TY - CHAP A1 - Scholz, Alexander-Wigbert K. A1 - Krenkel, Lars A1 - Terekhov, Maxim A1 - Friedrich, Janet A1 - Rivoire, Julien A1 - Köbrich, Rainer A1 - Wolf, Ursula A1 - Kalthoff, Daniel A1 - David, Matthias A1 - Wagner, Claus A1 - Schreiber, Laura Maria ED - Hirschel, Ernst Heinrich ED - Schröder, Wolfgang ED - Fujii, Kozo ED - Haase, Werner ED - Leer, Bram ED - Leschziner, Michael A. ED - Pandolfi, Maurizio ED - Periaux, Jacques ED - Rizzi, Arthur ED - Roux, Bernard ED - Shokin, Yurii I. ED - Klaas, Michael ED - Koch, Edmund ED - Schröder, Wolfgang T1 - Magnetic Resonance Imaging and Computational Fluid Dynamics of High Frequency Oscillatory Ventilation (HFOV) T2 - Fundamental Medical and Engineering Investigations on Protective Artificial Respiration N2 - In order to better understand the mechanisms of gas transport during High Frequency Oscillatory Ventilation (HFOV) Magnetic Resonance Imaging (MRI) with contrast gases and numerical flow simulations based on Computational Fluid Dynamics(CFD) methods are performed. Validation of these new techniques is conducted by comparing the results obtained with simplified models of the trachea and a first lung bifurcation as well as in a cast model of the upper central airways with results achieved from conventional fluid mechanical measurement techniques like e.g. Laser Doppler Anemometry (LDA). Further it is demonstrated that MRI of experimental HFOV is feasible and that Hyperpolarized 3He allows for imaging the gas re-distribution inside the lung. Finally, numerical results of oscillatory flow in a 3rd generation model of the lung as well as the impact of endotracheal tubes on the flow regime development in a trachea model are presented. KW - Central Airway KW - computational fluid dynamics KW - Computational Fluid Dynamics Simulation KW - Laser Doppler Anemometry KW - Magnetic Resonance Imaging Measurement Y1 - 2011 SN - 978-3-642-20325-1 U6 - https://doi.org/10.1007/978-3-642-20326-8_7 VL - 116 SP - 107 EP - 128 PB - Springer CY - Berlin, Heidelberg ER - TY - RPRT A1 - Steiger, Tamara A1 - Foltan, Maik A1 - Philipp, Alois A1 - Müller, Thomas A1 - Gruber, Michael A1 - Bredthauer, Andre A1 - Krenkel, Lars A1 - Birkenmaier, Clemens A1 - Lehle, Karla T1 - Accumulations of von Willebrand factor within ECMO oxygenators: Potential indicator of coagulation abnormalities in critically ill patients? N2 - Clot formation within membrane oxygenators (MOs) remains a critical problem during extracorporeal membrane oxygenation (ECMO). The composition of the clots—in particular, the presence of von Willebrand factor (vWF)—may be an indicator for prevalent nonphysiological flow conditions, foreign body reactions, or coagulation abnormalities in critically ill patients. Mats of interwoven gas exchange fibers from randomly collected MOs (PLS, Maquet, Rastatt, Germany) of 21 patients were stained with antibodies (anti‐vWF and anti‐P‐selectin) and counterstained with 4′,6‐diamidino‐2‐phenylindole. The extent of vWF‐loading was correlated with patient and technical data. While 12 MOs showed low vWF‐loadings, 9 MOs showed high vWF‐loading with highest accumulations close to crossing points of adjacent gas fibers. The presence and the extent of vWF‐fibers/“cobwebs,” leukocytes, platelet–leukocyte aggregates (PLAs), and P‐selectin‐positive platelet aggregates were independent of the extent of vWF‐loading. However, the highly loaded MOs were obtained from patients with a significantly elevated SOFA score, severe thrombocytopenia, and persistent liver dysfunction. The coagulation abnormalities of these critically ill patients may cause an accumulation of the highly thrombogenic and elongated high‐molecular‐weight vWF multimers in the plasma which will be trapped in the MOs during the ECMO therapy. Y1 - 2019 ER - TY - CHAP A1 - Stelzer, Vera A1 - Tauwald, Sandra Melina A1 - Vielsmeier, Veronika A1 - Cieplik, Fabian A1 - Kandulski, Arne A1 - Schneider-Brachert, Wulf A1 - Wünsch, Olaf A1 - Rütten, Markus A1 - Krenkel, Lars ED - Dillman, Andreas ED - Heller, Gerd ED - Kraemer, Ewald ED - Wagner, Claus ED - Weiss, Julien T1 - Generation and Distribution of Surgical Smoke During High Frequency Electrocauterization T2 - New Results in Numerical and Experimental Fluid Mechanics XIV. STAB/DGLR