@techreport{Krenkel, author = {Krenkel, Lars}, title = {Investigation of the impact of vortex generators on the shock/boundary-layer interaction}, issn = {1434-8454}, abstract = {Comprehensive experimental and numerical parameter studies on the impact of isolated vortex generator pairs and complex vortex generator arrays onto a strong shock-/boundary layer interaction are presented within the context of this thesis. The effects of vortices, especially as they interact with each other are discussed in terms of their impact on the boundary layer development, the shock characteristics and the overall aerodynamic performance of the aerofoil. The presented results have been obtained from wind tunnel experiments with a simple flat plate with superimposed pressure gradient as well as with a more comprehensive model of a supercritical transonic aerofoil. In addition complex numerical parameter studies on a supercritical aerofoil in free stream conditions have been conducted. This work is designed for gaining a better understanding of the fundamental mechanisms of vortex generator/shock/boundary-layer interaction in order to achieve improved flight performance in terms of drag reduction, avoidance or at least postponement of separation onset and shock oscillation as well as lift improvement by application of optimised vortex generator configurations.}, language = {en} } @book{Krenkel, author = {Krenkel, Lars}, title = {Untersuchung des Einflusses von Wirbelgeneratoren auf die Stoß-/Grenzschicht-Wechselwirkung}, publisher = {Rheinisch-Westf{\"a}lische Technische Hochschule Aachen}, address = {Aachen}, issn = {1434-8454}, abstract = {Im Rahmen dieser Arbeit werden experimentelle und numerische Parameterstudien von einzelnen Wirbelgeneratorpaaren und komplexeren Wirbelgeneratoranordnungen bez{\"u}glich ihres Einflusses auf eine starke Stoß-/Grenzschicht-Wechselwirkung vorgestellt. Dabei werden die Einfl{\"u}sse von Wirbeln, insbesondere die Auswirkungen ihrer Wechselwirkungen untereinander, auf das Grenzschichtverhalten, die Stoßcharakteristik und insgesamt auf die aerodynamische Leistung des betrachteten Profils diskutiert. Dazu wurden sowohl Windkanalversuche am einfachen Modell einer ebenen Platte mit aufgepr{\"a}gtem Druckgradienten sowie an einem Modell eines superkritischen transsonischen Profils durchgef{\"u}hrt. Erg{\"a}nzend wurden komplexe nume-rische Parameteruntersuchungen an einem Profil in freier Anstr{\"o}mung ausgef{\"u}hrt. Es ist das Ziel, ein besse-res Verst{\"a}ndnis der Mechanismen der Wirbelgenerator-/Stoß-/Grenzschicht-Wechselwirkung zu gewinnen, um durch optimierte Anwendung von Wirbelgeneratoren eine Verbesserung der Flugleistungen erzielen zu k{\"o}nnen. Die Schwerpunkte liegen dabei auf der Reduktion des Widerstandes, der Vermeidung bzw. Verz{\"o}ge-rung von Str{\"o}mungsabl{\"o}sung und Stoßschwingung sowie auf der Erh{\"o}hung des Auftriebs.}, language = {de} } @inproceedings{MarkusRuettenKrenkelKessler, author = {Markus R{\"u}tten, and Krenkel, Lars and Kessler, Roland}, title = {Secondary Flow Effects as Physical Mechanism of Molecular Species Transport in Highly Oscillating Generic-Trachea Flows}, series = {83rd Annual Scientific Conference of the International Association of Applied Mathematics and Mechanics, 26.-30. M{\"a}rz 2012, Darmstadt, Germany}, booktitle = {83rd Annual Scientific Conference of the International Association of Applied Mathematics and Mechanics, 26.-30. M{\"a}rz 2012, Darmstadt, Germany}, abstract = {The high frequency oscillation artificial respiration technique is often the last hope for patients to survive highly damaged lung tissue. The mortality can significantly be reduced. In comparison to conventional artificial respiration the applied volume flow rate and pressure is significantly lowered in order to avoid further damaging of lung tissue and remaining intact alveolae. However, the physical mechanism of transport of oxygen to the aeriols under high frequency oscillation is not well understood. In the upper part of the lung convection is dominant, in contrast, the gas exchange in the lower parts of the lung is mainly driven by diffusion. It is not clear how associated gradients of concentrations of different molecular species are then achieved. Highly oscillating fluid flows has been a long research topic in fluid dynamics. It is known that oscillating pressure fluctuations are able to induce secondary flows, in particular, in curved ducts and pipes. The question is, whether the trachea enforces the generation of secondary flow by its kidney like cross section geometry. The influence of molecular species of different densities onto the formation of secondary flows and the convectional transport within the trachea is investigated. In order to clarify the physical mechanisms behind flow simulations have been conducted by using state of the art CFD techniques.}, language = {en} }