Large-Eddy Simulation of Spatially Developing Aircraft Wake

Development of aircraft’s wake vortex from the roll-up until vortex decay is studied. An aircraft model and a surrounding flow field obtained from high-fidelity Reynolds Averaged Navier-Stokes simulation are swept through a ground fixed computational domain to initialize the wake. After the initialization, large-eddy simulation of the vortical wake is performed until vortex decay, i.e., 2-3 minutes after the passage of aircraft. Here, the methodology and some results from the simulations using the DLR-F6 wing-body model are presented

Application of Ensemble Kalman Filter to Pedestrian Flow

We adopted the Ensemble Kalman Filter (EnKF) methodology in our computational simulation code for pedestrian flows. The EnKF, which is a type of data assimilation methodology, has been developed in the field of weather forecast where the atmospheric condition varies hour by hour. The EnKF estimates the parameters or boundary/initial conditions in the numerical model based on the updated measured data. We considered the EnKF a promising tool for the simulation of pedestrian flows, which are notoriously difficult to predict. In this study, two scenarios were conducted to confirm the usefulness of the EnKF. The first case was unidirectional pedestrian flow in straight corridors, and the second case was Mataf scenario at the Kaaba in Mecca. Needless to say, the second scenario was very challenging because of the number of pilgrims and the degrees of freedom. In each scenario, we conducted the numerical simulation using the original parameter set and then applied the EnKF to improve the accuracy of the simulation

Vortex bursting and tracer transport of a counter-rotating vortex pair

Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low

Evolution of the primate glutamate taste sensor from a nucleotide sensor

霊長類におけるグルタミン酸の旨味の起源 --体の大きな霊長類は旨味感覚で葉の苦さを克服--. 京都大学プレスリリース. 2021-08-30.Taste perception plays an essential role in food selection. Umami (savory) tastes are sensed by a taste receptor complex, T1R1/T1R3, that detects proteinogenic amino acids. High sensitivity to l-glutamate (l-Glu) is a characteristic of human T1R1/T1R3, but the T1R1/T1R3 of other vertebrates does not consistently show this l-Glu response. Here, we demonstrate that the l-Glu sensitivity of T1R1/T1R3 is a derived state that has evolved repeatedly in large primates that rely on leaves as protein sources, after their divergence from insectivorous ancestors. Receptor expression experiments show that common amino acid substitutions at ligand binding sites that render T1R1/T1R3 sensitive to l-Glu occur independently at least three times in primate evolution. Meanwhile T1R1/T1R3 senses 5′-ribonucleotides as opposed to l-Glu in several mammalian species, including insectivorous primates. Our chemical analysis reveal that l-Glu is one of the major free amino acids in primate diets and that insects, but not leaves, contain large amounts of free 5′-ribonucleotides. Altering the ligand-binding preference of T1R1/T1R3 from 5′-ribonucleotides to l-Glu might promote leaf consumption, overcoming bitter and aversive tastes. Altogether, our results provide insight into the foraging ecology of a diverse mammalian radiation and help reveal how evolution of sensory genes facilitates invasion of new ecological niches

Variation in ligand responses of the bitter taste receptors TAS2R1 and TAS2R4 among New World monkeys

Background New World monkeys (NWMs) are unique in that they exhibit remarkable interspecific variation in color vision and feeding behavior, making them an excellent model for studying sensory ecology. However, it is largely unknown whether non-visual senses co-vary with feeding ecology, especially gustation, which is expected to be indispensable in food selection. Bitter taste, which is mediated by bitter taste receptors (TAS2Rs) in the tongue, helps organisms avoid ingesting potentially toxic substances in food. In this study, we compared the ligand sensitivities of the TAS2Rs of five species of NWMs by heterologous expression in HEK293T cells and calcium imaging. Results We found that TAS2R1 and TAS2R4 orthologs differ in sensitivity among the NWM species for colchicine and camphor, respectively. We then reconstructed the ancestral receptors of NWM TAS2R1 and TAS2R4, measured the evolutionary shift in ligand sensitivity, and identified the amino acid replacement at residue 62 as responsible for the high sensitivity of marmoset TAS2R4 to colchicine. Conclusions Our results provide a basis for understanding the differences in feeding ecology among NWMs with respect to bitter taste