Symposium 2022 N2 - Surgical Smoke is generated during the cauterization of tissue with high-frequency (HF) devices and consists of 95% water vapor and 5% cellular debris. When the coagulation tweezers, which are supplied with HF voltage by the HF device, touch tissue, the electric circuit is closed, and smoke is generated by the heat. In-vivo investigations are performed during tracheotomies where surgical smoke is produced during coagulation of tissue. Furthermore, in-vitro parametric studies to investigate the particle number and size distribution and the spatial distribution of surgical smoke with laser light sheet technique are conducted. With higher power of the HF device, the particles generated are larger in size and the total number of particles generated is also higher. Adding artificial saliva to the tissue shows even higher particle counts. The study by laser light sheet also confirms this. The resulting characteristic size distribution, which may include viruses and bacterial components, confirms considering the risk arising from surgical smoke. Furthermore, the experiments will provide the database for further numerical investigations. KW - Surgical smoke KW - Fluid Mechanics KW - Aerosols KW - Tracheotomies Y1 - 2023 SN - 978-3-031-40481-8 U6 - https://doi.org/10.1007/978-3-031-40482-5_53 SP - 559 EP - 568 PB - Springer Nature Switzerland AG CY - Cham, Switzerland ER - TY - CHAP A1 - Rütten, Markus A1 - Krenkel, Lars ED - Hirschel, Ernst Heinrich ED - Schröder, Wolfgang ED - Fujii, Kozo ED - Haase, Werner ED - Leer, Bram ED - Leschziner, Michael A. ED - Pandolfi, Maurizio ED - Periaux, Jacques ED - Rizzi, Arthur ED - Roux, Bernard ED - Shokin, Yurii I. ED - Dillmann, Andreas ED - Heller, Gerd ED - Klaas, Michael ED - Kreplin, Hans-Peter ED - Nitsche, Wolfgang T1 - Vortex-Generator Pairs for Vortex-Induced Heat-Transfer Enhancement in Heat-Exchanger Channels T2 - New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008 N2 - The objective of the presented work is to investigate possibilities for increasing the heattransfer in heat-exchanger channels for aircraft applications by using flow-manipulating devices. Focal point of the investigation are different arrangements of vortex-generator pairs within a generic heat-exchanger channel. The DLR URANS CFD solver THETA has been used to carry out numerical simulations of the laminar flow within a rectangular channel with integrated vortex generators. In particular, the analysis of the interaction of generated vortices with the stratified thermal boundary layer, the impact of vortical flow structures on heated walls and the enforced mixed-convection flow is of special interest. The final goal is the evaluation of the applicability of oppositely arranged vortex-generator pairs for the enhancement of vortex-induced heat-transfer. KW - Heat Exchanger KW - Heat Transfer KW - Heated Wall KW - Thermal Boundary Layer KW - Vortex Generator Y1 - 2010 SN - 978-3-642-14242-0 SN - 978-3-642-14243-7 U6 - https://doi.org/10.1007/978-3-642-14243-7_68 SP - 555 EP - 562 PB - Springer Berlin Heidelberg CY - Berlin, Heidelberg ER - TY - BOOK A1 - Krenkel, Lars T1 - Untersuchung des Einflusses von Wirbelgeneratoren auf die Stoß-/Grenzschicht-Wechselwirkung N2 - Im Rahmen dieser Arbeit werden experimentelle und numerische Parameterstudien von einzelnen Wirbelgeneratorpaaren und komplexeren Wirbelgeneratoranordnungen bezüglich ihres Einflusses auf eine starke Stoß-/Grenzschicht-Wechselwirkung vorgestellt. Dabei werden die Einflüsse von Wirbeln, insbesondere die Auswirkungen ihrer Wechselwirkungen untereinander, auf das Grenzschichtverhalten, die Stoßcharakteristik und insgesamt auf die aerodynamische Leistung des betrachteten Profils diskutiert. Dazu wurden sowohl Windkanalversuche am einfachen Modell einer ebenen Platte mit aufgeprägtem Druckgradienten sowie an einem Modell eines superkritischen transsonischen Profils durchgeführt. Ergänzend wurden komplexe nume-rische Parameteruntersuchungen an einem Profil in freier Anströmung ausgeführt. Es ist das Ziel, ein besse-res Verständnis der Mechanismen der Wirbelgenerator-/Stoß-/Grenzschicht-Wechselwirkung zu gewinnen, um durch optimierte Anwendung von Wirbelgeneratoren eine Verbesserung der Flugleistungen erzielen zu können. Die