Unsteady CFD Analysis of a Delta Wing Fighter Configuration by Delayed Detached Eddy Simulation

While the flow physics of generic delta wings with sharp leading edges are largely understood, realistic configurations with rounded leading edges and canards are still of scientific and industrial interest. The goal of the presented study is the investigation of such a realistic delta wing configuration at 15° angle of attack and at high Reynolds number in comparison with detailed wind tunnel measurements. Former studies have shown the superior results of large and Detached-eddy simulations (DES) for delta wings in comparison with RANS computations. The original standard formulation of DES has shown the drawback of only grid based prediction of the boundary layer edge. To overcome this deficiency the technique of Delayed DES (DDES) was developed some years ago. This new model is based on a simple modification of the original formulation to provide a dependency of the RANS-LES switch on turbulent flow properties. The numerical DES and DDES results are compared with data from the TU Munich wind tunnel facility. Comparison of statistical data as well as velocity spectra in the flow field with experiments will be presented

Numerical Investigation of Space Launch Vehicle Base Flows with Hot Plumes

The flow field around generic space launch vehicles with hot exhaust plumes is investigated numerically. Reynolds-Averaged Navier-Stokes (RANS) simulations are thermally coupled to a structure solver to allow determination of heat fluxes into and temperatures in the model structure. The obtained wall temperatures are used to accurately investigate the mechanical and thermal loads using Improved Delayed Detached Eddy Simulations (IDDES) as well as RANS. The investigated configurations feature cases both with cold air and hot hydrogen/water vapour plumes as well as cold and hot wall temperatures. It is found that the presence of a hot plume increases the size of the recirculation region and changes the pressure distribution on the nozzle structure and thus the loads experienced by the vehicle. The same effect is observed when increasing the wall temperatures. Both RANS and IDDES approaches predict the qualitative changes between the configurations, but the reattachment location predicted by IDDES is up to 7% further upstream than that predicted by RANS. Additionally, the heat flux distribution along the nozzle and base surface is analysed and shows significant discrepancies between RANS and IDDES, especially on the nozzle surface and in the base corner

Relationship between ecosystem productivity and photosynthetically-active radiation for northern peatlands

We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = α PPFD Pmax/(α PPFD + Pmax) + R) better described the NEE-PPFD relationship than did a linear fit (NEE = β PPFD + R). Poor and rich fens generally had similar NEE-PPFD relationships, while bogs had lower respiration rates (R = −2.0μmol m−2s−1 for bogs and −2.7 μmol m−2s−1 for fens) and lower NEE at moderate and high light levels (Pmax = 5.2 μmol m−2s−1 for bogs and 10.8 μmol m−2s−1 for fens). As a single class, northern peatlands had much smaller ecosystem respiration (R = −2.4 μmol m−2s−1) and NEE rates (α = 0.020 and Pmax = 9.2μmol m−2s−1) than the upland ecosystems (closed canopy forest, grassland, and cropland) summarized by Ruimy et al. [1995]. Despite this low productivity, northern peatland soil carbon pools are generally 5–50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils

In Vivo Assessment of Cold Adaptation in Insect Larvae by Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

Background Temperatures below the freezing point of water and the ensuing ice crystal formation pose serious challenges to cell structure and function. Consequently, species living in seasonally cold environments have evolved a multitude of strategies to reorganize their cellular architecture and metabolism, and the underlying mechanisms are crucial to our understanding of life. In multicellular organisms, and poikilotherm animals in particular, our knowledge about these processes is almost exclusively due to invasive studies, thereby limiting the range of conclusions that can be drawn about intact living systems. Methodology Given that non-destructive techniques like 1H Magnetic Resonance (MR) imaging and spectroscopy have proven useful for in vivo investigations of a wide range of biological systems, we aimed at evaluating their potential to observe cold adaptations in living insect larvae. Specifically, we chose two cold-hardy insect species that frequently serve as cryobiological model systems–the freeze-avoiding gall moth Epiblema scudderiana and the freeze-tolerant gall fly Eurosta solidaginis. Results In vivo MR images were acquired from autumn-collected larvae at temperatures between 0°C and about -70°C and at spatial resolutions down to 27 µm. These images revealed three-dimensional (3D) larval anatomy at a level of detail currently not in reach of other in vivo techniques. Furthermore, they allowed visualization of the 3D distribution of the remaining liquid water and of the endogenous cryoprotectants at subzero temperatures, and temperature-weighted images of these distributions could be derived. Finally, individual fat body cells and their nuclei could be identified in intact frozen Eurosta larvae. Conclusions These findings suggest that high resolution MR techniques provide for interesting methodological options in comparative cryobiological investigations, especially in vivo

