Der Einfluß der Reynoldszahl auf die Strömungsverluste in ebenen Schaufelgittern

Es wird eine zusammenfassende Darstellung des Einflusses der Reynoldszahl auf die Strömungsverluste von ebenen Schaufelgittern gegeben. Der Einfluß der Reynoldszahl hängt in erster Linie von der Druckverteilung am Profil ab, aber auch von der Lage des Umschlagpunktes laminar-turbulent und der Oberflächenrauhigkeit. Außerdem tritt mit der Änderung der Reynoldsschen Zahl auch eine grundlegende Änderung im Charakter der Strömung auf. Man kann drei Gebiete unterscheiden: laminare Ablösung in Vorderkantennähe bei kleinen Reynoldszahlen, laminare Ablösung mit turbulentem Wiederanlegen und schließlich bei großen Reynoldszahlen natürlicher Umschlag laminar-turbulent mit turbulenter Ablösung in Hinterkantennähe. An Hand von Beispielen wird gezeigt, daß der Einfluß der Reynoldszahl auf die Strömungsverluste sehr gut von der Grenzschichttheorie wiedergegeben werden kann, solange keine Ablösung oder nur geringe Ablösung in Hinterkantennähe auftritt.A survey is presented about the influence of Reynolds Number on the flow losses in two-dimensional cascades. Primarily the Reynolds Number effect is depending on the pressure distribution of the blade, but also on the transition from laminar to turbulent flow and on the surface roughness. Generally the losses are considerably decreasing, when the Reynolds Number increases. Furthermore, the pattern of flow through the cascade changes considerably with variation of Reynolds Number. There are three different types of flow in the boundary layer: 1) Separation of the laminar boundary layer near the leading edge at low Reynolds Numbers, 2) local separation of the laminar boundary layer enclosing a "bubble of turbulence" and 3) at high Reynolds Numbers usual transition from laminar to turbulent flow, separation of turbulent boundary layer near trailing edge. From the presented examples it can be shown that the Reynolds Number effect on the flow losses in cascades can be calculated by theoretical methods in a very good manner, as long as separation of boundary layer is insignificant

Berechnung der aerodynamischen Beiwerte von Tragflügeln endlicher Spannweite in Bodennähe

Die bekannten Verfahren zur Berechnung der Auftriebsverteilung von Tragflügeln endlicher Spannweite im unbegrenzten Raum werden auf Tragflügel in Bodennähe erweitert. Dabei wird der Bodeneinfluß durch das Spiegelungsprinzip erfaßt. Die bisher in der Tragflügeltheorie benutzten Wirbelmodelle erfordern die Beschränkung auf kleine Anstellwinkel (lineare Theorie). Bei Annäherung an den Boden nimmt der Auftrieb sowohl bei festem Anstellwinkel als auch bei festem Klappenwinkel zu, der induzierte Widerstand bei festem Auftrieb nimmt dagegen ab. Der aerodynamische Neutralpunkt rückt nach hinten (stabilisierend). An Hand von Beispielrechnungen wird der Einfluß von Bodenabstand, Seitenverhältnis und Pfeilung auf den Bodeneffekt ermittelt.The well-known methods for calculating the lift distribution on wings of finite aspect ratio in an unbounded flow field are extended for wings near the ground. The ground effect is taken into account by the reflection method. The vortex models used till now in the wing theories require a restriction to small angles of attack (linear theory). Approaching to the ground the lift increases for a constant angle of attack as well as for a constant flap angle, the induced drag, however, decreases at constant lift. The aerodynamic centre is displaced backwards (stabilizing). By means of calculated examples the dependence of the ground effect on the height above ground, the aspect ratio and the angle of sweep is determined

Experimenteller Beitrag zum Reibungseinfluß auf die Strömung durch ebene Schaufelgitter

In order to clarify the influence of viscosity in cascade problems, two very simple cascade arrangements have been investigated experimentally: 1) a flat plate cascade with an angle of stagger of 45° and inflow direction parallel to the plates, 2) a cascade consisting of circular cylinders with angle of inflow of 45°. The pressure drop across the cascade and the angle of deflection have been measured for different solidity ratios, both being due purely to viscosity effects. For the flat plate cascade the deflection is towards the trailing edge plane, but for the circular cylinder cascade in the opposite direction. For the flat plate cascade there is good agreement of experimental and theoretical results as obtained from boundary layer theory. For the circular cylinder cascade the deflection is caused by asymmetrical separation of the flow, but there is no theory available

Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications

Boundary-layer theory

This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject