Jet Misalignment Research Articles

Digital Twin for Vibration Monitoring of Pelton Units

Abstract The development of a digital twin to simulate the vibrational behaviour of a Pelton hydropower unit during startups offers significant potential for enhanced maintenance by detecting early warning signs of anomalies. The proposed methodology, combining high-frequency vibrational data acquisition with an offline digital twin to improve data interpretation, is applied in this study to a 15MW horizontal dual Pelton unit located in the Swiss Alps. The digital twin models fluid-structure interactions during startup with a combination of CFD simulations and transient FEM analysis, predicting the vibrational response of the unit. This numerical model allows investigating the effect of specific anomalous cases, such as jet misalignment, on the excited frequencies of the runner, enabling the creation of a library of frequency responses for predictive maintenance. Experimental modal analysis and in-situ vibration data acquisition validate the numerical model. Preliminary results show the effectiveness of this approach in understanding and predicting the vibrational behaviour of a Pelton unit during startup. Further refinement is needed, especially in conducting transient modal analysis of the full runner and shaft line, which will be conducted as part of the Horizon ReHydro project.

Signatures of feedback in the spectacular extended emission region of NGC 5972

ABSTRACT We present Chandra X-ray Observatory observations and Space Telescope Imaging Spectrograph spectra of NGC 5972, one of the 19 ‘Voorwerpjes’ galaxies. This galaxy contains an extended emission-line region (EELR) and an arcsecond scale nuclear bubble. NGC 5972 is a faded active galactic nucleus (AGN), with EELR luminosity suggesting a 2.1 dex decrease in Lbol in the last ∼5 × 104 yr. We investigate the role of AGN feedback in exciting the EELR and bubble given the long-term variability and potential accretion state changes. We detect broad-band (0.3–8 keV) X-ray emission in the near-nuclear regions, coincident with the [O iii] bubble, as well as diffuse soft X-ray emission coincident with the EELR. The soft nuclear (0.5–1.5 keV) emission is spatially extended and the spectra are consistent with two apec thermal populations (∼0.80 and ∼0.10 keV). We find a bubble age >2.2 Myr, suggesting formation before the current variability. We find evidence for efficient feedback with $P_{\textrm {kin}}/L_{\textrm {bol}}\sim 0.8~{{\ \rm per\ cent}}$, which may be overestimated given the recent Lbol variation. [O iii] kinematics show a 300 km s−1 high-ionization velocity consistent with disturbed rotation or potentially the line-of-sight component of a ∼780 km s−1 thermal X-ray outflow capable of driving strong shocks to photoionize the precursor material. We explore possibilities to explain the overall jet, radio lobe and EELR misalignment including evidence for a double supermassive black hole which could support a complex misaligned system.

3D hydrodynamic simulations of large-scale precessing jets: radio morphology

ABSTRACT The prospect of relativistic jets exhibiting complex morphologies as a consequence of geodetic precession has long been hypothesized. We have carried out a 3D hydrodynamics simulation study varying the precession cone angle, jet injection speed, and number of turns per simulation time. Using proxies for the radio emission we project the sources with different inclinations to the line of sight to the observer. We find that a number of different precession combinations result in characteristic ‘X’ shaped sources which are frequently observed in radio data, and some precessing jet morphologies may mimic the morphological signatures of restarting radio sources. We look at jets ranging in scale from tens to hundreds of kiloparsecs and develop tools for identifying known precession indicators of point symmetry, curvature, and jet misalignment from the lobe axis and show that, based on our simulation sample of precessing and non-precessing jets, a radio source that displays any of these indicators has a 98 per cent chance of being a precessing source.

Observational signatures of disc and jet misalignment in images of accreting black holes

ABSTRACT Black hole (BH) accretion is one of nature’s most efficient energy extraction processes. When gas falls in, a significant fraction of its gravitational binding energy is either converted into radiation or flows outwards in the form of BH-driven jets and disc-driven winds. Recently, the Event Horizon Telescope (EHT), an Earth-sized submillimetre radio interferometer, captured the first images of M87’s BH. These images were analysed and interpreted using general relativistic magnetohydrodynamics (GRMHD) models of accretion discs with rotation axes aligned with the BH spin axis. However, since infalling gas is often insensitive to the BH spin direction, misalignment between accretion disc and BH spin may be a common occurrence in nature. In this work, we use the general relativistic radiative transfer code bhoss to calculate the first synthetic radio images of (highly) tilted disc/jet models generated by our GPU-accelerated GRMHD code h-amr . While the tilt does not have a noticeable effect on the system dynamics beyond a few tens of gravitational radii from the BH, the warping of the disc and jet can imprint observable signatures in EHT images on smaller scales. Comparing the images from our GRMHD models to the 43 and 230 GHz EHT images of M87, we find that M87 may feature a tilted disc/jet system. Further, tilted discs and jets display significant time variability in the 230 GHz flux that can be further tested by longer-duration EHT observations of M87.

