Computational simulation of Scramjet combustor at Mach 2.5 through two struts and with three angle of attack (α = −3°, α = 0° and α = 3°) have been presented and discussed in the present research ...article. Here the fuel which is injected through two struts is placed parallel to the air stream. The geometry and model used here is slight modification of the DLR (German Aerospace Center) scramjet model. Steady two and three dimensional (2D and 3D) Reynolds-averaged Navier–stokes (RANS) simulation and SST k-ω turbulence model is used to predict the shock structure and combustion phenomenon inside the scramjet combustor. All the simulations are done by using ANSYS 14-FLUENT code. Eddy dissipation along with finite rate chemistry model is used as combustion model for the present geometry because of the absence of Arrhenius calculations where turbulence controls the reaction rate. The effect of variation of angle of attack on the efficiency of two-strut scramjet combustor is also discussed in the research article. Present results show that the geometry with zero angle of attack i.e. α = 0°, have smallest ignition delay and it improves the performance of scramjet combustor as compared to geometry with α = −3° and α = 3°. The combustion phenomena as well as efficiency is also found to be highest in case of geometry with α = 0°. In order to validate the results, the numerical data for single strut injection is compared with experimental result which is taken from the literature.
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•Effects of presence of two struts over single strut are presented.•Two-strut based scramjet combustor gives the possibility to enhance combustion.•Variation of angle of attack in Two-strut based scramjet combustor was investigated.•Flow field in two-strut is more prominently affected by combustion phenomenon.
ABSTRACT
A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based on 141 h of data obtained with the Low-Frequency Array (LOFAR). The analysis includes ...significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted power spectrum inference. Previously seen ‘excess power’ due to spectral structure in the gain solutions has markedly reduced but some excess power still remains with a spectral correlation distinct from thermal noise. This excess has a spectral coherence scale of 0.25–0.45 MHz and is partially correlated between nights, especially in the foreground wedge region. The correlation is stronger between nights covering similar local sidereal times. A best 2-σ upper limit of $\Delta ^2_{21} \lt (73)^2\, \mathrm{mK^2}$ at $k = 0.075\, \mathrm{h\, cMpc^{-1}}$ is found, an improvement by a factor ≈8 in power compared to the previously reported upper limit. The remaining excess power could be due to residual foreground emission from sources or diffuse emission far away from the phase centre, polarization leakage, chromatic calibration errors, ionosphere, or low-level radiofrequency interference. We discuss future improvements to the signal processing chain that can further reduce or even eliminate these causes of excess power.
•Scramjet internal flow field in investigated for the basic and a novel strut fuel injector.•The turbulence development and its effect concerning strut design has been evaluated.•The effects of ...various shock waves and their reflections on simple and wavy wall double struts have been studied.•The rate of reaction was used to assess the combustion rate in relation to strut design.•It has been discovered that the wavy wall double strut have a significant effect on fuel and air mixing enhancement.
The demand for the enhancement of scramjet performance is increasing worldwide due to its tremendous and upcoming applications. The major challenge in scramjet engines is the mixing of fuel and air and succeeding combustion at supersonic speed. In a scramjet combustor flow field, the development of high turbulence (flow disturbance), shear-mixing layer, and oblique shock waves are the key factors to magnify the mixing efficiency of fuel and air at the significantly less resident time of air in the combustion chamber. Based on these techniques, an innovative strut fuel injector with a wavy wall surface and double strut has been investigated for possible mixing enhancement of fuel and air. These results are compared with the basic single wedge strut available in the open literature to identify the performance improvement. The computational geometries are modeled with Reynolds-averaged Navier Stokes equations, SST k-ω model, and global one-step reaction mechanism. All the flow modeling has been solved with finite volume and a second ordered upwind discretization scheme. The evaluation of scramjet internal flow structure and numerical results found that the double strut with a wavy-wall shape improved the mixing efficiency and combustion phenomenon significantly. The mixing and combustion profiles reveal that wavy-wall double strut generates an early complete mixing within a distance of 0.17 m with increased mixing and combustion efficiency of 18% and 20%, respectively.
