-27. The electric tail rotor drive is designed with an internal level of redundancy that allows to compensate for subsystem failures
STORM, the new AIRBUS rotorcraft simulation tool based on 60 years of cumulated experience in digital flight physics
No full textThe paper presents the new in-house rotorcraft aeromechanic simulation tool developed by Airbus. STORM (Simulation Tool for Overall Rotorcraft Modelling) gathers more than sixty years of experience in rotorcraft simulation and paves the way towards great perspectives thanks to its open architecture. STORM was developed to replace the former in-house aeromechanic simulation tool, HOST (Helicopter Overall Simulation Tool) developed in the nineties and widely used on engineering side by various disciplines, and also for building flight loops for real time training simulators. From the requirements given by the community of users, a new architecture was envisaged based on HOST foundations. A first feasibility analysis was launched for one year before deciding to run the development of the future Airbus Helicopters aeromechanic simulation tool. Key features of what STORM brings to rotorcraft aeromechanic simulation are presented, and the future capabilities are detailed
Aerodynamics of small rotors in hover and forward flight
Get PDFA wind tunnel test of eleven two- and three-bladed small-scale rotors was conducted in an open-jet, lowspeed wind tunnel. The goal was to study the influence of number of blades, blade pitch and geometry on the hover performance. Two rotors were also studied in forward flight with varying rotational speeds, rotor tilt angles and flow velocities covering a wide range of operating conditions. The experimental results were used to develop a simple, empirical model of the studied rotor based on dimensionless quantities. The model can be used in the preliminary design of multicopters. The performance measurements were supplemented with optical background-oriented schlieren (BOS) measurements to visualize the blade tip vortices in the rotor wake in order to gain a better understanding of the flow state. Simulations with DLR’s free wake unsteady panel code (UPM) were carried out for comparison
High fidelity simulation of a drone propeller in hover
Get PDFEven though drones were initially developed for military purposes during World War I, they are now being widely used due to their large range of applications. Technological improvements enabled their use for many private and professional applications. Although drones have been widely studied in the field of flight control, their aerodynamic behavior is yet to be completely understood. Recently, some aerodynamic and aeroacoustic studies have been performed and published using Computational Fluid Dynamics (CFD) methods. Among these, some simulations use Reynolds-Averaged Navier-Stokes (RANS) models and others Large Eddy Simulation (LES) models and they tend to rely on 3D scanned geometries of commercial propellers. There are plenty of drones flying around the world (the US Federal Aviation Administration has registered 865 thousands of drones across the US in May 2022) and a lot of manufacturers. However, limited information on the aerodynamics of industrial propellers can be found
Exhaust gases thermal impact simulation on helicopter rear structure using CFD
Get PDFExhaust gases ejected by helicopters engines can be assimilated to jets in crossflow as they interact with a complex flow field composed of rotor downwash, relative wind and ground effect for some flight cases. This jet in crossflow configuration is characterized by a strong temperature gradient between the jet and the crossflow as exhaust gases are ejected at temperatures close to 600°C to 700°C. Their interaction with the external flow field can lead to thermal issues such as the overheating of structural parts or external equipment items and the re-ingestion of hot gases through engine and avionics bays air intakes. Hence, being able to predict exhaust gases trajectory and their turbulent mixing with the surrounding flow is critical for design purpose. The present work investigates the capability of aerothermal CFD simulations to correctly reproduce trajectory and mixing of such flows in order to support design, through two representative configurations. Different Steady RANS and SAS/LES approaches are first compared on a dedicated hot jet in crossflow database collected at ONERA. It is shown that even advanced RANS modelling cannot reproduce the jet mixing with a high level accuracy, contrary to unsteady methods. The suggested unsteady methodology is then applied on a real helicopter wind tunnel experiment and shows a very satisfactory reproduction of the near wall temperature field in the helicopter region of interest
Tip vortex study of a rotor with double-swept blade tips
No full textAn experimental aerodynamic study was conducted, analyzing the wake structure of a four-bladed model rotor with a forward-backward swept tip geometry inspired by the ONERA-DLR “ERATO” design. Similar tip designs are used on some modern helicopter main rotors. The experiments were conducted at the rotor test stand Göttingen in hover-like conditions using a stereoscopic high-speed particle image velocimetry system. The results are compared with a reference rotor using a conventional parabolic blade tip. The test parameters include both constant-pitch cases and pitch-oscillating cases with a cyclic swashplate input. The constant-pitch tests show a two-step stall behavior for the double-swept tip, with the first step characterized by a reduced thrust slope and a reduced rotor efficiency. This effect is explained by a repositioning and a structural change of the tip vortex generation. The pitch-oscillating cases show that the double-swept tip results in an earlier tip stall compared to the parabolic geometry while maintaining high thrust levels. The dynamic tip stall yields a break-down of the wake’s tip vortex system, which is replaced by a spanwise band with small-scale turbulent structures and trailed vorticity, but no large-scale vortices
Smart Twisting Active Rotor (STAR) – Pretest predictions
No full textA Mach-scaled model rotor with active twist capability is in preparation for a wind tunnel test in the large low-speed facility (LLF) of the German-Dutch wind tunnel (DNW) with international participation by DLR, US Army, NASA, ONERA, KARI, Konkuk University, JAXA, Glasgow University and DNW. To get the maximum benefit from the test and the most valuable data within the available test time, the tentative test matrix was covered by predictions of the partners, active twist benefits were evaluated, and support was provided to the test team to focus on the key operational conditions