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This paper discusses the analysis performed on a supersonic ramjet engine inlet for flight in the atmosphere of Jupiter. Since the Jovian atmosphere lacks oxygen, the thrust will be generated by nuclear fission heating in the heat chamber. The first task to solve in the design in a ramjet engine is to design the supersonic inlet. The developed design methodology utilizes theoretical calculations and Computational Fluid Dynamics (CFD) simulations. The analytical model used to calculate the gas parameters in front of the heat chamber, and the CFD analysis, used to define the inlet geometry, are discussed. The results from the analytical model and CFD are compared and used for validation of the design approach. The calculated pressure losses and the mass flow allow the determination of important parameters required for the design of the aircraft, such as the reactor power, the thrust, the maximum mass, and the overall external dimensions.
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An effective method for detailed observation of the Solar System planets is the use of vehicles that can perform flight in their atmospheres, with the most promising of them being Flyers (aircraft for other planets atmospheres). Besides the advantage of probing the atmosphere directly, they have the ability to fly on selected direction and altitude, making them suitable for collecting information over large areas. Equipping the Flyer with nuclear propulsion will allow it to conduct flight for months without the need of combustible fuel or oxidizer to be carried on board. Among the planets of the Solar System and their satellites, Jupiter is a viable target for exploration, since it features thick atmosphere suitable for aerodynamic flight, there is no solid surface that can be contaminated after end of the mission, and the atmospheric data for designing a Flyer is readily available. This paper proposes a mathematical model for evaluating the thrust, the lift and the maximum allowable mass for horizontal steady flight as functions of the altitude and different heat chamber temperatures.
Shocks form the basis of our understanding for the density and velocity statistics of supersonic turbulent flows, such as those found in the cool interstellar medium (ISM). The variance of the density field, $sigma^2_{rho/rho_0}$, is of particular interest for molecular clouds (MCs), the birthplaces of stars in the Universe. The density variance may be used to infer underlying physical processes in an MC, and parameterises the star formation (SF) rate of a cloud. However, models for $sigma^2_{rho/rho_0}$ all share a common feature -- the variance is assumed to be isotropic. This assumption does not hold when a trans/sub-Alfvenic mean magnetic field, $vec{B}_0$, is present in the cloud, which observations suggest is relevant for some MCs. We develop an anisotropic model for $sigma_{rho/rho_0}^2$, using contributions from hydrodynamical and fast magnetosonic shocks that propagate orthogonal to each other. Our model predicts an upper bound for $sigma_{rho/rho_0}^2$ in the high Mach number $(mathcal{M})$ limit as small-scale density fluctuations become suppressed by the strong $vec{B}_0$. The model reduces to the isotropic $sigma_{rho/rho_0}^2-mathcal{M}$ relation in the hydrodynamical limit. To validate our model, we calculate $sigma_{rho/rho_0}^2$ from 12~high-resolution, three-dimensional, supersonic, sub-Alfvenic magnetohydrodynamical (MHD) turbulence simulations and find good agreement with our theory. We discuss how the two MHD shocks may be the bimodally oriented over-densities observed in some MCs and the implications for SF theory in the presence of a sub-Alfvenic $vec{B}_0$. By creating an anisotropic, supersonic density fluctuation model, this study paves the way for SF theory in the highly anisotropic regime of interstellar turbulence.
We investigate the clustering and dynamics of nano-sized particles (nano-dust) in high-resolution ($1024^3$) simulations of compressible isothermal hydrodynamic turbulence. It is well-established that large grains will decouple from a turbulent gas flow, while small grains will tend to trace the motion of the gas. We demonstrate that nano-sized grains may cluster in a turbulent flow (fractal small-scale clustering), which increases the local grain density by at least a factor of a few. In combination with the fact that nano-dust grains may be abundant in general, and the increased interaction rate due to turbulent motions, aggregation involving nano dust may have a rather high probability. Small-scale clustering will also affect extinction properties. As an example we present an extinction model based on silicates, graphite and metallic iron, assuming strong clustering of grain sizes in the nanometre range, could explain the extreme and rapidly varying ultraviolet extinction in the host of GRB 140506A.
VHF radar echoes from the valley region plasma irregularities, displaying ascending pattern, are often observed during the active phase of equatorial plasma bubble in the close vicinity of the geomagnetic equator and have been attributed to bubble-related fringe field effect. These irregularities however are not observed at a few degrees away from the equator. In this paper, we attempt to understand this contrasting observational result by comparing fringe field at the geomagnetic equator and low latitudes. We use parallel plate capacitor analogy of equatorial plasma bubble and choose a few capacitor configurations, consistent with commonly observed dimension and magnetic field-aligned property of plasma bubble, for computing fringe field. Results show that fringe field decreases significantly with decreasing altitude as expected. Further, fringe field decreases remarkably with latitude, which clearly indicates the role of magnetic field-aligned property of plasma bubble in reducing the magnitude of fringe field at low latitudes compared to that at the geomagnetic equator. The results are presented and discussed in the light of current understanding of plasma bubble-associated fringe field-induced plasma irregularities in the valley region.
Earths magnetotail region provides a unique environment to study plasma turbulence. We investigate the turbulence developed in an exhaust produced by magnetic reconnection at the terrestrial magnetotail region. Magnetic and velocity spectra show broad-band fluctuations corresponding to the inertial range, with Kolmorogov $-5/3$ scaling, indicative of a well developed turbulent cascade. We examine the mixed, third-order structure functions, and obtain a linear scaling in the inertial range. This linear scaling of the third-order structure functions implies a scale-invariant cascade of energy through the inertial range. A Politano-Pouquet third-order analysis gives an estimate of the incompressive energy transfer rate of $sim 10^{7}~mathrm{J,kg^{-1},s^{-1}}$. This is four orders of magnitude higher than the values typically measured in 1 AU solar wind, suggesting that the turbulence cascade plays an important role as a pathway of energy dissipation during reconnection events in the tail region.
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