Schwerpunkte liegen dabei auf der Reduktion des Widerstandes, der Vermeidung bzw. Verzöge-rung von Strömungsablösung und Stoßschwingung sowie auf der Erhöhung des Auftriebs. KW - CFD KW - Numerische Simulation KW - Stoß-/Grenzschicht-Wechselwirkung KW - Strömungsablösung KW - Strömungssteuerung KW - transsonische Strömung KW - Verdichtungsstoß KW - Windkanal KW - Wirbelgeneratoren Y1 - 2012 UR - https://elib.dlr.de/78972/ SN - 1434-8454 PB - Rheinisch-Westfälische Technische Hochschule Aachen CY - Aachen ER - TY - CHAP A1 - Krenkel, Lars A1 - Pennecot, Julien A1 - Lenz, Christian A1 - Feldmann, Daniel A1 - Wagner, Claus ED - Füssel, Jens ED - Koch, Edmund ED - Malberg, Hagen T1 - Optimierung der Hochfrequenz-Oszillationsventilation mittels strömungsmechanischer Methoden und kontrastgasgestützter Magnetresonanztomografie - Teilprojekt: Rekonstruktion von Geometrien aus medizinischen Bilddaten und Erstellung von Modellen für experimentelle Strömungsuntersuchungen T2 - Laseranwendung in der Medizin, Erfassen und Verarbeiten kardiovaskulärer Signale, protektive Beatmungskonzepte : 3. Dresdner Medizintechnik-Symposium - mit DFG-Forschungsschwerpunkt Protektive Beatmungskonzepte, 6. bis 9. Dezember 2010, Dresden N2 - Der vorliegende Artikel skizziert die neu entwickelte Prozesskette für detailgenaue Rekonstruktion von Geometrien anhand medizinischer Bilddaten sowie die Herstellung von transparenten Modellen für experimentelle Untersuchungen mit bildgebenden Strömungsmessverfahren. Die Geometriedaten und Modelle werden für systematische Untersuchungen der komplexen Transportvorgänge in den Atemwegen bei künstlicher Beatmung mittels Hochfrequenzoszillationsventilation (HFOV) verwendet. Y1 - 2010 UR - https://elib.dlr.de/66863/ SN - 978-3-942710-02-2 SP - 107 EP - 114 PB - TUDpress CY - Dresden ER - TY - GEN A1 - Tauwald, Sandra Melina A1 - Quadrio, Maurizio A1 - Rütten, Markus A1 - Stemmer, Christian A1 - Krenkel, Lars T1 - High Spatial Resolution Tomo-PIV of the Nasopharynx Focussing on the Physiological Breathing Cycle T2 - 23. DGLR Fach-Symposium Strömungen mit Ablösung, 09./10. November 2022, Berlin, Deutschland N2 - Investigations of complex patient-specific flow in the nasopharynx requires high resolution numerical calculations validated by reliable experiments. When building the validation base and the benchmark of computational fluid dynamics, an experimental setup of the nasal airways was developed. The applied optical measurement technique of tomo-PIV supplies information on the governing flow field in three dimensions. This paper presents tomo-PIV measurements of the highly complex patient-specific geometry of the human trachea. A computertomographic scan of a person’s head builds the basis of the experimental silicone model of the nasal airways. An optimised approach for precise refractive index matching avoids optical distortions even in highly complex non-free-of-sight 3D geometries. A linear-motor-driven pump generates breathing scenarios, based on measured breathing cycles. Adjusting of the CCD cameras‘ double-frame-rate PIV-Δt enables the detailed analysis of flow structures during different cycle phases. Merging regions of interest enables high spatial resolution acquisition of the flow field. KW - Tomographic PIV KW - Flow visualisation KW - Physiological Breathing KW - Nasal airflow Y1 - 2022 UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/Jahresbericht2022.pdf CY - Göttingen ER - TY - GEN A1 - Stelzer, Vera A1 - Tauwald, Sandra Melina A1 - Vielsmeier, Veronika A1 - Cieplik, Fabian A1 - Kandulski, Arne A1 - Schneider-Brachert, Wulf A1 - Wuensch, Olaf A1 - Rütten, Markus A1 - Krenkel, Lars T1 - Generation, Distribution, and Contagiousness of Surgical Smoke during Tracheotomies T2 - 23. DGLR Fach-Symposium Strömungen mit Ablösung, 09./10. November 2022, Berlin, Deutschland N2 - Surgical smoke has been a little discussed topic in the context of the current pandemic. Surgical smoke is generated during the cauterization of tissue with heat-generating devices and consists of 95% water vapor and 5% cellular debris in the form of particulate matter. In-vivo investigations are performed during tracheotomies where surgical smoke is produced during tissue electrocautery. Furthermore, in-vitro parametric