Experimental validation of the quadratic constitutive relation in supersonic streamwise corner flows

The quadratic constitutive relation is a simple extension to the linear eddy-viscosity hypothesis and has shown some promise in improving the computation of flow along streamwise corner geometries. In order to further investigate these improvements, the quadratic model is validated by comparing RANS simulations of a Mach 2.5 wind tunnel flow with high-quality experimental velocity data. Careful set up and assessment of computations using detailed characterisation data of the overall flow field suggests a minimum expected discrepancy of approximately 3% for any experimental–computational velocity comparisons. The corner regions of the rectangular cross-section wind tunnel exhibit velocity differences of 7% between experimental data and computations with linear eddy-viscosity models, but these discrepancies are reduced to 4–5% when the quadratic constitutive relation is used. This improvement can be attributed to a better prediction of the corner boundary-layer structure, due to computations reproducing the stress-induced streamwise vortices which are known to exist in this flow field. However, the strength and position of these vortices do not correspond exactly with those in the measured flow. A further observation from this study is the appearance of additional, non-physical vortices when the value of the quadratic coefficient in the relation exceeds the recommended value of 0.3.This material is based upon work supported by the US Air Force Office of Scientific Research under award number FA9550–16–1–0430

An Aeroacoustic Investigation of a Tiltwing eVTOL Concept Aircraft

With the advancement in electric battery design, aircraft designers and manufacturers are no longer constrained to established configurations. Developments in Vertical Take-off and Landing (VTOL) aircraft have also been seen in recent times through the design of modern tiltrotor aircraft such as the AW609 and the V-280 Valor. The combination of these developments allowed engineers to propose designs which utilise the vertical take-off and landing capabilities of a tiltrotor aircraft with electrically driven propulsion systems, deemed eVTOL (Electrically driven Vertical Take-off and Landing). This investigation aims to develop an understanding of the aeroacoustic emissions associated with an eVTOL aircraft, due to acoustics being one of the key components in future certification. The study will consist of an investigation into the baseline design, followed by an optimisation study aiming to reduce the amount of noise generated

Recalibration of the Shear Stress Transport Model to Improve Calculation of Shock Separated Flows

The Menter Shear Stress Transport (SST) k . turbulence model is one of the most widely used two-equation Reynolds-averaged Navier-Stokes turbulence models for aerodynamic analyses. The model extends Menter s baseline (BSL) model to include a limiter that prevents the calculated turbulent shear stress from exceeding a prescribed fraction of the turbulent kinetic energy via a proportionality constant, a1, set to 0.31. Compared to other turbulence models, the SST model yields superior predictions of mild adverse pressure gradient flows including those with small separations. In shock - boundary layer interaction regions, the SST model produces separations that are too large while the BSL model is on the other extreme, predicting separations that are too small. In this paper, changing a1 to a value near 0.355 is shown to significantly improve predictions of shock separated flows. Several cases are examined computationally and experimental data is also considered to justify raising the value of a1 used for shock separated flows

Simulation of a Shear Coaxial GO2/GH2 Rocket Injector with DES and LES Using Flamelet Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97098/1/AIAA2012-3744.pd

Shock control of a low-sweep transonic laminar flow wing

This paper presents a combined experimental and computational study of a low-sweep transonic natural laminar flow (NLF) wing with shock-control bumps (SCBs). A transonic NLF wing with a relatively low sweep angle of 20 deg was chosen for this study. To avoid the complexity of the flow introduced by perforated/slotted walls commonly used for transonic wind-tunnel tests for reducing the wall interference, both experimental tests and computational simulations were conducted with solid wind-tunnel wall conditions. This allows for like-to-like validation of the computational simulation. Optimization of the shock-control bumps was first conducted to design the wind-tunnel test model with bumps. Two critical parameters of the three-dimensional SCBs for shock control (i.e., bump crest position and bump height) were optimized in terms of total drag reduction at the given design point in the wind tunnel. We show that the strong shock wave on the low-sweep NLF wing can be effective controlled by well-designed SCBs deployed along the wing span. The optimized SCBs result in 18.5% pressure drag reduction with 5% viscous drag penalty, and the SCBs also bring some benefits at off-design conditions. The wind-tunnel tests include pressure measurement, particle image velocimetry, and temperature-sensitive paint to provide detailed insight into the shock-control flowfield and to validate the computational simulations. Comparisons include surface pressure profile, velocity distribution, and transition location

