Markus Rütten

Investigation of Vortex Breakdown over a Pitching Delta Wing applying the DLR TAU-Code with Full, Automatic Grid Adaptation

This paper covers a description of the complete process chain used to investigate the vortex breakdown over a pitching delta wing. Special attention is given to the dynamic adaptation strategies used to capture the main flow structures as well as the analysis of vortex breakdown and the formation of primary and secondary vortices. The demonstrated approach with hybrid grids and a standard URANS flow solver shows extraordinary good results for this type of application.

Detecting vortical phenomena in vector data by medium-scale correlation

The detection of vortical phenomena in vector data is one of the key issues in many technical applications, in particular in flow visualization. Many existing approaches rely on purely local evaluation of the vector data. In order to overcome the limits of a local approach, we choose to combine a local method with a correlation of a pre-defined generic vortex with the data in a medium-scale region. Two different concepts of generic vortices were tested on various sets of flow velocity vector data. The approach is not limited to the two generic patterns suggested here. The method was found to successfully detect vortices in cases were other methods fail.

Analyzing Vortex Breakdown Flow Structures by Assignment of Colors to Tensor Invariants

Topological methods are often used to describe flow structures in fluid dynamics and topological flow field analysis usually relies on the invariants of the associated tensor fields. A visual impression of the local properties of tensor fields is often complex and the search of a suitable technique for achieving this is an ongoing topic in visualization. This paper introduces and assesses a method of representing the topological properties of tensor fields and their respective flow patterns with the use of colors. First, a tensor norm is introduced, which preserves the properties of the tensor and assigns the tensor invariants to values of the RGB color space. Secondly, the RGB colors of the tensor invariants are transferred to corresponding hue values as an alternative color representation. The vectorial tensor invariants field is reduced to a scalar hue field and visualization of iso-surfaces of this hue value field allows us to identify locations with equivalent flow topology. Additionally highlighting by the maximum of the eigenvalue difference field reflects the magnitude of the structural change of the flow. The method is applied on a vortex breakdown flow structure inside a cylinder with a rotating lid

A Stereo PIV Investigation of a Vortex Breakdown Above a Delta Wing by Analysis of the Vorticity Field.

The vortex breakdown above a generic delta wing was experimentally investigated in order to contribute to the better understanding of this flow phenomenon. The velocity field inside the breakdown region was measured with a three component Particle Image Velocimetry (PIV) system with a high spatial resolution and accuracy, such that the vortical structure could be analysed based on the vorticity field. One research goal was to get more information about the physical mechanism which lead to the dominant vortex breakdown phenomenon. Another important goal of the performed measurement campaign was to investigate the influence of the lower sweep angle on the flow structures. Additionally we compared our PIV and force measurement data with results of numerical simulations and the therewith identified structure of the vortex breakdown in the front part of the delta wing. We were able to confirm the occurrence of a bubble type vortex breakdown predicted by the numerical simulations.

Simulation of the Flow in a Human Nose

The human nose is a very complex organ. The main airways together with a multiplicity of nasal cavities and sinuses are involved in the various functions of the nose. It warms and humidifies the inspired air, filters out small particles and supports the olfaction process by transporting odor-bearing particles to the muscous membranes. The flow simulations presented in this paper are based on the geometry of a real human nose. Based on a series of CT images, a body-fitted, hybrid numerical grid was built up. The DLR THETA code is used to simulate the unsteady flow inside the nose. The transport of a marker gas is simulated to visualise the entrainment of air from the sinuses to the inspired air.

Unsteady Numerical Simulation of the Turbulent Flow around a Wind Turbine

A study of the turbulent air flow around a wind turbine based on unsteady Reynolds-averared Navier-Stokes (URANS) simulation in order to determine the induced loads on its blades for off-design flow cases is performed. In particular the impact of applied turbulence models on the flow simulation results will be discussed.

Experimental Investigations on the Influence of Ingesting Boundary Layers into a Diverterless S‐Duct Intake

An experimental study of the combined effects of boundary layer ingestion and an Sduct diffuser on flow conditions at the engine face is presented. A main focus of the investigations is on the impact of boundary layers on intake performance and on limitations of diverterless intakes due to boundary layer ingestion. The dependence of total pressure distortions on flow parameters has been examined in a parametric study in a blow-down wind tunnel. The free-stream Mach number was varied between M = 0.30 and M = 0.65. In order to form a boundary layer of well-defined thickness ahead of the intake the model is arranged on a flat plate. In the introduction the importance of boundary layer ingesting highly integrated intakes is briefly discussed. This is followed by a description of the analytical design of the generic intake model, the cryogenic blowdown tunnel DNW-KRG in which the experimental tests have been performed, and the measurement techniques. Thereafter, experimental findings are discussed in detail and conclusions are drawn.

