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The two-dimensional laminar flow over a simultaneously pitching-heaving teardrop airfoil is studied numerically. The influence of frequency and amplitude on the wake structure and aerodynamic performance is investigated at a constant Reynolds number, Re=2640. The computational modeling accurately depicts the changes in the wake structure that occur between the von Karman, reverse von Karman and deflected conditions. Investigations at low flapping frequencies and amplitudes identified the presence of additional wake structures that had not been reported previously. The interaction between the flapping frequency and vortex shedding frequency appears to govern the formation of such multiple vortex wakes. The wake structures identified are presented in the form of a wake map where the transitions between the wake structures are visible. This study correlates the wake arrangement with the variation in force coefficients and explains why the presence of a reverse von Karman street is necessary but not a sufficient condition for thrust production. The time history of the drag coefficient and the phase relation between lift and drag show the dynamics of the wake. The variation of force coefficients and efficiency at different flapping conditions is evaluated, and the influence of flapping parameters is assessed. The underlying vortex interactions that influence the aerodynamic performance are identified. The development and distribution of stress fields developed due to periodic fluctuations behind the flapping airfoil have not been discussed previously. The velocity fluctuations in the wake due to the periodic flapping are presented, and regions of maximum stress distribution are identified. [ABSTRACT FROM AUTHOR]

The flapping kinematics have revealed a new paradigm of locomotion which is highly maneuverable and efficient compared to traditional propulsion systems. This work numerically investigates a three-dimensional wing undergoing pitching oscillations using Large eddy simulation (LES). The wake structure is presented using the Q -function, and the influence of pitching frequency on the structure of the wake is discussed. The vortices appear to travel as interconnected vortex rings in the bifurcated wake and are completely different from the two-dimensional investigations. The increase in pitching frequency ( St D) generates the interlinking structures between the two limbs of the bifurcated wake. The interlinking between the two limbs increases with St D and will get disrupted at sufficiently high St D . The increase in St D increased the force generated by the pitching wing, and the periodic dynamics between the force coefficients slowly transformed to quasi-periodic dynamics. The transition to quasi-periodic dynamics has not reduced the force generation of the pitching wing. The disruption of interlinking structures between the two limbs enhanced the lift generated by the pitching wing. The present investigation shows that the wake vortex structure strongly depends on St D . The generation of a jet in the wake is visible in the mean velocity profile indicating the thrust developed by the wing. The formation of multiple peak profiles indicated the formation of multiple jets, which resulted in enhanced thrust production. The Reynolds stress field generated from the velocity fluctuations appears to be influenced by both the pitching oscillations and vortex interactions. This study can guide the selection of better kinematic parameters to enhance the propulsive performance. [ABSTRACT FROM AUTHOR]

The three-dimensional flow around a custom wing performing pitching oscillation is analyzed numerically using large-eddy simulation with the wall adapting local eddy-viscosity subgrid-scale model. The wake characteristics behind the pitching wing with three different aspect ratios, AR = 2 / 3 , 1 , 4 / 3 , is investigated in an upstream flow with Reynolds number, Re = 2640. The Q − function is employed to identify the swirling structures in the flow field, and four primary vortices, namely, primary leading edge vortex (PLEV), secondary leading edge vortex, wing tip vortices, and trailing edge vortex, are identified. The evolution of vortices over the wing surface is presented in detail, and the arrangement of vortex rings in the wake is compared for three different aspect ratios. The PLEV develops into an arch vortex using the self-induction phenomenon, and the interlinking between the subsequent vortex rings depends on the arch vortex leaving the trailing edge. The force coefficient computed over the wing shows a positive thrust for AR = 4 / 3. The mean velocity field contours indicate a spanwise loading on the wing, which is unaccountable in two-dimensional studies. The Reynolds stresses generated due to large-scale periodic velocity fluctuations in the wake are presented. The vorticity field in the midplane of the wing appears to be diffusive at higher aspect ratios. The comparison of vorticity from the three-dimensional and two-dimensional models suggests that a two-dimensional model will over predict the vorticity distribution and force coefficients in the wake. [ABSTRACT FROM AUTHOR]