Calculations of Shock-Boundary Layer Interaction for a Supersonic Ramp Flow by DNS, Using a Fourth order Finite Difference Method

Despite intensive theoretical and experimental research, transition to turbulence in separated hypersonic ramp flows is still a challenge to predict. One of the most successful approaches to model the dominant mechanisms is the direct numerical simulation approach, which has demonstrated, despite the well known drawback of computationally costly simulations, the capability to generate reliable datasets. To allow calculations of the transition process on ramp configurations a validated DNS code with high resolution of the turbulent structures in the hypersonic flow regime is a necessity. The abilities of the 4th-order finite-difference version of the DLR FLOWer code, derived originally for Large Eddy Simulations (LES) over recent years is a promising choice for the requested properties. In fact, it was shown in former studies that the resolution of transitional instabilities in supersonic boundary layers is very well within the range of this code. In the present study, different supersonic test cases are chosen from literature and compared with the actual simulations using this high-order version of the DLR FLOWer code. The results using higher-order Pade-filter approaches are encouraging. With this validation as a background, a supersonic ramp-test case was chosen for study. To resolve the transition process, different ramp-angles and Reynolds numbers were investigated to determine a transitional test case, for which turbulence can be resolved behind re-attachment. A hypersonic ramp with 12 degree angle of attack at a moderate Reynolds number was then chosen for three-dimensional DNS calculations of the transition process. These DNS were carried out with various grid densities and grid extents in the wall-normal and spanwise direction with good success. The investigation of different spanwise extents of the simulation region has demonstrated the capabilities of the code to predict the supersonic transition process

Das Erprobungsträgersystem Phoenix als Testfall für den TAU-Code im Unterschall

Im Mittelpunkt des deutschen Entwicklungsprogramms ASTRA stehen Bau und Test des Erprobungsträgers Phoenix. Dieser dient als Vorläufer des kostensparenden wiederverwendbaren Trägersystems HOPPER. Der Einsatz eines solchen Demonstrators ermöglicht praktische Erfahrungen, welche die Entwicklung von wiederverwendbaren Raumtransportsystemen auf eine realistische Basis stellen. Der Phoenix ist knapp sieben Meter lang, wiegt 1200 Kilogramm und hat eine Spannweite von 3.8 Metern. Im Rahmen einer numerischen Studie wurden im vorliegenden Bericht aerodynamische Beiwerte für den subsonischen Flug bestimmt und mit experimentellen Daten verglichen. Das Ziel dieser Studie besteht im Wesentlichen in der Validierung des unstrukturierten DLR-Strömungslösers TAU an realistischen Landefällen für Raumfahrzeuge. Die dabei gesammelten Erfahrungen, insbesondere im Bereich der Netzgenerierung und Präkonditionierung bei niedrigen Machzahlen, sind im vorliegenden Bericht zusammengefaßt

INTERIOR FLOW SIMULATION OF SUCTION CHAMBERS FOR HLFC PROFILES

Abstract For a simplified but effective suction chamber concept for hybrid laminar flow control by boundary-layer suction, which is investigated on a vertical tail, the velocity distribution inside suction chambers is simulated. Within the current study, CFD simulations of the flow inside these chambers are carried out by the DLR FLOWer code to predict this velocity as well as the pressure distribution inside the chambers. Variations of the suction pressure and the tap-distance are carried out

