Octavian Frederich

Numerical Simulation of the Flow Around a Finite Cylinder with Ground Plate in Comparison to Experimental Measurements

Simulations and experiments were performed to capture the spatio-temporal flow field around a finite circular cylinder mounted on a ground plate. In order to provide a combined database and testcase for future simulations and experiments, the flow is investigated using state-of-the-art techniques with a high resolution in time and space, namely Large-Eddy Simulation and Detached-Eddy Simulation for the numerics and time-resolved PIV as well as LDA for the measurements. The predicted time-averaged and unsteady flow field from simulations corroborate well the experiments, giving new insights into the complex turbulent separated flow behind a quite simple geometry.

Flow Simulation around a Finite Cylinder on Massively Parallel Computer Architecture

Publisher Summary The purpose of the of the research project “Imaging Measuring Methods for Flow Analysis” funded by the German Research Foundation (DFG) is to develop flow measuring techniques and improve their performance. Because of the scarcity of experimental methods capable of producing similar results to simulations, the development of improved measurement methods for the analysis of complex flows is to be furthered in the scope of this program. The numerical simulations are to yield all flow quantities with a high resolution in time and space. The provision of the highly spatially and temporally resolved simulated flow field together with the unsteady experimental data will form a combined database for the verification of newly developed visualization methods and numerical turbulence models, and establish a reference test-case. The chapter also explains the detached-eddy simulation (DES) and the large-eddy simulation (LES).

Large-scale dynamics in the flow around a finite cylinder with a ground plate

To date, physically meaningful representations of the nonstationarity in complex 3D flows with converged turbulent statistics are scarce and shed little light on the nonlinear processes in turbulent motion. This study attempts to address part of this deficit by concentrating on the kinematics of larger scales of motion. Two methods are utilized to describe the kinematics of large-scale unsteady motion in the flow around a wall-mounted finite circular cylinder at Reynolds number ReD = 200?000. The first, Proper Orthogonal Decomposition (POD), is a global method resulting in spatial modes defined over the whole domain and their corresponding temporal coefficients. The second, Coherent Structure Tracking (CST), belongs to a class of local methods that extracts connected domains in the flow data. Modes specific for distinct harmonics are extracted by temporal harmonic filtering. Based on time coefficients of the dominant mode pairs provided by POD or harmonic filtering, phase-averaging has been performed. A scalar-field version of CST is proposed, yielding an intuitively more accessible description of the flow. The extent to which POD and CST are complementary is discussed, as well as the extent to which they partially overlap. The combination of POD, filtering, phase-averaging and CST allowed for identification and quantification of important flow patterns in a complex turbulent flow field.

Numerical Simulation and Analysis of the Flow Around a Wall-Mounted Finite Cylinder

Numerical studies employing LES and DES are presented for the flow around a wall-mounted finite cylinder at a Reynolds number of Re D = 200,000. Very good agreement between the numerical and experimental results is achieved for the steady mean motion, turbulence quantities and the motion of large coherent structures. The synergy between the joint studies within the research unit “Imaging Measurement Methods for Flow Analysis” and the application of POD, particle and structure tracking algorithms allow for a more complete description of the unsteady flow investigated. New insight to the coherent turbulent motion is obtained.

Application of the Immersed Boundary Method for the Simulation of Incompressible Flows in Complex and Moving Geometries

A new variant of the Immersed Boundary Method (IBM) has been implemented into an established flow solver. Important aspects of the implementation towards the application of this approach for flow simulations in complex and moving geometries are characterised. Simple validation test cases are addressed first, followed by a moving boundary example and more complex geometries like the Weibel lung model.

Analysis of the Flow in Dynamically Changing Central Airways

To analyse the dynamic flow in central airways, a workflow has been established which finally enables numerical simulation with simultaneous consideration of natural deformed geometries and inversion of flow direction. A comprehensive description of the radiologic experiments, the segmentation methods and the simulation procedure is given. Finally results gained from simulations in static and dynamic airways are presented and discussed.

Towards numerical simulation and analysis of the flow in central airways

To analyse the flow in natural geometries of central airways an interdisciplinary project by medical and engineering partners has been created. The work presented summarises necessary developments, preliminary investigations and new insights into the unsteady flow with a focus on numerical fluid mechanics. The objective of the investigations is the analysis and physical understanding of the dynamic flow in central airways, which should later allow to improve artificial ventilation towards a more lung protective approach than actual strategies.

Flow Prediction Around an Oscillating NACA0012 Airfoil at Re = 1,000,000

The maximum obtainable lift of a rotationally-oscillating airfoil is significantly higher than in the static or quasi-static case. The correct prediction of dynamic stall as the basis of the dynamically increased lift is essential to quantify the time-dependent load on the airfoil structure. This study applies unsteady RANS (URANS) and detached-eddy simulation (DES) with various turbulence models and parameter variations in order to capture the physics around an oscillating NACA0012 airfoil at a relatively high Reynolds number and to identify possible advantages and potential drawbacks of the given methods. The quality of the flow prediction is assessed primarily on the basis of integral force coefficients compared to experimental results, revealing the influence of resolution on maximum lift and the corresponding angle of incidence.