Investigation of the Flow within Partially Submerged Scoop Type Air Intakes

Design constraints for air intakes of unmanned combat aerial vehicles (UCAVs) or manned combat aircrafts have been tightened and partially changed due to addional requirements in regard to infrared and radar signature. These requirements have a crucial impact on the aerodynamic shape of air intakes and their integration in aircraft systems. Especially, radar signature is the reason why submerged or partially submerged air intakes are preferred solutions for UCAVs. Moreover, in order to further reduce the radar signature and to avoid backscattering it is also necessary that air intake associated ram air channels have to be S-shaped. Unfortunately, those intake and channel designs reveal a severe impact on the aerodynamic properties, in particular, under transonic flight condition: Especially partially submerged air intakes are very sensitive to onflow conditions. For example, in dependence of the thickness of the boundary layer in front of the intake fluid with more or less momentum enters the air intake which, consequently, effects the total pressure recovery. In fact, a thicker boundary layer means less total pressure recovery. Consequently a partially submerged air intake and its integrated ram air S-duct together exhibit the disadvantage that in regard to the pressure distribution the inhomogenity of the onflowing air at the engine throat plane might be critical for the performance of the engine. Moreover, an intake and duct shape design, which might be beneficial for one flight condition, may not be robust enough for those varying flow conditions which have to be faced over a full mission. Experimental and numerical studies are necessary in order to clarify the essential dependencies between boundary layer thickness, the effect of shock boundary layer interaction and the required engine performance coe�cients. This study addresses these problems by comparing experimental and numerical results.

Surface-Based Structure Analysis and Visualization for Multifield Time-Varying Datasets

This paper introduces a new feature analysis and visualization method for multifield datasets. Our approach applies a surface-centric model to characterize salient features and form an effective, schematic representation of the data. We propose a simple, geometrically motivated, multifield feature definition. This definition relies on an iterative algorithm that applies existing theory of skeleton derivation to fuse the structures from the constitutive fields into a coherent data description, while addressing noise and spurious details. This paper also presents a new method for non-rigid surface registration between the surfaces of consecutive time steps. This matching is used in conjunction with clustering to discover the interaction patterns between the different fields and their evolution over time. We document the unified visual analysis achieved by our method in the context of several multifield problems from large-scale time-varying simulations.

Streamline and Vortex Line Analysis of the Vortex Breakdown in a Confined Cylinder Flow

The vortex breakdown phenomenon occurring in a rotating flow within a closed cylinder is still a challenging research field. In particular the goal to describe all significant order parameters of vortex breakdown is not reached. For further insight the viscous and laminar Newtonian flow inside a cylinder with a rotating lid has been calculated by solving the full Navier Stokes equations. During the sim ulation the rotational speed of the lid has been increased, which causes a gradual transition of the internal flow field topology. Starting from a flow field without any reversed flow at the vortex axis the vortex breakdown phenomenon develops indi cated by one or more vortex breakdown bubbles. A phenomenological description of the vortex breakdown process is given by applying a topological analysis to the flow field, which illustrates the main flow structures, their behaviour and changes. By visualization of critical points, at which the velocity magnitude vanishes, the topological flow structure change of the velocity field becomes obvious. Additionally their associated separatrices are integrated into the field, which allows to illustrate the shape of the vortex breakdown bubbles. In particular the spherical shape of the first appearing breakdown bubble leads to the idea to introduce a streamfunction, which describes the spherical breakdown bubble approximately. Applying a Taylor expansion of the velocity field leads to an analytical description of the local stream line topology nearby one critical point of a breakdown bubble. The interpretation of the appendant differential equations allows a deeper insight into the dynamical behaviour of the breakdown phenomenon and its main enforcing parameters. The paper presents the results of a local streamline and vortex line topology analysis, especially the dynamical relation between the velocity and vorticity field in regard to the topological structure of the vortex breakdown phenomenon in the lid driven cylinder.