High-resolution Jet Research Articles

High-Fidelity Simulation of the Light-to-Dense Stratification Transient in the HiRJET Facility

Density stratification in a large enclosure is a crucial phenomenon to heat transfer and sustainable passive heat removal of a sodium fast reactor during reactivity transients. However, engineering turbulence models were identified to have unsatisfactory performance in predicting propagation of a stratified front. Yet, the scarcity of high-resolution data for stratification hampers the development of models. To explor e applications of leveraging direct numerical simulation (DNS) data to support turbulence model development, this work conducted DNS using NekRS to study a long stratification transient in the High-Resolution Jet (HiRJET) experimental facility. This work considers an experiment run where light fluid is injected into a tank containing a denser fluid with a relative density difference of 1.5%. Formation of the stratified layer is identified as impingement of the buoyant jet promoting mixing of the two fluids. Based on the transient statistics, transport of the concentration can be characterized by regions with dominating effects of turbulent mixing, buoyant dissipation, and molecular diffusion, respectively, as moving away from the elevation of jet impingement. Concentration near the stratified front also exhibits oscillation at Brunt-Väisälä frequency. Preliminary validation of the simulation showed encouraging agreement of the concentration distribution with the reference experiment.

Validation of RANS-Based Turbulence Models Against High-Resolution Experiments and DNS for Buoyancy-Driven Flow with Stratified Fronts

To provide computational fluid dynamics (CFD)–grade experimental data for studying stratification, measurements on the High-Resolution Jet (HiRJet) facility at the University of Michigan have been conducted with density differences of 1.5 % and − 1.5 % , respectively. Fluid with a density different from the fluid initially present in the HiRJet tank was injected, and the propagation of the time-dependent density stratification was captured on a two-dimensional plane with the aid of the wire-mesh sensor technique for Reynolds numbers near 5000 and Richardson numbers near 0.29. Direct numerical simulations (DNSs) of the two cases have also been conducted to expand the multifidelity database. The novel experimental and DNS data were then used to assess the predictive capabilities of the Standard k − ε (SKE) model and the Reynolds Stress Transport (RST) model. In particular, the propagation speed and thickness of the stratification fronts were assessed by comparing the CFD results against the experimental and DNS data. It was found that the general trends of the stratified density fronts were well predicted by the CFD simulations; however, slight overprediction of the thickness of the stratification layer was found with the SKE model while the RST model gave a larger overprediction of the mixing. Examination of the turbulent statistics showed that the turbulent viscosity was largely overpredicted by the RST model compared to the SKE model.

Study of Stable Stratification in HiRJET Facility With Direct Numerical Simulation

Stable density stratification in a large enclosure could significantly hamper the effectiveness of natural convection cooling in pool-type liquid metal or gas-cooled advanced reactors. In addition, accurate prediction of stratified front behavior remains to be a challenging task for turbulence modeling. With the rapid growth of high-performance-computing capabilities in recent years, conducting high-fidelity simulations for a large-timescale transient has become more affordable and hence a valuable data source to support turbulence modeling as well as to gain further physical insights. In this work, direct numerical simulation is performed at experiment-consistent conditions to simulate the density stratification transient High-Resolution Jet (HiRJET) facility. Specifically, we focus on the case where an injected aqueous sugar solution has 1.5% density higher than that in the enclosure. In the early stage of the transient, the impingement of the denser jet to the bottom surface of the enclosure promoted turbulent mixing locally. This rendered the establishment of the mixture layer, formation and swift upward propagation of the stratified front, and elevation with (locally) the highest vertical concentration gradient. As the front rose, the diminishing turbulent mass flux slowed down the propagation, and a larger vertical concentration gradient was established. In this stage, both the velocity and the concentration scalar showed large-timescale fluctuation behavior around the stratified front. For the concentration time signal, the characteristic frequency in the power spectral density was found to agree well with the Brunt-Väisällä frequency. The preliminary validation endeavor showed that the stratified front location and the corresponding concentration gradient magnitude in the simulation agreed well with the experiment data. Further validation will mainly revolve around benchmarking against high-resolution density measurement and high-order flow statistics.

Understanding the high-resolution spectral signature of the N2-H2O van der Waals complex in the 2OH stretch region.