DLR-ONERA accurate CFD support for the Pre-X project

During the development of Pre-X demonstrator supported by CNES , industrials are in charge of aerodynamic and aerothermodynamic defintion and characterisation of the vehicle. For this preliminary phase of the project, most of the time industrials only used Euler computations associated to boundary layer, so that a lot of parametric analysis can be carried out and the feasibility of the project was globally checked. It is clear that deeper analyses for some critical trajectory points are required to overcome potential infeasibilities. The main objective of the accurate CFD support, provided by DLR and ONERA consists in assessing these high level objectives. Two critical issues are investigated. The heat fluxes level on the windward side of the body, the deflected flap in the hypersonic regime and the aerodynamic static margin at the end of the trajectory in the supersonic regime. Two relevant codes where used: the TAU code from DLR and CELHYO3D from ONERA. * The unstructured TAU code is a finite volume Navier-Stokes solver which is validated in a wide range of sub- trans- and hypersonic cases. Different one and two equation turbulence models are implemented and chemical equilibrium as well as non equilibrium flows can be modelled. Furthermore adaptation of tetrahedral grids on any given output quantity is possible. * The structured CELHYO3D code is a finite volume Navier-Stokes solver with upwind schemes adapted to supersonic and hypersonic flows. Flows of air or CO2 in chemical or thermo-chemical non-equilibrium can be considered. A specific grid management procedure is used in order to provide shock-adapted grids together with information of the grid-convergence of the results. The results of the computations with TAU and CELHYO3D confirm the feasibility of the project with respect to the heat-flux and static-margin issues

CFD investigations of Axi-symmetric steady state nozzle plume flow for the Volvo S6 and Vulcain2 nozzle

In the afterbody region of the Ariane 5 ECA launcher, the flow around the launcher interacts with the plumes of the propulsion systems, i.e. the plumes from the \mbox{Vulcain-2} engine and from the solid rocket boosters. A dedicated experiment or analysis to evaluate the influence of the plumes on buffeting has not been performed up to now. However, the good agreement of the wind tunnel results obtained from the model without plumes to the flight data of Ariane 5 indicates that, for the investigated flight situations, the plume influence is limited. Nevertheless, the experimental investigation of the plume influence on buffeting remains an important topic and its simulation seems mandatory whenever the base configuration is modified. The design of a sub-scale nozzle that uses a different working gas, but behaving as closely as possible to the full-scale launcher in terms of base flow, is a very challenging task. It can only be solved by taking considerable compromises into account since only low total temperatures are available in wind tunnels. For example air condensation and thick nozzle walls are required for pressure measurements to give a few design constraints in such a facility. Since perfect similarity is impossible to realise, a numerical study was proposed in prior to the wind tunnel tests to assess how representative the plume flow flight conditions can be realised. The results will be used to decide whether modifications of the existing models would be needed or if a new model is required. They will furthermore provide the basis to prepare a research program focusing on the experimental investigation of the plume effect on buffeting. Apart from detailed three-dimensional unsteady CFD-studies, the described work package is supported by 2D axis symmetric numerical computations of the plumes, carried out by the DLR TAU-code in order to characterise the shear layers emanating from the nozzle lip. In the scope of the work-package 8000 of the ESA-TRP on buffeting coupling a study of both configurations was carried out which is the objective of the following report

CRV-Early Tasks, Interim Report CFD Analysis

This document summarises the CFD activities during the early task phase of the CRV-Local Aerothermodynamic development. In this period the final structured CRV grid was developed from the X-38 grid topology. The actual given flap geometry was derived from the current CAD geometry with special attention on the critical regions around the flap, for which the topology was modified and extended. To check the grid quality and validate the generated CFD results a comparison with data from the Langley Mach 10 Wind tunnel was carried out for selected surface cuts as far as possible