An aeroacoustic investigation into the effect of self-oscillating trailing edge flaplets

The aeroacoustics of a NACA 0012 aerofoil with an array of self-oscillating flexible flaplets attached on the trailing edge has been investigated at low to moderate chord based Reynolds number (50,000 -- 350,000) and at geometric angles of attack from $\alpha_g = 0^\circ$ -- $20^\circ$. When the aerofoil is untripped, tonal peaks are observed on the baseline aerofoil. When the passive flaplets are attached to the pressure side of the aerofoil, the tonal peak is removed. If the flaplets are then placed on the suction side, the tonal peak is reduced, but not removed. It is therefore hypothesised that the flaplets on the pressure side modifies the laminar separation bubble situated on the pressure side of the aerofoil, a key mechanism for tonal noise. Throughout all cases, both tripped and untripped, a low frequency (0.1 kHz -- 0.6 kHz) noise reduction and a slight increase at higher frequencies (>2 kHz) is seen. This gives an average overall sound pressure level (OSPL) reduction of 1.5 -- 2 dB for the flaplets affixed to the pressure side. The cases where the tonal noise component is removed an OSPL reduction of up to 20 dB can be seen

Upstream Shear Layer Stabilisation via Self-Oscillating Trailing Edge Flaplets

The flow around a symmetric aerofoil (NACA 0012) with an array of flexible flaplets attached to the trailing edge has been investigated at Reynolds numbers of 100,000 - 150,000 by using time resolved particle image velocimetry (TR-PIV) and high speed motion tracking of the flaplets' tips. Particular attention has been made on the upstream effect on the boundary layer evolution along the suction side of the wing. For the plain aerofoil, without flaplets, the boundary layer on the second half of the wing undergoes shear-layer roll-up in the fundamental mode, but with rapid growth of non-linear modes which initiate the merging of rollers. When the flaplets are attached, it is shown that the flow-induced oscillations of the flaplets are able to create a lock-on effect that stabilises the linear state of the shear layer whilst damping the growth of non-linear modes. In addition, it is concluded that the modified trailing edge reduces aeroacoustic noise production in the lower frequency band, as indicated by an initial acoustic investigation

Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing

This work describes a novel mechanism of laminar flow control of a backward swept wing with a comb-like leading edge device. It is inspired by the leading-edge comb on owl feathers and the special design of its barbs, resembling a cascade of complex 3D-curved thin finlets. The details of the geometry of the barbs from an owl feather were used to design a generic model of the comb for experimental and numerical flow studies with the comb attached to the leading edge of a flat plate. Examination was carried out at different sweep angles, because life animal clearly show the backward sweep of the wing during gliding and flapping. The results demonstrate a flow turning effect in the boundary layer inboards, which extends along the chord over distances of multiples of the barb lengths. The inboard flow-turning effect described here, thus, counter-acts the outboard directed cross-span flow typically appearing for backward swept wings. From recent theoretical studies on a swept wing, such a way of turning the flow in the boundary layer is known to attenuate crossflow instabilities and delay transition. A comparison of the comb-induced cross-span velocity profiles with those proven to delay transition in theory shows excellent agreement, which supports the laminar flow control hypothesis. Thus, the observed effect is expected to delay transition in owl flight, contributing to a more silent flight

The Peregrine Falcon's Dive: On the Pull-Out Maneuver and Flight Control Through Wing-Morphing

During the pull-out maneuver, Peregrine falcons were observed to adopt a succession of specific flight configurations which are thought to offer an aerodynamic advantage over aerial prey. Analysis of the flight trajectory of a falcon in a controlled environment shows it experiencing load factors up to 3 and further predictions suggest this could be increased up to almost 10g during high-speed pull-out. This can be attributed to the high maneuverability promoted by lift-generating vortical structures over the wing. Wind-tunnel experiments on life-sized models in the different configurations together with high fidelity CFD Simulations(LES) show that deploying the hand-wing in a pull-out creates extra vortex-lift, similar to that of combat aircraft with delta wings. The aerodynamic forces and the position of aerodynamic center were calculated from the Simulations of the flow around the different configurations. This allowed for an analysis of the longitudinal static stability in the early pull-out phase, confirming that the falcon is flying unstably in pitch with a positive slope in the pitching moment and a trim angle of attack of about 5◦, possibly to maximize responsiveness. The hand-wings/primaries were seen to contribute to the augmented stability acting as ‘elevons’ would on a tailless blended-wing-body aircraft

A parametric study of the effect of self-oscillating trailing-edge flaplets on aerofoil self-noise

