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International audience; The increased focus on supersonic and hypersonic flows necessitates methods to study such flows in laboratory-based facilities, thus motivating researchers to find effective, efficient, and affordable methods to produce them in laboratories. It is desirable for the rocket nozzles to operate efficiently at different altitudes, which made the Altitude Compensating Nozzles emerge as a solution. In this work, we propose a new design for such nozzles, namely, the ringed nozzle. The proposed nozzle consists of a stack of parallel rings that serve as a nozzle with bleeding slots. This design can be utilised to obtain different exit Mach numbers and attain the desired performance according to the pressure ratio, serving as an Altitude Compensating Nozzle. The stack of rings might be altered to tailor nozzle shape and area ratio corresponding to the nozzle requirement. The nozzle is analysed from an engineering perspective by comparing the thrust coefficient and specific impulse, and the numerical simulations show promising results.

Computational investigation is carried out to estimate the drag force and surface heating load for hypersonic reacting flows. An in-house viscous nonequilibrium finite volume-based reacting gas solver has been utilized. This solver is capable of investigating 11 chemical elementary reactions and temperature-dependent specific properties to reveal the effect of lower as well as higher freestream stagnation enthalpy conditions. Initially, the calorically perfect-gas and real-gas model-based simulations are carried out to understand the real-gas effects in the presence of a metallic spike. Computed surface pressure and heat flux are compared for the freestream stagnation enthalpy of 2 MJ/kg. The real-gas model predicts a 5% higher drag and 57.21 kW/m2 higher peak heat flux compared to the perfect-gas model. However, lower enthalpy conditions predict almost the same drag force for any spike length. Further, a counterflowing jet is installed at the root of the spike, and flow field alterations are studied for this proposed integrated configuration. The root jet further pushes the conical shock in the upstream direction and provides an extra-large recirculation zone. Here, the possibility of drag and surface heat flux reduction is very much evident due to the decrease in surface pressure and presence of low-temperature jet gas in the vicinity of the object. Various freestream stagnation enthalpies, as well as the jet pressures, are considered to investigate the performance alterations by the combination technique. It is observed that the drag and surface heat load reduction efficiency of the combined configuration decreases with an increase in the freestream stagnation enthalpy. Moreover, it increases when increasing the root jet pressure for given enthalpy conditions. Hence, instead of attaching a long spike at the stagnation region of a blunt-shaped object, the use of a short spike and low-pressure root jet is recommended for a better reduction in drag and surface heat load.

Inspired by the polyp leaf of the Orange sea-pen (Ptilosarcus gurneyi), a novel blade shape of the Savonius vertical-axis wind rotor is developed. The similarities between the aerodynamic and the hydrodynamic aspects of the Savonius rotor blade profile and the sea-pen leaf are reviewed, and an appropriate analogy is thereby established. The shape of the sea-pen leaf is then extracted to fabricate the rotor blades. The performance of this sea-pen bladed rotor is evaluated in a low-speed subsonic wind tunnel at different wind velocities. The two-dimensional (2D) numerical analysis is also performed to support the experimental findings and to study the influence of blade shape on the pressure and the torque distributions of the rotor. The novel sea-pen bladed rotor, having lesser material requirements, is seen to demonstrate higher performance than that of the conventional semicircular bladed rotor in the tested range of low tip-speed ratio.

This is an attempt to reconstruct the theory of a well-posed problem for the dual-phase-lag heat conduction developed by Quintanilla in the context of time-fractional derivatives of order $\alpha \in (0,2] $. The heat conduction equation has been derived in the context of two temperature theory. The well-posedness of the problem has been proved by showing continuous dependence of the solution on the initial data and energy supply term. Moreover, the existence and uniqueness of the solution also have been proved subject to stability condition for the constitutive coefficients on the point spectrum. Due to the application of phase-lag $\tau$ = $\tau_{q}$ - $\tau_{T}$ satisfying $\tau$ $> 0$, thermal wave propagates with the finite speed. As a special case, an illustrative example has been discussed for heat transfer and thermal stress analysis of the solid heat conductor in the Cartesian domain. The analytical solutions have been achieved in the Laplace domain. The time domain inversions of the Laplace transforms have been numerically accomplished using the Gaver-Stehfest algorithm, satisfying Kuznetsov's convergence condition. The localized heat conduction $\alpha =0$, the classical thermoelasticity $\alpha =1$, the fractional thermoelasticity $\alpha =0.5$ and thermoelasticity without energy dissipation $\alpha =2$ have been discussed numerically and illustrated graphically. Mathematics Subject Classification (2010) 26A33 · 35L35 · 44A10 · 65R10 · 74F05

The knowledge of surface heat flux over aerodynamic surfaces is highly desirable for high-speed applications. Impulse test facilities like shock tubes and shock tunnels are invariantly employed for...

