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NASA NTRS2000

Wintertime East Asian Jet Stream and Its Association with the Asian-Pacific Climate

Interannual variability of the wintertime East Asian westerly jet stream and the linkage between this variability and the Asian-Pacific climate are investigated. The study emphasizes on the variability of the jet core and its association with the Asian winter monsoon, tropical convection, upper tropospheric wave patterns, and the teleconnection of the jet with other climate systems. The relationship between the jet and North Pacific sea surface temperature pattern (SST) is also explored. NCEP/NCAR reanalysis, NASA GISS surface temperature, NASA GEOS reanalysis, NOAA reconstructed SST, GPCP precipitation, and NOAA snow cover data sets are analyzed in this study. An index of the East Asian jet has been defined by the December-February means of the 200 mb zonal winds that are averaged within a box enclosing the jet maximum, which shifts only moderately from one year to another especially in the south-north direction. The jet links to a teleconnection pattern whose major climate anomalies appear over the Asian continent and western Pacific (west of the dateline). This pattern differs distinctly from the teleconnection pattern associated with El Nino/Southern Oscillation (ENSO), which causes the Pacific/North American pattern to the east of the dateline. A strong jet is accompanied clearly by an increase in the intensity of the atmospheric circulation over Asia and the Pacific. In particular, the winter monsoon strengthens over East Asia, leading to cold climate in the region, and convection intensifies over the tropical Asia-Australia sector. Changes in the jet are associated with broad-scale modification in the upper tropospheric wave patterns that leads to downstream climate anomalies over the eastern Pacific. Through this downstream influence, the East Asian jet causes climate signals in North America as well. A strong jet gives rise to warming and less snow cover in the western United States but reverse climate anomalies in the eastern part of the country, although these signals are relatively weaker than the jet-related anomalies in East Asia. There is a strong association between the East Asian jet and the North Pacific SST (NPSST). A strong jet is accompanied by a cooling in the extratropical Pacific and a warming in the tropical-subtropical Pacific. Evidence also indicates that the extratropical NPSST pattern plays a role in modulating the intensity of the jet stream. ENSO, the jet, and the NPSST are mutually interactive on certain time scales and such an interaction links closely to the climate anomalies in the Asian-Pacific-American regions.

Yang, Song↗

DOE OSTI2024

Jet radius dependence of dijet momentum balance and suppression in Pb + Pb collisions at 5.02 TeV with the ATLAS detector

This paper describes a measurement of the jet radius dependence of the dijet momentum balance between leading back-to-back jets in 1.72 nb -1 of Pb + Pb collisions collected in 2018 and 255 pb -1 of pp collisions collected in 2017 by the ATLAS detector at the LHC. Both datasets were collected at $\sqrt{s_{NN}}$ = 5.02 TeV. Jets are reconstructed using the anti-k t algorithm with jet radius parameters R = 0.2, 0.3, 0.4, 0.5, and 0.6. The dijet momentum balance distributions are constructed for leading jets with transverse momentum p T from 100 to 562 GeV for R = 0.2, 0.3, and 0.4 jets, and from 158 to 562 GeV for R = 0.5 and 0.6 jets. The absolutely normalized dijet momentum balance distributions are constructed to compare measurements of the dijet yields in Pb + Pb collisions directly to the dijet cross sections in pp collisions. For all jet radii considered here, there is a suppression of more balanced dijets in Pb + Pb collisions compared with pp collisions, while for more imbalanced dijets there is an enhancement. There is a jet radius dependence to the dijet yields, being stronger for more imbalanced dijets than for more balanced dijets. Additionally, jet pair nuclear modification factors are measured. The subleading jet yields are found to be more suppressed than leading jet yields in dijets. A jet radius dependence of the pair nuclear modification factors is observed, with the suppression decreasing with increasing jet radius. These measurements provide new constraints on jet quenching scenarios in the quark-gluon plasma.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

A precise measurement of the jet energy scale derived from single-particle measurements and in situ techniques in proton–proton collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector

