Search

The effects of the aspect ratio, the sweep angle, and the leading-edge geometry of wings placed in a turbulent wake were investigated in wind-tunnel experiments at a chord Reynolds number of [Formula: see text]. The poststall lift enhancement due to the leading-edge vortex formation was studied at optimal locations in the wake. The effects of the strength of the leading-edge vortices, the ratio of the spanwise length scale of the incident vortex to the wingspan, and the degree of two-dimensionality of the wake–wing interaction were studied. The competition between the effects of the spanwise length scale of the incident wake and the strength of the leading-edge vortices determined the optimal aspect ratio, which was found to be around four. Increasing the sweep angle decreased the mean lift due to the decreased two-dimensionality of the vortex formation. Airfoils with sharp leading edge produced the strongest leading-edge vortices but further away from the wing surface, resulting in lower maximum lift. Relative to the performance in the undisturbed freestream, the increases in the stall angle and maximum lift coefficient were not significantly affected by the leading-edge shape.

The post-stall flow control using compliant flags of varying thickness and length, placed upstream a NACA0012 airfoil, was shown to be possible at an airfoil chord Reynolds number of 100,000. The flag wakes produced substantial increase in the stall angle and the maximum lift coefficient of the airfoil placed at optimal cross-stream locations from the wake centerline. Oscillating flags could generate periodic wakes with better spanwise coherence than the stationary bluff body. This resulted in the excitation, formation and shedding of the leading-edge vortices periodically, providing mean lift enhancement. There is an optimal range of the flag mass ratio for which the flag frequency coincides with the natural frequency of the vortex shedding instability or its subharmonic of the baseline airfoil wake. The flag dimensionless frequency is a function of the mass ratio only, which can be predicted by a reduced order model in the limit of very large mass ratio and by using the modified free-streamline theory for the separated flow. There is also an optimal range of the flag dimensionless frequency. Graphical abstract

Hand, foot, and mouth disease (HFMD) is an infection that is common in children under 5 years old. This disease is not a serious disease commonly, but it is one of the most widespread infectious diseases which can still be fatal. HFMD still poses a threat to the lives and health of children and adolescents. An effective prediction model would be very helpful to HFMD control and prevention. Several methods have been proposed to predict HFMD outpatient cases. These methods tend to utilize the connection between cases and exogenous data, but exogenous data is not always available. In this paper, a novel method combined time series composition and local fusion has been proposed. The Empirical Mode Decomposition (EMD) method is used to decompose HFMD outpatient time series. Linear local predictors are applied to processing input data. The predicted value is generated via fusing the output of local predictors. The evaluation of the proposed model is carried on a real dataset comparing with the state-of-the-art methods. The results show that our model is more accurately compared with other baseline models. Thus, the model we proposed can be an effective method in the HFMD outpatient prediction mission.

A nearly two-dimensional vortex of small core size has been produced by the transient plunging motion of an upstream airfoil and it interacted with the downstream wings. Depending on the offset distance of the vortex and wing angle of attack, the incident vortex filament deforms, diffuses, and loses coherence, while inducing leading-edge vortex formation and shedding from the wing. No significant spanwise flow develops in the incident vortices during the interaction. The interaction with the swept wing at each spanwise plane appears to be unaffected by the other spanwise planes. The counter-clockwise vortex induces a positive lift peak as it approaches the wing, which can be predicted by the potential flow assumption. The peak lift force is proportional to the circulation of the incident vortex and has its maximum near the zero-offset distance. The minimum lift coefficient is reached after the vortex has just passed and caused flow separation on the lower surface. The maximum lift coefficients for the finite unswept and swept wings can be estimated by making a correction for the aspect ratio and using the independence principle. The only exception is observed for the swept wing at a post-stall angle of attack for which the leading-edge vortex shedding becomes parallel to the leading-edge and increases the peak lift force. Graphical abstract

A stationary wing placed in the wake of a bluff body experiences lift enhancement. The quasi-periodic flow in the wake causes excitation of the separated flow in the post-stall conditions. The increase in the time-averaged lift force is associated with the flow separation, leading-edge vortex formation and subsequent reattachment in a process similar to the dynamic stall of oscillating wings. The lift enhancement is maximum for an optimal offset distance from the wake centerline. At the optimal location, potential flow oscillations, rather than the direct impingement of large vortices in the wake, provide the excitation. The smaller amplitude flow oscillations lead to a large separation bubble in the time-averaged sense in the post-stall regime. The delayed flow separation in the wake has a similar mechanism and frequency to those of the active flow control methods for separation. The degree of the lift enhancement is remarkable, given that the wake at a Reynolds number of 50,000 is expected to be highly three-dimensional.