Disorders of sex development (DSD) are a group of clinical conditions with variable presentation and genetic background. Females with or without development of secondary sexual characters and presenting with primary amenorrhea (PA) and a 46,XY karyotype are one of the classified groups in DSD. In this study, we aimed to determine the genetic mutations in 25 females with PA and a 46,XY karyotype to show correlations with their phenotypes. Routine Sanger sequencing with candidate genes like SRY, AR, SRD5A2, and SF1, which are mainly responsible for 46,XY DSD in adolescent females, was performed. In a cohort of 25 patients of PA with 46,XY DSD, where routine Sanger sequencing failed to detect the mutations, next-generation sequencing of a targeted gene panel with 81 genes was used for the molecular diagnosis. The targeted sequencing identified a total of 21 mutations including 8 novel variants in 20 out of 25 patients with DSD. The most frequently identified mutations in our series were in AR (36%), followed by SRD5A2 (20%), SF1 (12%), DHX37 (4%), HSD17B3 (4%), and DMRT2 (4%). We could not find any mutation in the DSD-related genes in five (20%) patients due to complex molecular mechanisms in 46,XY DSD, highlighting the possibility of new DSD genes which are yet to be discovered in these disorders. In conclusion, genetic testing, including cytogenetics and molecular genetics, is important for the diagnosis and management of 46,XY DSD cases.

Studying the underexpanded jet has been essential for many fields of research because it might occur intentionally or spontaneously wherever a high-speed gas flow is possible. Therefore, an in-hous...

Numerical investigations are carried out to assess the performance of unsteady energy and steady energy depositions in the supersonic reacting flow. For this, a finite volume-based structured inviscid axisymmetric flow in-house solver is employed. This solver accounts for 5 species (O 2 , O, N 2 , N, and NO) and 11 chemical reactions. Initially, unsteady simulations are carried by depositing energy pulse upstream of the standing bow shock ahead of a sphere. With time, this pulse advances, grows and interacts with the bow shock. Both perfect gas (PGS) and reacting gas solvers (RGS) are used for this analysis. It has been noted that RGS based predictions show lesser stagnation pressure and thus wall pressure at the same interaction time. It has also been found that better drag reduction depends on the strength of low-density vortex which is formed due to the interaction between shock wave and blast wave. This vortex is stronger for the perfect gas case and thus portrays higher reduced propulsion energy or power effectiveness as compared to RGS based prediction. Simulation with the higher freestream stagnation enthalpy (3.0 MJ/kg) shows that there is 90% decrement in the density of the pulse as compared to lower enthalpy case (0.3 MJ/kg). However, there is 60.5% increment in the pressure of cell or outer part of the pulse as compared to 0.3 MJ/kg case. Further, the diameter of the pulse also increases by 19.67% for this higher freestream enthalpy condition. It has been noticed that, lower density of the pulse leads to the formation of stronger vortex and thus deepens the first valley of drag signal with increases in the freestream stagnation enthalpy. The formation of such stronger vortex, introduces one more valley in the drag signal for 3.0 MJ/kg case, where, 152% higher power effectiveness is registered. But, for steady energy deposition power effectiveness decreases with the inlet stagnation enthalpy. In all, it is strongly recommended to use unsteady pulse deposition instead of steady one for drag reduction in high enthalpy flow situations.

Ensuring correct functionality is the basic objective of any digital design and this can be done only if the circuit obeys all the timing constraints. Static Timing Analysis is the procedure perfor...

The accuracy of force measurement and prediction is of prime importance in the calibration of a force balance in aerodynamic models. Multi-point calibration has recently been introduced which has proven to be a more accurate prediction technique than the traditional single-point calibration technique. This paper describes the multi-point calibration of a double cone model using tri-axial and uniaxial accelerometers to obtain the maximum number of responses with accurate prediction using a minimum number of accelerometers. The multi-point calibration was performed by applying forces at nine locations on a double cone model considering two configurations. Firstly, accelerations were measured simultaneously using one tri-axial and two uniaxial accelerometers which were fixed at three locations of the model-balance assembly. Secondly, forces were measured from the responses obtained simultaneously using one uniaxial and one triaxial accelerometer fixed at two locations of the model-balance assembly. The prediction of the forces was performed using Adaptive Neuro Fuzzy Inference System (ANFIS). Genetic algorithm was used to obtain pure normal and pure axial forces from the components of applied forces at different calibration locations. The forces were predicted accurately from the responses measured using two accelerometers (one uniaxial and one triaxial accelerometer) as well as from the responses of three accelerometers (one tri-axial and two uniaxial accelerometers). Thus, tri-axial accelerometers can be used rather than using multiple numbers of uniaxial accelerometers. The use of tri-axial accelerometers leads to the ease of experimentation as mounting of multiple number of uniaxial accelerometers makes the calibration set-up complex and response measurement challenging. The attainment of responses in three directions at a single location is possible only using tri-axial accelerometer which helps in understanding the actual degrees of freedom experienced by the model. Thus, the use of tri-axial accelerometers for obtaining the responses in dynamic calibration is a better alternative than using uniaxial accelerometers.

