Improving Rudder Effectiveness with Sweeping Jet Actuators

The application of active flow control on a vertical tail of a typical twin engine aircraft was investigated. Sweeping jets installed into the rudder surface were used and their effect was assessed by force measurements, flow visualization and local pressure distributions. The airfoil forming the tail is a NACA 0012 with a rudder using 35% of its chord. The tests were carried out at the Lucas Wind Tunnel at the California Institute of Technology at representative Reynolds numbers of up to Re=1.5 million. Multiple flap deflections and spanwise actuator configurations were tested resulting in an increase of up to 50-70% in side force depending on the free stream velocity and momentum input

Nonlinear approximation in bounded orthonormal product bases

We present a dimension-incremental algorithm for the nonlinear approximation of high-dimensional functions in an arbitrary bounded orthonormal product basis. Our goal is to detect a suitable truncation of the basis expansion of the function, where the corresponding basis support is assumed to be unknown. Our method is based on point evaluations of the considered function and adaptively builds an index set of a suitable basis support such that the approximately largest basis coefficients are still included. For this purpose, the algorithm only needs a suitable search space that contains the desired index set. Throughout the work, there are various minor modifications of the algorithm discussed as well, which may yield additional benefits in several situations. For the first time, we provide a proof of a detection guarantee for such an index set in the function approximation case under certain assumptions on the sub-methods used within our algorithm, which can be used as a foundation for similar statements in various other situations as well. Some numerical examples in different settings underline the effectiveness and accuracy of our method

The uniform sparse FFT with application to PDEs with random coefficients

We develop the uniform sparse Fast Fourier Transform (usFFT), an efficient, non-intrusive, adaptive algorithm for the solution of elliptic partial differential equations with random coefficients. The algorithm is an adaption of the sparse Fast Fourier Transform (sFFT), a dimension-incremental algorithm, which tries to detect the most important frequencies in a given search domain and therefore adaptively generates a suitable Fourier basis corresponding to the approximately largest Fourier coefficients of the function. The usFFT does this w.r.t. the stochastic domain of the PDE simultaneously for multiple fixed spatial nodes, e.g., nodes of a finite element mesh. The key idea of joining the detected frequency sets in each dimension increment results in a Fourier approximation space, which fits uniformly for all these spatial nodes. This strategy allows for a faster and more efficient computation due to a significantly smaller amount of samples needed, than just using other algorithms, e.g., the sFFT for each spatial node separately. We test the usFFT for different examples using periodic, affine and lognormal random coefficients in the PDE problems

Improving Rudder Effectiveness with Sweeping Jet Actuators

The application of active flow control on a vertical tail of a typical twin engine aircraft was investigated. Sweeping jets installed into the rudder surface were used and their effect was assessed by force measurements, flow visualization and local pressure distributions. The airfoil forming the tail is a NACA 0012 with a rudder using 35% of its chord. The tests were carried out at the Lucas Wind Tunnel at the California Institute of Technology at representative Reynolds numbers of up to Re=1.5 million. Multiple flap deflections and spanwise actuator configurations were tested resulting in an increase of up to 50-70% in side force depending on the free stream velocity and momentum input

Einflussdes tool diameter on the thermal cycles and to the damage of the indexable insert for milling

In dieser Arbeit werden verschiedene Werkzeugdurchmesser des CERATIZIT Frässystems Maximill A490-12 mit der Wendeschneidplatte SDMT 1205ZZSN-29 der Firma CERATIZIT Austria GmbH nach ihrem Verschleiß- und Schädigungsverhalten beurteilt. Dazu wurden verschiedene Frässtrategien bei gleichen Schnittparametern als Einzahn-Standzeitversuche durchgeführt. Anhand von REM-Aufnahmen wurde das Schädigungsverhalten der verschiedenen Werkzeugdurchmesser bei den jeweiligen Einsatzbedingungen beurteilt. Am Ende wird eine Aussage des Einflusses zur Frässtrategie in Abhängigkeit des Werkzeugdurchmessers getroffen

