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Experimental Wind Characterization with the SuperCam Microphone under a Simulated martian Atmosphere
Get PDFLocated on top of the mast of the Mars 2020 Perseverance rover, the SuperCam instrument suite includes a microphone to record audible sounds from 100 Hz to 10 kHz on the surface of Mars. It will support SuperCam’s Laser-Induced Breakdown Spectroscopy investigation by recording laser-induced shock-waves but it will also record aeroacoustic noise generated by wind flowing past the microphone. This experimental study was conducted in the Aarhus planetary wind-tunnel under low CO2 pressure with wind generated at several velocities. It focused on understanding the wind-induced acoustic signal measured by microphones instrumented in a real scale model of the rover mast as a function of the wind speed and wind orientation. Acoustic spectra recorded under a wind flow show that the low-frequency range of the microphone signal is mainly influenced by the wind velocity. In contrast, the higher frequency range is seen to depend on the wind direction relative to the microphone. On the one hand, for the wind conditions tested inside the tunnel, it is shown that the Root Mean Square of the pressure, computed over the 100 Hz to 500 Hz frequency range, is proportional to the dynamic pressure. Therefore, the SuperCam microphone will be able to estimate the wind speed, considering an in situ cross-calibration with the Mars Environmental Dynamic Analyzer. On the other hand, for a given wind speed, it is observed that the root mean square of the pressure, computed over the 500 Hz to 2000 Hz frequency range, is at its minimum when the microphone is facing the wind whereas it is at its maximum when the microphone is pointing downwind. Hence, a full 360° rotation of the mast in azimuth in parallel with sound recording can be used to retrieve the wind direction. We demonstrate that the SuperCam Microphone has a priori the potential to determine both the speed and the direction of the wind on Mars, thus contributing to atmospheric science investigations
A generic process modelling – LCA approach for UF membrane fabrication: Application to cellulose acetate membranes
Get PDFThe purpose of the research is to elaborate and implement a decision-making tool for greener membrane fabrication. The scientific novelty put forth in this study is the generic process modelling – LCA approach applied to the field. The resulting parameterized model allows to obtain material and energy flows as a function of operating conditions for ultrafiltration hollow fibers prepared by non-solvent induced phase separation. Its modular configuration allows for flexibility and adaptation to various membrane materials and industrial practices. Contributions of inputs on environmental impacts can be assessed, as well as the influence of operating conditions. Results for cellulose acetate membranes show major contributions of NMP (i.e. solvent) and glycerol (i.e. pre-conditioning liquid). Improvement strategies for environmental mitigation include acting on glycerol-related operating conditions and are to be considered within the geographic context of membrane fabrication; further technical and economic feasibility studies would embed these strategies in a full eco-design approach. Such a methodology and results should be taken into account for the elaboration of “green membranes” whatever the application and coupled with the impact of membrane use and end-of-life
A New Composite Biomaterial Made from Sunflower Proteins, Urea and Soluble Polymers Obtained from Industrial and Municipal Biowastes to Perform as Slow Release Fertiliser
Get PDFControlled-release fertilizers (CRF) are needed under current agriculture practice to decrease the environmental impact caused by fertilizer doses applied in excess of plants’ uptake rate. Commercial CRF are available. They are manufactured from mineral fertilizers encapsulated into a synthetic polymer matrix or coated by a polymer layer. However, substitution of fossil sourced organic polymers with biopolymers is a major environmental concern. In the present paper, we describe the manufacture by a continuous twin-screw extrusion process, and the mechanical and chemical properties of injection-molded composite pellets containing 90% sunflower protein concentrate (SPC) matrix, and 5–10% of a biopolymer (BP) obtained from municipal biowastes (MBW), and/or urea (U). The reported results show that SPC-BP-U behaves as an efficient eco-friendly CRF. BP contributes to several benefits to the performance of the composite pellets, upon increasing surface hardness, and controlling the formation of ammonia from urea hydrolysis and the release of organic nitrogen. The SPC-BP-U appears a powerful eco-friendly CRF to supply organic C and the three major N, P, and K nutrients to soil and plants. It offers worthwhile scope for being tested in the cultivation of specific plants under the real operational conditions of agriculture practices