Wake-Vortex Topology, Circulation, and Turbulent Exchange Processes

Large eddy simulations () of aircraft wake vortex evolution in various turbulent and stably stratified atmospheric environments have been conducted with two different LES codes. Passive tracers are used to investigate exchange processes between the vortex cores, the vortex oval and its environment as well as redistribution processes along the vortex tubes. A post processing method is employed to identify the vortex center lines even in progressed states of vortex decay where the coherent vortex structure is getting lost. This method allows, for example, analyzing the circulation evolution of vortex rings, establishing statistics of vortex deformation, and revealing the mechanisms of the vortex bursting phenomenon. Vortex bursting is related to the collision of secondary vorticity structures propagating along the vortex lines. In neutrally and weakly stratified environments long-living vortex rings are observed where circulation decay proceeds in three phases. During the initial diffusion phase vortex decay may depend on integral turbulence length scales. On average, the detrainment of a passive tracer from the primary vortices is correlated with circulation decay

Aircraft Wake Vortex Decay in Ground Proximity : Physical Mechanisms and Artificial Enhancement

Aircraft wake vortex evolution in ground proximity is investigated numerically with large eddy simulations (LES). The simulations are performed with different modifications of the ground surface in order to trigger rapid vortex decay or to simulate the landing of an aircraft. The impact of environmental turbulence in terms of turbulent winds is taken into account, where wall-resolved and wall-modeled LES are performed for low and high Reynolds number cases, respectively. In order to understand wake vortex decay mechanisms in ground proximity the interaction of primary and secondary vortices is thoroughly investigated. The results show that vortex decay is initiated and accelerated with obstacles at the ground. In order to optimize obstacle shape and size we show that we can achieve a similar effect with relatively small plates as with large block-shaped barriers. Concerning large Reynolds numbers we show that turbulence effects triggered by the ground can not be modeled by a simple wall model. As a first approximation of landing we use a ramp at the ground and show that the flow disturbances are similar to the result of flat ground with obstacles. In particular two kinds of so-called end effects are superposed: pressure waves in the vortex core and the propagation of the secondary vortex structures

Large-Eddy Simulations of Wake Vortices in Ground Proximity and Crosswind

Results from large eddy simulations of the wake vortex behaviour in ground effect with turbulent crosswinds are presented. We have conducted wall-resolved and wall-modelled simulations at different Reynolds numbers to investigate the Reynolds-number dependency. Vortex displacement and decay has been validated with experimental data. In order to understand wake vortex decay mechanisms in ground proximity the interaction of primary and secondary vortices is thoroughly investigated. Obstacles at the ground surface are introduced to trigger rapid vortex decay

Large-Eddy Simulation of Wake Vortex Evolution from Roll-Up to Decay

The development of an aircraft wake vortex from the roll-up until vortex decay is studied. An aircraft model and the surrounding flow field obtained from high-fidelity Reynolds-averaged Navier-Stokes simulation are swept through a ground-fixed computational domain to initialize the wake. After the wake initialization, the large-eddy simulation of the vortical wake is performed until vortex decay. The methodology is tested with the NACA0012 wing and applied to the DLR-F6 wing-body model. The roll-up process of the vorticity sheet from a main wing and the merge of an inboard wing vortex into the wingtip vortex are simulated. Vortex parameters such as the averaged circulation, vortex core radius and vortex separation are also evaluated. The growth rate of the vortex core radius is relatively small during the roll-up where the fine mesh resolution in the LES is required to capture the tiny vortex core in the RANS simulation. A high-lift configuration of a landing large transport aircraft was also studied where the wingtip vortices merge with the co-rotating and stronger outboard flap vortices