The design of a vented foldable bullnose Krueger (VFBK) leading-edge flap and an ultra-high bypass ratio (UHBR) through-flow nacelle as an extension of the Common Research Model in High-Lift configuration (CRM-HL) is presented. The modified model is representative of a modern, aerodynamically efficient transport aircraft in landing configuration. The design of the two modifications was performed using Reynolds-averaged Navier–Stokes simulations and was developed within the German Aerospace Center (DLR) project ADaMant. Cross-investigations were made since the VFBK and the UHBR nacelle can also be examined in combination with the original slat and through-flow nacelle of the CRM-HL. In addition, the CRM-HL and its modifications were analyzed in full-scale and as a 5.2% model with the physical environmental conditions of the atmospheric low-speed wind tunnel DNW-NWB (Niedergeschwindigkeits-Windkanal Braunschweig [Low-Speed Wind Tunnel Braunschweig]), where the model will be tested. The VFBK nearly achieves the target of providing a similar lift coefficient at maximum lift at full-scale conditions compared to the CRM-HL with slat. Furthermore, the UHBR nacelle design including pylon and strake achieves a significant improvement by mitigating the separation on the wing and the nacelle, resulting in a similar maximum lift coefficient compared to the CRM-HL with the original nacelle both in full- and in wind tunnel scaling.

Gust loads on aircraft are critical for the structural wing design. This paper investigates the impact of a critical vertical “1-cos” type gust event and different wing flap deflections on the aerodynamics of the Horizontal Tail Plane (HTP) and thus the pitching moment behavior of the aircraft. The wing flaps are deployed for the purpose of active gust load control and comprise spanwise segmented trailing edge flaps and leading edge flaps. URANS simulations are used for the simulations of two generic aircraft configurations with and without empennage at transonic flow conditions. The simulations reveal a significant impact of the wing-gust interaction and the wing flap deflections on the wing’s downwash angle. The change in the downwash affects the effective angle of attack at the HTP. However, the effects of the wing flap deflections on the HTP loads are less significant than the effect introduced by the reference gust. The deflections of the trailing and leading edge flaps on the wing are shown to be uncritical with regard to the pitching moment behavior of the aircraft. The gust and the wing flap induced maximum pitching moments can be significantly reduced via moderate elevator deflections on the HTP. A first approximation based on parametric 2D studies reveals a reduction by approx. 70

The design of a Vented Foldable Bullnose Krueger (VFBK) leading edge flap and an ultra-high bypass ratio (UHBR) through flow nacelle as extension of the Common Research Model in High-Lift Configuration (CRM-HL) is presented. The modified model is an example of a modern, aerodynamically efficient transport aircraft in landing configuration. The design of the two modifications for the CRM-HL were performed using RANS CFD methods and were developed within the DLR project ADaMant. Special attention was paid to the mitigation of premature separations on the wing and the nacelle. Cross investigations were made, since the VFBK can also be examined with the existing NASA through flow nacelle of the CRM-HL and the UHBR nacelle can also be examined in combination with the existing slat of the CRM-HL. In addition, the aerodynamical performance of the CRM-HL and its modifications were analyzed in full-scale and as 5.2% model with the physical environmental conditions of the atmospheric low-speed wind tunnel DNW-NWB, where the model will be tested. The VFBK nearly achieves the target of providing a similar lift coefficient at maximum lift at full-scale conditions compared to the CRM-HL configuration with slat. In wind tunnel scaling and therefore at the low Reynolds number of the wind tunnel model a premature separation on the outboard VFBK prevents to achieve this goal. In contrast, the UHBR nacelle design including pylon and strake achieves a significant improvement by mitigating the flow separation on the wing and the nacelle itself. Thus, the UHBR nacelle integration achieves its goal of a comparable maximum lift coefficient in full- and in wind tunnel scaling with reference to the CRM-HL with original nacelle both in combination with VFBK and with slat.

. This work describes the cooperative/competitive design process that led to the definition of the Krueger flap to be used in the numerical and experimental tests of the European project UHURA. The project requirements are particularly challenging because it is necessary to develop a device with good aerodynamic high-lift characteristics, but it is necessary to consider many constraints of structural and kinematic nature. Indeed, the kinematics for its deployment is quite complex and imposes hard constraints on the Krueger shape, and the structural characteristics must allow it to withstand considerable structural stresses in the deployment phase which is studied in the wind tunnel.

