![An F9F-2 of VF-21 aboard the USS Midway in 1952 [59]. Figure 1.3: Full-scale application of suction and blowing on the Breguet "Vultur", 1956 [134].](https://www.researchgate.net/profile/Marco-Burnazzi/publication/311742123/figure/fig2/AS:651528171954187@1532347829617/An-F9F-2-of-VF-21-aboard-the-USS-Midway-in-1952-59-Figure-13-Full-scale-application_Q320.jpg)
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Design of Efficient High-Lift Configurations with Coanda Flaps (Dissertation)
Abstract and Figures
Active flow control applied to high-lift systems is a promising solution to improve low-speed flight capabilities and reduce noise emissions of commercial aircraft. However, too high power requirements in relation to the achieved lift gains have prevented active high-lift systems from being largely employed in the aeronautical industry. In this context, this work develops technologies to enhance the aerodynamic efficiency of an active high-lift system by means of RANS numerical simulations. The transonic airfoil DLR-F15 is equipped with an active internally-blown flap, which consists of a thin air jet tangentially blown over the shoulder of a simple-hinged flap deflected by 65°. To improve the lift generated by the airfoil, the effects of a flexible droop-nose device, wall suction and unsteady blowing are investigated. The fundamentals of gap-less droop-nose design are presented, describing the aerodynamic sensitivities of the main geometrical parameters and the physical phenomena that determine the lift performance. The efficiency of the resulting droop-nose configuration is also tested on a wing-body aircraft model. The analysis reveals three-dimensional flow mechanisms that limit the lift performance in operative conditions.
The airfoil efficiency is then further improved by adding a boundary-layer suction device. The effects of shape and location of the suction slot are studied to maximize the lift coefficient and pressure recovery. Finally, the effectiveness of unsteady excitation of the mixing layer by means of dynamic blowing is investigated. As a final result, a target maximum lift coefficient of 5.0 can be achieved with a 43% lower jet-momentum coefficient with respect to the baseline airfoil configuration.
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... This leads to an increase in lift, which has been investigated extensively [5-7, 9, 11, 16, 23]. As a side effect, a suction peak can be observed at the leading edge, which is decisive for the stall behaviour [1]. To reduce the suction peak at the so called clean nose a different nose shape, called droop nose, is designed to counteract the weaknesses of the active system [2]. ...
... The original Spalart-Allmaras model is used for turbulence modelling [22]. The mesh used was adopted from previous detailed investigations in the CRC [1,2]. ...
... The resulting lift and pitching moment coefficients are shown in Figs. 8 and 9. Discrete results are marked and approximated by a parameterised spline function depending on the angle of attack, flap deflection angle and momentum coefficient. The coefficients and the related mechanisms of both profile shapes have already been discussed in detail for angles of attack above − 10 • [1,2,4,15]. According to Fig. 6 the effective angle of attack is reduced significantly by applying the 3D-correction. ...
The aeroelastic behaviour of a wing with an over-the-wing pylon-mounted ultra-high bypass ratio engine and high-lift devices is studied with a reduced-order model. Wing, pylon and engine structures are reduced separately using the modal approach and described by their natural frequencies and modes. The characteristic aerodynamic loads are investigated with steady and unsteady flow simulations of a two-dimensional profile section. These results indicate possible heave instabilities at strongly negative angles of attack. Three-dimensional effects are taken into account using an adapted lifting line theory according to Prandtl. Due to high circulations resulting from the high-lift systems, the effective angles of attack are in the range of the potential instabilities. The substructures and aerodynamic loads are coupled in modal space. For the wing without three-dimensional effects, the bending instability occurs at the corresponding negative angles of attack. Even though there is potential for improvement, including the three-dimensional effects shifts the endagered area to possible operation points.
... However, the online version of record will be different from this version once it has been copyedited and typeset. (a non-dimensional distance from the wall to the first mesh node) [7]. It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. ...
... It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. To improve the behavior of the SA model in problems with curved flow lines, curvature correction can also be incorporated into the calculations [7,8]. Since turbulent kinetic energy (TKE) is not defined in this turbulence model, the Reynolds stress cannot be calculated. ...
