Airfoil Tip Leakage Aeroacoustics Predictions using a Lattice Boltzmann Based Method

International audienceThe noise produced by rotating systems such as fans and turbo machines is of growing importance in the academic and engineering communities. The prediction and understanding of the physical mechanisms associated with noise generation are required in order to develop innovative solutions able to efficiently reduce radiated acoustics levels. The flow-induced noise generation mechanisms related to rotating devices are various and complex, and one of them is related to the blade tip flow. The tip flow noise, or tip leakage noise, is particularly important for free-tip configurations, for which the tip flow induced by the pressure gradient between the suction and pressure sides can be particularly intense. The experimental investigation of this mechanism is practically challenging. Consequently, a simplified non-rotating representative configuration has been proposed, and has been previously investigated experimentally. In this paper, transient, compressible, and time-explicit Computational Fluid Dynamics/Computational Aero-Acoustics (CFD/CAA) simulations of an airfoil tip leakage flow for this simplified geometry are performed using a Lattice Boltzmann Method (LBM) based approach. The studied configuration is a NACA 5510 airfoil profile at high Reynolds number flow conditions, for which a variable size gap is introduced between the airfoil and one of the end plates, modeling the tip gap encountered in free-tip fans. First, the simulation results are compared with experimental results to validate the numerical approach. Further investigation of the numerical results underlines the connection between the tip vortex structures and noise radiation, including a parametric study on the Angle of Attack (AoA) and the tip gap width

Overabundant ungulates in French Sologne? Increasing red deer and wild boar pressure may not threaten woodland birds in mature forest stands

Increasing ungulate populations have been considered to drive changes in woodland bird communities in temperate and boreal forests. Ungulates may negatively affect understory-dependent woodland birds either directly or indirectly. For instance ungulates may prey on nests, or they may reduce the availability of nesting sites, foraging resources or cover for understory-dependent bird species. We conducted ungulate pressure, vegetation and bird surveys on 95 plots, in nineteen mature forest stands (9 fenced and 10 unfenced properties) located in the Sologne region (France). In such private forests, ungulate population densities are highly variable; we were therefore able to explore the effects of varying red deer (Cervus elaphus) browsing and wild boar (Sus scrofa) rooting intensity on bird communities. Bayesian Binomial mixture models indicated that ground-nesting birds were more abundant in forests with high observed wild boar rooting intensity. Generally, increasing deer browsing pressure did not have any negative effect on woodland birds in mature forest stands with a developed canopy, and did not result in lower shrub cover. Most previous studies documenting a negative effect of browsing on birds focused on young forest stands where overstory vegetation was scarce. Our results suggest that the impact of ungulate pressure on forest birds may decrease with forest stand age

Airfoil Tip Leakage Aeroacoustics Predictions using a Lattice Boltzmann Based Method

The noise produced by rotating systems such as fans and turbo machines is of growing importance in the academic and engineering communities. The prediction and understanding of the physical mechanisms associated with noise generation are required in order to develop innovative solutions able to efficiently reduce radiated acoustics levels. The flow-induced noise generation mechanisms related to rotating devices are various and complex, and one of them is related to the blade tip flow. The tip flow noise, or tip leakage noise, is particularly important for free-tip configurations, for which the tip flow induced by the pressure gradient between the suction and pressure sides can be particularly intense. The experimental investigation of this mechanism is practically challenging. Consequently, a simplified non-rotating representative configuration has been proposed, and has been previously investigated experimentally. In this paper, transient, compressible, and time-explicit Computational Fluid Dynamics/Computational Aero-Acoustics (CFD/CAA) simulations of an airfoil tip leakage flow for this simplified geometry are performed using a Lattice Boltzmann Method (LBM) based approach. The studied configuration is a NACA 5510 airfoil profile at high Reynolds number flow conditions, for which a variable size gap is introduced between the airfoil and one of the end plates, modeling the tip gap encountered in free-tip fans. First, the simulation results are compared with experimental results to validate the numerical approach. Further investigation of the numerical results underlines the connection between the tip vortex structures and noise radiation, including a parametric study on the Angle of Attack (AoA) and the tip gap width

