Lars Reimer

CFD-based Gust Load Analysis for a Free-flying Flexible Passenger Aircraft in Comparison to a DLM-based Approach

Gust load analysis is a relevant part of the certification process of aircraft. In need of low computing times, industrial analysis procedures often rely mainly on low-fidelty numerical aerodynamics methods, such as the Doublet Lattice method (DLM). However, their accuracy with respect to loads has not been assessed sufficiently in comparison to high-fidelity methods in the past. In this paper, simulation results of a classical DLM-based gust load analysis process are compared to the results of an alternative process in which the DLM solver is replaced by the CFD solver TAU. The investigation is performed with a realistic modern passenger aircraft. It is studied how the consideration of different levels of multidisciplinarity in the simulations affects the overall loads. The simulation methodologies exploited in the CFD-based analysis process are outlined. It is shown that the gust load factors predicted with CFD are significantly lower than those of the classical DLM-based process, not only in the transonic flow regime, where benefits from the CFD-based analysis are expected, but also in the subsonic flow regime.

Validation of a Time-Domain TAU-Flight Dynamics Coupling Based on Store Release Scenarios

A six degrees of freedom flight dynamics module was coupled to DLR’s CFD solver TAU. The algorithms implemented in the flight dynamics module for solving the 6-DoF equations of motion are explained in detail. The coupling is validated using one analytic test case and two store release experiments. The effects on the prediction accuracy of a strong coupling approach using an error-based coupling convergence criterion are compared to classical weak coupling.

Modeling of Movable Control Surfaces and Atmospheric Effects

The paper reports on meshing strategies for modeling of movable control surfaces. In the course of the project ComFliTe, different meshing strategies have been investigated. As central test cases a generic wing-aileron configuration based on the LANN wing [1] was studied. Approaches based on mesh deformation, the Chimera technique and a combination of Chimera technique and mesh deformation were considered. As second test case a generic wing-spoiler configurations was studied. The challenging thing about the latter test case was that the simulation was supposed to start when the spoiler is still fully recessed in the contour of the wing. The pros and cons of the different modeling approaches applied to the aileron and the spoiler test case are discussed and recommendations for modeling of particularly moving control surfaces are given. In addition, the so-called disturbance velocity approach is presented in the second part of this paper as a very efficient technique for the modeling of atmospheric effects striking an aircraft; e.g. gusts.

DLR Pilot Applications in ComFliTe

In ComFliTe, a lot of work has been carried out to improve the multi-disciplinary simulation of free flying aircraft relying on highfidelity methods. To enable the simulation of gust encounter situations, techniques for the modeling of atmospheric effects have been implemented in the CFD solver TAU. To take into account the reaction of the aircraft due to additional air-loads created, e.g., by gusts or control surface movement, TAU has been coupled to a flight mechanics module. Enhanced techniques for the handling of movable control-surfaces have been developed, to improve the simulation of aircraft maneuver. Within this paper selected applications are described demonstrating the new capabilities of the multi-disciplinary simulation environment developed in ComFliTe. As highlight, the gust encounter simulation of a full Airbus A340 configuration and the maneuver of a generic fighter aircraft is presented.

A Mesh-Free Parallel Moving Least-Squares-based Interpolation Method for the Application in Aeroelastic Simulations With the Flow Simulator

A mesh-free interpolation method for the use in aeroelastic aircraft simulations was implemented. The method is based on a weighted moving least-squares (MLS) approach for solving the spatial coupling problem arising in such problems. The paper presents the fundamentals of the MLS-based method and its advantages over the popular and often-used mesh-free interpolation method of Wendland et al. [1, 2]. Further emphasis is put on the description of the parallel implementation of the MLS-based method. The effectiveness of the method is demonstrated with selected interpolation test cases.

Integrated Process Chain for Aerostructural Wing Optimization and Application to an NLF Forward Swept Composite Wing

This contribution introduces an integrated process chain for aerostructural wing optimization based on high fidelity simulation methods. The architecture of this process chain enables two of the most promising future technologies in commercial aircraft design in the context of multidisciplinary design optimization (MDO). These technologies are natural laminar flow (NLF) and aeroelastic tailoring using carbon fiber reinforced plastics (CFRP). With this new approach the application of MDO to an NLF forward swept composite wing will be possible. The main feature of the process chain is the hierarchical decomposition of the optimization problem into two levels. On the highest level the wing planform including twist and airfoil thickness distributions as well as the orthotropy direction of the composite structure will be optimized. The lower optimization level includes the wing box sizing for essential load cases considering the static aeroelastic deformations. Additionally, the airfoil shapes are transferred from a given NLF wing design. The natural laminar flow is considered by prescribing laminar-turbulent transition locations. Results of wing design studies and a wing optimization using the process chain are presented for a forward swept wing aircraft configuration. The wing optimization with 12 design parameters shows a fuel burn reduction in the order of 9% for the design mission.