We present the observation of the N2-H2O van der Waals complex in the 2OH stretch overtone region. The high-resolution jet cooled spectra were measured using a sensitive continuous wave cavity ringdown spectrometer. Several bands were observed and vibrationally assigned in terms of ν1, ν2, and ν3, the vibrational quantum numbers of the isolated H2O molecule, as (ν1'ν2'ν3')←(ν1″ν2″ν3″)=(200)←(000) and (101) ← (000). A combination band involving the excitation of the in-plane bending motion of N2 and the (101) vibration of water is also reported. The spectra were analyzed using a set of four asymmetric top rotors, each associated with a nuclear spin isomer. Several local perturbations of the (101) vibrational state were observed. These perturbations were assigned to the presence of the nearby (200) vibrational state and to the combination of (200) with intermolecular modes.

Multiscale Analysis of the Instantaneous Eccentricity Oscillations of the Planets of the Solar System from 13 000 BC to 17 000 AD

The high-resolution Jet Propulsion Laboratory DE431 and DE432 planetary ephemeris are used to evaluate the instantaneous eccentricity functions of the orbits of the planets of the solar system from 13 000 BC to 17 000 AD at different time scales. Spectral analyses are performed to determine the frequencies and the amplitudes of the detected perturbations from 0.1-year to 10 000-year periods. Taken as contiguous pairs (Mercury-Venus, Earth-Mars, Jupiter-Saturn, and Uranus-Neptune), we found anti-phase patterns between contiguous planets at specific time scales (30 000 years): namely, the eccentricity of one planet increases while the other decreases. Venus and Earth instead appear in phase. However, on shorter time scales the phase coupling becomes more complex and irregular. Yet, Jupiter and Saturn present a π/2 phase coupling at the 1000-year scale. Periodogram analysis of the planetary eccentricity functions shows several fast fluctuations whose magnitudes indicate the strength of their mutual interactions where the Jovian planets significantly perturb the orbits of the inner planets. Besides, the wavelet power spectrum and wavelet squared coherence spectrum analyses are adopted to examine the relationships in time-frequency space between the eccentricity functions of each couple of terrestrial and Jovian planets. The analysis reveals the complexity and the evolution of the gravitational couplings perturbing each other planetary orbits. In some cases and for specific frequencies, this analysis technique also led to the discovery that the coherence phase can rotate clockwise or anticlockwise. The eccentricity function of the orbit of Jupiter presents large oscillations with periods of about 60 and 900- 960 years, mostly due to the interaction with Saturn. These oscillations also correspond to oscillations found in several geophysical records. The eccentricity functions of Uranus and Neptune are characterized by a large 4300-year oscillation. The eccentricity function of Pluto is characterized by a large nearly 20 000-year modulation.

High resolution experiments of velocity and concentration fluctuations in a jet flow

In this paper we present a novel experimental technique aimed at the simultaneous measurement of velocity and scalar fluctuations with high spatial and time resolution. Measurements have been performed using wire-mesh sensors in combination with Stereo Particle Image Velocimetry (SPIV) to achieve synchronized measurements of both velocity and scalar fluctuations, and therefore of the turbulent fluxes uj′φ′‾. The proof-of-concept of this measurement technique was obtained on a jet flow experimental facility HiRJet (High Resolution Jet) developed and built in the Experimental and Computational Multiphase Flow (ECMF) laboratory at the University of Michigan. Acquired experimental data indicates a high temporal resolution of proposed technique and capabilities of achieving a high level of synchronization which is confirmed by cross-correlation between wire-mesh and SPIV signals.

Mechanisms, Capabilities, and Applications of High‐Resolution Electrohydrodynamic Jet Printing

This review gives an overview of techniques used for high-resolution jet printing that rely on electrohydrodynamically induced flows. Such methods enable the direct, additive patterning of materials with a resolution that can extend below 100 nm to provide unique opportunities not only in scientific studies but also in a range of applications that includes printed electronics, tissue engineering, and photonic and plasmonic devices. Following a brief historical perspective, this review presents descriptions of the underlying processes involved in the formation of liquid cones and jets to establish critical factors in the printing process. Different printing systems that share similar principles are then described, along with key advances that have been made in the last decade. Capabilities in terms of printable materials and levels of resolution are reviewed, with a strong emphasis on areas of potential application.