We present an experimental investigation of the flow structure in the near wake of a NACA0012 airfoil plunging sinusoidally at a chord Reynolds number of Re = 20 000 and for a wide range of reduced frequency k and Strouhal number based on peak-to-peak amplitude St. Estimated mean thrust coefficients using the mean and fluctuating velocity fields confirm the St2 dependence as well as a significant effect of the reduced frequency for k ≤ 1. Generally, time-averaged flow quantities are better correlated with St than k in the range tested (k ≤ 3.14 and St ≤ 0.24). Analysis of the streamwise flow and cross-flow in the near wake using two-point cross-correlations and proper orthogonal decomposition reveals that the unsteady characteristics are even better correlated with St than the mean flow quantities. The percentage energy of the fundamental wake modes of the streamwise flow and the flapping mode of the cross-flow increases with increasing St, but at different rates in the drag-producing and thrust-producing wakes. There are similarities to the wake synchronisation behind oscillating bodies. The spanwise-averaged cross-correlation coefficient in the measurement domain grows linearly for small St (in drag-producing wakes), and is nearly constant at a high value for larger St (in thrust-producing wakes). Results show that the Strouhal number is the most important parameter that determines the degree of two-dimensionality of the wake, and suggest that spanwise vortices are quasi-two-dimensional for St ≥ 0.05 and x/c ≤ 4. The implications for experimental gust generators using oscillating airfoils are discussed.

The aerodynamics of a stationary wing in a turbulent wake are investigated. Force and velocity measurements are used to describe the unsteady flow. Various wakes are studied with different dominant frequencies and length scales. In contrast to the pre-stall angles of attack, the time-averaged lift increases substantially at post-stall angles of attack as the wing interacts with the von Kármán vortex street and experiences temporal variations of the effective angle of attack. At an optimal offset distance from the wake centreline, the time-averaged lift becomes maximum despite of small amplitude oscillations in the effective angle of attack. The stall angle of attack can reach 20° and the maximum lift coefficient can reach 64 % higher than that in the freestream. Whereas large velocity fluctuations at the wake centreline cause excursions into the fully attached and separated flows during the cycle, small-amplitude oscillations at the optimal location result in periodic shedding of leading edge vortices. These vortices may produce large separation bubbles with reattachment near the trailing-edge. Vorticity roll-up, strength and size of the vortices increase with increasing wavelength and period of the von Kármán vortex street, which also coincides with an increase in the spanwise length scale of the incident wake, and all contribute to the remarkable increase in lift.

The vortex dynamics of leading-edge vortices on plunging high-aspect-ratio (AR = 10) wings and airfoils were investigated by means of volumetric velocity measurements, numerical simulations and stability analysis to understand the deformation of the leading-edge vortex filament and spanwise instabilities. The vortex filaments on both the wing and airfoil exhibit spanwise waves, but with different origins. The presence of a wing-tip causes the leg of the vortex to remain attached to the wing upper surface, while the initial deformation of the filament near the wing tip resembles a helical vortex. The essential features can be modelled as the deformation of an initially L-shaped semi-infinite vortex column. In contrast, the instability of the vortices is well captured by the instability of counter-rotating vortex pairs, which are formed either by the trailing-edge vortices or the secondary vortices rolled-up from the wing surface. The wavelengths observed in the experiments and simulations are in agreement with the stability analysis of counter-rotating vortex pairs of unequal strength.

Heat load prediction is essential for energy efficiency and carbon reduction in district heating systems. However, heat load is influenced by many factors, such as building characteristics, consumption behavior, and climate, making its prediction challenging. Traditional methods based on physical models are complex and insufficiently accurate, whereas most data-driven statistical methods ignore customer energy consumption behaviors and their correlation, and do not account for the temporal inertia of consumption. This paper proposes a graph ambient intelligence (GAIN) method for heat load prediction, which classifies customers based on their load profiles and uses collaborative attention on temporal graphs to capture their associations and the weather impact on heat loads. GAIN also incorporates recursive and autoregressive methods to model the temporal inertia of consumption. The proposed method is evaluated on four metrics and compared with fifteen baseline methods. The results show that GAIN achieves the lowest daily forecasting errors in terms of RMSE, MAE, and CV-RMSE, with values of 6.972, 4.442, and 0.191, respectively. Besides, the proposed method achieves a maximum reduction of 25%, 29%, and 25% in RMSE, MAE, and CV-RMSE, respectively, compared to other methods when taking meteorological factors into account.