The present work studied various models for predicting turbulence in the problem of injecting a fluid microjet into the boundary layer of a turbulent flow. For this purpose, the one-equation Spalart–Allmaras (SA), two-equation k–ε and k–ω, multi-equation transition k-kL–ω, transition shear stress transport (SST), and Reynolds stress models were used for solving the steady microjet into the turbulent boundary layer, and their results are compared with experimental results. Comparing the results indicated that the steady solution methods performed sufficiently we for this problem. Furthermore, it was found that the four-equation transition SST model was the most accurate method for predicting turbulence in this problem. This model predicted the velocity along the x-axis in near- and far-jet locations with about 1% and 5% average errors, respectively. It also outperformed the other methods in predicting Reynolds stresses, especially at the center (nearly 5% error). Moreover, the modified four-equation transition SST model has improved the system's performance in predicting the studied parameters by utilizing Sørensen correlations in predicting Reθt (the transition momentum thickness Reynolds number), Flength (an empirical correlation that controls the length of the transition region), and Reθc (the critical Reynolds number where the intermittency first starts to increase in the boundary layer).
... gradient. The model yields satisfactory solutions nearly up to Y + = 30 (a non-dimensional distance from the wall to the first mesh node) [7]. It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. ...
... It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. To improve the behavior of the SA model in problems with curved flow lines, curvature correction can also be incorporated into the calculations [7,8]. Since turbulent kinetic energy (TKE) is not defined in this turbulence model, the Reynolds stress cannot be calculated. ...
The present work studied various models for predicting turbulence in the problem of injecting a fluid microjet into the boundary layer of a turbulent flow. For this purpose, the one-equation Spalart-Allmaras (SA), two-equation k-ε and k-ω, multi-equation transition k-kL-ω, transition shear stress transport (SST), and Reynolds stress models were used for solving the steady microjet into the turbulent boundary layer, and their results are compared with experimental results. A comparison of the results indicated that the steady solution methods performed sufficiently well for this problem. Furthermore, it was found that the four-equation transition SST model was the most accurate method for predicting turbulence in this problem. This model predicted the velocity along the x-axis in near- and far-jet locations with about 1% and 5% errors, respectively. It also outperformed the other methods in predicting Reynolds stresses, especially at the center (nearly 5% error). Moreover, the modified four-equation transition SST model has improved the system’s performance in predicting the studied parameters by utilizing Sørensen correlations in predicting 𝑅𝑒 𝜃𝑡 (the transition momentum thickness Reynolds number), 𝐹 𝑙ength (an empirical correlation that controls the length of the transition region), and 𝑅𝑒𝜃𝑐 (the critical Reynolds number where the intermittency first starts to increase in the boundary layer).
... It also provides satisfactory solutions for boundary layer flows, especially those included with an inverse pressure gradient. The model yields satisfactory solutions nearly up to Y + = 30 [7]. It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. ...
... It calculates the deformation tensor through vorticity-based or strain/vorticity-based production methods. To improve the behavior of the SA model in problems with curved flow lines, curvature correction can also be incorporated into the calculations [7,8]. Since turbulent kinetic energy (TKE) is not defined in this turbulence model, the Reynolds stress cannot be calculated. ...
The present work studied various models for predicting turbulence in the problem of injecting a fluid microjet into the boundary layer of a turbulent flow. For this purpose, the one-equation Spalart-Allmaras (SA), two-equation k-{\epsilon} and k-{\omega}, multi-equation transition k-kL-{\omega}, transition shear stress transport (SST), and Reynolds stress models were used for solving the steady flow. Moreover, the transition SST, scale-adaptive simulation (SAS), and detached eddy simulation (DES) models were used for the transient flow. A comparison of the results indicated that the steady solution methods performed sufficiently well for this problem. Furthermore, it was found that the four-equation transition SST model was the most accurate method for the prediction of turbulence in this problem. This model predicted the velocity along the x-axis in near- and far-jet locations with about 1% and 5% errors, respectively. It also outperformed the other methods in predicting Reynolds stresses, especially at the center (with an about 5% error).
A reduced-order model is developed to study the parameter-dependent aeroelastic behaviour of two wing configurations with high-lift devices. One is the wing of a conventional turboprop aircraft, the other a wing with over-the-wing mounted ultra high bypass ratio engine. Characteristic aerodynamic loads are investigated with steady and unsteady flow simulations of a 2D profile section. 3D effects are taken into account using an adapted lifting line theory according to Prandtl. Structure and aerodynamic loads are coupled in modal space to predict aeroelastic instabilities. Bending and bending-torsion instabilities due to the high-lift systems become visible.
