Validation of Aerodynamic and Aeroacoustic Simulations of Contra-Rotating Open Rotors at Low-Speed Flight Conditions

Contra Rotating Open Rotor (CROR) propulsion systems have been the focus of a number of research projects in recent years, aiming to establish this propulsion system as an economic and environmentally friendly powerplant for future transport aircraft. In the frame of the EU 7th Framework Joint Technology Initiative Smart Fixed Wing Aircraft project, the DLR Institute of Aerodynamics and Flow Technology is participating as an associated partner in the Airbus-led studies of the Contra-Rotating Open Rotor. Due to significant technical challenges in terms of noise emissions, installation effects and certification that still need to be addressed, the numerical activities require the use of sophisticated multidisciplinary analysis tools and approaches covering both aerodynamics and aeroacoustics. Having been widely applied to the simulations of single as well as contra-rotation propellers, the DLR CFD code TAU and the aeroacoustic analysis tool APSIM+ allow for a detailed analysis and an improved understanding of the complex aerodynamics and aeroacoustics of this type of propulsion system. Drawing benefit from a set of high- quality results from aeroacoustic wind tunnel tests of a generic Airbus designed CROR configuration, this paper will present an in-depth analysis and validation of the DLR numerical approach to coupled CFD-CAA-simulations to enable reliable predictions of the aerodynamic and aeroacoustic performance of CROR propulsion systems

Parallel Implementation of a Dynamic Overset Unstructured Grid Approach

This paper describes the parallelization of a dynamic overset grid approach with predefined holes. The algorithm has been designed for massive parallel applications. Numerical results are presented of a parallel 3D Euler calculation of an isolated propeller

Assessing Turbofan Modeling Approaches in the DLR TAU-Code for Aircraft Aerodynamics Investigations

In the context of an increased focus on fuel efficiency and environmental impact, turbofan engine developments continue towards larger bypass ratio engine designs, with UltraHigh Bypass Ratio (UHBR) engines becoming a likely powerplant option for future commercial transport aircraft. These engines promise low specific fuel consumption at the engine level, but the resulting size of the nacelle poses challenges in terms of the installation on the airframe. Thus their integration on an aircraft requires careful consideration of complex engine-airframe interactions impacting performance, aeroelastics and aeroacoustics both on the airframe and the engine sides. As a partner in the EU funded Clean Sky 2 project ASPIRE, the DLR Institute of Aerodynamics and Flow Technology is contributing to an investigation of numerical analysis approaches, which draws on a generic representative UHBR engine configuration specifically designed in the frame of the project. In the present paper, project results will be discussed, which aimed at comparing various engine modeling approaches in the context of external aerodynamics focused CFD simulations with the DLR TAU-Code. The primary focus is the high-fidelity approach with a geometrically fully modeled fan stage, with an in-depth study on spatial and temporal resolution requirements, which will provide the reference data for simpler approaches using classical engine boundary conditions and, in subsequent work, actuator disc or body force models to represent the rotor and stator. The primary aim is to identify the capabilities and shortcomings of each model, develop a best-practice approach in each case and determine the best application scenarios

The Case for Counter-Rotation of Installed Contra-Rotating Open Rotor Propulsion Systems

Contra Rotating Open Rotor (CROR) propulsion systems have seen renewed interest as a possible economic and environmentally friendly powerplant for future transport aircraft. Installation effects, i.e. the mutual interactions between airframe components and the rotors, have a pronounced impact on the aerodynamic and aeroacoustic performance for this type of engine. In this paper, the impact on aerodynamic performance and noise emissions caused by the presence of a pylon as well as a variation in the sense of rotation of the rotors is numerically studied for a representative 10x8-bladed pusher-configuration CROR engine at typical take-off conditions. In particular, the sense of rotation influence on blade and rotor performance and loadings as well as on the handling quality relevant in-plane rotor forces is analyzed, as is the resulting impact on the noise emissions in the near- and farfield and the flyover noise results. Having been widely applied to the simulations of single as well as contra-rotation propellers, the DLR CFD code TAU and the aeroacoustic analysis tool APSIM allow for a detailed analysis and an improved understanding of the complex aerodynamics and aeroacoustics of this type of propulsion system

Numerical Simulation of Manoeuvring Aircraft by CFD Aerodynamic and Flight-Mechanic Coupling