This article presents an experimental investigation of a passive-adaptive slat concept, an aerodynamic control mechanism aimed at avoiding separation in the inwards region of a horizontal axis wind turbine blade. The passive-adaptive slat is designed to autonomously adjust its position due to the aerodynamic forces acting on it, without the need of any active control system or external power source. The slat opens when the angle of attack increases beyond a certain threshold so that stall is delayed and closes for smaller angles of attack to increase the lift-to-drag ratio of the airfoil. A thorough aerodynamic characterisation of the passive-adaptive slat is performed in the wind tunnel followed by testing it under different sinusoidal inflows generated by a 2D active grid. It is observed that the slat system is able to leverage the advantages of both a clean airfoil and an airfoil with a fixed slat. It has the capability of delaying stalls for higher angles of attack, as well as having higher lift-to-drag ratio for lower angles of attack. It is also observed that, for fluctuating inflow, the passive-adaptive slat is able to achieve similar mean lift values as an airfoil with fixed slat while showing significant reduction in the lift fluctuations.

Active gust load alleviation techniques exhibit a high potential in significantly reducing the transient gust loads on aircraft. In this work the aerodynamic potential of trailing-edge flaps and leading-edge flaps is numerically studied with the purpose to significantly reduce the structural gust loads. The utilized spanwise-segmented flaps represent slight modifications of existing devices for high-lift and maneuvering. The investigations based on unsteady Reynolds-averaged Navier–Stokes computations are conducted by employing a generic wing–fuselage aircraft configuration at transonic flow conditions. Idealized discrete “[Formula: see text]”-type vertical gusts that are relevant for the certification process are used as representative atmospheric disturbances. The focus of this paper is to introduce a practicable prediction method for required trailing- and leading-edge flap deflections for a significant mitigation of gust-induced wing loads. The three-dimensional flap deflections are determined by parametric two-dimensional simulations at representative wing sections. Different extensions of the estimation approach are investigated to assess the influence of the wing planform, the finite wing span, the aerodynamic phase lags, and the flap scheduling. It is shown that the trailing- and leading-edge flaps are promising in terms of alleviation of gust-induced wing bending and wing torsional moments, respectively. However, at high leading-edge flap deflections that are necessary for a full compensation of the wing torsional moment large-scale flow separation is identified. The introduced gust load alleviation approach indicates a good transferability between two-dimensional airfoil and three-dimensional wing aerodynamics for unsteady flap deflections.

The rotor of a large diameter wind turbine experiences more substantial and more dynamic loads due to the fluctuating and heterogeneous wind field. The project SmartBlades 2.0 investigated rotor blade design concepts that alleviate aerodynamic loading using active and passive mechanisms. The present work evaluates the acoustics of the two load alleviating concepts separately, an inboard slat and an outboard flap, using the Fast Random Particle Mesh/Fast Multipole Code for Acoustic Shielding (FRPM/FMCAS) numerical prediction toolchain developed at DLR with input from the averaged flow field from RANS. The numerical tools produce a comparable flap side-edge noise spectrum with that of the measurement conducted in the Acoustic Wind Tunnel Braunschweig (AWB). The validated FRPM/FMCAS was then used to analyze the self-noise from a slat at the inboard section of a rotor blade with a 44.45 m radius and compared with that from the outboard trailing edge. Furthermore, the rotational effect of the rotor was included in the post-processing to emulate the noise observed at ground level. The findings show an increase in the slat's overall sound pressure level and a maximum radiation upwind of the wind turbine for the case with the largest wind speed that represents the off-design condition. In operational conditions, the slat adds at most 2 dB to the overall sound pressure level. The toolchain evaluates wind turbine noise with conventional or unconventional blade design, and the problem can be scaled up for a full-scale analysis. As such, the tools presented can be used to design low-noise wind turbines efficiently.

