搜索结果：Supersonic

The accurate prediction of compressible high-speed jet flows remains a critical challenge in computational aerodynamics due to the strong coupling between shock waves, expansion fans, shear-layer turbulence, and mixing processes downstream of nozzles. While density-based (DB) solvers are conventionally used for supersonic and transonic regimes, pressure-based (PB) solvers have recently gained attention for their reduced computational cost; however, their suitability for underexpanded jet modeling remains insufficiently explored. This study provides a systematic evaluation of PB and DB solvers available in ANSYS Fluent for simulating compressible flow discharged from an axisymmetric convergent nozzle over a range of nozzle pressure ratios (PR&#x2009;=&#x2009;1.92&#x2013;5). Experimental Schlieren flow visualization was conducted using a custom optical setup to qualitatively assess shock structures and validate near-field flow features. Numerical simulations employed compressible Reynolds Average Navier-Stokes (RANS) formulations with a standard k&#x2013;&#x3b5; turbulence model, structured quadrilateral meshes, and consistent boundary conditions for both solvers. Validation against published measurements demonstrated that both solvers accurately predict Mach disk formation and the streamwise location of the first shock cell, with a maximum deviation of 4.5% in peak Mach number. For PR&#x2009;>&#x2009;1.92, both solvers captured the characteristic diamond shock pattern and the progressive increase in shock cell strength and spacing; the first shock cell occurred at X/De&#x2009;&#x2248;&#x2009;1.09, 1.57, and 2 for PR&#x2009;=&#x2009;3, 4, and 5, respectively. While PB and DB solvers exhibited comparable performance in resolving centerline Mach number and pressure oscillations, the DB solver overpredicted turbulent kinetic energy in the far-field subsonic region due to its known sensitivity at low Mach numbers. Discharge coefficients predicted by both solvers showed close agreement, with differences&#x2009;<&#x2009;0.2%. Results demonstrate that the PB solver, despite being traditionally associated with incompressible and low-speed flows, can reliably model underexpanded supersonic jets at significantly reduced numerical cost. The findings provide practical guidance for CFD practitioners seeking cost-effective tools for compressible nozzle flow modeling and contribute to broader discussions on solver strategy selection for high-speed aerodynamic simulations.

While supersonic cooling revolutionized spectroscopic studies of neutral molecules, cooling molecular ions remains far more challenging, especially for ions generated from electrospray ionization (ESI). Cryogenic cooling has been transformative, particularly for ESI-produced ions, by enabling intrinsically cold spectroscopic interrogation of solution-phase species transferred into the gas phase. This perspective focuses on cryogenic photoelectron spectroscopy (PES) and photodetachment spectroscopy (PDS) of complex anions produced by ESI and cooled in a 3D Paul trap, a platform that has been widely adopted because of its relative simplicity and robust performance. We discuss the technical evolution from the initial ESI-PES for solution species to cryogenic ESI-PES with a magnetic-bottle analyzer, and the current cryogenic PDS and high-resolution photoelectron imaging. We emphasize significant advances enabled by coupling the cryogenic 3D Paul trap first to ESI sources-highlighting studies of temperature-dependent phenomena, solution-phase chemistry in the gas phase, nonvalence excited states, vibrationally induced autodetachment, and resonant PES-and more recently to a laser-vaporization cluster source, demonstrating more effective vibrational cooling for cluster ions than supersonic expansion.

This article challenges standard accounts about technological disillusionment in the late 1960s and 1970s that locate opposition to new technologies primarily in environmentalists and the "New Left" or declining trust in expertise. Looking at the critics of the Anglo-French supersonic jet Concorde in Britain, it argues for the importance of political economy to understand the demise of techno-nationalism. Drawing on debates within government, Parliament, the press, and extraparliamentary opposition, the article demonstrates that actually economic and industrial critiques-often voiced privately within the state-were decisive. What united these ideologically diverse opponents was not environmentalism but a shared wariness of state power and the conviction that official deception sustained a looming commercial disaster. It also shows how a lack of transparency and powerful state propaganda masked Concorde's effective cancellation, which demonstrated a deep rejection of techno-nationalism. The conclusion reflects on why Britain sustained its supersonic commitment longer than the United States.

Shock waves, disturbances that propagate with supersonic velocity in a fluid, are prevalent in nature and across nearly all natural sciences. They find diverse applications in fields such as medicine, aerospace engineering and physical chemistry, where experiments are conducted mostly in macroscopic tubes with an inner diameter ranging from more than 1 mm up to the meter scale. While the theoretical framework for macroscopic shock waves is well-established, the behavior of shock waves in capillaries with diameters in the micrometer range-referred to as "micro-shock waves"-remains largely unexplored. This paper presents novel experimental investigations on the collision of shock waves in micro-capillaries, a fundamental research that has never been done before. These investigations, involving both steady and unsteady drivers, are of significant importance for shock wave physics in general, especially given the limited research on unsteady shock wave collisions. Even more, they play a crucial role in the analysis of micro-shock waves, since they contribute to a more complete characterization of the post-shock region. With the growing interest in microfluidic devices, this research is also important to advance the understanding of supersonic flows at the microscale. Even in the application of high-repetition-rate laser sources, micro-shock wave physics is involved.