A mesh adaptation strategy for complex wall-modeled turbomachinery LES
Get PDFA mesh adaptation methodology for wall-modeled turbomachinery Large Eddy Simulation (LES) is proposed, simultaneously taking into account two quantities of interest: the average kinetic energy dissipation rate and the normalized wall distance y+. This strategy is first tested on a highly loaded transonic blade with separated flow, and is compared to wall-resolved LES results, as well as experimental data. The adaptation methodology allows to predict fairly well the boundary layer transition on the suction side and the recirculation bubble of the pressure side. The method is then tested on a real turbofan stage for which it is shown that the general operating point of the computation converges toward the experimental one. Furthermore, comparison of turbulence predictions with hot-wire anemometry show good agreement as soon as a first adaptation is performed, which confirms the efficiency of the proposed adaptation method
Depth distribution of soil organic matter and burrowing activity of earthworms—mesocosm study using X-ray tomography and luminophores
Get PDFEarthworms feed on organic matter present at the soil surface or within the soil. Thus, its distribution in the soil profile is likely to greatly influence earthworm behavior and, in turn, their burrow system. To test this idea, two anecic and two endogeic earthworm species were introduced into repacked soil cores (depth = 30 cm) upper half filled with a top soil containing 4% organic matter (0–15 cm) and lower half filled with a deep soil at 2% organic matter (15–30 cm). Earthworm behavior was studied using X-ray tomography combined with luminophores (colored particulate tracers of 63–125 μm size) placed at 0, 3, and 12 cm depth, a method widely used in sediment ecology. We observed that anecic and endogeic earthworms had contrasting reactions to the conditions with only endogeic species burrowing more intensively in the upper part. From a quantitative point of view, only a few percent of luminophores were displaced. However, luminophore displacements also provided qualitative information to complement the tomography: (i) endogeic species and especially Aporrectodea caliginosa bioturbated the most soil close to the surface (3 cm depth) and (ii) the two anecic species influenced the luminophore distribution differentially with Lumbricus terrestris displacing significantly more luminophores, whatever their initial depth, than Aporrectodea nocturna due to intense surface cast activity. Beyond methodological developments, our study found that endogeic earthworms burrow more in zones with higher organic matter contents and this explains why they are mainly found close to the soil surface in non-tilled soils
Time scale analysis of the homogeneous flame inhibition by alkali metals
Get PDFA time scale analysis of the homogeneous flame inhibition problem is carried out to identify the main param- eters controlling the gas phase chemical interaction of the alkali metal inhibitors with the flame chemistry. First, kinetic sub-models for the interaction of alkali metals with the flame are analyzed to show that a simplified 2-step inhibition cycle can capture the essential features of this interaction. Second, it is shown that this cycle is auto-catalytic, which explains the high efficiency of alkali metals in inhibiting flames even at low concentrations. Third, the time scales associated to this inhibition cycle are linked to the free flame termina- tion time scale via a non-dimensional parameter characterizing the efficiency of an inhibitor at promoting radical scavenging. It is shown that this parameter accounts for the main trends observed in the literature and can also be used to provide estimates for the chemical flame suppression limit
Stabilization mechanisms of CH4 premixed swirled flame enriched with a non-premixed hydrogen injection
