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In recent years, helicopter manufacturers have developed an increasing number of nonconventional configurations in order to extend flight envelopes of helicopters towards higher cruise speed. Airbus Helicopters' approach is the compound helicopter RACER, which is equipped with a boxwing and lateral pusher rotors. As the combination of these components with the main rotor induces a variety of mutual interactions, influencing their individual aerodynamic performance depending on the flight conditions, the understanding of these interactions is vital for the evaluation of the overall system. For this reason, the respective mutual influence of main rotor, wings, and lateral rotors is analyzed in this paper for hover. With the help of high-fidelity coupled aerodynamic simulations for the full RACER (Rapid And Cost-Efficient Rotorcraft) configuration as well as for setups omitting individual components, first- and second-order interactions of these components are isolated and analyzed for their effect on the helicopter's aerodynamic performance.

With the pursuit of extending the flight envelopes of helicopters toward higher cruise speed, helicopter manufacturers increasingly have come up with nonconventional configurations in recent years. Among these, Airbus Helicopters' RACER (Rapid And Cost-Efficient Rotorcraft) is a compound helicopter equipped with a boxwing and lateral pusher rotors. In combination with the main rotor, these additional components determine the aerodynamic characteristics of the helicopter. Thereby, depending on the flight conditions, their individual performance is influenced by a variety of interactions. As the understanding of these interactions is vital for the evaluation of the overall system, the respective mutual influence of main rotor, wings, and lateral rotors is analyzed in this paper for cruise flight. For this reason, high-fidelity coupled aerodynamic simulations are conducted not only for the full RACER configuration but also for reduced setups omitting individual components to isolate the effect of these components on the helicopter's aerodynamic performance.

Recent enhancements and applications of the flow solver FLOWer are presented. First, an Adaptive Mesh Refinement technique (AMR) is implemented and an AMR cycle is built around FLOWer. Depending on the application case, the usage of AMR significantly reduces the overall computational cost—and thus increases efficiency—of the flow solution. Exemplary, for a complete helicopter simulation a reduction in computational time of 45% is achieved without any observable loss of accuracy. Second, the implementation of a new shielding approach for detached eddy simulations is shown. This applies a sophisticated communication method to exchange flow variables in wall normal direction. As an application case, the computation of the highly resolved rotor wake in hover highlights the possibilities of high performance computing in combination with advanced numerical methods for rotorcraft flows.

In recent years, various helicopter manufacturers have been focusing increasingly on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics or aeroacoustic noise emission, to name only a few. In the following study, the behaviour of RACER in hover under the influence of crosswinds from eight different directions is investigated to support AH at the de-risking of RACER for this flight condition prior to the first flight. Therefore, a multidisciplinary, high-fidelity tool chain for coupled and trimmed aerodynamic simulations of the complete rotorcraft is applied. The presentation of the results is organized in three parts. In the first part, the flight mechanic behaviour is analysed and successful de-risking of ground clearance is shown. The second part focuses on the performance of the main rotor, the lateral rotors and the tail surfaces under wind conditions and shows that minimal power is required for headwind. In the last part, an analysis of the engines is performed, including a closer look at the inflow quality to the core engine and the convection of the hot exhaust gases.

In recent years, various helicopter manufacturers increasingly have been focusing on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER (rapid and cost-efficient rotorcraft) of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics, or aeroacoustic noise emission, to name only a few. To support AH at the minimization of risk of RACER's first flight, the Institute of Aerodynamics and Gas Dynamics provides high-fidelity coupled and trimmed aerodynamic and aeroacoustic simulations of the complete helicopter by the application of a multidisciplinary tool chain. In its first part, the work focuses on the description of this advanced tool chain and on important features for the analysis of this new configuration. In the second part, exemplary simulation results for a hover and a high-speed cruise flight condition are shown, and the main aerodynamic interactions between the different components are identified. As expected for this configuration, numerous interactions are found for both flight cases, e.g., main rotor–propeller interaction in hover or main rotor–wing interaction in high-speed flight. Finally, aeroacoustic results are shown for hover with a close look at the propellers' contribution.

In the past years, the aeroacoustic noise emission of a helicopter became one of the most important, but also challenging issues in helicopter development. The blade vortex interaction phenomenon is one of the dominant phenomena characterizing the helicopter's aeroacoustic footprint, which is insufficiently predicted by low fidelity computational methods. For a high fidelity noise prediction of a helicopter configuration, a multidisciplinary CFDCSD-CAA tool chain has been established at the Institute of Aerodynamics and Gas Dynamics of the University of Stuttgart. With higher order CFD computed noise generation at the near field and the noise convection using a Ffowcs-Williams Hawkings based CAA code, very good agreement to measured aeroacoustic noise in wind tunnel as well as free flight experiments of helicopters is achieved. However, the simulations had been limited to the main rotor's geometry up to now, where some residual deviations to the experiment still exist. In this paper, we present a high fidelity aeroacoustic simulation of a complete helicopter configuration and the benefit compared to an isolated rotor simulation in predicting its aeroacoustic noise emission. Shading and reflection effects are clearly resolved, influencing the behaviour of the helicopter's noise radiation. The simulated aeroacoustic noise emission of the helicopter lies within the experimental variation and shows therefore highly promising results for the next generation of aeroacoustic noise prediction.

This work presents the correlation of simulation results and flight-test data for a high-speed (V = 220 kt), high advance ratio (μ > 0.5) flight of the compound helicopter X3. The simulation tool chain consists of state-of-the-art coupling between the computational fluid dynamics (CFD) code FLOWer and the comprehensive analysis tool HOST. By applying a freeflight trim procedure, the experimental flight state is accurately represented in the simulation. The deviations of most trim controls is below 1°, and the maximum deviation is less than 1.4°. The analysis of the high-fidelity CFD results illustrates key features of the flow physics at this high advance ratio, such as wake interactions, reverse flow, and advancing side loading. The correlation of rotor dynamics data between simulation and flight test is favorable. Good accordance is demonstrated for flap bending moments, torsion moments, and pitch link loads. In contrast, the correlation is weaker for the chord bending moments for which it is shown that the interblade damper and drive train model mostly determine the structural loads.