The jet energy calibration and its uncertainties are derived from measurements of the calorimeter response to single particles in both data and Monte Carlo simulation using proton–proton collisions at $\sqrt{s} = 13$ TeV collected with the ATLAS detector during Run 2 at the Large Hadron Collider. The jet calibration uncertainty for anti-$k_T$ jets with a jet radius parameter of R$_\textrm{jet} = 0.4$ and in the central jet rapidity region is about 2.5% for transverse momenta ($p_{\text {T}}$) of 20 $\text {GeV}$ , about 0.5% for $p_{\text {T}} = 300$ GeV and 0.7% for $p_{\text {T}} = 4$ TeV . Excellent agreement is found with earlier determinations obtained from -balance based in situ methods ($Z/\gamma$ +jets). The combination of these two independent methods results in the most precise jet energy measurement achieved so far with the ATLAS detector with a relative uncertainty of 0.3% at $p_\textrm{T} = 300$ GeV and 0.6% at 4 TeV. The jet energy calibration is also derived with the single-particle calorimeter response measurements separately for quark- and gluon-induced jets and furthermore for jets with R jet varying from 0.2 to 1.0 retaining the correlations between these measurements. Differences between inclusive jets and jets from boosted top-quark decays, with and without grooming the soft jet constituents, are also studied.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Medium-induced modification of groomed and ungroomed jet mass and angularities in Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

The ALICE Collaboration presents a new suite of jet substructure measurements in Pb–Pb and pp collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV. These measurements provide access to the internal structure of jets via the momentum and angle of their constituents, probing how the quark–gluon plasma modifies jets, an effect known as jet quenching. Jet grooming additionally removes soft wide-angle radiation to enhance perturbative accuracy and reduce experimental uncertainties. We report the groomed and ungroomed jet mass m jet and jet angularities λ$^{κ}_{α}$ using κ = 1 and α > 0. Charged-particle jets are reconstructed at midrapidity using the anti-k T algorithm with resolution parameter R = 0.2. A narrowing of the jet mass and angularity distributions in Pb–Pb collisions with respect to pp is observed and is enhanced for groomed results, confirming modification of the jet core. By using consistent jet definitions and kinematic cuts between the mass and angularities for the first time, previous inconsistencies in the interpretation of quenching measurements are resolved, rectifying a hurdle for understanding how jet quenching arises from first principles and highlighting the importance of a well-controlled baseline. These results are compared with a variety of theoretical models of jet quenching, providing constraints on jet energy-loss mechanisms in the quark–gluon plasma.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Visualizing How the Structure of Large-Radius Jets Shapes Their Wakes

The ATLAS collaboration has introduced and implemented a strategy for selecting and analyzing large-radius jets composed of skinny $R=0.2$ subjets in heavy ion collisions at the LHC. We show how measurements of these jets teach us about the resolution length $L_{\rm res}$ of quark-gluon plasma (QGP) and can teach us how jet substructure shapes the wakes that jets excite in the QGP droplets through which they pass. We use Hybrid Model calculations to reproduce measurements of $R_{AA}$ for large-radius jets in PbPb collisions, and study their dependence on the angle between the two skinny subjets involved in the final reclustering step of an $R=1$ jet. We show how these observables can constrain the value of $L_{\rm res}$ and demonstrate that the ATLAS data rule out any picture in which an entire parton shower loses energy coherently as if it were a single entity. Determining the degree to which the QGP can resolve partons within a jet is central to the broader program of using jet quenching measurements to probe QGP. We make further use of this setup by analyzing the response of the medium to the passage of large-radius $R=2$ jets containing two skinny subjets in gamma-jet events. We introduce novel jet-shape observables that allow us to visualize the angular shape of the soft hadrons originating from the wakes that wide jets with two skinny subjets excite in a droplet of QGP, as a function of the angular separation between the subjets. We find that even when they are $\sim 0.8- 1$ radian apart, a single broad wake is produced. Only when the two subjets are even farther apart is the presence of two sub-wakes revealed. We show that the way in which jet structure shapes jet wakes can be visualized with similar clarity in experiments by using only those hadrons with low $p_T$. These observables thus offer a new and distinctive way of seeing jet wakes in heavy ion collision data.