We report Langmuir–Blodgett (LB) films of molybdenum disulphide (MoS2) and gold nanoparticles (AuNP) composite being utilized as a biosensing platform for dengue detection. The LB films of the ...MoS2–AuNP composite have been transferred from the air-water interface to the indium tin oxide-coated glass substrate under optimized conditions. Further, antibodies specific to dengue NS1 antigen were immobilized onto these LB films. The fabricated immunosensor has been explored for NS1 antigen detection in standard samples as well as in spiked sera samples using electrochemical impedance spectroscopy. The NS1 antigen is present in the blood of infected persons from day one of the onset of clinical symptoms in primary dengue infection. The limit of detection for the standard and the spiked samples is found to be 1.67 and 1.19 ng mL–1, respectively, which is suitable for clinical applications, as NS1 antigen levels in patient’s sera range from 0.04 to 2 μg mL–1 in primary infection and from 0.01 to 2 μg mL–1 in secondary infection.
The multi-strut injector is one of the most favourable perspectives for the mixing improvement in between the hydrogen and the high-speed air, and its parametric investigation has drawn an increasing ...attention among the researchers. Hence the flow-field aspects of a particular multi-strut based scramjet combustor have been investigated numerically with the addition of four wall injectors and at the same time, the influence of combination of different strut as well as wall injector scheme on the performance of multi-strut scramjet engine has also been explored. Moreover, the current computational approach has been validated against the experimental data present in the open literature in case of single strut scramjet engine. The attained results reveal that the collaboration of multi-strut along with 2 wall injectors' improves the efficiency of scramjet as compared to other multi-strut + wall injection scheme as this combination achieve higher penetration height which will boost to a wider temperature and robust combustion area adjacent to the wall. Again, the appearance of extra H2 in the separated flow region precisely ahead of the wall injection region is mainly reasonable for the abrupt decrease in the mixing as well combustion efficiency plot in all the multi-strut + wall injection strategy.
•Flow-phenomena in multi-strut + wall scramjet combustor were explored numerically.•Validations are performed using SST k-ω turbulence model.•The collaboration of multi-strut with 2 wall injectors' yields better air-H2 mixing.•Near the wall injection location, sudden decrease in combustion efficiency is noticed.•Wall injectors' have significant impact on the performance of scramjet combustor.
The two equation standard k–ɛ turbulence model and the two-dimensional compressible Reynolds-Averaged Navier–Stokes (RANS) equations have been used to computationally simulate the double cavity ...scramjet combustor. Here all the simulations are performed by using ANSYS 14-FLUENT code. At the same time, the validation of the present numerical simulation for double cavity has been performed by comparing its result with the available experimental data which is in accordance with the literature. The results are in good agreement with the schlieren image and the pressure distribution curve obtained experimentally. However, the pressure distribution curve obtained numerically is under-predicted in 5 locations by numerical calculation. Further, investigations on the variations of the effects of the length-to-depth ratio of cavity and Mach number on the combustion characteristics has been carried out. The present results show that there is an optimal length-to-depth ratio for the cavity for which the performance of combustor significantly improves and also efficient combustion takes place within the combustor region. Also, the shifting of the location of incident oblique shock took place in the downstream of the H2 inlet when the Mach number value increases. But after achieving a critical Mach number range of 2–2.5, the further increase in Mach number results in lower combustion efficiency which may deteriorate the performance of combustor.
•Mixing and combustion phenomena in a double-cavity combustor were explored numerically.•k–ɛ Turbulence model captures the shock waves and combustion distinctly and clearly.•There exists an optimal L/D ratio for achieving efficient combustion confined to the combustor region.•The combustion occurs more strongly and completely in the Mach number range of 2–2.5.
Relativistic millicharged particles (χq) have been proposed in various extensions to the standard model of particle physics. We consider the scenarios where they are produced at nuclear reactor core ...and via interactions of cosmic rays with the Earth’s atmosphere. Millicharged particles could also be candidates for dark matter and become relativistic through acceleration by supernova explosion shock waves. The atomic ionization cross section of χq with matter are derived with the equivalent photon approximation. Smoking-gun signatures with significant enhancement in the differential cross section are identified. New limits on the mass and charge of χq are derived, using data taken with a point-contact germanium detector with 500 g mass functioning at an energy threshold of 300 eV at the Kuo-Sheng Reactor Neutrino Laboratory.
