Jochen Wild

An integrated design approach for low noise exposing high- lift devices

The DLR project LEISA combines and focuses activities in the research areas of high lift system design, flow control and aero-acoustic design methods, which have been carried out rather independently up to now. Furthermore, the competence in the fields of aerodynamics, aero-acoustics, structures and flight systems will be integrated to provide an interdisciplinary assessment of high lift system design for transport aircraft configurations. The project LEISA started at the beginning of 2005, so up to now only few results are available. This paper addresses the integrated design approach and first results for a noise reduced slat device and combined wind tunnel testing results for aerodynamics and aero-acoustics.

Mach and Reynolds Number Dependencies of the Stall Behavior of High-Lift Wing-Sections

Experimental investigations have been carried out with the two-dimensional DLR-F15 high-lift wing-section model in the Cryogenic Wind-tunnel Cologne DNW-KKK to differentiate between the influence of Mach and Reynolds numbers on the stall behavior. Because of the cryogenic environment, Mach and Reynolds numbers have been varied independently between M=0.1–0.25 and Re=1.4×106−15.6×106. The investigation covers two- and three-element configurations at various slat and flap settings and two different slat shapes. The focus of the investigation is to identify conditions of turbulent leading-edge stall, shock-related lift limitations, and flap separations and their influence on achievable maximum lift coefficient.

Advanced High-Lift Design by Numerical Methods and Wind Tunnel Verification within the European Project EUROLIFT II

The design activity within the European 6th framework project EUROLIFT II is targeted towards an improvement of the take-off performance of a generic transport aircraft configuration by a redesign of the trailing edge flap. The involved partners applied different optimization strategies as well as different types of flow solvers in order to cover a wide range of possible approaches for aerodynamic design optimization. The optimization results obtained by the different partners have been cross-calculated in order to eliminate solver dependencies and to identify the best obtained design. The final selected design has been applied to the wind tunnel model and the test in the European Transonic Wind Tunnel (ETW) at high Reynolds number confirms the predicted improvements.

Multi-objective constrained optimisation in aerodynamic design of high-lift systems

This work deals with the application of numerical optimisation to the aerodynamic design of high-lift systems, which is a multi-objective constrained design problem. A description of the design targets and constraints for high-lift wings is given, followed by a detailed analysis of the required properties of the flow calculation for use within optimisation and the suitability of various optimisation algorithms for this type of design problem. Another focus is the validation and application of numerical optimisation to the aerodynamic design of high-lift systems.

Active Flow Control for an Outer Wing Model of a Take-off Transport Aircraft Configuration - A Numerical Study

This contribution discusses the implementation of fluidic actuators that produce a pulsed outlet flow on a three dimensional model of the outer wing of a long-range transport aircraft at take-off, by high-fidelity numerical simulations. The leading-edge high-lift unprotected wing extension, including a wingtip device, designed for high performance at cruise flight, is subject to local flow separation at high angles of attack and low speed flight conditions. Active flow control (AFC) applied at the outer wing can prevent the formation of large turbulent flow separation and increase the aircraft lift to drag ratio (L/D), decrease the drag (D), and increase the angle of attack (AoA) for maximum lift (CLmax). The performed unsteady Reynolds-averaged Navier-Stokes (URANS) simulations prove the flow changes by the local AFC application and include a variation of the actuator’s geometrical setup. The results suggest a successful implementation on a transport aircraft and with an acceptable blowing momentum coefficient.

Advanced Design by Numerical Methods and Wind-Tunnel Verification Within European High-Lift Program

The design activity within the European 6th framework project EUROLIFT II is targeted towards an improvement of the take-off performance of a generic transport aircraft configuration by a redesign of the trailing edge flap. The involved partners applied different optimization strategies as well as different types of flow solvers in order to cover a wide range of possible approaches for aerodynamic design optimization. The optimization results obtained by the different partners have been cross-calculated in order to eliminate solver dependencies and to identify the best obtained design. The final selected design has been applied to the wind tunnel model and the test in the European Transonic Wind Tunnel (ETW) at high Reynolds number confirms the predicted improvements.