We present experiments demonstrating that a small flag attached to the surface of an airfoil near the leading edge exhibits self-excited oscillations when the airfoil is set at a post-stall angle of attack. The limit cycle oscillations of the flag between the airfoil surface and the freestream have a dominant frequency and promote reattachment of the flow, producing a remarkable increase in the maximum lift coefficient and stall angle. Leading-edge vortex shedding and formation of a separation bubble are observed when the flag tip reaches around the maximum displacement. The instantaneous flow and the range of oscillation frequency have strong similarities to those of the active flow control methods for separation, yet this is a passive flow control method that relies on unsteady effects. The flag oscillations occur mostly in the first structural mode, while the higher modes reveal the three-dimensionality of the flag displacement field. The oscillation frequencies of the flag are in the same range of vortex shedding frequency of the baseline airfoil, suggesting that the wake resonance mechanism may be behind the observations of the enhanced lift at the post-stall angles of attack. There is virtually no effect of the compliant flag on the mean lift at small angles of attack.

Although the lithium-sulfur battery has a high theoretical specific capacity (1675 mAh g−1), its actual capacity is low, and the cycle stability is poor, because the active material undergoes the polarity and the nonpolarity transformation in the battery discharge/charge reaction. There are obvious limitations of using single polar or nonpolar binding, and it is needed to effectively combine the polar materials to the nonpolar matrix/sulfur. Here, we mechanically mixed 1-ethyl-3-methylimidazolium dicyanamide (Emim-dca)-based pore-making polar carbon (P-ILC) with nonpolar cotton carbon activated by KOH/sulfur (CKOH/S) to study the influence of the polar mixture on specific capacity and cycle stability of the battery. Comparing with the nonpolar cathode, the nonpolar-polar cathode has better electrochemical performance. The CKOH/S cathode with polar mixture of P-ILC shows a higher specific capacity (500 mAh g−1 at 100th 1C) and cyclic stability (average attenuation 0.34%). It is because the P-ILC+CKOH/S effectively combines the nonpolar physical binding and polar chemical anchoring by using the method of zonal binding of active materials.

Anexperimental study was performed in a water tunnel to evaluate the effects of continuous and pulsed blowing jets on the counter-rotating vortices generated by the afterbody of a slanted base cylinder. Drag reductions from continuous blowing through circular jets were found to vary significantly with direction and location, and approached 7% when blowing outboard from upstream locations on the upswept face. However, for all circular jets tested, the external power required was larger than the power saved due to the drag reduction. Jet vortices restricted shear layer development, leading to smaller afterbody vortex cores further from the surface. A high-aspect-ratio jet flap, ejecting nearly parallel to the freestream, achieved drag reductions close to 9%, equating to the net energy savings of almost 3% for the best case. Jet vortices shortened the shear layer, resulting in vortices with reduced circulation, which were displaced away from the upswept face. Pulsing the jet flap resulted in improved drag reductions and energy savings (up to around 6%) compared with the equivalent continuous blowing case at the same time-averaged jet momentum coefficient. Pulsed blowing caused an increase in vortex separation and meandering, whereas the circulation was reduced by up to 10% of that for continuous blowing.

With the vigorous development of the photovoltaic industry, how to improve the efficiency of photovoltaic power generation has become an important issue, among which partial shadow occlusion is an important reason affecting the efficiency. The efficiency of photovoltaic power generation can be effectively improved by adopting the maximum power point tracking method (MPPT), but the traditional MPPT method is not ideal in the partial shadow occlusion of the photovoltaic array. To solve this problem, this paper proposes an improved particle swarm optimization method to effectively improve the tracking efficiency of MPPT when multiple peaks appear in the photovoltaic arrays power curve (P-V) under the partial shadow. The proposed method improves the learning factor of the traditional particle swarm optimization algorithm and designs the initial position of the particles according to the characteristics of the photovoltaic array. By adding the particle elimination mechanism, the number of particles changes dynamically, and the tracking speed of the algorithm for the maximum power of the photovoltaic array is improved. Through the result of the simulation, it is not difficult to get the conclusion that the improved particle swarm optimization algorithm can effectively improve the performance of the photovoltaic system under partial shadows.

