Numerische Simulation des konjugierten Wärmeübergangs in einem mit überkritischem Stickstoff durchströmten Kühlkanal eines Flüssigraketentriebwerks

Im Rahmen einer Zusammenarbeit des DLR, der ESA und der Ariane-Group wird das Versagen der Wandstruktur bei zyklischer Belastung von regenerativ gekühlten kryogenen Brennkammern untersucht. Das Ziel der Studie ist es, die hohe thermische und mechanische Belastung zu reduzieren, indem neuartige Materialien verwendet und die Kühlbedingungen verbessert werden. Der Wärmeübergang von der Brennkammerwandstruktur zum Kühlmedium ist hierfür ausschlaggebend. Eine wichtige Einflussgröße ist dabei die maximal auftretende Temperatur in der Struktur. In einer Vorstudie werden die thermischen Eigenschaften einer hochleitfähigen Kupferlegierung durch Kombinationen von Wärme-, Massenströmen und Oberflächentemperaturen am DLR Standort in Lampoldshausen experimentell untersucht. Um Kosten zu reduzieren wird eine thermomechanische Ermüdungsplatte, die einen kleinen Ausschnitt der Geometrie der Brennkammerwand darstellt, verwendet. Heutzutage werden neue Triebwerke hauptsächlich mit numerischen Methoden entwickelt. Für genaue numerische Analysen ist es jedoch wichtig, die zugrunde liegenden Algorithmen mit experimentellen Daten zu validieren. In der vorliegenden Arbeit wird der konjugierte Wärmeübergang mittels einer Fluid-Thermal Analyse in ANSYS modelliert. Unter Berücksichtigung der Messfehler der experimentellen Daten zeigt ein detaillierter Vergleich der numerischen und experimentellen Ergebnisse, dass eine sehr gute Übereinstimmung erzielt wird. Dies ermöglicht es, den Gültigkeitsbereich der experimentellen Daten mittels numerischer Auswertung zu erweitern. Zusätzlich zeigt eine Sensitivitätsanalyse, dass die Wärmestromdichte den größten Einfluss auf die Oberflächentemperatur hat und die Fluidtemperatur am Kanaleingang den Druckverlust am stärksten beeinflusst. Für die Charakterisierung des Wärmeübergangs an der Kanalwand werden einige Nusseltkorrelationen aus der Literatur verwendet. Dabei zeigen, je nach Oberflächentemperatur, unterschiedliche Nusseltkorrelationen gute Übereinstimmungen mit der experimentellen Nusseltzahl. Aus diesem Grund wird für das Wärmeübergangsproblem eine Nusseltkorrelation für rechteckige Kanäle, welche mit überkritischem Stickstoff durchströmt werden, bestimmt

Poetics/Poelitics of materiality in latin american digital poetry

Este artículo propone leer la poesía digital latinoamericana en vinculación con el acontecimiento poético-político que emerge cuando se considera su materialidad. Dar visibilidad a la materialidad habilita limitar la naturalización de los sentidos que vienen asociados a la cultura digital hegemónica contemporánea. Esto se logra desde procedimientos que ponen de relieve tanto los diversos niveles de materialidad inherentes a cada evento artístico literario digital —materialidad textual de superficie, materialidad relacional de las interfaces tanto de software como de hardware, materialidad del código— como los modos convencionales de ser con y hacer sentido de los entramados técnicos digitales que organizan nuestra vida cotidiana.This paper aims to read Latin American digital poetry in regards to the poetic-political event that emerges whenever its materiality is considered. To make materiality visible enables one to restrict the naturalization of meanings associate with contemporary hegemonic digital culture. This is accomplished through artistic procedures that emphasize, on the one hand, the multiple levels of materiality inherent to digital literary works— surface/textual materiality, software and hardware interface relational materiality, code materiality—and, on the other hand, the conventional ways to interact with and build meaning within the digital space that organize everyday life.Fil: Kozak, Claudia. Universidad de Buenos Aires. Facultad de Ciencias Sociales. Instituto de Investigaciones "Gino Germani". Estudios Culturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tres de Febrero; Argentin

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Dependency of Surface Temperature on Coolant Mass Flow and Heat Flux in Rocket Combustion Chambers

This paper presents the simulation and experimental results of the dependency of the surface temperature of a heat transfer test (HTT) panel representing liquid rocket engine combustion chamber geometry on the coolant mass flow rate and heat flow rate. The HTT panel is made of a high-conductivity copper material. This material is appropriate for the inner liner of lowly loaded regeneratively cooled combustion chambers like upper stages. In the experimental setup the HTT panel uses only a small section of the actual combustion chamber geometry, typically five cooling channels. The panel is heated by a high power diode laser providing realistic amounts of heat flux. For safety and cost reasons supercritical nitrogen is used as coolant instead of hydrogen or methane. Within the experiment differ ent combinations of surface temperature, heat flux and mass flow rate were examined, in total 24 different test conditions. Subsequently a coupled steady state thermal fluid-structureinteraction analysis was conducted in ANSYS and validated with the experimental data. ANSYS CFX was used to analyze the nitrogen coolant fluid flow with a Shear Stress Turbulence (SST) model. ANSYS Mechanical was used for the thermal finite element analysis. The relevant thermophysical parameters like heat conductivity, diffusivity and heat capacity were measured for temperatures above 273 K. For lower temperatures these parameters were determined theoretically. The results gained in this study will be used for the accurate modeling of the heat transfer in a thermomechanical fatigue life analysis by adding a dedicated structural Finite Element (FE) Analysis in ANSYS Mechanical. The accurate modeling of thermomechanical fatigue is particularly important for reusability of rocket engines. Furthermore the results of the validated numerical simulation are useful for the estimation of heat transfer in new developments of liquid rocket engines, particularly upper stages

Development and testing of a fast fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization

A fast Fourier transform (FFT) based wide range millimeter wave diagnostics for spectral characterization of scattered millimeter waves in plasmas has been successfully brought into operation. The scattered millimeter waves are heterodyne downconverted and directly digitized using a fast analog-digital converter and a compact peripheral component interconnect computer. Frequency spectra are obtained by FFT in the time domain of the intermediate frequency signal. The scattered millimeter waves are generated during high power electron cyclotron resonance heating experiments on the TEXTOR tokamak and demonstrate the performance of the diagnostics and, in particular, the usability of direct digitizing and Fourier transformation of millimeter wave signals. The diagnostics is able to acquire 4 GHz wide spectra of signals in the range of 136-140 GHz. The rate of spectra is tunable and has been tested between 200 000 spectra/s with a frequency resolution of 100 MHz and 120 spectra/s with a frequency resolution of 25 kHz. The respective dynamic ranges are 52 and 88 dB. Major benefits of the new diagnostics are a tunable time and frequency resolution due to postdetection, near-real time processing of the acquired data. This diagnostics has a wider application in astrophysics, earth observation, plasma physics, and molecular spectroscopy for the detection and analysis of millimeter wave radiation, providing high-resolution spectra at high temporal resolution and large dynamic range