Flow regimes and mixing characteristics in non-aligned T-jets reactors

Flow regimes and mixing characteristics in non-aligned T-jets reactors were investigated by Planar Laser Induced Fluorescence (PLIF) at 30 ≤ Re ≤ 400. The misalignment of inlet jets in non-aligned T-jets reactors leads to a steady engulfment flow at low Reynolds numbers. With the increase of Re, the unsteady engulfment flows with different oscillation behaviors occur. Unlike the vortex-merging oscillation in reactors of ws/h = 0 and 0.5 (ws and h are the misalignment degree and height of inlet jets), an S-shaped self-excited oscillation is identified in reactor of ws/h = 1. Mixing in non-aligned T-jets reactors is quantified by time-averaged Intensity of Segregation (IOS) and the mixing mechanism is revealed. The mixing is significantly enhanced in non-aligned T-jets reactors at low Re due to the earlier emergence of the steady engulfment flow. Both the vortex-merging oscillation in reactors of ws/h = 0 and 0.5 and the S-shaped self-excited oscillation in reactor of ws/h = 1 contribute to the mixing enhancement.

Effect of pre-impingement length and misalignment in the hydrodynamics of multijet impingement atomization

The multijet impingement atomization strategy is proposed as a competitive one in designing atomizers with relatively simple geometries, producing sprays from the impact of multiple jets at low-flow rate conditions (<1.5 l/min). Most theoretical studies have been made for the spray produced by the impact of two jets. However, there are two important geometric issues related with the atomizer design, scarcely approached in the literature, which are the pre-impingement length of jets before impact and jet misalignment. This work analyses the influence of these parameters on the structure of the liquid sheet as well as on drop size. First, the liquid sheet structure has two hydrodynamic regimes: closed-rim and open-rim. The results evidence that higher pre-jet-impingement distances influence only the open-rim regime, namely, producing shorter liquid sheet breakup lengths, smaller drop sizes, and more droplets. The jet misalignment elongates the liquid sheet in the closed-rim regime, and anticipates breakup in the open-rim regime.

Impulse (Turgo and Pelton) turbine performance characteristics and their impact on pico-hydro installations

Pico-hydropower is a viable technology that can be integrated into a decentralized, off-grid approach to rural electrification in regions that currently have only limited access to electricity. The Turgo turbine is classified as an impulse turbine, similar to the Pelton wheel, often used in pico-hydro systems. Both offer high efficiency for a broad range of site conditions, but the primary difference is that the Turgo can handle significantly higher water flow rates, allowing for efficient operation in lower head ranges and thus potentially expanding the geographic viability. Published data on Turgo operating performance are limited; despite the differences, discussion thereof in design manuals is generally lumped in with the discussion of Pelton wheels. In this study, a laboratory-scale test fixture was constructed to test the operating performance characteristics of impulse turbines. Tests were carried out to determine the effect on turbine efficiency of variations in speed ratio and jet misalignment on two Turgo turbines. The results were compared to similar tests in the same fixture on a Pelton turbine. Under the best conditions, the Turgo turbine efficiency was observed to be over 80% at a speed ratio of approximately 0.46, which is quite good for pico-hydro-scale turbines. Peak efficiencies for both the Pelton and the Turgo turbines occurred at lower than theoretical ideal speed ratios based on a momentum balance; the reduction in speed ratio at which peak efficiency occurs is likely caused by inefficiencies in the turbine. Tests of jet misalignment showed that moving the jet to the inside or outside edge of the turbine blades caused a drop in Turgo efficiency of 10–20% and reduced the optimal speed ratio by 0.03 (6.5%). Radial misalignment had a significant adverse impact on both Turgo and Pelton turbines, however, angular misalignment of the jet is more of a concern for the Turgo turbine. The results stress the importance of proper system design and installation, and increase the knowledge base regarding Turgo turbine performance that can lead to better practical implementation in pico-hydro systems.