Über den Nachlauf eines angestellten Kreiszylinders

Diese Arbeit begann mit einer Machbarkeitsstudie über die potentielle Nutzung aktiver Strömungskontrolle für die Lagekontrolle eines Tankrüssels für die Luftbetankung, der vereinfachend als angestellter Kreiszylinder betrachtet werden kann. Die Vorversuche an einem einfachen Modell wurden sehr erfolgreich abgeschlossen. Daran anschließend wurde eine grundlegende Untersuchung der Umströmung eines unendlichen angestellten Kreiszylinders mit aktiver Strömungskontrolle durchgeführt. Druckverteilungen um den Zylinder und im fernen Nachlauf wurden zur Bestimmung der auf den Zylinder wirkenden Kräfte aufgenommen, der Schwerpunkt dieser Arbeit lag allerdings auf den kohärenten Strukturen im nahen Nachlauf. Die Analyse dieser Strukturen ermöglichte ein tieferes Verständnis der Wirbeldynamik in dieser komplexen dreidimensionalen Strömung. Die Anwendung von asymmetrischer periodischer zero-mass-flux Anregung durch einen einzelnen Schlitz entlang des Zylinders erzeugte deutlichen Auftrieb, die Anregung über zwei symmetrisch auf dem Umfang angeordnete Schlitze reduzierte den Formwiderstand merklich. Auftrieb und Widerstand konnten durch Anregung mit unterschiedlicher Stärke auf beiden Seiten des Zylinders unabhängig voneinander variiert werden. Dies beweist, dass die Kontrolle eines Tankrüssels mittels aktiver Strömungskontrolle möglich wäre und dadurch der Einsatz von hervorstehenden und deshalb leicht zu beschädigenden Kontrollflächen vermieden werden könnte. Die im Laufe dieser Arbeit entwickelte POD-basierte dynamische Analyse des Strömungsfeldes im nahen Nachlauf enthüllte die Komplexität der kohärenten Strukturen und ihrer Dynamik nahe des Zylinders. Deutliche Fluktuationen der Positionen der kohärenten Strukturen konnten sowohl in radialer als auch in Umfangsrichtung nachgewiesen werden. Diese Fluktuationen wurden bei grösserer Anregungsstärke unterdrückt und damit die auf den Zylinder wirkenden Wechselbelastungen deutlich reduziert. Da angestellte runde Zylinder in vielen technischen Anwendungen vorkommen, könnte sich die so mögliche aktive Dämpfung strömungsinduzierter Schwingungen als sehr nützlich für die Reduzierung von Strukturversagen durch Ermüdung erweisen.This work evolved from a feasibility study targeted at a specific application: the control of a refuelling boom. Presently, the attitude of the refuelling boom on tanker airplanes, basically a finite cylinder with pitch and yaw, is adjusted by means of control surfaces extending from the boom. These control surfaces are bulky and very sensitive to damage by unintended contact with the tanker itself or the refuelling airplanes. Preliminary experiments were carried out on a relative simple model to evaluate the potential to alternatively control the attitude of the refuelling boom by altering lift and drag of this finite inclined cylinder by means of active flow control. The results were very promising. Based on these findings, a detailed investigation was carried out to improve the understanding of the general problem of the flow past an inclined cylinder, in particular with application of active flow control. The forces on the cylinder were determined by pressure measurements on the surface and in the far wake to obtain easily comparable quantitative results. To gain a better insight into the vortex dynamics in this complex three-dimensional flow, focus was put on the coherent structures in the near wake of an infinite inclined cylinder and their interaction with it. Substantial lift was generated by applying periodic zero-mass-flux excitation asymmetrically from a single slot running along the span of the cylinder. Excitation from two slots located symmetrically on the circumference of the cylinder reduced the form drag significantly. Lift and drag were altered independently of each other by adjusting the level of excitation differently on both sides of the cylinder. This proves that the full control of a refuelling boom by active flow control is possible, eliminating the necessity of protruding control surfaces that are easily damaged. A POD based technique was developed for the dynamic analysis of the flow field in the near wake. It revealed the complexity of the coherent structures and their dynamics close to the cylinder. Considerable fluctuations of the positions of the coherent structures were identified, in radial as well as in azimuthal direction. These fluctuations were suppressed at higher levels of excitation, reducing the unsteady loads significantly. As inclined circular cylinders are found in many engineering applications the so enabled active damping of flow induced oscillations could prove to be very useful to greatly reduce the risks of structural failure due to fatigue