Non-polar porous carbon/doped polar carbon composite hosts have been proved effective for sulfur in lithium–sulfur (Li–S) battery. Pores in carbon can adsorb sulfur and Li2S, and nitrogen–doped surface shows a stronger affinity for polysulfides through additional chemisorptions. However, how the physical properties of doped carbon, e.g., surface area and porosity, affect the performance of the non-polar carbon/doped polar carbon composite hosts is unknown. Herein, we reported the cotton-derived carbon/porous 1-ethyl-3-methylimidazolium dicyanamide (Emim-dca) derived N-doped carbon, named C/PNC, and the cotton-derived carbon/imporous Emim-dca derived N-doped carbon, named C/NC. The surface area and porosity of the doped polar carbon in C/PNC and C/NC are controlled. The higher surface area of N-doped carbon makes more surface of cotton-derived carbon coated and more sulfur located on the surface of composite hosts. The micro-mesopores in the N-doped carbon can restrain sulfur but shows slow reactive kinetics at a higher current rate. The C/PNC cathode showed a higher discharge capacity of 1100 mAh g−1 than that of 1027 mAh g−1 for the C/NC cathode at 0.1 C and a lower capacity of 208.1 mAh g−1 than that of 349.2 mAh g−1 for C/NC cathode at 2 C.

As the next generation battery, the lithium-sulfur battery with high theoretical specific capacity and energy density needs to overcome the low practical discharge capacity and the poor cycle performance for the poor conductivity of sulfur and the shuttle effect of polysulfide. In this study, a hierarchical micro-mesoporous carbon (HPC) is designed and synthesized as a sulfur host from the cotton textile with KOH activation at 700 °C to combine the advantages of these two structures, where mesoporous structure can improve the infiltration of electrolyte to act as fast ionic channel and micropores have an excellent ability of binding sulfur. The HPC showed an excellent high specific surface area (2835.47 m2 g−1) and a high pore volume (2.82 cm3 g−1), and the ratio of the mesoporous reaches 57.85%. The sulfur in HPC/S was uniformly distributed in the host structure and no surface crystallization was observed by TEM characterization. Assembled in the lithium-sulfur battery, the cathode mixed with HPC/S and conductive agent delivers an initial discharge capacity of 1577 mAh g−1 at 0.1C, and a reversible capacity of 434.5 mAh g−1 after 300 cycles at the current rate of 1C.

Folded core sandwich structures are promising multifunctional structures for both load bearing and radar absorbing capability. This paper presents an experimental study on the radar absorbing characteristics of folded core structures. The influences of various factors on the folded core radar cross section (RCS) are investigated. The experiments were carried out in an anechoic chamber. Comparisons are made between folded core samples and an aluminium flat panel. The results show that the folded core height has significant effects on the radar absorbing performance of V-pattern folded core, while core material only leads to a slight difference. The RCS of V-pattern folded core is lower than that of the flat panel, while the RCS of M-pattern folded core is of the same order of magnitude as that of the flat panel with a much wider range.

Location, strength, and structure of tip and edge vortices shed from wings and bodies can be manipulated by using flow control techniques. Flow physics of these approaches involve flow separation from the edge, roll-up into the vortex, wing flow regime, vortex instabilities, vortex–vortex interactions, and vortex–turbulence interactions. Actuators include continuous and unsteady blowing as well as suction, bleed, and control surfaces, which add momentum, vorticity, and turbulence into the vortices. It is noted that actuation may have effects on more than one aspect of the flow phenomena. A comparative review of the control of delta-wing vortices, tip vortices, and afterbody vortices is presented. The delay of vortex breakdown and the promotion of flow reattachment require different considerations for slender and nonslender delta wings and may not be possible at all. Tip vortices can be controlled to increase the effective span, to generate rolling moment, to attenuate wing rock, and to attenuate vortex–wing interactions. Although there are different approaches for each application, opportunities for future research on turbulence ingestion, bleed, and excitation of vortex instabilities exist. Recent research also indicates that active and passive flow control can be used to manipulate the afterbody vortices to reduce the drag.