AbstractA passive‐adaptive slat concept was designed to avoid separation in the root region of a horizontal‐axis wind turbine blade. This concept incorporates an autonomously moveable slat device only driven by the aerodynamic forces acting on it without the need for mechanical or electrical actuation. It opens at high local angles of attack to delay the stall angle and closes for small angles of attack to increase the lift to drag ratio of the blade segment. This article describes the development of a passive‐adaptive slat for a DU‐91‐W2‐250 airfoil, which is a segment of the reference rotor blade in the project SmartBlades 2.0. In the course of the passive‐adaptive slat design, the optimization of the slat and its extended position is presented. This is followed by the development of two passive‐adaptive slat kinematics, which are opening and closing the slat passively at different angles of attack. With the designed passive‐adaptive slat the stall of the airfoil is delayed by 20° in incidence and the maximum lift of the airfoil is increased by about 130% at the same time in comparison to the original airfoil. Furthermore, the DU‐91‐W2‐250 airfoil with moveable passive‐adaptive slat has in most conditions a higher climb index and therefore a better aerodynamic performance than the same airfoil with a fixed integrated slat.

The feasibility of laminar flow control technology for future wing is bound to the development of a leading edge high-lift system that complies with the requirements on smooth surfaces to enable maintaining the laminar boundary layer flow, such as a Krueger flap. Although in principle the aerodynamic performance of a Krueger flap is known, the unsteady behaviour of the flow during deployment and retraction is completely unknown. This is as even more important as during deployment the Krueger flap is exposed to highly unfavourable positions perpendicular to the flow. To mitigate the risk of unfavourable aircraft behaviour, it is therefore expected that a Krueger flap has to be deflected significantly fast and may trigger unsteady aerodynamic effects. The European H2020 project UHURA, running from September 2018 to August 2022, has been focusing on the unsteady flow behaviour around such high-lift system and will first time deliver a deeper understanding of critical flow features at this type of high-lift device during their deployment and retraction together with a validated numerical procedure for its simulation. UHURA performed detailed experimental measurements in several wind tunnels to obtain a unique data set for validation purposes of Computational Fluid Dynamics (CFD) software, including detailed flow measurements by Particle Image Velocimetry (PIV) and other optical measurement technologies.

The feasibility of laminar flow control technology for future wing is bound to the development of a leading edge high-lift system that complies with the requirements on smooth surfaces to enable maintaining the laminar boundary layer flow. Classical leading edge high-lift devices like slats are not suitable as they introduce disturbances in the very sensitive upper surface leading edge area. Within the European AFLoNext (Active Flow, Loads & Noise Control on Next Generation Wing) project, a full scale HLFC leading edge demonstrator was designed and built that incorporated the vented foldable bull nose Krueger. In summer 2018 this demonstrator was wind tunnel tested in the CIRA Icing Wind Tunnel facility. Within this test the aerodynamic design was verified. Additionally, it was tested whether the Krueger device would need a distinct de-icing system. The contribution summarizes the design of the Kruger device together with the findings from the full-scale wind tunnel test of the Krueger flap configuration.

The feasibility of laminar flow control technology for future wing is bound to the development of a leading edge high-lift system that complies with the requirements on smooth surfaces to enable maintaining the laminar boundary layer flow, such as a Krueger flap. Although in principle the aerodynamic performance of a Krueger flap is known, the unsteady behaviour of the flow during deployment and retraction is completely unknown. This is as even more important as during deployment the Krueger flap is exposed to highly unfavourable positions perpendicular to the flow. To mitigate the risk of unfavourable aircraft behaviour, it is therefore expected that a Krueger flap has to be deflected significantly fast and may trigger unsteady aerodynamic effects. Within the European H2020 project UHURA (Unsteady High-Lift Aerodynamics—Unsteady RANS Validation), currently a wind tunnel test is conducted incorporating the vented foldable bull nose Krueger flap. A wind tunnel model based on the DLR-F15 airfoil has been designed and manufactured that features a part span and a full span Krueger device, which can be actuated at high deflection rates up to 360°/s. First wind tunnel tests have been conducted at the ONERA L1 wind tunnel in Lille in October 2020. The tests included the measurements of internal forces, steady and unsteady pressures, as well as phase-locked Particle Image Velocimetry (PIV) to achieve high quality validation data for comparison with numerical methods.

This paper investigates active gust alleviation on a forward swept transport aircraft at transonic speeds. A gust study reveals a critical gust wave length of 50m leading to highest aerodynamic loads under cruise conditions. Gust induced separation is observed for particular cases. Deflection of a wing tip flap and aileron at the outer part of the wing have a remarkable short response time and offer a very promising flow actuation to reduce gust induced lift. The droop nose can be used to control the pitching moment. The flap deflection angle has to be chosen carefully to avoid flow separation. Adding the aileron, increases the effectiveness of the gust alleviation system significantly.

