Published by Oldenbourg Wissenschaftsverlag

Volume 89 Issue 3 - Themenheft: Nichtinvasive Messverfahren für Mikro- und Makroströmungen / Andreas Fischer

Issue of tm - Technisches Messen

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Contents
Journal Overview

Publicly Available March 2, 2022

Frontmatter

Page range: I-IV

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Editorial

Publicly Available February 2, 2022

Nichtinvasive Messverfahren für Mikro- und Makroströmungen

Andreas Fischer

Page range: 147-147

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Beiträge

January 21, 2022

Simultaneous PIV and shadowgraph measurements of thermo-electrohydrodynamic convection in a differentially heated annulus

Peter S. B. Szabo, Antoine Meyer, Martin Meier, Vasyl Motuz, Yaraslau Sliavin, Christoph Egbers

Page range: 148-157

Abstract

Convection in a silicone oil with a temperature dependant fluid property is investigated experimentally in a differentially heated cylindrical annulus. A convective flow is induced by terrestrial gravity in axial direction and combined with an electrical tension applied between both cylinders to induce thermo-electrohydrodynamic convection. To capture the evolving velocity and temperature fields a novel combination of simultaneous PIV and shadowgraph technique is utilized. Results reveal azimuthal modes with cold and hot jets from inner and outer cylinder that are referred to the electric tension. The lack of information in the shadowgraph pictures were recovered by the PIV technique providing a deeper understanding in the nature of the development of the azimuthal mode number and the surrounding axial flow of natural convection. In addition, the results provide a robust framework in the capability of combining both techniques to investigate complex flow patterns that are non-axisymmetric.

February 2, 2022

Laser-Doppler-Anemometrie-Messungen in einem quadratischen Kanal mit eng beieinanderliegenden Rippen an einer Wand

Sebastian Ruck, Frederik Arbeiter, Torben Petri

Page range: 158-167

Abstract

Zusammenfassung In der vorliegenden Arbeit werden Ergebnisse von Laser-Doppler-Anemometrie (LDA)-Geschwindigkeitsmessungen in einem einseitig mit transversal orientierten Rippen-Rauheiten strukturierten quadratischen Kanal für die Strömung mit einer Reynolds-Zahl von Re H = 5 , 0 · 10 4 {\mathit{Re}_{H}}=5,0\cdot {10^{4}} vorgestellt. Das Rippenabstand-Rippenhöhe-Verhältnis war 3 und die Verblockungsrate betrug 6 , 7 %6,7\hspace{0.1667em}\% . Es werden Verteilungen der mittleren Geschwindigkeiten, Reynolds-Spannungen sowie Triple-Geschwindigkeit-Korrelationen präsentiert. Die Ergebnisse zeigen die Entwicklung einer dreidimensionalen Sekundärströmung oberhalb der Rippen, wodurch sich ein schwach advektiver wandnormaler Fluidtransport zwischen der rippennahen Strömung und der Kanalkernströmung einstellt. Der Einfluss der Rippen-Rauheiten auf das turbulente Strömungsgeschehen und die einhergehenden turbulenten Austauschvorgänge ist jedoch auf die unmittelbare Rippennähe begrenzt. Die anhand der statistischen Momente höherer Ordnung beschriebenen rippeninduzierten instationären Strömungsvorgänge sowie der diffusive Transport treten oberhalb der Rippen nur in einem schmalen Band auf.

February 3, 2022

Combined temperature and velocity field measurements in thermal fluid systems with magnetic resonance velocimetry

Martin Bruschewski, Kristine John, Michael J. Benson, Sven Grundmann

Page range: 168-177

Abstract

A method for the combined measurement of velocity and temperature fields in water using magnetic resonance velocimetry (MRV) is presented. MRV can provide accurate volumetric, time-averaged temperature and velocity field data. However, the choice of the flow medium and other materials is limited due to the requirements placed on the magnetic properties. There are also limitations to the measurable fluid velocities and temperatures. The echo time TE, which typically defines the temperature sensitivity, is particularly important for temperature measurement in fluid flows. A longer TE means better temperature precision, but measurement errors are increased. In addition, material properties such as magnetic susceptibility and electrical conductivity are temperature-dependent and this can lead to systematic errors in the temperature results. The design of the MRV experiment must take all of these effects into account. Here, a measurement method is proposed that includes various corrective measures. The capabilities are demonstrated with two types of experiments, a pin-fin heat exchanger and a jet-in-crossflow experiment. The fluid in these systems is water with velocities of up to 1 m/s and a temperature between 20 °C and 50 °C. These experiments demonstrate the possibilities of performing quick parameter studies with MRV while achieving low measurement uncertainty and low systematic errors.