FOS: Physical sciences↗

NASA NTRS1985

Behavior of turbulent gas jets in an axisymmetric confinement

The understanding of the mixing of confined turbulent jets of different densities with air is of great importance to many industrial applications, such as gas turbine and Ramjet combustors. Although there have been numerous studies on the characteristics of free gas jets, little is known of the behavior of gas jets in a confinement. The jet, with a diameter of 8.73 mm, is aligned concentrically in a tube of 125 mm diameter, thus giving a confinement ratio of approximately 205. The arrangement forms part of the test section of an open-jet wind tunnel. Experiments are carried out with carbon dioxide, air and helium/air jets at different jet velocities. Mean velocity and turbulence measurements are made with a one-color, one-component laser Doppler velocimeter operating in the forward scatter mode. Measurements show that the jets are highly dissipative. Consequently, equilibrium jet characteristics similar to those found in free air jets are observed in the first two diameters downstream of the jet. These results are independent of the fluid densities and velocities. Decay of the jet, on the other hand, is a function of both the jet fluid density and momentum. In all the cases studied, the jet is found to be completely dissipated in approximately 30 jet diameters, thus giving rise to a uniform flow with a very high but constant turbulence field across the confinement.

So, R. M. C.↗

NASA NTRS2001

Instability Analysis of a Low-Density Gas Jet Injected into a High-Density Gas

The objective of this study was to determine the effects of buoyancy on the absolute instability of low-density gas jets injected into high-density gas mediums. Most of the existing analyses of low-density gas jets injected into a high-density ambient have been carried out neglecting effects of gravity. In order to investigate the influence of gravity on the near-injector development of the flow, a linear temporal stability analysis and a spatio-temporal stability analysis of a low-density round jet injected into a high-density ambient gas were performed. The flow was assumed to be isothermal and locally parallel; viscous and diffusive effects were ignored. The variables were represented as the sum of the mean value and a normal-mode small disturbance. An ordinary differential equation governing the amplitude of the pressure disturbance was derived. The velocity and density profiles in the shear layer, and the Froude number (signifying the effects of gravity) were the three important parameters in this equation. Together with the boundary conditions, an eigenvalue problem was formulated. Assuming that the velocity and density profiles in the shear layer to be represented by hyperbolic tangent functions, the eigenvalue problem was solved for various values of Froude number. The temporal growth rates and the phase velocity of the disturbances were obtained. It was found that the presence of variable density within the shear layer resulted in an increase in the temporal amplification rate of the disturbances and an increase in the range of unstable frequencies, accompanied by a reduction in the phase velocities of the disturbances. Also, the temporal growth rates of the disturbances were increased as the Froude number was reduced (i.e. gravitational effects increased), indicating the destabilizing role played by gravity. The spatio-temporal stability analysis was performed to determine the nature of the absolute instability of the jet. The roles of the density ratio, Froude number, Schmidt number, and the lateral shift between the density and velocity profiles on the jet s absolute instability were determined. Comparisons of the results with previous experimental studies show good agreement when the effects of these variables are combined together. Thus, the combination of these variables determines how absolutely unstable the jet will be. Experiments were carried out to observe the qualitative differences between a round low-density gas jet injected into a high-density gas (helium jet injected into air) and a round constant density jet (air jet injected into air). Flow visualizations and velocity measurements in the near-injector region of the helium jet show more mixing and spreading of the helium jet than the air jet. The vortex structures develop and contribute to the jet spreading causing the helium jet to oscillate.