This article discusses the utilization of an active slat concept to reduce turbulence induced fluctuating loads on an airfoil. The performance of the active slat is tested in the wind tunnel under different complex inflows created by an active grid resulting in variations in the angle of attack. Different open loop control strategies are developed to mitigate the load fluctuations on the airfoil. The aerodynamics around the airfoil is changed by actively moving the trailing edge of the slat. It is observed that the active slat concept is able to alleviate load fluctuations on the airfoil for inflow angle fluctuations of different scales.

Gust load analysis plays a substantial role in the certification process of aircraft. Active gust load alleviation techniques exhibit a high potential in significantly reducing the transient gust loads and thus the overall structural weight. In this paper, two dynamic actuator concepts are studied by means of CFD methods on a generic wing-fuselage aircraft configuration. The concepts comprise spanwise segmented trailing edge flaps (TEF) and leading edge flaps (LEF), which are already existent on the research model for high-lift and maneuvering purposes. Simulations based on Euler and RANS equations are utilized to assess the aerodynamic potential of the actuators regarding alleviation of critical idealized "1-cos" type vertical gusts. 2D simulations of a representative wing section are considered in an extended parametric study to derive an initial guess for the required actuation deflections on the aircraft configuration. An iterative analysis of spanwise varying actuator amplitudes is conducted in order to obtain strong control authority over the wing bending moment (WBM) and wing torsional moment (WTM). It is shown that the TEFs are promising in terms of mitigation of gust induced WBM and the LEFs are able to compensate the WTM induced by the deflected TEFs. Unsteady phenomena are identified at large TEF deflections resulting in unfavorable response of the aircraft. The transient behavior of the force coefficients shows significant dependencies on the flap scheduling. Only small improvements are achieved through segmented flap actuation compared to continuous flap actuation for the limited investigated setups.

In modern aircraft design the accurate prediction of dynamic control surface deflections is crucial for the evaluation and application of new load alleviation techniques. Time-marching approaches, such as the unsteady Reynolds-averaged Navier-Stokes equations, do provide a complete modeling of the aerodynamic flowfield; however, they are extremely time-consuming and still too expensive for design applications. In this paper a model is presented, which enables the fast and accurate prediction of aerodynamic responses for arbitrary control surface deflections. The model hereby reflects the time signal of the control surface deflection as a superposition of frequency components and computes the dynamic response behavior of the control surface using the linear frequency domain. The frequency responses are precomputed in a surrogate model for a wide parameter space of Mach number, Reynolds number, angle of attack and flap chord ratio, so that a frequency response for a new flight condition can be computed by mere interpolation. After building the surrogate model, the method achieves reduction in computational time of up to six orders of magnitude in comparison to time-marching simulations, while still covering the viscous and unsteady aerodynamic effects in the flow.

A method is presented, that is able to mitigate gust loads on an airfoil induced by an incoming gust velocity field. It thereby computes the lift coefficient response to a specified arbitrary gust velocity profile and predicts the required time-accurate control surface deflection. The method uses the linear frequency domain solver to predict frequency responses for the gust and control surface derivative of the lift coefficient efficiently. The frequency responses are computed and then subsequently filled as samples into a surrogate model. For a new flight condition the surrogate model predicts the frequency response by mere interpolation. Because the aerodynamic response on the gust and the behavior of the control surface are known, the aerodynamic lift response and the required flap deflection for alleviation can both be predicted from a given gust velocity field. The method is thereby able to predict the aerodynamic response and a time-accurate deflection for any flight condition in the design space within milliseconds. Results of the method are shown and analyzed on a 2D profile of a transonic airfoil with an implemented plain flap. The parameter studies were made in low speed with variation of Mach number, Reynolds number, angle of attack, flap chord size and initial flap deflection. In comparison to unsteady Reynoldsaveraged Navier-Stokes computations, the presented method can predict the aerodynamic responses with the same accuracy and it saves more than 6 orders of magnitude in computation time. Using the linear frequency domain solver it is also able to predict the arising unsteady aerodynamic behavior and still cover the viscous effects in the flow.