The wake characteristics of a custom-designed airfoil performing pitching oscillations, heaving oscillations, and a combination of pitch and heave oscillations are compared in this study. The influence of flapping parameters are investigated at a constant Reynolds number Re and is presented for the Strouhal numbers based on the oscillation amplitude, StA, varying in the range. The generation of vorticity above and below the airfoil depends on the airfoil's initial direction of motion and remains the same for all types of flapping oscillations investigated. The evolution of the leading-edge and trailing-edge vortices is presented. The heaving oscillations of the airfoil are found to have a greater influence on the characteristics of the leading edge vortex. The wake behind the combined pitch-heave oscillations appears to be governed by pitching oscillations below , whereas it is driven by heaving oscillations above . The force computations indicate that the mere existence of the reverse von Kármán street is not sufficient to develop the thrust on the airfoil. The periodic component of velocity fluctuations significantly influences the wake characteristics. The anisotropic stress field developed around the airfoil due to the periodic fluctuations of the velocity is presented. The coherent structures developed in the wake are identified using the proper orthogonal decomposition and a qualitative comparison of the structures for different flapping oscillations is presented. The energy transfer from the flapping airfoil to the fluid for different flapping oscillations is highest for heaving oscillations followed by combined pitch-heave oscillations and pitching oscillations. [ABSTRACT FROM AUTHOR]

Most common signs and symptoms of typhoid are localised to gastrointestinal system. Less commonly, extraintestinal infectious complications occur with enteric fever. The present case report is about a 29-year-old female, without risk factors, who presented with fever, loose stools and cough of five days duration. The patient was diagnosed to have paratyphi A bacteraemia, with clinical and radiological features of pneumonia. Her sputum cultures were sterile, and hence paratyphi A pneumonia was diagnosed. She received 14 days of antimicrobial therapy and recovered. Vi-based monovalent vaccines do not offer protection against most paratyphoid fever, because only Salmonella serovars Typhi, and paratyphi C carry the Vi antigen. Further studies are needed on bivalent and polyvalent typhoid vaccines covering all serovars. [ABSTRACT FROM AUTHOR]

The application of a flapping wing mechanism offers a vast range of development possibilities for unmanned aerial vehicles (UAVs) and autonomous underwater vehicles (AUVs). The influence of wake transitions on flapping wing mechanism's capabilities is not fully understood particularly at low Reynolds numbers. The numerical investigation of a symmetric airfoil performing sinusoidal heaving oscillations is performed to explore the wake transitions. The influence of heaving parameters on wake transitions when exposed to a constant velocity flow is investigated. The existence of reverse von Karman vortex street, deflected wake and chaotic wake is observed. The wake deflection is found to switch its direction before transforming into a chaotic wake. The coherent structures and its evolution with the flow are presented using proper orthogonal decomposition (POD). The underlying structures and their interactions for different wake situations are identified. Correlations for the nondimensional maximum velocity in the wake in terms of frequency and amplitude is proposed. The wake dynamics is found to depend significantly on the leading edge vortices. The time-varying velocity fluctuations in the flow field are presented and discussed in detail. The velocity fluctuation contours are used to identify the regions of momentum transfer. The transient nature of the flow field is studied using the phase plot. A transition route from the periodic to chaotic regime though a quasi-periodic regime is established using time series analysis. The wake transitions are observed to be more sensitive towards heaving frequency than the heaving amplitude. [ABSTRACT FROM AUTHOR]

Background & objectives: There are limited data from India on the post-COVID multisystem inflammatory syndrome in adults (MIS-A). The objective of the present study was to evaluate the clinical profile of patients with MIS-A admitted to a tertiary care centre in southern India. Methods: This single-centre retrospective study was conducted from November 2020 to July 2021, and included patients aged >18 yr admitted to the hospital as per the inclusion and exclusion criteria. Results: Nine patients (5 male, mean age 40±13 yr) met the criteria for MIS-A. Five patients had proven COVID-19 infection or contact history 36.8±11.8 days back. All patients were positive for SARS-CoV-2 IgG antibody, negative for COVID-19 PCR, and had negative blood, urine and sputum cultures. All patients had fever and gastrointestinal (GI) symptoms, and five patients had left ventricular dysfunction. All patients had neutrophilic leucocytosis at presentation and elevated biomarkers such as C-reactive protein serum procalcitonin, D-dimer and ferritin. The majority of the patients (7/9 i.e. 77.78%) were treated with intravenous hydrocortisone (50-100 mg q6h-q8h). Six patients recovered completely whereas three patients expired. Interpretation & conclusions: Fever and GI symptoms were the most common presentation of MIS-A. Elevated serum procalcitonin may not be useful in differentiating bacterial sepsis from MIS-A. Most patients responded to corticosteroids. [ABSTRACT FROM AUTHOR]