Lawson, Anthony Layiwola↗

NASA NTRS2012

The Impact of Subsonic Twin Jets on Airport Noise

Subsonic and supersonic aircraft concepts proposed through NASA s Fundamental Aeronautics Program have multiple engines mounted near one another. Engine configurations with multiple jets introduce an asymmetry to the azimuthal directivity of the jet noise. Current system noise predictions add the jet noise from each jet incoherently, therefore, twin jets are estimated by adding 3 EPNdB to the far-field noise radiated from a single jet. Twin jet effects have the ability to increase or decrease the radiated noise to different azimuthal observation locations. Experiments have shown that twin jet effects are reduced with forward flight and increasing spacings. The current experiment investigates the impact of spacing, and flight effects on airport noise for twin jets. Estimating the jet noise radiated from twin jets as that of a single jet plus 3 EPNdB may be sufficient for horizontal twin jets with an s/d of 4.4 and 5.5, where s is the center-to-center spacing and d is the jet diameter. However, up to a 3 EPNdB error could be present for jet spacings with an s/d of 2.6 and 3.2.

Bozak, Richard, F.↗

NASA NTRS2012

The Impact of Subsonic Twin Jets on Airport Noise

Bozak, Richard F.↗

NASA NTRS2014

Miniature Filament Eruptions and their Reconnections in X-Ray Jets: Evidence for a New Paradigm

We investigate the onset of approximately10 random X-ray jets observed by Hinode/XRT. Each jet was near the limb in a polar coronal hole, and showed a ``bright point'' in an edge of the base of the jet, as is typical for previously-observed X-ray jets. We examined SDO/AIA EUV images of each of the jets over multiple AIA channels, including 304 Ang, which detects chromospheric emissions, and 171, 193, and 211 Ang, which detect cooler-coronal emissions. We find the jets to result from eruptions of miniature (size less than approximately 10 arcsec) filaments from the bases of the jets. Much of the erupting-filament material forms a chromospheric-temperature jet. In the cool-coronal channels, often the filament appears in absorption and the jet in emission. The jet bright point forms at the location from which the miniature filament is ejected, analogous to the formation of a standard solar flare in the wake of the eruption of a typical larger-scale chromospheric filament. Thus these X-ray jets and their bright points are made by miniature filament eruptions. They are evidently produced the same way as an on-disk coronal jet we observed in Adams et al. (2014); that on-disk jet had no obvious emerging magnetic field in its base. We conclude that, for many jets, the standard idea of X-ray jets forming from reconnection between emerging flux and preexisting coronal field is incorrect. ACS and RLM were supported by funding from NASA/LWS, Hinode, and ISSI.

Sterling, Alphonse C.↗

NASA NTRS2016

A Model for Straight and Helical Solar Jets: II. Parametric Study of the Plasma Beta

Context. Jets are dynamic, impulsive, well-collimated plasma events that develop at many different scales and in different layers of the solar atmosphere. Aims. Jets are believed to be induced by magnetic reconnection, a process central to many astrophysical phenomena. Within the solar atmosphere, jet-like events develop in many different environments, e.g. in the vicinity of active regions as well as in coronal holes, and at various scales, from small photospheric spicules to large coronal jets. In all these events, signatures of helical structure and/or twisting/rotating motions are regularly observed. The present study aims to establish that a single model can generally reproduce the observed properties of these jet-like events. Methods. In this study, using our state-of-the-art numerical solver ARMS, we present a parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model of solar jet-like events. Within the MHD paradigm, we study the impact of varying the atmospheric plasma beta on the generation and properties of solar-like jets. Results. The parametric study validates our model of jets for plasma beta ranging from 10(sup 3) to 1, typical of the different layers and magnetic environments of the solar atmosphere. Our model of jets can robustly explain the generation of helical solar jet-like events at various beta less than or equal to 1. We show that the plasma beta modifies the morphology of the helical jet, explaining the different observed shapes of jets at different scales and in different layers of the solar atmosphere. Conclusions. Our results allow us to understand the energisation, triggering, and driving processes of jet-like events. Our model allows us to make predictions of the impulsiveness and energetics of jets as determined by the surrounding environment, as well as the morphological properties of the resulting jets.