Investigations of ramp-induced shock-wave boundary-layer interaction have been carried out for real gas flows of air and carbon dioxide through hypersonic laminar flow simulations corresponding to Earth and Mars atmospheres. An in-house-developed solver, which accounts for the real gas effects, has been employed for these studies. Effects of various parameters like wall temperature, freestream stagnation enthalpy, freestream Mach number, and blunt leading edge are explored on the intensity of shock-wave boundary-layer interaction (SWBLI). In either case, an increase in separation length is observed with an increase in wall temperature and a decrease in Mach number as well as freestream stagnation enthalpy. Here, the intensity of alteration is always noted to have a higher percentage for the Mars gas model. Further, separation length is found to be almost equal for the same wall to total temperature ratio in both of the flow mediums. The present study also affirms the fact that the leading edge bluntness can be used as a tool to reduce the size of the separation region in these planetary atmospheres. Revised correlations have been proposed for hypersonic Earth atmospheric flow with real gas effects to predict the extent of upstream influence and separation bubble size. The outcomes of simulations have also helped to device new correlations for these flow features of SWBLI for Mars atmospheric conditions. In all, the need for consideration of real gas effects and an exclusive real gas flow solver for the Mars atmosphere are the prominent recommendations of current studies.

This paper explores the function approximation characteristics of Artificial Neural Network (ANN) by implementing it on the vertical-axis Savonius wind rotor technology. In this regard, a suitable experimental dataset documented in literature is exploited to train the ANN comprising the rotor performance as output and 11 different design and operating parameters as input with the help of matlab R2020b software. Multiple ANN models are trained by varying the number of hidden neurons which are then evaluated based on their estimation error and correlation coefficient (R) as decision criteria. The optimum ANN architecture demonstrates R ≈ 0.96 and 0.98 for the testing and training datasets, respectively. Further, in the quest of finding the optimum performance from the entire power curve of the rotor, the Golden Section Method (GSM) is linked with the trained ANN model. Using these soft computing techniques, a parametric study is carried out to understand the dependency of rotor performance on their design and operating parameters. At the end, a graphical interface is developed as a product so as to allow the user to predict the performance of the new rotor designs intuitively.

Thin film gauges (TFGs) are most commonly used for heat transfer measurement, especially in short duration test facilities. Performance improvement of these sensors through alteration in their geometric construction or through additives like nanomaterials in the sensing material has been attempted. Present studies propose a robust methodology for sensor making which accounts the effect of surface roughness of the backing material. Total four TFGs are fabricated using Quartz as substrate material which is specially prepared with different artificial roughness values using commercially available silicon carbide sand papers. These in-house fabricated TFGs are assessed through static and dynamic calibrations and their performance is compared. It is observed that substrate roughness has a significant effect on calibration parameters and adhesion, since a rough gauge is seen to over predict the heat flux while remaining TFGs under predict the same. Self-heating of TFG is accounted and confirmed for this over prediction. The optimum activation current range for the present rough TFG is thus noted to be 3 mA to 7 mA due to minimum error in inverse prediction of heat flux. Finally, it is recommended that the gauge substrate should be sufficiently rough for better adhesion of the thin film to the substrate but it should not be highly finished.

In the current investigation, a four stroke, variable speed, single cylinder, variable compression ratio (VCR) SI engine is operated with raw biogas at wide open throttle (WOT) condition and at five different CRs ranging from CR 10 to CR 14 over the operating speed range of the engine. The ignition timing (IT) of the engine is also varied from 23○CA to 47○CA before top dead centre (bTDC) at each operating CR. The optimized operating CR and IT of the engine are obtained through series of experiments and its effects on the performance, combustion and emission characteristic are analysed herein. The rise in operating CR from CR 10 to CR 12 enhanced the power output and efficiency of the biogas fueled SI engine by 12.72% and 5.68%, respectively and reduced fuel consumption by 5.42% at 1400 rpm. Enhancing the CR from CR 10 to CR 12, limited the intensification of NOx and unburnt hydrocarbon emission by 10.17% and 15.6%, respectively at 1400 rpm. Hence, CR 12 is recommended as the optimum CR and its combination with 1400 rpm and WOT setting is recommended as the best operating condition of the engine.