The performance of the solar air collector is experimentally investigated at the climate of North Eastern India. Various governing parameters considered for the present investigation are collector ...tilt angles (30⁰, 45⁰, and 60°), single and double glazing, mass flow rate (0.0039–0.0118 kg/s) and two different absorber plates (plain and corrugated). Results reveal that double glazing absorber plate always gives better performance both energy and exergy point of view, because of reduction of top loses. Increase in mass flow rate of air enhances the energy efficiency. An overall increment of the efficiency with the increase of mass flow rate and number of glazing is as high as 10.35–17.42%. Use of corrugated plate enhances the energy efficiency by 14%, because of improved turbulence effect and increment of the heat transfer area. The maximum enhancement of exergy efficiency for double glazing collector is 6.867% for mass flow rate 0.0118 kg/s compared to single glazing collector. Corrugated absorber plate show 30Pa higher pressure drop than plain absorber plate. Thermo-hydraulic efficiency is found to deviate by almost 6.35% from the corresponding thermal efficiency. Mass flow rate of air in the range of 0.0078–0.0094 kg/s is found to yield qualitative heat transfer.
•Comparison of flat and corrugated plate solar air collector is presented.•Double glazing reduces losses and increase the thermal efficiency by 6.87%.•Increase in mass flow rate by 3 times results in 6%increase of efficiency.•Corrugated plate provides 14% higher efficiency than flat plate collector.•Mass flow rate of air enhances energy efficiency and reduce exergetic efficiency.
This paper mainly focuses on the influence of transverse magnetic field as well as thermal radiation on three-dimensional free convective flow of nanofluid over a linear stretching sheet. One ...remarkable aspect of this study is that a new micro-convection model namely Patel model has been introduced in view of enhancement of thermal conductivity and hence more heat transfer capability of nanofluid. The non-linear partial differential equations have been converted into strong non-linear ordinary differential equations by employing suitable transformations and these transformed equations are solved by Runga-Kutta method of fourth order along with Shooting technique as well as Secant method for better approximation. From this study, it is found that the presence of magnetic field slows down the fluid motion while it enhances the fluid temperature leading to a reduction in heat transfer rate from the surface. It is also found that enhancing thermal radiation parameter causes a reduction in heat transfer rate.
Fig. 1. Schematic representation of three dimensional permeable stretching sheet under the effects of transverse magnetic field. Display omitted
•This paper investigates the 3D steady flow of nanofluids through permeable stretching sheet.•This model is applicable in controlling the cooling rate which is imperative for many process industries.•Velocity profile enhances and temperature profile reduces with increasing the buoyancy effects.•Thermal boundary layer thickness elaborates for high value of radiation parameter and Peclet number.•Isotherms converge to the origin for all values of nanoparticle volume fraction.
The detonation combustion phenomenon is supersonic combustion process and follows on thermal explosion in combustor. Deflagration to detonation transition occurs in detonation tube due to pressure ...oscillation in PDE combustor, which is driven by acoustic combustion phenomena in detonation tube. As this combustion process has great significance role for future propulsion system, the present objective is to investigate the effect of modify ejector having half angles of
α
= (− 4°, 0°, + 4°) on detonation combustion wave propagation regime. Further the propulsion thrust of liquid kerosene and gaseous hydrogen–air mixture are also analyzed. This numerical simulation has been analyzed by LES turbulence model for DDT and shock wave pressure oscillation in pulse detonation combustor at Fluent based CFD plat form. The one-step irreversible chemical kinetics model analyzes the details exothermic chemical reaction mechanism inside the combustor. However, the shrouded ejector with taper angle of
α
= +4° performed the strong starting vortex generation and shortest possible time of 0.032 s for fully developed detonation wave. The simulation results also shows that thrust force augmentation of hydrogen–air mixture is greater compared to combustion process of liquid kerosene–air mixture with significant magnitude of 38 N. Although kerosene–air mixture produces less pollutant number but the propagation flame velocity is 2550 m s
−1
for hydrogen/air mixture, which is near about
C
–
J
velocity and comparatively higher than kerosene/air combustion process.
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