Get PDFHigh-fidelity Large Eddy Simulations (LES) are performed to study the effect of hydrogen injection on a lean turbulent CH4 /Air premixed flame. An Analytically Reduced Chemistry (ARC) mechanism is used to achieve a detailed description of CH4/Air-H2 chemistry. First, a validation of this kinetic scheme against the detailed GRI-Mech 3.0 mechanism is presented considering both simplified and complex transport properties. When hydrogen is added to the mixture, large variations of the mixture Prandtl and of the N2 Schmidt numbers are observed depending on the local species concentrations, features that are missed by simplified models. LES is then applied to study the structure and stabilization mechanisms of a lean (φ = 0.8) premixed CH4/Air swirled flame enriched with hydrogen by using different transport modeling strategies. First, the fully pre- mixed CH4/Air case is considered and results are found to validate the LES approach. In agreement with experiments, a classical V-shape flame is stabilized in the low-velocity region near the flame holder created by a central recirculation zone (CRZ). Then, hydrogen enrichment is achieved injecting 2% of the CH4 thermal power with a central fuel injection lance. Both premixed and diffusion flame branches are present in this case, impacting flame stabilization and flame angle. The flame root of the main premixed flame is stabilized by a diffusion flame kernel created by the injected hydrogen reacting with the oxygen in excess of the premixed stream. Moreover, the H2 consumed with the remaining oxygen in burnt gases leads to the formation of a second flame branch inside the CRZ which is responsible of an increase of the flame angle. Given the high concentration of hydrogen, an impact of the molecular transport models is observed on the flame lift-off height highlighting the importance of using complex transport properties in any LES involving hydrogen combustion
Constraining Martian Regolith and Vortex Parameters From Combined Seismic and Meteorological Measurements
Get PDFThe InSight mission landed on Mars in November 2018 and has since observed multiple convective vortices with both the high performance barometer and the low-noise seismometer SEIS that has unprecedented sensitivity. Here, we present a new method that uses the simultaneous pressure and seismic measurements of convective vortices to place constraints on the elastic properties of the Martian subsurface and the Martian vortex properties, while also allowing a reconstruction of the convective vortex trajectories. From data filtered in the (0.02–0.3 Hz) frequency band, we estimate that the mean value of η (η = E/[1 − ν2], where E is the Young's modulus and ν is the Poisson's ratio) of the Martian ground in the region around SEIS is 239 ± 140 MPa. In addition, we suggest that the previously reported paucity of vortex seismic observations to the west of InSight may be due to the fact that the ground is harder to the west than to the east, consistent with geomorphological surface interpretations
Measuring Fundamental and Higher Mode Surface Wave Dispersion on Mars From Seismic Waveforms
Get PDFOne of the goals of the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission is to constrain the interior structure of Mars. We present a hierarchical transdimensional Bayesian approach to extract phase velocity dispersion and interior shear‐wave velocity (VS) models from a single seismogram. This method was adapted to Mars from a technique recently developed for Earth (Xu & Beghein, 2019, https://doi.org/10.1093/gji/ggz133). Monte Carlo Markov Chains seek an ensemble of one dimensional (1‐D) VS models between a source and a receiver that can explain the observed waveform. The models obtained are used to calculate the phase velocities of fundamental and higher modes at selected periods, and a subsequent analysis is performed to assess which modes were reliably measured. An advantage of our approach is that it can also fit unknown data noise, which reduces the risk of overfitting the data. In addition, uncertainties in the source parameters can be propagated, yielding more accurate model parameter uncertainties. In this study, we first present our technique and discuss the challenges stemming from using a single station to characterize both structure and the source and from the absence of a Mars reference model. We then demonstrate the method feasibility using the Mars Structure Service blind test data and our own synthetic data, which included realistic noise levels based on the noise recorded by InSight
On the role of impurities on spheroidal graphite degeneracy in cast irons
Get PDFThough manufacturing spheroidal graphite cast irons is a well-established industrial process, good nodularity which is essential for mechanical properties may be hampered by several factors. Amongst them is the presence of impurities at trace level which lead to the growth of protrusions and the question is how they can destroy the spheroidizing effect of magnesium. For the first time, it is shown that such impurities are present together with magnesium at the interface between spheroid and protrusion. For getting this result, site-specific electron transparent lamellae were prepared using Focused Ion Beam and characterized at nanometric scale using atomic resolution scanning-transmission electron microscope. It is also shown by automatic crystal orientation mapping that there is no definite crystallographic relationship between protrusions and underlying spheroids