Institute of Fluid Mechanics

Mechanics, Germany

Institute of Fluid Mechanics

Mechanics, Germany
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Schutte A.,German Aerospace Center | Schutte A.,German Institute of Aerodynamics and Flow Technology | Hummel D.,TU Braunschweig | Hummel D.,Institute of Fluid Mechanics | Hitzel S.M.,Airbus
Journal of Aircraft | Year: 2012

Within the NATO Research and Technology Organisation Applied Vehicle Technology (AVT)-161 task group, titled "Assessment of Stability and Control Predictions for NATO Air and Sea Vehicles," a 53 swept and twisted lambda wing with rounded leading edges is considered. In a first step, the symmetric flow conditions are analyzed in this paper in order to understand the corresponding flow physics. Experiments by the task group are used to develop proper numerical simulation tools for further applications in the design process of unmanned combat aerial vehicles as a part of future air-combat systems. The philosophy of the configuration under consideration is explained. The vortical flowfield is simulated using the DLR, German Aerospace Center TAU-Code applied with different turbulence models on various computational grids. Finally, a best practice is evaluated for medium and large angles of attack. A combination of these numerical results and experimental data lead to a proper understanding of the complex flow structure. Furthermore, this paper addresses the necessity for the predictability and understanding of controlled and uncontrolled flow separation, together with the interaction of the corresponding vortex systems in order to estimate stability and control issues for the entire flight envelope.

Burnazzi M.,TU Braunschweig | Burnazzi M.,Institute of Fluid Mechanics | Radespiel R.,TU Braunschweig | Radespiel R.,Institute of Fluid Mechanics
Journal of Aircraft | Year: 2014

The present study describes the fundamentals of droop nose design for improving the aerodynamics of airfoils with active high-lift using an internally blown Coanda-type flap. The main objectives are to increase the stall angle of attack and reduce the power required by the high-lift system. A two-dimensional sensitivity analysis explores the effects of varying airfoil camber and thickness in the first 20% of the chord. The resulting droop nose configuration improves the maximum lift coefficient by about 20% and increases the stall angle of attack by around 10-15 deg. A target lift coefficient of about 4.7 is reached with28%less jetmomentumcoefficient, compared to the clean nose. As the modified leading-edge geometry presents different stall mechanisms, the aerodynamic response to variations of jet momentum is also different. In particular, for a jet momentum coefficient above 0.035, the stall angle of attack increases with jet momentum, in contrast with the behavior observed with the clean nose. Copyright © 2014 by Indian Institute of Space Science and Technology, Thiruvananthapuram, India. Published by the American Institute of Aeronautics and Astronautics, Inc.

Bansmer S.E.,TU Braunschweig | Bansmer S.E.,Institute of Fluid Mechanics | Radespiel R.,TU Braunschweig
AIAA Journal | Year: 2012

A combined experimental and computational study is presented for a wing segment undergoing a combined pitching, plunging, and rolling motion at Reynolds number of 100,000, where transition takes place along laminar separation bubbles. The numerical simulation approach addresses unsteady Reynolds-averaged Navier-Stokes solutions and covers three-dimensional transition prediction for unsteady mean flows. The numerical simulations are validated using high-resolution, phase-locked stereoscopic particle image velocimetry for a three-dimensional flapping case with a reduced frequency of k = 0:25. The flow reveals strong unsteadiness resulting in moving laminar separation bubbles, whose spatial extensions are varying in the spanwise direction. The experimental results are well captured by the numerical simulations performed in this study. Because of the vortex structure in the wake of the wing segment, the three-dimensional aerodynamics cannot be reproduced as a spanwise sequence of two-dimensional results. Copyright © 2011.

Masood R.M.A.,Institute of Fluid Mechanics | Rauh C.,TU Berlin | Delgado A.,Institute of Fluid Mechanics
International Journal of Multiphase Flow | Year: 2014

CFD study of flow hydrodynamics has been conducted in transient Euler-Euler environment by using commercial simulation software Ansys CFX 14.0. First, three different wall lubrication force models are compared. Afterwards, the influence of turbulent dispersion force models has been analyzed. Finally, the performance of Explicit Algebraic Reynolds Stress Model (EARSM) combined with k - ε and Baseline (BSL) models has been tested. Three different combinations of EARSM were included with two cases incorporating the Bubble Induced Turbulence (BIT) as well (i.e. EARSM k - ε BIT, EARSM BSL, EARSM BSL BIT). All simulations were compared for average velocity and turbulent kinetic energy profiles with experiments. The performance of these models was also compared with Re-Normalization Group (RNG) and k - ε models. EARSM k - ε model was unable to capture the axial liquid as well as gas phase velocities close to experimental values. On contrary, EARSM BSL and EARSM BSL BIT were more successful in predicting the velocity profiles and showed good agreement with experiments, with EARSM BSL slightly less accurate in predicting axial velocity profiles. All models predicted the turbulent kinetic energy profiles reasonably good both quantitatively as well as qualitatively, while near the bottom of the column; EARSM k - ε slightly under predicted the turbulent quantities. Thus, EARSM combined with BSL and BIT can be effectively exploited for simulating flow fields and turbulent quantities. © 2014 Elsevier Ltd.