NLC Climatology from GOMOS Observations

Noctilucent clouds (NLC), also called polar mesospheric clouds when observed from space, are the visible manifestation of water ice particles persistently present in the polar summer mesopause region, which is the coldest place on Earth. Because of their extraordinary height of about 83 km, they can become visible to the naked eye when the sun sinks below the horizon, providing a dazzling display of bluish light. Since these clouds are extremely sensitive to changes in their environment, their observation conveys unique information concerning the various processes taking place in the mesosphere. GOMOS is a stellar occultation instrument combining 4 spectrometers in the spectral range 250 to 950 nm (UV - visible - near IR) and 2 fast photometers (470-520 nm and 650-700 nm). On the day side, in addition to star light, GOMOS measures also the solar light scattered by the atmospheric molecules. In the summer polar days, NLC are clearly detected using the photometers signals. The sun-synchronous orbit of ENVISAT allows observing them in both hemispheres. The main properties of these clouds (occurrence frequency, radiance, altitude) have been retrieved from GOMOS data. A very high accuracy is possible thanks to the stellar occultation technique. Moreover, the observation of these clouds with the spectrometers provides the spectral dependence of the light scattered by the NLC particles, from which it is possible to derive their radii. These clouds at the edge of space have been studied using GOMOS data from 2002 to 2010. After a brief overview of retrieval methods, the climatology obtained for the main NLC characteristics will be presented, focusing on the seasonal and latitudinal coverage

Polar Mesospheric Cloud Particle Size Retrieval from GOMOS / ENVISAT Observations

International audienceGOMOS (Global Ozone Monitoring by Occultation of Stars) is a stellar occultationinstrument, combining four spectrometers and two fast photometers, that flew on board theEuropean platform ENVISAT from 2002 to 2012. Polar mesospheric clouds (PMCs), that formduring summer in the polar upper mesosphere, could be detected using the photometers' signals.Their main properties (occurrence frequency, peak altitude, radiance) have been retrieved from2002 to 2010, leading to a 16-summer (in both hemispheres) database of more than 21000 clouds.PMCs are very sensitive to changes in their environment. That makes them importanttracers for the complex mechanisms that control the summer mesopause region. A betterunderstanding of the microphysical processes going on in this atmospheric region is essential in order tomodel of their growth, their transport mechanisms and their lifetime. To that purpose, the particlesize distribution is an important parameter.This presentation will be focused on PMC particle sizes retrieved from GOMOS spectralobservations in the northern hemisphere. The retrieval method will be explained, and results basedon the obtained 8-year dataset will be described and compared to PMC particle sizes derived fromthe measurements of other instruments

A Comparison of the Mesospheric Clouds on Mars and on the Earth

We will present an overview of mesospheric cloud observations on the Earth and on Mars, discuss their similarities and differences, and the possible (similar) formation mechanisms related to atmospheric circulations and microphysics

ETV4 is a useful marker for the diagnosis of CIC-rearranged undifferentiated round-cell sarcomas: a study of 127 cases including mimicking lesions

International audienceSubsets of primitive round-cell sarcomas remain difficult to diagnose and classify. Among these is a rare round-cell sarcoma that harbors a CIC gene rearrangement known as CIC-rearranged undifferentiated round-cell sarcoma, which is most commonly fused to the DUX4 gene. Owing to its aggressive clinical behavior and potential therapeutic implications, accurate identification of this novel soft tissue sarcoma is necessary. Definitive diagnosis requires molecular confirmation, but only a few centers are as yet able to perform this test. Several studies have shown that PEA3 subfamily genes, notably ETV4 (belonging to the family of ETS transcription factors), are upregulated in CIC-rearranged undifferentiated round-cell sarcomas. We performed a detailed immunohistochemical analysis to investigate ETV4 expression in CIC-rearranged undifferentiated round-cell sarcomas and their potential mimics (especially Ewing sarcomas). The study cohort included 17 cases of CIC-rearranged undifferentiated round-cell sarcomas, and 110 tumors that morphologically mimic CIC-rearranged undifferentiated round-cell sarcomas: 43 Ewing sarcomas, 25 alveolar rhabdomyosarcomas, 20 poorly differentiated round-cell synovial sarcomas, 10 desmoplastic round-cell tumors, 5 BCOR-CCNB3 sarcomas, 5 lymphoblastic lymphomas, and 2 rhabdoid tumors. All CIC-rearranged undifferentiated round-cell sarcomas (on core needle biopsies and open biopsies) were ETV4-positive with a strong diffuse nuclear pattern. Among the other 110 tumors, only six cases (four Ewing sarcomas, one alveolar rhabdomyosarcoma, and one desmoplastic round-cell tumor) showed focal (o5% of tumor cells) and very weak nuclear expression of ETV4; all other tumors were completely negative for ETV4. We conclude that systematic immunohistochemical analysis of ETV4 makes it possible to diagnose undifferentiated round-cell sarcomas (with no molecular markers for sarcoma-associated translocation) such as CIC-rearranged undifferentiated round-cell sarcoma