Engineering experience shows that in noise and vibration control for ships and aircraft, measures like stiffening can reduce vibration but may fail to lower radiated noise, as they disrupt structural continuity and create new radiation sources. This paper investigates the sub-critical frequency sound radiation from the boundaries of semi-infinite plates using analytical and discrete Fourier transform methods. A force-excited finite plate is also considered, generating its supersonic sound intensity map. Results demonstrate that the near- and far-field sound pressure and supersonic sound intensity manifest the radiation patterns of different boundary conditions as monopole, dipole, and quadruple pole patterns. At resonance, boundary acoustic radiation dominates in finite structures. Furthermore, as the plate size and frequency increase, the radiation differences among various boundary conditions converge to the results observed in semi-infinite plates. This study provides a mechanistic understanding of the relationship between vibration and sound radiation, offering valuable insights for controlling sound radiation in engineering applications.

This article outlines engineering challenges that were involved in the design innovations required to successfully deliver not one but two landers for Viking. The mission faced unique challenges such as dealing with Mars' thin atmosphere, managing entry heating, soft landing, and adhering to launch payload constraints. These necessitated the development of new technologies and designs, including a bio-shield, an aerodynamic aeroshell, a thermal protection system, a supersonic parachute, and a terminal descent propulsion system. The developments took no more than 8 years, but their legacy has lasted far longer and has enabled Mars lander mission successes for five decades. With the emerging emphasis on human missions to Mars, the challenges of landing larger payloads will require new innovations and approaches to entry, descent, and landing, which will represent a grand new challenge for scientists and engineers.

The screeching of peeling tape is a familiar albeit annoying sound. However, despite decades of study, its source has remained elusive. Herein we demonstrate that this sound is produced by a discrete train of weak shocks emanating from the fine fractures which travel supersonically with respect to the surrounding air, in the transverse direction within the detaching adhesive. Each sound pulse is generated when a fracture tip reaches the edge of the tape. We verify this using two microphones synchronized with clips from two simultaneous high-speed video cameras, one observing the fracture motions in the adhesive through the transparent substrate, while the other captures schlieren imaging of the shock fronts in the air.

The hydrogen-bonded complexes of phenol with the chiral molecule methyloxirane (MOx) have been studied under supersonic jet conditions by photoelectron circular dichroism (PECD) experiments based on a resonance-enhanced two-photon ionization scheme. Ionization of the achiral phenol moiety within the complex leads to a strong photoelectron circular dichroism signal, due to chirality induction from the methyloxirane. We observe and characterize two conformers of the complex by IR-UV spectroscopy. They show PECD of similar magnitude and opposite in sign, which is explained in terms of a pseudo-enantiomer relation between them due to the complexation with one or the other of the two lone electron pairs of the MOx oxygen atom, leading to opposite out-of-plane deformation of the phenol hydroxyl group. Chirality indicators are used to quantify the chirality of the wave function localized on phenol. It is therefore possible to differentiate two diasterotopic electron lone pairs by chiroptical spectroscopy in the gas phase.

Like most chiroptical spectroscopy techniques, photoelectron circular dichroism (PECD), that is, the forward-backward asymmetry in the angular distribution of the electron resulting from the ionization of a chiral molecule by a circularly polarized light, is very sensitive to structural changes, in particular conformational isomerism. Moreover, because of the large associated asymmetries (up to a few 10's of %), PECD is uniquely adapted to gas-phase studies of flexible chiral molecules and exists, for the case of valence-shell, in several variants relying upon one vaccum-ulraviolet (VUV) photon or multiple-photon ionization. We describe here recent advances in PECD spectroscopy that make this method conformer-selective. In addition to partial population selection in one-photon PECD, two-photon PECD resting on a resonance-enhanced ionization scheme allows complete conformer selection, as long as the studied system displays an electronic transition in the near UV. These experiments thus provide a direct connection between structures (conformations) and chirality (PECD), which both influence phenomena such as molecular recognition. The low temperature achieved under supersonic expansion conditions and the narrow-band nanosecond laser used allow deciphering conformers with very similar structures, like ring-inversion conformers or those related to a hydrogen bond, or even distinguishing the lone electron pairs in a diastereotopic molecule.

Interest in interstellar noble gas chemistry has been stimulated by the recent detection of ArH+ and HeH+ in a variety of astrophysical environments ranging from diffuse clouds to supernova remnants. In this context, it seems timely to explore or revisit chemical reactions involving noble gas ions, such reactions being an efficient way to form noble gas bearing molecules in the interstellar medium. The reaction of Ar+ ions with methane, CH4, and ethylene, C2H4, at low temperatures, i.e., 24.1 and 71.6&#xa0;K, was investigated in the laboratory with the help of a dedicated instrument combining a uniform supersonic flow reactor with a mass selective ion source. Computational flow dynamics and ion trajectory simulations were conducted to assess the thermalization of the ions in the flow. Ab initio and transition state theory calculations were employed to complement, at a microphysical scale, the interpretations derived from the macroscopic measurements of the Ar+ + CH4 and Ar+ + C2H4 reactions. The branching between the products is reasonably well explained by theoretical calculations.