The improvement of manoeuvrability and agility is a substantial requirement of modern fighter aircraft. Today rolling rates of 200°/s and more will be achieved especially by unstable design of the aircraft. Most of today's and probably future fighter aircraft will be Delta-Wing-Configurations. The flow field of such configurations is dominated by vortices developing by flow separation at the wings and the fuselage. The delay in time of vortex position and condition to the on flow conditions of the manoeuvring aircraft can lead to significant phase shifts in the distribution of loads. In this case reliable results for the analysis of flight properties can only be obtained by a non-linear integration of the unsteady stationary aerodynamic and real flight movement. Today this can only be realised by flight tests and not during the design period. Flight tests as well as modifications after the definition phase lead normally to a substantial increase in cost and time. To help decrease these post-definition-phase modifications, it is useful to have a numerical tool which enables aircraft designers to analyse and evaluate the dynamic behaviour of their designs during the design phase itself. To accomplish this task, a simulation tool which can simulate the dynamic behaviour of aircraft has been designed within the DLR project AeroSUM-"Aerodynamic Simulation of Unsteady Manoeuvres". The main objective of the current simulations is the coupling between the aerodynamic and flight-mechanic interactions. The software package which is used for these simulations is divided into several modules, all of which are communicating through a central computational interface. The computational interface manages both the data- and work-flow between the software modules. The numerical simulation of the flow-field is performed with an unstructured, time accurate Navier-Stokes flow solver, TAU, which has been developed by DLR. For the Simulation of configurations with moveable control panels, the chimera technique for unstructured meshes is implemented within the TAU-Code. For the coupling between the aerodynamics and flight-mechanics, the simulation tool SIMPACK is used, which contains the flight mechanic equations and is used as a GUI for the simulation environment. For the validation of the results of the numerical simulation software, comparisons to experimental data will be performed. The experimental data will be obtained from extensive wind-tunnel testing of a generic delta-wing aircraft model, see Figure 1 and 2. The AeroSUM wind-tunnel model is a cropped-delta-wing configuration consisting of a fuselage and wings with trailing edge flaps. It is specially designed for testing in the "Transonic Wind-Tunnel Göttingen (TWG)". The experimental set-up is capable of simulating both controlled and free-to-roll manoeuvres, at various angles-of-attack, as well as static flight conditions. In this paper we will present several results from the current simulations. The first results to be shown are the static aerodynamic parameters of the configuration, and the structure of the vortex-dominated flow-field, at various angles-of-attack and roll-angle settings, see Figure 3 and 4. The surface-pressure and roll-moments will be shown to compare favourably with the experimental data. The static simulation cases are the starting points for each unsteady simulation. Additionally to this, some unsteady manoeuvre simulations will be shown. The delta wing is set in guided periodic roll-motion with a given velocity respectively in an oscillating motion with a given frequency and amplitude. Comparisons with the experimental data will be shown as well. Finally we will present some coupled simulation, i.e. free-roll manoeuvres initiated by flap deflection of the delta wing trailing edge flaps. The desired manoeuvrability capabilities of fighter aircraft keep increasing, thus the design and development of such aircraft become ever more complex. It is hoped that the use of coupled simulation-packages like TAU-SIMPACK will assist in keeping the complexity of fighter aircraft development at a manageable level for years to come. Therefore, the final aim of the project is the capability to simulate a fully configured, manoeuvring fighter aircraft, i.e. an aircraft with several control-surfaces and thrust-vector devices

Numerical Simulation of Manoeuvring Aircraft by Aerodynamic and Flight-Mechanic Coupling

This paper presents results of simulations performed within the scope of the DLR-Project AeroSUM- “Aerodynamic Simulation of Unsteady Manoeuvres”. The objective of the AeroSUM-Project is to develop a numerical tool to simulate the unsteady aerodynamics of a free flying aircraft, by use of coupled aerodynamic and flight-mechanic computations. To achieve this objective, the unstructured, time accurate CFD flow-solver Tau is coupled with a computational module solving the flight-mechanic equations of motion. By use of an overlapping grid technique (chimera), simulations of a complex configuration with movable control-surfaces is possible. Results of static calculations are presented to show the basic aerodynamics of the vortex dominated flowfield of the delta wing. The static simulation cases also serve as starting solutions for the unsteady simulations. Results of the unsteady manoeuvre simulations are divided into guided motion and freeflight motion. For the guided motion an oscillating motion with a given frequency and amplitude is presented. For the free-flight motion, the following cases are presented: free-to-roll from a non-zero initial roll-angle (without flap deflection), and free-to-roll initiated by flap deflection from an initial rollangle of zero. These calculations demonstrate the functionality of the simulation system. A 65-degree cropped delta wing model, with fuselage and movable trailing edge flaps, is used to gather experimental data. Several forced and free-to-roll experiments around the body fixed axes, both with and without flap deflection, are performed in order to validate the computational results obtained with the simulation tool