HYPERSONIC BUCKSHOT: ASTROPHYSICAL JETS AS HETEROGENEOUS COLLIMATED PLASMOIDS

Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma traveling at hypersonic velocities. Structure within jet beams is often attributed to periodic or ``pulsed'' variations of conditions at the jet source. Simulations based on this scenario result in knots extending across the jet diameter. Observations and recent high energy density laboratory experiments shed new light on structures below this scale and indicate they may be important for understanding the fundamentals of jet dynamics. In this paper we offer an alternative to ``pulsed'' models of protostellar jets. Using direct numerical simulations we explore the possibility that jets are chains of sub-radial clumps propagating through a moving inter-clump medium. Our models explore an idealization of this scenario by injecting small ($r<r_{jet}$), dense ($\rho>\rho_{jet}$) spheres embedded in an otherwise smooth inter-clump jet flow. The spheres are initialized with velocities differing from the jet velocity by $\sim15$%. We find the consequences of shifting from homogeneous to heterogeneous flows are significant as clumps interact with each other and with the inter-clump medium in a variety of ways. Structures which mimic what is expected from pulsed-jet models can form, as can previously unseen ``sub-radial'' behaviors including backward facing bow shocks and off-axis working surfaces. While these small-scale structures have not been seen before in simulation studies, they are found in high resolution jet observations. We discuss implications of our simulations for the interpretation of protostellar jets with regard to characterization of knots by a ``lifetime'' or ``velocity history'' approach as well as linking observed structures with central engines which produce the jets.

Source location prediction of subsonic isothermal jet flows

The location of jet noise sources is a far from trivial problem that is of great importance for both understanding the noise production and radiation mechanisms and also for finding new jet noise reduction strategies. This paper presents comparisons of theoretical results with data for a number of jets. The theory used is based on the MGBK method but including a novel time scale based on the rate of energy transfer through the turbulent cascade. This new technique has been shown to give a number of advantages over existing models. The experimental results were obtained using the Polar Correlation Technique and were made at QinetiQ's Jet Noise Facility in the UK as part of the EU FP6 programme CoJeN. The high resolution jet noise images resulted from using a 64 microphone polar arc array set at two reference angles, namely 60 and 90 degrees to the jet axis. Comparisons with experimental data are made for coplanar and short cowl nozzles at different working conditions for predictions from different theoretical models. It is shown that the best agreement is obtained for the prediction methodology using the energy transfer rate timescale

Status and perspectives of detectors for experiments in HEP and related fields

Developments in the field of particle detectors are reviewed. Due to increasing physics demands, intrinsic detector limitations are becoming more and more of an issue, necessitating fundamental R&D. The example of high-resolution jet spectroscopy is chosen to illustrate this.

A High‐Resolution18O Isotope Study in the Vacuum Ultraviolet of theA1Π →X1Σ+4th Positive System of CO

High-resolution jet emission spectra of 12C18O in the 1380-1650 A region of the 4th positive bands, A1Π → X1Σ+, have been recorded photographically and have been reduced to upper-state term values for low to medium rotational quantum numbers in the 10 lowest vibrational levels of A1Π. The deperturbation of the A state from spin-orbit and rotation-electronic interactions with singlet and triplet Σ and Δ states has established the percentage 1Π character of the observed excited-state rovibronic levels. Dunham series expansion coefficients representing the deperturbed energies have also been determined.

High-resolution jet absorption study of nitrogen near 800 Å

The absorption spectrum of a supersonic free jet expansion of 14N2 in He has been photographically recorded in the region of the He continuum from ∼900 to 650 Å at reciprocal dispersions of 0.26 and 0.19 Å/mm. The low rotational temperature of close to 20 K results in a drastic simplification of the band structures compared to room or even liquid nitrogen temperature spectra. This report concentrates on the region from 835 to 790 Å and presents a survey of vibronic structures up to the first ionization potential. The Rydberg series of np complexes converging to v=0 in the ground state X 2Σ+g of the ion can be followed to n=39, the low-J rotational structure being clearly discernible in complexes as high as n=19. The application of multichannel quantum defect theory to a least-squares analysis of four series of rovibronic levels associated with the lowest rotational levels N+=0, 1, and 2 of the ion leads to very substantially reduced error limits for the ionization potential of 14N2 and reveals a number of irregularities that point to perturbations by Rydberg levels derived from A 2Πu of N+2.

Theoretical study of rotational fine structure in radiationless transitions

In the previous paper, it is shown that, at least for the case of formaldehyde, individually resolved rovibronic levels show a systematic dependence on J and K. Here a general theory is evolved which includes the effects of rotational energy gap, vibration–rotation coupling, and Coriolis effects on radiationless transitions. This general theory in contrast to existing pessimism, predicts a clear systematic variation of the radiationless rate for formaldehyde, in reasonable agreement with the experiment. This shows that these variations are the results of a general effect and not due to particular unsystematic resonances in this molecule. Hence, it is felt that this constitutes an interesting tiepoint between high-resolution jet measurements and a successful quantitative theory of a radiationless transition.