studies to investigate the particle number and size distribution and the spatial distribution of surgical smoke with laser light sheet technique are conducted. The higher the power of the high-frequency-device the larger the particles in size and the higher the resulting particle counts. The images taken show the densest smoke at 40W with artificial saliva. The resulting characteristic size distribution, which may include viruses and bacterial components, confirms that the risk arising from surgical smoke should be considered. Furthermore, the experiments will provide the database for further numerical investigations. Y1 - 2022 UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/Jahresbericht2022.pdf CY - Göttingen ER - TY - JOUR A1 - Stelzer, Vera A1 - Krenkel, Lars T1 - 2D numerical investigations derived from a 3D dragonfly wing captured with a high-resolution micro-CT JF - Technology and health care : official journal of the European Society for Engineering and Medicine N2 - BACKGROUND: Due to their corrugated profile, dragonfly wings have special aerodynamic characteristics during flying and gliding. OBJECTIVE: The aim of this study was to create a realistic 3D model of a dragonfly wing captured with a high-resolution micro-CT. To represent geometry changes in span and chord length and their aerodynamic effects, numerical investigations are carried out at different wing positions. METHODS: The forewing of a Camacinia gigantea was captured using a micro-CT. After the wing was adapted an error-free 3D model resulted. The wing was cut every 5 mm and 2D numerical analyses were conducted in Fluent® 2020 R2 (ANSYS, Inc., Canonsburg, PA, USA). RESULTS: The highest lift coefficient, as well as the highest lift-to-drag ratio, resulted at 0 mm and an angle of attack (AOA) of 5∘. At AOAs of 10∘ or 15∘, the flow around the wing stalled and a Kármán vortex street behind the wing becomes CONCLUSIONS: The velocity is higher on the upper side of the wing compared to the lower side. The pressure acts vice versa. Due to the recirculation zones that are formed in valleys of the corrugation pattern the wing resembles the form of an airfoil. KW - aerodynamics KW - computational fluid dynamics KW - Dragonfly wing KW - gliding flight KW - insect flight Y1 - 2022 U6 - https://doi.org/10.3233/THC-219010 N1 - Corresponding author: Vera Stelzer VL - 30 IS - 1 SP - 283 EP - 289 PB - IOS Press ER - TY - JOUR A1 - Schecklmann, Martin A1 - Schmausser, Maximilian A1 - Klinger, Felix A1 - Kreuzer, Peter M. A1 - Krenkel, Lars A1 - Langguth, Berthold T1 - Resting motor threshold and magnetic field output of the figure-of-8 and the double-cone coil JF - scientific reports N2 - The use of the double-cone (DC) coil in transcranial magnetic stimulation (TMS) is promoted with the notion that the DC coil enables stimulation of deeper brain areas in contrast to conventional figure-of-8 (Fo8) coils. However, systematic comparisons of these two coil types with respect to the spatial distribution of the magnetic field output and also to the induced activity in superficial and deeper brain areas are limited. Resting motor thresholds of the left and right first dorsal interosseous (FDI) and tibialis anterior (TA) were determined with the DC and the Fo8 coil in 17 healthy subjects. Coils were orientated over the corresponding motor area in an angle of 45 degrees for the hand area with the handle pointing in posterior direction and in medio-lateral direction for the leg area. Physical measurements were done with an automatic gantry table using a Gaussmeter. Resting motor threshold was higher for the leg area in contrast to the hand area and for the Fo8 in contrast to the DC coil. Muscle by coil interaction was also significant providing higher differences between leg and hand area for the Fo8 (about 27%) in contrast to the DC coil (about 15%). Magnetic field strength was higher for the DC coil in contrast to the Fo8 coil. The DC coil produces a higher magnetic field with higher depth of penetration than the figure of eight coil. KW - ANTERIOR CINGULATE CORTEX KW - CONNECTIVITY KW - Depression KW - FRONTAL-CORTEX KW - PREDICTOR KW - RTMS KW - STIMULATION KW - TMS Y1 - 2020 U6 - https://doi.org/10.1038/s41598-020-58034-2 VL - 10 IS - 1 PB - Nature ER -