Aerodynamic and Acoustic Design of Silent Leading Edge Devices

The high lift system noise of current transport aircraft is dominated by slat noise under certain operating conditions. Suitable means to reduce the noise impact in the vicinity of airports are (i) to increase the distance between the source and the observer and (ii) to reduce source noise levels. Both objectives can only be achieved by means of a multi-disciplinary aerodynamic and acoustic development since the slat is at the same time a very important element to achieve the necessary high lift performance and the dominant noise source of a high lift system1. First attempts to reduce slat noise by means of a slat setting optimization were conducted at DLR in the mainframe of the project Leiser Flugverkehr2. This purely acoustically driven study revealed that a slat gap reduction results in a local flow speed decrease at the slat trailing edge and thus to remarkable noise reductions of up to 10 dB, the latter of course depending on the magnitude of the slat gap reduction. The drawback of this approach was that at the same time the aerodynamic performance of the high lift system was degraded by a non-acceptable level. However, this study was the starting point of the DLR project LEISA (Low noise exposing integrated design for start and approach) that combined activities in the research areas of high lift system design and aero-acoustic design, which were carried out rather independently up to this point in time. In the project LEISA different types of high lift configurations were addressed and investigated in a 2-dimensional approach. The first one is a long chord slat that provided a source noise reduction of about 6 dB while maintaining the aerodynamic performance of the reference slat system. The second, and more radical concept was to omit the slat and apply a droop nose system in order to reduce the aerodynamic losses as much as possible. The finally achieved source noise reduction with the droop nose system was about 8 dB while from the aerodynamic point of view about 50% of the losses were recovered. Based on these promising results the transposition of these high lift systems to a real 3-dimensional wing was carried out in the follow-up project SLED (Silent Leading Edge Devices). The final outcome of the project SLED can be summarized as follows. From the aerodynamic point of view the performance of the 3-dimensional long chord slat compares very well to the reference slat system. The final droop nose design was capable to recover about 40% of the lift loss due the omitted slat. The final acoustic results in terms of source noise levels are an overall 4 dB noise reduction for the long chord slat and about 6 dB noise reduction in case of the droop nose. The obtained aerodynamic and acoustic characteristics were finally transposed to flight in order to assess the effect on community noise which can be expressed in terms of noise iso-contour areas. Regarding the 60 dB(A) and the 65 dB(A) noise iso contour areas the achieved benefit is a reduction of up to 40% of the respective area’s size.

Separation Control on a High-Lift Airfoil using Vortex Generator Jets at High Reynolds numbers

This paper describes an active flow control wind tunnel experiment with a 2D two element high-lift airfoil at high Reynolds numbers of up to Re = 12:2 10 6 and for a corresponding Mach number of M = 0:2. Additional test cases with variations of the Reynolds and Mach number were also conducted. The measurements allow to study Reynolds and Mach number scaling effects. The wind tunnel experiments were performed in the cryogenic test facility DNW-KKK at Cologne, Germany. The main wing is equipped with vortex generator jets which are located close to the leading edge on the pressure side. The objective of the active flow control system is to suppress or delay a turbulent leading edge stall. The experiments clearly show that the active flow control system can prevent stall but the increase of the maximum lift coefficient decreases the higher the Reynolds number is. The benefits primarily depend on the flow rate. In most cases dynamic blowing is superior to static blowing. The actuation frequency seems to be more efficient with higher value. In range of the tested active flow control parameters the Mach number has a small influence.

On the Potential of Numerical Optimization of High-Lift Multi-Element Airfoils based on the Solution of the Navier-Stokes-Equations

The objective of the presented work is to demonstrate the benefits of using numerical optimization of high-lift multi-element airfoils based on RANS-simulation in practical design. It is first shown, that the design methodology chosen in the presented framework is able to detect optimal configurations determined by wind tunnel tests. Beneath this basic statement sensitivities for the validity of the obtained results are outlined. Finally the method is applied to the drag reduction of a 3-element airfoil.

Numerical Studies of Active Flow Control applied at the Engine-Wing Junction

This paper presents a numerical study of active flow control applied at the engine-wing junction to increase the high-lift performance of a generic full scale wind tunnel model representing a landing configuration of conventional airliners with engines mounted under backward swept wings. The use of UHBR (Ultra High Bypass Ratio) engines is currently one of the most promising approaches to further increase the efficiency of transport aircraft. However their large engine diameter prevents the mounting of leading edge devices at the engine-wing junction. This leads to a local flow separation on the wing suction side in the wake of the nacelle which may trigger the total wing stall and hence compromises the high-lift performance and therefore the total aircraft efficiency. At DLR (German Aerospace Center) numerical simulations of AFC (active flow control) at the engine-wing junction were conducted to study the capability of suppressing this local flow separation. The effects of steady and pulsed jet blowing with the same actuator geometry are compared. The results show that the steady blowing reduces the size of the nacelle-wake separation. However the pulsed blowing of the analyzed setup shows a low effect on the size of the nacelle-wake separation.