In this study, the unipolar resistive switching (RS) effect is exhibited in porous perovskite-like Bi3.15Nd0.85Ti3O12 (BNT) thin films fabricated on Pt/Ti/SiO2/Si substrates through chemical solution deposition technique employed PEG template. The unipolar RS characteristics can be adjusted by the size and density of the pores in the porous perovskite-like Bi3.15Nd0.85Ti3O12 thin films. The size and density of the pores are controlled by the processing parameters of the annealing temperature or the dwell time or the both during the preparation of the porous perovskite-like Bi3.15Nd0.85Ti3O12 thin films. The porous BNT thin films annealed at 720 °C for 10 min show large current ratio of low/high resistance state of four orders and low operating voltage of 5 V for SET and 1.5 V for RESET. Moreover, the LRS/HRS can be reversed repeatedly without large decay. After the retention test of 104 s for low/high resistance state, the devices still show as large current ratio of low/high resistance state as about four orders. The present study should have guide to develop a unipolar RS memory using the perovskite oxides.

Aiming to mitigate the aerodynamic heating during hypersonic re-entry, the aerothermodynamic optimization of aerospace plane airfoil leading edge is conducted. Lift-to-drag ratio at landing condition is taken as a constraint to ensure the landing aerodynamic performance. First, airfoil profile is parametrically described to be more advantageous during the optimization process, and the Hicks-Henne type function is improved considering its application on the airfoil leading edge. Computational Fluid Dynamics models at hypersonic as well as landing conditions are then established and discussed. Design of Experiment technique is utilized to establish the surrogate model. Afterwards, the previously mentioned surrogate model is employed in combination with the Multi-Island Genetic Algorithm to perform the optimization procedure. NACA 0012 is taken as the baseline airfoil for case study. The results show that the peak heat flux of the optimal airfoil during hypersonic flight is reduced by 7.61% at the stagnation point, while the lift-to-drag remains almost unchanged under landing condition.

The effect of suction on an airfoil surface at various locations downstream of the leading edge of a thin flat-plate airfoil was studied in a wind tunnel at a low Reynolds number. At poststall angles of attack, substantial lift enhancement and delay of stall can be achieved if a large separation bubble is generated by reattaching the massively separated flow near the trailing edge. The effects of location and volumetric flow rate of suction were investigated by means of force and velocity field measurements. There is an optimal location of suction around xs/c=0.4, which generates the maximum lift coefficient for suction coefficients less than 3%. When suction is applied closer to the leading edge, it may be possible to reattach the flow for smaller suction coefficients, but the resulting small separation bubble causes smaller lift increase. Large separation bubbles are needed for the maximum time-averaged lift enhancement, however, they exhibit shear layer flapping, intermittent reattachment, and larger l...

Olfactory flow in fishes is a little-explored area of fundamental and applied importance. We investigated olfactory flow in the pike, Esox lucius, because it has an apparently simple and rigid nasal region. We characterised olfactory flow by dye visualisation and computational fluid dynamics, using models derived from X-ray micro-computed tomography scans of two preserved specimens. An external current induced a flow of water through the nasal chamber at physiologically relevant Reynolds numbers (200−300). We attribute this externally-induced flow to: the location of the incurrent nostril in a region of high static pressure; the nasal bridge deflecting external flow into the nasal chamber; an excurrent nostril normal to external flow; and viscous entrainment. A vortex in the incurrent nostril may be instrumental in viscous entrainment. Flow was dispersed over the olfactory sensory surface when it impacted on the floor of the nasal chamber. Dispersal may be assisted by: the radial array of nasal folds; a complementary interaction between a posterior nasal fold and the ventral surface of the nasal bridge; and the incurrent vortex. The boundary layer could delay considerably (up to ~ 3 s) odorant transport from the external environment to the nasal region. The drag incurred by olfactory flow was almost the same as the drag incurred by models in which the nasal region had been replaced by a smooth surface. The boundary layer does not detach from the nasal region. We conclude that the nasal bridge and the incurrent vortex are pivotal to olfaction in the pike.

Infectious diarrhea has high morbidity and mortality around the world. For this reason, diarrhea prediction has emerged as an important problem to prevent and control outbreaks. Numerous studies have built disease prediction models using large-scale data. However, these methods perform poorly on diarrhea data. To address this issue, this paper proposes a parsimonious model (PM), which takes historical outpatient visit counts, meteorological factors (MFs) and Baidu search indices (BSIs) as inputs to perform prediction. An experimental evaluation was done to compare the short-term prediction performance of ten algorithms for four groups of inputs, using data collected in Xiamen, China. Results show that the proposed method is effective in improving the prediction accuracy.