The aerodynamic benefit of over-the-wing mounted engines for commercial aircraft withSTOL capabilities in cruise flight conditions is explored. Favorable aerodynamic installation effects and less space constraints, like landing gear length for under-the-wing mounted engines, offer a promising potential for future transport aircraft configurations in combination with ultra-high bypass ratio engines. Nevertheless, the aerodynamic interaction between wing and engine, located at the wing upper side close to the trailing edge, is crucial and involves a design challenge to exploit the full aerodynamic performance potential. Especially the aerodynamics of the wing experiences a significant alteration due to the installation of the engine, which differs from engines mounted under a wing. The shock position and topology changes significantly and, consequently, also the spanwise load distribution is significantly changed. Therefore, the wing shape has to be adapted to the presence of the engine to meet the performance requirements and utilize potentially positive engine installation effects. Targeting on a low noise aircraft with short take-off and landing capabilities, two optimization steps were accomplished. As a first step, the wing-twist of a wing/body/engine/pylon (WBEP) configuration was adapted to improve the spanwise load distribution followed by a shape optimization. For this purpose, a surrogate-based optimization approach was applied.
Historically, powered lift takeoff analysis has been prohibitively expensive for use in preliminary design. For powered lift, the coupling of aircraft systems invalidates traditional simplistic methods often used in early aircraft sizing. This research creates a tool that will automate the process of takeoff and balanced field length calculations for a circulation control wing aircraft. The process will use high fidelity techniques, such as computational fluid dynamics in order to capture the coupled effects present in circulation control along with Gaussian processes to create a metamodel of that same data to be implemented in a modular takeoff/BFL model. The model was used to examine the performance of a STOL transport and it showed an optimal flap deflection of 64˚ and diminishing returns on mass flow rates exceeding 12 kg/s. Additional analysis of the STOL transport showed that delaying either the mass flow or the flap deflection until later in the ground roll reduced the balanced field length by up to 8%. In the process of creating the takeoff code, additional consideration was put into the determination of the rotation velocity. It was found that a relationship between lift to weight better defined the rotation velocity with the circulation control model and was found to be within about 10% of traditional techniques.
Computational Fluid Dynamics (CFD) is an important design tool in engineering and also a substantial research tool in various physical sciences as well as in biology. The objective of this book is to provide university students with a solid foundation for understanding the numerical methods employed in todays CFD and to familiarise them with modern CFD codes by hands-on experience. It is also intended for engineers and scientists starting to work in the field of CFD or for those who apply CFD codes. Due to the detailed index, the text can serve as a reference handbook too. Each chapter includes an extensive bibliography, which provides an excellent basis for further studies. The accompanying CD-ROM contains the sources of 1-D and 2-D Euler and Navier-Stokes flow solvers (structured and unstructured) as well as of grid generators. Provided are also tools for Von Neumann stability analysis of 1-D model equations. Finally, the CD-ROM includes the source code of a dedicated visualisation software with graphical user interface.
An active high-lift set up is employed on a wing-body aircraft configuration and the stall behavior is analyzed by means of CFD RANS simulations. The high-lift system is composed of a trailing-edge gap-less Coanda flap and a leading-edge flexible droop nose. The effect of the leading-edge device is studied by using comparisons with the cruise leading-edge configuration. Comparisons with previous 2D simulations highlight lower lift performances for the wing section of the 3D model with respect to the airfoil data. This is due to 3D flow dynamics that limit the lift generated by the wing and induce stall with mechanisms not observed in 2D. Cross flow at the wing leading edge, or over the suction side of the wing root, increase the boundary layer thickness over the wing, thus reducing the efficiency of the Coanda flap.
Boussinesq-type closures for the Reynolds Averaged Navier-Stokes (RANS) equations fail to correctly predict Reynolds stress components for flow over curved surfaces and flow in rotating fluids [2], [33]. Two classes of vortical correction (VC) model are discussed with respect to the improvements in the predictive capability of RANS they offer for flows where substantial streamline curvature/ rotation effects exist. The work is intended to improve the fidelity of vortical flow computations within the RANS/URANS modeling framework of the DLR TAU code.