ANATOMY OF HELICAL EXTRAGALACTIC JETS: THE CASE OF S5 0836+710

Helical structures are common in extragalactic jets. They are usually attributed in the literature to periodical phenomena in the source (e.g., precession). In this work, we use VLBI data of the radio-jet in the quasar S5 0836+710 and hypothesize that the ridge-line of helical jets like this corresponds to a pressure maximum in the jet and assume that the helically twisted pressure maximum is the result of a helical wave pattern. For our study, we use observations of the jet in S5 0836+710 at different frequencies and epochs. The results show that the structures observed are physical and not generated artificially by the observing arrays. Our hypothesis that the observed intensity ridge-line can correspond to a helically twisted pressure maximum is confirmed by our observational tests. This interpretation allows us to explain jet misalignment between parsec and kiloparsec scales when the viewing angle is small, and also brings us to the conclusion that high-frequency observations may show only a small region of the jet flow concentrated around the maximum pressure ridge-line observed at low frequencies. Our work provides a potential explanation for the apparent transversal superluminal speeds observed in several extragalactic jets by means of transversal shift of an apparent core position with time.

Robust Fault Diagnosis strategies for Spacecraft Application to LISA Pathfinder experiment

AbstractThis paper presents research activities conjointly led by EADS Astrium Satellites and the European Space Agency on innovative and robust health monitoring system for the next generation of spacecraft. Two robust FDI schemes are presented to detect and isolate faults affecting the micro-Newton colloidal thrust system of the LISA Pathfinder spacecraft. The first FDI strategy is based on a bank of eight H∞/H− residual generators designed according to the Generalized Observer Strategy whereas the second strategy consists of Kalman-based projected observers. The efficiency of the proposed FDI techniques is assessed through non linear simulations performed under realistic conditions (physical parameter uncertainties, disturbances, measurement noises, measurement delays, thruster jet misalignment,…). The results are quite encouraging, illustrate the effectiveness of the proposed techniques and suggest that the solutions could be practical viable candidates.

The Radio Structure of High-Energy–Peaked BL Lacertae Objects

We present VLA and first-epoch VLBA observations that are part of a program to study the parsec-scale radio structure of a sample of fifteen high-energy-peaked BL Lacs (HBLs). The sample was chosen to span the range of logarithmic X-ray to radio flux ratios observed in HBLs. As this is only the first epoch of observations, proper motions of jet components are not yet available; thus we consider only the structure and alignment of the parsec- and kiloparsec-scale jets. Like most low-energy-peaked BL Lacs (LBLs), our HBL sample shows parsec-scale, core-jet morphologies and compact, complex kiloparsec-scale morphologies. Some objects also show evidence for bending of the jet 10-20pc from the core, suggesting interaction of the jet with the surrounding medium. Whereas LBLs show a wide distribution of parsec- to kpc-scale jet misalignment angles, there is weak evidence that the jets in HBLs are more well-aligned, suggesting that HBL jets are either intrinsically straighter or are seen further off-axis than LBL jets.

The Pearson‐Readhead Survey of Compact Extragalactic Radio Sources from Space. II. Analysis of Source Properties

We have performed a multidimensional correlation analysis on the observed properties of a statistically complete core-selected sample of compact radio-loud active galactic nuclei based on data from the VLBI Space Observing Programme (Paper I) and previously published studies. Our sample is drawn from the well-studied Pearson-Readhead (PR) survey and is ideally suited for investigating the general effects of relativistic beaming in compact radio sources. In addition to confirming many previously known correlations, we have discovered several new trends that lend additional support to the beaming model. These trends suggest that the most highly beamed sources in core-selected samples tend to have (1) high optical polarizations; (2) large parsec- kiloparsec-scale jet misalignments; (3) prominent VLBI core components; (4) one-sided, core, or halo radio morphology on kiloparsec scales; (5) narrow emission line equivalent widths; and (6) a strong tendency for intraday variability at radio wavelengths. We have used higher resolution space and ground-based VLBI maps to confirm the bimodality of the jet misalignment distribution for the PR survey and find that the sources with aligned parsec- and kiloparsec-scale jets generally have arcsecond-scale radio emission on both sides of the core. The aligned sources also have broader emission line widths. We find evidence that the BL Lacertae objects in the PR survey are all highly beamed and have very similar properties to the high optically polarized quasars, with the exception of smaller redshifts. A cluster analysis on our data shows that after partialing out the effects of redshift, the luminosities of our sample objects in various wave bands are generally well correlated with each other but not with other source properties.

The Caltech-Jodrell Bank VLBI Surveys

AbstractThe Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35° were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJl survey (together with the older “PR” survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the “compact symmetric objects” (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size-redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets.