January 29, 2022

Flow-measurements in the wake of an oscillating sessile droplet using laser-Doppler velocity profile sensor

Sebastian Burgmann, Veronika Krämer, Michael Dues, Jonas Steinbock, Lars Büttner, Juergen Czarske, Uwe Janoske

Page range: 178-188

Abstract

Although relevant in many technical applications, the removal of sessile droplets on surfaces by an (air-) flow is still hard to predict. The flow around the droplet has not been investigated in detail so far but knowledge on the flow structure is essential for the assessment of appropriate drag force correlation. Small droplets (in the range of 5–40 µl) on PMMA substrate in an air flow are investigated. Due to the small size of the droplet the laser-Doppler velocity profile sensor with frequency shift is applied to measure the flow in the wake of the oscillating, still adhering droplet. Thanks to the high spatial and temporal resolution of Laser-Doppler velocity profile sensor and its capability to measure bidirectional flows, the flow behind the droplet can be precisely analyzed. Additional hot-film measurements are used to investigate the temporal behavior of the flow. Complementary, numerical simulation is performed applying a modified VOF (Volume-of-Fluid) method. The combination of the experimental and numerical data gives new insight in the wake flow structure of sessile droplets: With increasing Reynolds number, a backflow can be detected in the wake of the droplet. A separated shear layer stemming from the upper side of the droplet leads to a vortex shedding with formation of a recirculation region in the temporal mean. In contrast to rigid hemispheres, the movement of the air-liquid interface of the droplet leads to an internal flow which is driven by the outer flow structure and vice versa. This is a hint that drag coefficients of sessile droplets cannot be simply derived by analyzing flows of rigid hemispherical structures. Additionally, droplet contour and wake flow exhibit the same characteristic oscillation frequency. The corresponding Strouhal number is almost constant at 0.03 compared to the Strouhal number of a rigid hemisphere of 0.28. Therefore, it can be assumed that an aeroelastic self-excitation effect may be present that eventually leads to droplet movement.

Open Access February 16, 2022

Particle-Image-Velocimetry zur strömungsmechanischen Analyse des thrombogenen Potentials von Transkatheter-Aortenklappenprothesen

Finja Borowski, Sebastian Kaule, Jan Oldenburg, Klaus-Peter Schmitz, Alper Öner, Michael Stiehm

Page range: 189-200

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Abstract

Zusammenfassung Die minimalinvasive Implantation einer Transkatheter-Aortenklappenprothese (TAVR) hat sich zur Standardtherapie für Patienten mit schwerer Aortenklappenstenose und erhöhtem Operationsrisiko etabliert. Postoperative Komplikationen, wie die subklinische Klappenthrombose, rufen langfristig eine Funktionsstörung der TAVR hervor, die ohne Revisionstherapie zum Tod des Patienten führen kann. Mit der Abschätzung des Thromboserisikos von TAVR werden strömungsmechanische Mechanismen assoziiert. Die Particle Image Velocimetry (PIV) bietet ein etabliertes Messverfahren zur Bestimmung des Geschwindigkeitsfeldes einer TAVR, aus dem beispielsweise die Verweilzeit von Blut im Umfeld einer TAVR abgeleitet werden kann. Ein traversierbarer stereo-PIV Aufbau, bei dem zwei CMOS-Kameras im 45 ° Winkel zur Lichtschnittebene positioniert wurden, ermöglichte die Detektion von Tracerpartikeln in den relevanten Bereichen im Umfeld des TAVR. Mit einer geeigneten Messkammer, die in die hydraulische Nachbildung eines kardiovaskulären Kreislaufs implementiert wurde, konnte eine quasi-volumetrische Messung des physiologischen Geschwindigkeitsfeldes durchgeführt werden. Dafür wurde anhand radiologischer Daten eine realistische Implantationsumgebung rekonstruiert. Mit einem Blutersatzfluid (NaCl-Glycerin-Gemisch) wurde die normativ (ISO 5840:2021) geforderte kinematische Viskosität von ν = 3,5 cSt realisiert. Phasengetriggerte Aufnahmen ermöglichten die Messung zu definierten Zeitpunkten im kardiologischen Zyklus. Insgesamt ist es gelungen die komplexe Strömungstopologie mit dem dargestellten Messaufbau in allen relevanten Bereichen zu erfassen und damit zukünftig das Thromboserisiko abschätzen zu können.

February 19, 2022

Reynolds stress tensor and velocity measurements in technical flows by means of magnetic resonance velocimetry

Data acquisition in the flow field behind the sudden expansion of the FDA benchmark nozzle and identification of systematic errors

Kristine John, Carolin Wüstenhagen, Simon Schmidt, Sebastian Schmitter, Martin Bruschewski, Sven Grundmann

Page range: 201-209

Abstract

Magnetic Resonance Velocimetry (MRV), an imaging method based on Magnetic Resonance Imaging (MRI), enables the measurement of flow parameters such as the velocity and the Reynolds Stress Tensor (RST) in complex structures without optical or physical access to the flow field. Several previous studies investigated the application of MRV velocity measurement in technical flows and obtained results that agreed well with reference data. However, only a few studies have investigated RST measurements using MRV beyond medical applications, and even though the qualitative results were promising, further work is required to establish this method. This study demonstrates the application of two-dimensional three-component (2D3C) velocity and six-component (2D6C) RST measurements in the flow field behind the sudden expansion of a scaled replica of the FDA benchmark nozzle. Particle Image Velocimetry (PIV) data accessible from an interlaboratory study was used for comparison. Furthermore, two different orientations of the imaging plane were measured to investigate the effect of the imaging orientation on the results. The measurement uncertainty of the mean axial velocity is 1.2 % related to the bulk velocity. The RST results agree well with the PIV data, but quantitative deviations occur in the areas where the influence of systematic errors was expected. Comparing different imaging orientations demonstrates that the sequence design affects the quantitative results of the measurement.

About this journal

Objective

The journal promotes dialogue between the developers of application-oriented sensors, measurement systems, and measurement methods and the manufacturers and measurement technologists who use them.

Topics

The manufacture and characteristics of new sensors for measurement technology in the industrial sector
New measurement methods
Hardware and software based processing and analysis of measurement signals to obtain measurement values
The outcomes of employing new measurement systems and methods