The olfactory epithelium of the sea catfish, Ariopsis felis, is found on a pinnate array of lamellae (the olfactory rosette) housed within a nasal chamber. The nasal anatomy of A. felis suggests an ability to capture external water currents. We prepared models from X-ray micro-computed tomography scans of two preserved specimens of A. felis. We then used dye visualisation and computational fluid dynamics to show that an external current induced a flow of water through a) the nasal chamber and b) the sensory channels of the olfactory rosette. The factors responsible for inducing flow through the nasal chamber are common to fishes from two other orders. The dye visualisation experiments, together with observations of sea catfishes in vivo, indicate that flow through the nasal chamber is regulated by a mobile nasal flap. The position of the nasal flap – elevated (significant flow) or depressed (reduced flow) – is controlled by the sea catfish’s movements. Flow in the sensory channels of the olfactory rosette can pass through either a single channel or, via multiple pathways, up to four consecutive channels. Flow through consecutive sensory channels (olfactory resampling) is more extensive at lower Reynolds numbers (200 and 300, equivalent to swimming speeds of 0.5 – 1.0 total lengths s-1), coinciding with the mean swimming speed of the sea catfishes observed in vivo (0.6 total lengths s-1). Olfactory resampling may also occur, via a vortex, within single sensory channels. In conclusion, olfactory flow in the sea catfish is regulated and thoroughly sampled by novel mechanisms.

The stock turnover values are sensitive to external factors, and remain great challenges in its prediction. The consideration is that search engine data can reflect market environment, policies and attentions on stocks. Therefore, a dual sides autoregression (DSAR) method is proposed to benefit from both observed turnover values and exogenous data. The proposed DSAR consists of linear representation stage and combination stage. In linear representation stage, the short-term patterns of turnover values and query data are represented, respectively. In combination stage, the outputs from previous stages are combined. Intensive experiments on two groups of data collections show the effectiveness of our proposed method.

Aiming at the low efficiency and low accuracy of traditional manual detection of workpiece circular features, a machine vision method is proposed to accurately detect circular features. By adopting algorithms such as iterative threshold segmentation, generating XLD contours, selecting feature contours and random Hough transforms, single or multiple circles on the workpiece can be quickly detected. Experiments show that the detection is efficient and accurate, and can meet the detection needs of industry.

Near-wakes of axisymmetric cylinders with slanted base were investigated in wind tunnel experiments for an upsweep angle of 28°. Effects of splitter-plate, cavity, and flaps on the afterbody vortices and separated flow were studied by means of surface pressure and Particle Image Velocimetry measurements. The splitter plate causes more diffused afterbody vortices due to the turbulence ingestion from the separation region. When the slanted base is replaced with a deep cavity, there is weaker roll-up of vorticity due to the lack of streamwise flow and a solid surface. Varying the splitter plate length in the range tested did not have significant influence on the flowfield, apart from affecting the strength of the splitter-plate vortex. With the splitter plate and cavity, unsteadiness is dominated by the flow separation region, as opposed to the afterbody vortices in the baseline case. A pair of vertical flaps attached to the side-edges of the splitter plate can reduce the unsteadiness at the measurement plane immediately downstream of the splitter plate.

Drag force, surface pressure and particle image velocimetry measurements havebeen carried out in wind tunnel experiments in order to study the effect of minispoilers on the drag of an axisymmetric cylinder with a slanted base that has an upsweep angle of Φ = 28°. Two different spoiler heights (h/D = 2.5% and 5%) were examined at various chordwise locations along the slanted surface. Placing the spoiler closer to the beginning of the slanted section caused an increased drag due to the separation induced by the spoiler itself, although a more diffused afterbody vortex was produced due to the turbulence ingestion. Drag reduction was observed when placing the spoiler closer to the trailing-edge, with the optimum location x′s /c = 87.5%, resulting in approximately 5% drag reduction for both spoiler heights. This reduction is due to the displacement of the afterbody vortex away from the surface as the mini-spoiler acts similarly to a Gurney flap. The same effect can also be produced by introducing a smaller co-rotating vortex to manipulate the afterbody vortextrajectory.

