Joachim Ebner

Flow structures inside a rotor-stator cavity

This paper describes an experimental investigation initiated to determine the threedimensional flow field inside the rim seal cavity of a double-shrouded rotor-stator system. Thereby, the effects caused by perturbances in the rotor wall were additionally examined. The objective of this work is to provide detailed information about the mechanisms that can promote elevated temperature levels in the high pressure section of a gas turbine. Both ingested hot gas and windage heating generated at the rotor-stator interface can severely affect the material temperatures and thus considerably increase the thermal load of the rotating parts.

Velocity Profiles in Shear-Driven Liquid Films: LDV-Measurements

In design and layout of fuel preparation systems for SI-engines or gas turbines as well as other technical systems working with shear-driven liquid films accurate information on the velocity distribution within the film as a function of film height is necessary for numerical modeling. To meet this requirements an improved LDV system was built which allows for the first time accurate velocity measurements in thin and wavy liquid films down to an average thickness of about 100 µm. Layout and the optical arrangement of the new system is presented in details together with some examplary applications.

An Experimental Study of Liquid Film Thickness in Annular Air/Oil Flow in a Vertical Pipe Using a Laser Focus Displacement Meter

The development of modern aero-engines is leading to increased pressure and temperature levels which makes increasing demands on the engines’ safety and reliability. In particular the vent-system of the bearing chambers located in the hot section of the engine represents a critical component in the design process due to the complex two-phase flow phenomena. The air/oil mixture that is discharged out of the bearing chambers has a strong influence on the overall pressure losses and it shows locally enhanced heat transfer where oil coking or oil fires with the risk of flashback into the bearing chamber can occur.In order to gain a deeper insight into the interacting flow of air and oil, a glass pipe test section with a inner tube diameter of 10 mm was integrated into the vent-line of the high speed bearing chamber test rig operated at the Institut fur Thermische Stromungsmaschinen, University of Karlsruhe, Germany. Therewith, an experimental study of the oil film along the wall in vertical annular upflow was performed by use of a laser focus displacement meter. This instrument which was introduced by Takamasa et al. [1] allows accurate measurements of film thickness to be made in real time with a sensitivity of 2 microns and a datarate of 1.5 kilohertz.Comprehensive measurements were conducted at two locations of the pipe 320 mm apart in flow direction. A wide range of oil and air flow rates was examined to study their impact on the local film thickness. Both fluids were heated up to the same temperature of 70°C and 100 °C, respectively, to vary the oil viscosity by a factor of 2.Copyright

Effect of Variable Liquid Properties on the Flow Structure within Shear-Driven Wall Films

Liquid wall films driven by air flow occur in fuel preparation processes of advanced prefilming gas turbine combustor nozzles or in intake manifolds of SI-engines. There is a need to develop new and more accurate models to describe the heat transfer from the wall to the film. To obtain data necessary for the modeling a new measurement device in combination with an enhanced data processing technique has been developed. The device combines two novel measurement systems. It consists of a film structure measurement system and a specially adapted LDV-system with a miniaturized probe volume. This combination allows simultaneous measurements of film thickness and flow velocity within the film. For the first time detailed information of the internal flow structure are provided under consideration of the effect of variable liquid properties on the film hydrodynamics.

Droplet Entrainment From a Shear-Driven Liquid Wall Film in Inclined Ducts: Experimental Study and Correlation Comparison

The primary objective of the present study is to clarify the droplet disintegration mechanism and the film properties of liquid oil films driven by shear stress, which is induced by a co-current gas flow. This work focuses on the flow behavior within the starting length of the complex two-phase flow and the effect of inclination on the entrainment rate. Many investigations have been performed in the past to determine the droplet entrainment in the gas core for fully developed flow conditions with respect to their relevance in pipes of power plants and various chemical engineering systems. In more recent work the effect of inclination has been studied in detail. Nevertheless, a lack of knowledge can be realized for droplet entrainment within the starting length of this complex flow type. Thus, fundamental experiments have been carried out to provide a data base for droplet entrainment of liquid disintegrated from an oil film within its starting length at several inclination angles of the flow. The experimental results have been compared with correlations from literature. Additionally, the wall film thickness has been measured to allow a fully coupled modeling of entrainment and liquid film properties depending on global flow parameters. Based on film Reynolds number, Weber number, a dimensionless film flow length, and a modified Froude number, taking into account the angle of inclination, correlations have been developed, where those from literature are not applicable.

Modelling of shear-driven liquid wall films: effect of accelerated air flow on the film flow propagation

Liquid wall films that are driven by the shear stress exerted from a co-current air stream occur in many technical systems, e.g. in rocket nozzles, heat exchangers and on steam turbine blades. They are also present in prefilming airblast atomisers which are used for the fuel preparation in modern aviation gas turbines. In many cases, an acceleration of the co-current air flow is imposed in order to improve the performance or because of the geometrical constraints in complex configurations. The film flow characteristics are strongly influenced by the additional pressure gradient and the associated increase of the interfacial shear forces at the gas-liquid interface. In order to predict the two-phase flow field, a model has been developed at the Institut fur Thermische Stromungsmaschinen (ITS), University of Karlsruhe (TH) which allows a fully coupled computation of the gas flow field and the liquid film. In the present paper the modifications are discussed which are required to take into account the effect of an imposed pressure gradient in the air flow on the film flow dynamics. It will be shown that the numerical approach is capable to predict the film propagation with a high accuracy, providing a powerful tool for the design and the improvement of technical applications where liquid film phenomena play an important role.