International audience; Behind the iconic "pop! " accompanying the uncorking of a champagne bottle hides a gas flow of surprising complexity. Its modeling is made delicate by its supersonic nature, its interaction with the cork stopper, the eminently unsteady character of the flow escaping from the bottle, and the continuous change of the geometry of the computational flow domain due to the displacement of the cork. Computational fluid dynamics (CFD) simulations revealed the formation, evolution, and dissipation of shock wave patterns during the first millisecond following champagne cork popping. A first crown-shaped shock wave pattern develops radially, which is then followed by the formation of a detached shock wave, or bow shock, induced by the presence of the cork in the axial path of the supersonic gas flow. Moreover, the good agreement between the position of the bow shock previously observed through high-speed imaging and that determined through CFD simulations argues in favor of the numerical method used to describe the ejection of the gas mixture expelled from the bottleneck immediately after the cork popping process. Published under an exclusive license by AIP Publishing.

International audience; Creating a supersonic jet in the laboratory is both a challenging and an expensive task. The supersonic flow is sensitive to the shape of the wall bounding it because a shock could be developed at the sharp edges. Moreover, the growth of boundary layer, within and outside the nozzle, makes the design of a convergent-divergent nozzle a sophisticated work. The present work proposes an optimization algorithm that is believed to be efficient in constructing a nozzle contour to deliver a shock-free radially uniform flow at the exit plane. The steepest descent optimization technique is employed to obtain the shape with minimum radial velocity at the outlet, along with restriction on the inlet angle, i.e., the angle of divergence immediately downstream the throat. Three different ways of implementing the constraints are discussed and compared with the experimental results after fabricating the nozzle. The optimized nozzle shows a potential core of 7 throat diameters height at the nozzle exit and an axial extent of 28 throat diameters downstream the exit plane. Further, the nozzle appears to operate efficiently even after increasing the nominal total temperature by 25% or decreasing it by 50%.

The fluid flow analysis over a cambered airfoil having three different cavity locations on the suction surface is reported in this paper. The Elliptical cavity is created at LE, MC, and TE along chordwise locations from the leading to trailing edge. In this regard, the steady simulation is carried out in the Fluent at Reynolds number of 105 based on their chord length. The lift and drag characteristics for clean and cavities airfoil are investigated at different angles of attack. For the clean airfoil, the stall point is observed at 18°. The presence of a cavity improves the stall and aerodynamic characteristics of airfoil. It has been seen that the lift and drag coefficients for pre-stalled or lower angles are nearly similar to clean and cavity at MC or TE positions. For the post-stall point, the improvement in the aerodynamic performance is seen for the cavity at MC or TE. The cavity placed at LE produces lower lift and higher drag characteristics against other configuration models. The overall cavity effect for the flow around the airfoil is that it creates vortices, thereby re-energizes the slower moving boundary layer and delays the flow separation in the downstream direction. The outcomes of this analysis are suggested that the cavity at a position before the mid chord from the leading edge does not improve the performance of the airfoil. Though vortex is formed in the confined spaces but it is unable to reattach the flow towards the downstream direction of an airfoil.

Vortex shedding phenomenon leads to a number of different features such as flow induced vibrations, fluid mixing, heat transfer and noise generation. With respect to aerodynamic application, the intensity of vortex shedding and the size of vortices play an essential role in the generation of lift and drag forces on an airfoil. The flat plates are known to have a better lift-to-drag ratio than conventional airfoils at low Reynolds number (Re). A better understanding of the shedding behavior will help aerodynamicists to implement flat plates at low Re specific applications such as fixed-wing micro air vehicle (MAV). In the present study, the shedding of vortices in the wake of a flat plate at low incidence has been studied experimentally in a low-speed subsonic wind tunnel at a Re of 5 × 104. The velocity field in the wake of the plate is measured using a hot wire anemometer. These measurements are taken at specific points in the wake across the flow direction and above the suction side of the flat plate. The velocity field is found to oscillate with one dominant frequency of fluctuation. The Strouhal number (St), calculated from this frequency, is computed for different angles of attack (AoA). The shedding frequency of vortices from the trailing edge of the flat plate has a general tendency to increase with AoA. In this paper, the generation and subsequent shedding of leading edge and trailing edge vortices in the wake of a flat plate are discussed.