Micro-Hall Magnetometry Studies of Thermally Assisted and Pure Quantum Tunneling in Single Molecule Magnet Mn12-Acetate

We have studied the crossover between thermally assisted and pure quantum tunneling in single crystals of high spin (S=10) uniaxial single molecule magnet Mn12-acetate using micro-Hall effect magnetometry. Magnetic hysteresis experiments have been used toinvestigate the energy levels that determine the magnetization reversal as a function of magnetic field and temperature. These experiments demonstrate that the crossover occurs in a narrow (~0.1 K) or broad (~1 K) temperature interval depending on the magnitude and direction of the applied field. For low external fields applied parallel to the easy axis, the energy levels that dominate the tunneling shift abruptly with temperature. In the presence of a transverse field and/or large longitudinal field these energy levels change with temperature more gradually. A comparison of our experimental results with model calculations of this crossover suggest that there are additional mechanisms that enhance the tunneling rate of low lying energy levels and broaden the crossover for small transverse fields.Comment: 5 pages, 5 figure

Numerical modeling and simulation of supersonic flows in propulsion systems by open-source solvers

Two open-source solvers, Eilmer and hyFoam, are here considered for their performance in simulating high-speed flows in different flow conditions and geometric configurations typical of propulsive systems at supersonic speeds. The goal is to identify the open-source platform providing the best compromise between accuracy, flexibility and computational cost to eventually simulate the flow fields inside ramjet and scramjet engines. The differences in terms of discretization and solution methods of the selected solvers are discussed in terms of their impact on solution accuracy and computational efficiency and in view of the aerothermodynamic analysis and design of future trans-atmospheric propulsive systems. In this work steady state problems are considered. Numerical results of two scramjet type engines demonstrated a similar predictive capability of both codes in non-reacting conditions. These results highlight their potential to be considered for further characterization of overall engine performance

Renewed investigations at Taung; 90 years after the discovery of Australopithecus africanus

2015 marked the 90th anniversary of the description of the first fossil ofAustralopithecus africanus, commonly known as the Taung Child, which was unearthed during blasting at the Buxton-Norlim Limeworks (referred to as the BNL) 15 km SE of the town of Taung, South Africa. Subsequently, this site has been recognized as a UNESCOWorld Heritage site on the basis of its importance to southern African palaeoanthropology. Some other sites such as Equus Cave and Black Earth Cave have also been investigated; but the latter not since the 1940s. These sites indicate that the complex of palaeontological and archaeological localities at the BNL preserve a time sequence spanning the Pliocene to the Holocene. The relationship of these various sites and how they fit into the sequence of formation of tufa, landscapes and caves at the limeworks have also not been investigated or discussed in detail since Peabody’s efforts in the 1940s. In this contribution we mark the 90th anniversary of the discovery and description of the Taung Child by providing a critical review of previous work at Taung based on our recent preliminary work at the site. This includes a reassessment of the Taung Child Type Site, as well as renewed excavations at Equus Cave and the lesser-known locality and little-investigated Black Earth Cave. Preliminary results suggest that much of our previous understandings of the BNL’s formational history and site formation processes need to be reassessed. Only through detailed analysis on the BNLas a whole can we understand this complex depositional environment.Australian Research Council Future Fellowship grant FT120100399 Palaeontological Scientific Trust (PAST) National Geographic grants (8774-10 and 3212)JNC2016https://www.wits.ac.za/esi/palaeontologia-africana