This paper presents an acoustic study of a standard NACA 0012 aerofoil with additional self-oscillating passive flaplets attached to the trailing edge. The tests with varying geometries of the flaplets were conducted in the anechoic wind tunnel at Brandenburg University of Technology, at chord based Reynolds numbers, $Re_c = 100,000 - 900,000$ at three geometric angles of attack $\alpha_g = 0^\circ, 10^\circ$ and $15^\circ$. It was observed that all flaplet configurations reduce tonal noise and that the key geometric parameter to reduce this noise component is the width of the flaplets. The narrowest configuration tested almost completely removed the tonal noise, leading to an average overall sound pressure level reduction of up to 9 dB across the entire $Re_c$ range at $\alpha_g = 10^\circ$. It was also observed that, in the low frequency regime, a further noise reduction can be achieved by tuning the natural frequency of the oscillating flaplets. The thereby affected frequency range in the noise spectrum moves to higher frequencies when the natural frequency of the flaplets is increased and vice versa. Hence we show a novel way to target specific frequencies in passive aerofoil self-noise cancellation

In situ radiometric dating on mars: investigation of the feasibility of K-Ar dating using flight-type mass and X-ray spectrometers

The absolute chronology of Mars is poorly known and as a consequence a key science aim is to perform accurate radiometric dating of martian geological materials. The scientific benefits of in situ radiometric dating are significant and arguably of most importance is the calibration of the martian cratering rate, similar to what has been achieved for the Moon, to reduce the large uncertainties on absolute boundary ages of martian epochs. The Beagle 2 Mars lander was capable of performing radiometric date measurements of rocks using the analyses from two instruments in its payload: (i) the X-ray Spectrometer (XRS) and (ii) the Gas Analysis Package (GAP). We have investigated the feasibility of in situ radiometric dating using the K-Ar technique employing flight-like versions of the Beagle 2 instrumentation. The K-Ar ages of six terrestrial basalts were measured and compared to the ‘control’ Ar-Ar radiometric ages in the range 171 – 1141 Ma. The K content of each basalt was measured by the flight spare XRS and the 40Ar content using a laboratory analogue of the GAP. The K-Ar ages of five basalts broadly agreed with their corresponding Ar-Ar ages. For the final basalt, the 40Ar content was below the detection limit and so an age could not be derived. The precision of the K-Ar ages was ~30% on average. The conclusions from this study are that careful attention must be paid to improving the analytical performance of the instruments, in particular the accuracy and detection limits. The accuracy of the K and Ar measurements are the biggest source of uncertainty in the derived K-Ar age. Having investigated the technique using flight-type planetary instrumentation, we conclude that come of the principle challenges of conducting accurate in situ radiometric dating on Mars using instruments of these types include determining the sample mass, ensuring all the argon is liberated from the sample given the maximum achievable temperature of the mass spectrometer ovens, and argon loss and non-radiogenic argon in the samples analysed

Saturn's equinoctial auroras

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95061/1/grl26673.pd

Distinct colonization patterns and cDNA-AFLP transcriptome profiles in compatible and incompatible interactions between melon and different races of Fusarium oxysporum f. sp. melonis

Background: Fusarium oxysporum f. sp. melonis Snyd. & Hans. (FOM) causes Fusarium wilt, the most important infectious disease of melon (Cucumis melo L.). The four known races of this pathogen can be distinguished only by infection on appropriate cultivars. No molecular tools are available that can discriminate among the races, and the molecular basis of compatibility and disease progression are poorly understood. Resistance to races 1 and 2 is controlled by a single dominant gene, whereas only partial polygenic resistance to race 1,2 has been described. We carried out a large-scale cDNA-AFLP analysis to identify host genes potentially related to resistance and susceptibility as well as fungal genes associated with the infection process. At the same time, a systematic reisolation procedure on infected stems allowed us to monitor fungal colonization in compatible and incompatible host-pathogen combinations. Results: Melon plants (cv. Charentais Fom-2), which are susceptible to race 1,2 and resistant to race 1, were artificially infected with a race 1 strain of FOM or one of two race 1,2 w strains. Host colonization of stems was assessed at 1, 2, 4, 8, 14, 16, 18 and 21 days post inoculation (dpi), and the fungus was reisolated from infected plants. Markedly different colonization patterns were observed in compatible and incompatible host-pathogen combinations. Five time points from the symptomless early stage (2 dpi) to obvious wilting symptoms (21 dpi) were considered for cDNA-AFLP analysis. After successful sequencing of 627 transcript-derived fragments (TDFs) differentially expressed in infected plants, homology searching retrieved 305 melon transcripts, 195 FOM transcripts expressed in planta and 127 orphan TDFs. RNA samples from FOM colonies of the three strains grown in vitro were also included in the analysis to facilitate the detection of in planta-specific transcripts and to identify TDFs differentially expressed among races/strains. Conclusion: Our data suggest that resistance against FOM in melon involves only limited transcriptional changes, and that wilting symptoms could derive, at least partially, from an active plant response. We discuss the pathogen-derived transcripts expressed in planta during the infection process and potentially related to virulence functions, as well as transcripts that are differentially expressed between the two FOM races grown in vitro. These transcripts provide candidate sequences that can be further tested for their ability to distinguish between races. Sequence data from this article have been deposited in GenBank, Accession Numbers: HO867279-HO867981