A Dramatic Millimeter Wavelength Flare in the Gamma‐Ray Blazar NRAO 530

We present 3 mm wavelength VLBI observations and up to 30 yr of monitoring at radio through submillimeter wavelengths of the gamma-ray blazar NRAO 530. We discuss the dramatic flare that tripled the millimeter wavelength flux in 1994 and 1995 following three decades of increasing activity. VLBI observations during the flare show the creation of new components in a bent jet on subparsec scales. The components move at an apparent velocity of 7c. The observations also imply expansion in a separate component with a speed greater than 26c. We apply synchrotron self-Compton models to the core and jet to determine magnetic field strengths, particle densities, and Doppler boosting factors. We are unable to provide a satisfactory physical explanation for the high apparent velocity component. The increase in millimeter and radio wavelength fluxes is correlated with a rise in the gamma-ray flux detected by EGRET. We show that gamma-ray detections do not always occur during or immediately prior to a millimeter wavelength flare, contrary to assertions in the literature. We associate the VLBI component creation with the gamma-ray activity, although not with a specific flare. We consider what may distinguish gamma-ray blazars from other variable, flat-spectrum radio objects. Our data strengthen the correlation between superluminal motion and gamma-ray emission in blazars. The distribution of jet misalignment angle for 28 EGRET sources, determined from a survey of the literature, does not differ significantly from that of other blazars. This suggests that the geometries of gamma-ray blazars do not differ from those of gamma-ray-quiet blazars on the scales sampled by VLBI.

Design verification of ground run-up noise suppressors for afterburning engines

New facilities for ground running of engines in Royal Australian Air Force F/A-18 aircraft feature air-cooled exhaust augmentors for noise suppression. Aerothermodynamic aspects of the augmentor designs were appraised in some detail, making use of isothermal scale model tests, ejector theory, and available empirical data. Quantitative assessments were made of cooling flow pumping performance, and geometric features were identified which are important to the symmetry of the flow in the augmentor ducts. The final designs displayed satisfactory aerodynamic behavior, tolerant to both inlet asymmetries and reasonable levels of engine jet misalignment. The estimated pumping performance exceeded the design requirements.

Flow Characteristics of Opposing Rows of Jets in a Confined Space

The influence of flow and geometric boundary conditions on the interaction of opposed rows of jets in a confined duct without cross-flow has been investigated by a flow visualization method. The effects of angular and axial misalignment of jets and of unequal mean jet velocities were found to be much greater than in configurations with cross-flow, and the effects of geometric asymmetries were more important than those of modest differences in mean jet velocities.

Dynamic Stability of a Missile in Rolling Flight

The paper sets down the equations of motion for a symmetric rolling missile with respect to axes attached to the missile. The missile may be jet (or rocket) propelled or coasting under accelerating or decelerating conditions, respectively, wherein the variable rolling velocity is derived from intentionally or unintentionally fins and/or wings. The equations contain a force and moment system that includes, in addition to the usual forces and moments, those due to magnus effects, misaligned surfaces, canted surfaces, jet misalignment, and the linear accelerations in the plane normal to the missile axis. The results present general stability criteria for a rolling missile which are summarized in the Discussion of Stability. LIST OP SYMBOLS (I) English Letters A — moment of inertia in roll about x axis, pd, lb0 sec. A = A/pd\itr B = moment of inertia about y axis, lb. sec. B = B/pd*. hr C ~ moment of inertia about z axis, lb. sec. CD = drag coefficient, dimensionless c = wing or tail chord, d — diameter of missile, ft, G = linear momentum vector H = angular momentum vector i, j = unit vectors along y and z axes, respectively L, M, N = moments about x, y, and z axes, respectively m = mass of missile, lb. sec. ft. m — m/pd, dimensionless P = rolling velocity of missile about x axis, rad. per sec. pz = P / F , r a d . p e r f t . q, r — angular velocities in pitch (about y axis) and in yaw (about z axis) 5 = area, sq.ft. T — thrust force, lbs. T = T/Pd\4 ft./sec. 2 t — time, sec. 11, v, w = components of linear velocity of the missile along x, y, z axes, respectively, per sec. u, v,w = derivatives with respect to time V = scalar velocity of missile along flight trajectory per sec. X, Y, Z — forces acting along x, y, z axes, respectively x, y, z = designations of coordinate axes z = distance along trajectory (II) Definition of Coefficients K = ?/V 1/ft. Kz , Km = dimensionless coefficients of force and moment, a a respectively, due to angle of attack or yaw Kz , Km = Kz ,/d and Km /d, respectively, 1/ft. Q'