Swirl Boundary Layer at the Inlet of a Rotating Circular Cone

International audienceWhen a fluid enters a rotating pipe, a swirl boundary layer with thickness of $δ_S$ appears at the wall and interacts with the axial momentum boundary layer with thickness of $δ$. The swirl is produced by the wall shear stress and not due to kinematic reasons as by a turbomachine. In the center of the pipe, the fluid is swirl-free and is accelerated due to axial boundary layer growth. Below a critical flow number $ϕ < ϕ_c$, there is flow separation, known in the turbomachinery context as part load recirculation. Previous work analyses the flow at the inlet of a rotating circular pipe. For a systematic approach to a turbomachine, the influence of the turbine's and pump's function, schematically fulfilled by a diffuser and a nozzle, on the evolution of the swirl and flow separation is to analyse. The radius of the rotating pipe depends linearly on the axial coordinate, yielding a rotating circular cone. The swirl evolution depends on the Reynolds number, flow number, axial coordinate and apex angle. The influence of the la er is the paper's main task. The circumferential velocity component is measured applying 1D Laser Doppler Anemometry to investigate the swirl evolution

Leichtbautilger für Fahrwerke

Konventionelle, passive Fahrwerkskonzeple bestehen aus einem Feder- und einem Dämpferelement und das Systemverhalten ist mit der Abstimmung der Steifigkeils- und Dämpfungswerte fest vorgegeben. Bei der Fahrwerksabstimmung werden die Zielfunktionen Fahrsicherheit und -komfort für das jeweilige Fahrzeugkonzept ausgelegt. Jede optimale Lösung stellt ein Kompromiss zwischen Fahrsicherheit und -komfort dar, da die beiden Zielfunktionen gegenläufig sind. Alle optimalen Lösungen liegen im sogenannten Konfliktdiagramm auf einer Pareto-Linie. In dieser Arbeit wird gezeigt, wie ein hydraulisch übersetzter Leichtbautilger - Fluid Dynamic Absorber - in das Fahrwerk integriert und das Systemverhalten durch die Veränderung der Systemtopologie verbessert wird. Prinzip bedingt bringt ein Tilger immer zusätzliche Masse in das System ein. Dieses unerwünschte Verhalten wird durch die hydraulische Übersetzung (Prinzip der virtuellen Masse) minimiert. Hierzu wird der Leichtbautilger an das Chassis, das als Quasi-Inertialsystem dient, angebunden

Vortex Structure and Kinematics of Encased Axial Turbomachines

This paper models the kinematics of the vortex system of an encased axial turbomachine at part load and overload applying analytical methods. Thus far, the influence of the casing and the tip clearance on the kinematics have been solved separately. The vortex system is composed of a hub, bound and tip vortices. For the nominal operating point &phi; &asymp; &phi; opt and negligible induction, the tip vortices transform into a screw. For part load operation &phi; &rarr; 0 the tip vortices wind up to a vortex ring, i.e., the pitch of the screw vanishes. The vortex ring itself is generated by bound vortices rotating at the angular frequency &Omega; . The hub vortex induces a velocity on the vortex ring causing a rotation at the sub-synchronous frequency &Omega; ind = 0.5 &Omega; . Besides, the vortex ring itself induces an axial velocity. Superimposed with the axial main flow this results in a stagnation point at the tube wall. This stagnation point may wrongly be interpreted as dynamic induced wall stall. For overload operation &phi; &rarr; &infin; the vortex system of the turbomachine forms a horseshoe, i.e., the pitch of the screw becomes infinite. Both hub and tip vortices are semi-infinite, straight vortex filaments. The tip vortices rotate against the rotating direction of the turbomachine due to the induction of the hub vortex yielding the induced frequency &Omega; ind = &minus; 0.5 &Omega; / s with the tip clearance s

Analytic Assessment of an Embedded Aircraft Propulsion

This paper investigates analytically the advantage of the embedded propulsion compared to a state of the art propulsion of an aircraft. Hereby, we are applying the integral method of boundary layer theory and potential theory to analyse the boundary layer thickness and the impact of the flow acceleration due to the embedded propulsion. The aircraft body is treated as a flat plate. The engine is treated as a momentum disc but there is a trade off, since the engine efficiency is effected by the boundary layer. The outcome of the energetic assessment is the following: the propulsion efficiency is increased by the embedded propulsion and the drag of the aircraft body is reduced. The optimized aircraft engine size depending on Reynolds number is given

A Second Turbulent Regime When a Fully Developed Axial Turbulent Flow Enters a Rotating Pipe

When a fluid enters a rotating circular pipe a swirl boundary layer with thickness of δ̃s appears at the wall and interacts with the axial momentum boundary layer with thickness of δ̃. We investigate a turbulent flow applying Laser-Doppler-Anemometry to measure the circumferential velocity profile at the inlet of the rotating pipe. The measured swirl boundary layer thickness follows a power law taking Reynolds number and flow number into account. A combination of high Reynolds number, high flow number and axial position causes a transition of the swirl boundary layer development in the turbulent regime. At this combination, the swirl boundary layer thickness as well as the turbulence intensity increase and the latter yields a self-similarity. The circumferential velocity profile changes to a new presented self-similarity as well. We define the transition inlet length, where the transition appears and a stability map for the two regimes is given for the case of a fully developed axial turbulent flow enters the rotating pipe