The interaction of meandering tip vortices shed from a leading wing with a downstream wing was investigated experimentally in a water tunnel using flow visualization, particle image velocimetry measurements, and volumetric velocity measurements. Counter-rotating upstream vortices may exhibit sudden variations of the vortex core location when the wing-tip separation is within approximately twice the vortex core radius. This is caused by the formation of vortex dipoles near the wing tip. In contrast, co-rotating upstream vortices do not exhibit such sensitivity. Large spanwise displacement of the trajectory due to the image vortex is possible when the incident vortex is further inboard. For both co-rotating and counter-rotating vortices, as long as there is no direct impingement upon the wing, there is a little change in the structure of the time-averaged vortex past the wing, even though the tip vortex shed from the downstream wing may be substantially weakened or strengthened. In the absence of the downstream wing, as well as for weak interactions, the most energetic unsteady modes represent the first helical mode |m| = 1, which is estimated from the three-dimensional Proper Orthogonal Decomposition modes and has a very large wavelength, on the order of 102 times the vortex core radius, λ/a = O(102). Instantaneous vorticity measurements as well as flow visualization suggest the existence of a smaller wavelength, λ/a = 5–6, which is not among the most energetic modes. These two-orders of magnitude different wavelengths are in agreement with the previous measurements of tip vortices and also exhibit qualitative agreement with the transient energy growth analysis. The very long wavelength mode in the upstream vortex may persist during the interaction, and reveal coupling with the trailing vortex as well as increased meandering.

Apply ANN for predicting infectious diarrhea of Shanghai for the first time.The ANN model are compared with the SVR, RFR and MLR models.ANN shows good prediction performance as compared to SVR, RFR and MLR models.The sensitivity analysis is used to determine the inputs influence on output. Infectious diarrhea is an important public health problem around the world. Meteorological factors have been strongly linked to the incidence of infectious diarrhea. Therefore, accurately forecast the number of infectious diarrhea under the effect of meteorological factors is critical to control efforts. In recent decades, development of artificial neural network (ANN) models, as predictors for infectious diseases, have created a great change in infectious disease predictions. In this paper, a three layered feed-forward back-propagation ANN (BPNN) model trained by Levenberg-Marquardt algorithm was developed to predict the weekly number of infectious diarrhea by using meteorological factors as input variable. The meteorological factors were chosen based on the strongly relativity with infectious diarrhea. Also, as a comparison study, the support vector regression (SVR), random forests regression (RFR) and multivariate linear regression (MLR) also were applied as prediction models using the same dataset in addition to BPNN model. The 5-fold cross validation technique was used to avoid the problem of overfitting in models training period. Further, since one of the drawbacks of ANN models is the interpretation of the final model in terms of the relative importance of input variables, a sensitivity analysis is performed to determine the parametric influence on the model outputs. The simulation results obtained from the BPNN confirms the feasibility of this model in terms of applicability and shows better agreement with the actual data, compared to those from the SVR, RFR and MLR models. The BPNN model, described in this paper, is an efficient quantitative tool to evaluate and predict the infectious diarrhea using meteorological factors.

The interaction of trailing vortices of an upstream wing with rigid and flexible downstream wings has been investigated experimentally in a wind tunnel, using particle image velocimetry, hot-wire, force and deformation measurements. Counter-rotating upstream vortices exhibit increased meandering when they are close to the tip of the downstream wing. The upstream vortex forms a pair with the vortex shed from the downstream wing, and then exhibits large displacements around the wing-tip. This coupled motion of the pair has been found to cause large lift fluctuations on the downstream wing. The meandering of the vortex pair occurs at the natural meandering frequency of the isolated vortex, with a low Strouhal number, and is not affected by the frequency of the large-amplitude wing oscillations if the downstream wing is flexible. The displacement of the leading vortex is larger than that of the trailing vortex, however it causes highly correlated variations of the core radius, core vorticity and circulation of the trailing vortex with the coupled meandering motion. In contrast, co-rotating vortices do not exhibit any increased meandering.

Trace level organic contaminants might not be completely removed from the municipal wastewater and the safety incurred by them had become a concern. These organic pollutants were extracted from water samples and detected by GC–MS. The estrogenic activity of the organic was tested using Yeast Estrogen Screen to detect the transcriptional activation of the estrogen receptor (ER) and immature mouse uterotrophic bioassays to study reproductive toxicity. The results of GC–MS demonstrated the organic extracts in the municipal wastewater and the WWTP effluents Included two major categories, benzenes and Phthalates. The estrogenic activity of organic extracts from the secondary effluent (SE) and tertiary effluent (TE) was below that of the raw wastewater (RW). Results of uterotrophic bioassay demonstrated that SE would bring some potential hazards on animals while TE was relatively safe.