Academic literature on the topic 'Supersonic flows'

We consider the Cauchy problem for a first-order differentialequation in a Banach space. The equation contains a small parameter in the highest derivative and a Fredholm operator perturbed by an operator addition on the right-hand side. Systems with small parameter in the highest derivative describe the motion of a viscous flow, the behavior of thin and flexible plates and shells, the process of a supersonic viscous gas flow around a blunt body, etc. The presence of a boundary layer phenomenon is revealed; in this case, even a small additive has a strong influence on the behavior of the solution. Asymptotic expansion of the solution in powers of small parameter is constructed by means of the Vasil’yeva- Vishik-Lyusternik method. Asymptotic property of the expansion is proved. To construct the regular part of the expansion, the equation decomposition method is used. It is consisted in a step-by-step transition to similar problems of decreasing dimensions.

Abstract We consider in this work the different possible stationary flows of a one dimensional quantum fluid in the mean-field regime. We focus on the supersonic regime where a transition from a time dependent flow to a stationary diffractive flow occurs at a given critical velocity.
We give nonperturbative results for this critical velocity in the presence of a localised obstacle of arbitrary size and strength. In addition, we discuss the existence of superfluid-like solution in the supersonic regime due to resonant transport and provide a complete map of the different regimes of stationary transport of a quantum fluid.

Abstract Radio-frequency (RF) inductively coupled plasma (ICP) torches using a supersonic nozzle have many industrial materials processing applications and have also been proposed as novel electrothermal plasma thrusters for space propulsion. The gas injection method in plasma torches plays an important role in both gas heating dynamics and overall discharge stabilization. Here, we investigate reverse vortex gas injection into a supersonic ICP torch for RF powers up to 1 kW, argon mass flow rates between 15-180 mg/s, and plasma torch pressures from 270 Pa to 50 kPa. In this configuration, gas is injected tangentially just upstream of the nozzle inlet. This produces a bidirectional vortex flow field where gas first spirals upwards along the outer edge of the plasma torch walls, before then reversing direction at the torch end and spiralling back down through the central plasma region towards the nozzle exit. Results are compared to a more conventional forward vortex configuration where gas is instead injected tangentially from the upstream end of the torch, and which forms a unidirectional vortex that spirals towards the downstream nozzle. While performance is similar for gas flows below 80 mg/s, we show that at higher mass flow rates both the effective torch stagnation temperature and thermal efficiency can be increased by almost 50% with reverse vortex injection. Considering that the measured RF antenna-plasma power transfer efficiency is similar for both configurations, this enhancement occurs because of the unique bidirectional vortex flow field which leads to reduced gas-wall heat losses and consequently an increased enthalpy flow leaving the torch.

Abstract Acoustic black holes are formed when a fluid flowing with subsonic velocities, accelerates and becomes supersonic. When the flow is directed from the subsonic to supersonic region, the surface on which the normal component of fluid velocity equals the local speed of sound acts as an acoustic horizon. This is because no acoustic perturbation from the supersonic region can cross it to reach the subsonic part of the fluid. One can show that if the fluid velocity is locally irrotational, the field equations for acoustic perturbations of the velocity potential are identical to that of a massless scalar field propagating in a black hole background. One, therefore, expects Hawking radiation in the form of a thermal spectrum of phonons. There have been numerous investigations of this possibility, theoretically, as well as experimentally, in systems ranging from cold atom systems to quark-gluon plasma formed in relativistic heavy-ion collisions. Here we investigate this possibility in the hydrodynamic flow of electrons. Resulting Hawking radiation in this case should be observable in terms of current fluctuations. Further, current fluctuations on both sides of the acoustic horizon should show correlations expected for pairs of Hawking particle.

The flow residence time in a scramjet combustor is of the order of a millisecond (10−3s). High energy density liquid fuels are the energy carriers of choice in scramjet engines, however liquid fuels must be atomized, evaporated and mixed before heat release by combustion can occur. Atomization, mixing and ignition require fnite time. Therefore it is important to study spray formation and its atomization in supersonic flows. Experiments are performed to study the spray formation from a water jet injected through a plain orifce atomizer with an exit diameter (d) of 1 mm, into a Mach 2.2 supersonic crossflow. High-speed shadowgraphy is performed using high-frequency nano-pulsed LASER as well as LED, to capture the local structures and spray features. The high-speed camera and nano-pulsed LASER is synchronized using a delay pulse generator. The pulse width of the LASER is kept at 8 and 14 ns, such that to freeze the spray features in time. The bow shock profles are observed to overlap between different momentum flux ratios (q) of the injected jet when shifted to the sonic point. The penetration height of the spray is evaluated using the upper spray boundary. The average spray trajectories are compared for three different momentum flux ratios. Wavelike disturbances are observed on the windward side of spray, which further develops into ligaments. Fundamental questions like ligament origin, speed and their breakup are addressed. The ligaments are present at spray boundary and observed to move with free stream flow near the injector. Further ligaments are tracked in successive shadowgraph images using cross-correlation technique to fnd their speed. The ligament speed is also compared for different momentum flux ratio and found to vary inversely with the momentum flux ratio. The wavelength associated with ligaments or surface waves is observed to increase linearly along the spray boundary irrespective of the momentum flux ratio. The ligament breakup is characterized using shear Weber number and wavelength is used as characteristic length scale. It is found that ligaments break due to shear from free stream flow. Small shocks (shocklets) are formed ahead of ligaments which are noted to increase the residence time. Shocklets also delay atomization of the ligaments.