Masood R.M.A.,Institute of Fluid Mechanics | Delgado A.,Institute of Fluid Mechanics
Chemical Engineering and Technology | Year: 2014

Numerical simulations were performed employing detached eddy simulation (DES) in a three-dimensional transient Euler-Euler framework for bubble columns, and all the computational fluid dynamics results were compared with a k-ε{lunate} model and available experimental data. The numerical results are in good agreement with the experiments in predicting the time-averaged axial velocity and turbulent kinetic energy profiles. The flow-resolving capabilities of the DES model are highlighted, and it is shown that the DES turbulence model can be efficiently used for simulating flow field and turbulent quantities in the case of bubble columns. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gundermann T.,Institute of Fluid Mechanics | Gunther S.,Institute of Fluid Mechanics | Borin D.,Institute of Fluid Mechanics | Odenbach S.,Institute of Fluid Mechanics
Journal of Physics: Conference Series | Year: 2013

A possibility to determine the microstructure of magneto active composites using micro-computed tomography (̈-CT) [1] was investigated in this work. The main interest of the current study has been an observation of the magnetic field dependent shift of individual particles from their initial positions inside an elastomeric matrix. For this purpose a ̈-CT system has been combined with a sample holder coupled with two permanent magnets, enabling the investigation of the micro-structure under influence of an external homogeneous field. In the experimental investigations samples based on carbonyl iron particles have been used. The particles have been dispersed in a polymeric matrix and the polymer has been created in the presence of a magnetic field driving structure formation of the particles. After the characterization of the sample in its initial state, i.e. without external stimuli, it has been subjected to the magnetic field and its internal structure has been once more studied by ̈-CT. As a result a comparison of the macroscopic change of the sample structure and the particle displacement could be undertaken. © Published under licence by IOP Publishing Ltd.

Scheit C.,Institute of Process Machinery and Systems Engineering | Karic B.,Institute of Fluid Mechanics | Becker S.,Institute of Process Machinery and Systems Engineering
Journal of Sound and Vibration | Year: 2012

Radial impellers have several technical applications. Regarding their aerodynamic performance, they are well optimized nowadays, but this is in general not true regarding acoustics. This work was therefore concerned with analyzing the flow structures inside isolated radial impellers together with the far-field sound radiated from them in order to optimize the aerodynamic and acoustic performance. Both numerical and experimental techniques were applied in order to study the effect of varying wrap angle and otherwise identical geometric configuration on aerodynamics and acoustics of the radial impellers. The results give a detailed insight into the processes leading to sound generation in radial impellers. Measurements were performed using laser Doppler anemometry for the flow field and microphone measurements to analyze the radiated noise. In addition, unsteady aerodynamic simulations were carried out to calculate the compressible flow field. An acoustic analogy was employed to compute far-field noise. Finally, the phenomena responsible for tonal noise and the role of the wrap angle could be identified. Using this knowledge, design guidelines are given to optimize the impeller with respect to the radiated noise. This work shows that improved aerodynamic efficiency for isolated impellers does not automatically lead to a smaller flow-induced sound radiation. © 2011 Elsevier Ltd. All rights reserved.

Masood R.M.A.,Institute of Fluid Mechanics | Khalid Y.,King Saud University | Delgado A.,Institute of Fluid Mechanics
Chemical Engineering Journal | Year: 2015

Numerical investigations using scale adaptive simulation (SAS) in 3D transient Euler-Euler framework for bubble columns have been carried out and all the simulation results are compared with available experimental data. The performance of SAS model was also compared with re-normalization group (RNG), large eddy simulation (LES) and k-. ε models. Numerical results are in good agreement with experiments in predicting time averaged turbulent kinetic energy and axial velocity profiles. The superior flow predicting ability of SAS model is highlighted and it has shown that SAS turbulence model can capture large scale turbulence behavior and can be used efficiently for simulating flow field and turbulent quantities in case of bubble column flows. © 2014 Elsevier B.V.

Huismann I.,Institute of Fluid Mechanics | Stiller J.,Institute of Fluid Mechanics | Frohlich J.,Institute of Fluid Mechanics
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

Current research in computational fluid dynamics focuses on higher-order methods. These possess a more extensive coupling between degrees of freedom, resulting in a larger runtime per degree of freedom compared to low-order methods. This work tries to tackle this issue by combining the static condensation method with tensor-product and sum factorization, leading to a well-scaling solver for the Helmholtz equation. © Springer International Publishing Switzerland 2016.

Engler H.,Institute of Fluid Mechanics | Lange A.,Institute of Fluid Mechanics | Borin D.,Institute of Fluid Mechanics | Odenbach S.,Institute of Fluid Mechanics
International Journal of Heat and Mass Transfer | Year: 2013

The material and flow properties of magnetic fluids-so called ferrofluids-can be significantly influenced by magnetic fields. Two of the most prominent phenomena are the thermomagnetic convection and the magnetoviscous effect. To date, these magnetic field induced effects have always been studied separately, although they can affect each other under certain conditions. With the help of magnetic fields it is possible to induce a convective heat flow in ferrofluids. In earlier studies it is assumed for that case that the classical material properties are constant. However the magnetoviscous effect describes an increase in viscosity under magnetic influence, which occurs in ferrofluids with a certain contingent of large particles. In this paper, experimental results concerning the influence of the magnetoviscous effect on thermomagnetic convection are shown and discussed. Ferrofluids with and without significant magnetoviscous effect have been investigated. © 2012 Elsevier Ltd. All rights reserved.

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