Magnetic Field↗

NASA NTRS2014

Trigger of Standard and Blowout Solar Jets: I. Parametric Studies of the Magnetic Field Geometry

Context. Jets are dynamic, impulsive, well collimated plasma events developing at many different scales and in differentlayers of the solar atmosphere.Aims. Jets are believed to be induced by magnetic reconnection a process central to many astrophysical phenomena.Studying their dynamics can help us to better understand the processes acting in larger eruptive events (e.g. flares andcoronal mass ejection) as well as mass, magnetic helicity and energy transfer at all scale in the solar atmosphere. Therelative simplicity of their magnetic geometry and topology, compared with larger solar active events, makes jets idealcandidate for studying the fundamental role of reconnection in energetic events. Methods. In this study, using our state-of-the-art numerical solver ARMS, we present several parametric studies of anumerical three-dimensional magneto-hydrodynamic model of solar jet-like events. We study the impact of the magneticfield inclination and photospheric field distribution on the generation and properties of two types of observed solar jets:the so-called standard and blowout jets.Results. The present parametric studies validate our model of jets for different geometric properties of the magneticconfiguration. On one hand, a blowout jets is eventually always trigger for the range of parameters that we tested. The3D magnetic null-point configuration is a very robust structure for the energy storage and impulsive release characteristicof blowout jets. On the other hand, the existence of the standard jet depends on the magnetic geometry. We show thatthe reconnection occurring during the standard jet phase influences the properties of the trigger of the blowout jet.Conclusions. Our results allow us to better understand the energization, triggering and driving processes of standardand blowout jets. Our model allows us to predict the impulsiveness and energetics of jets in terms of the surroundingmagnetic field configuration. Finally we discuss the interpretation of standard jets and blowout jets and the physicalfactors that determine which type of jets will occur.

Pariat, E.↗

DOE OSTI2025

Revisiting single inclusive jet production: timelike factorization and reciprocity

Factorization theorems for single inclusive jet production play a crucial role in the study of jets and their substructure. In the case of small radius jets, the dynamics of the jet clustering can be factorized from both the hard production dynamics, and the dynamics of the low scale jet substructure measurement, and is described by a matching coefficient that can be computed in perturbative Quantum Chromodynamics (QCD). A proposed factorization formula describing this process has been previously presented in the literature, and is referred to as the semi-inclusive, or fragmenting jets formalism. By performing an explicit two-loop calculation, we show the inconsistency of this factorization formula, in agreement with another recent result in the literature. Building on recent progress in the factorization of single logarithmic observables, and the understanding of reciprocity, we then derive a new all-order factorization theorem for inclusive jet production. The use of a jet algorithm, being only a modification of the infrared structure of the measurement, modifies the structure of convolutions in the factorization theorem, as compared to inclusive fragmentation, but maintains the universality of the inclusive hard function and its associated Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution, which are ultraviolet properties. However, the non-trivial structure of convolutions in the factorization theorem implies that the jet functions exhibit a modified evolution. We perform an explicit two-loop calculation of the jet function in both N = 4 super Yang-Mills (SYM), and for all color channels in QCD, finding exact agreement with the structure derived from our renormalization group equations. In addition, we derive several new results, including an extension of our factorization formula to jet substructure observables, a jet algorithm definition of a generating function for the energy correlators, and new results for exclusive jet functions. Our results are a key ingredient for achieving precision jet substructure at colliders.

Effective Field Theories↗

DOE OSTI2024

Girth and groomed radius of jets recoiling against isolated photons in lead-lead and proton-proton collisions at $\sqrt{s_{NN}} = 5.02$ TeV

This Letter presents the first measurements of the groomed jet radius R g and the jet girth g in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables R g and g provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7 nb -1 and 301 pb -1 , respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum $p^{γ}_{T} > 100$ GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum $p^{jet}_{T}$ such that $p^{jet}_{T}/p^{γ}_{T} > 0.4$ . The measured R g and g distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with $p^{jet}_{T}/p^{γ}_{T} > 0.8$ , i.e., those that closely balance the photon $p^{γ}_{T}$ , are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with $p^{jet}_{T}/p^{γ}_{T} > 0.4$ reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

𝐷 0 -meson-tagged jet axes difference in proton-proton collisions at $\sqrt{s}$ = 5.02 TeV

Heavy-flavor quarks produced in proton-proton (pp) collisions provide a unique opportunity to investigate the evolution of quark-initiated parton showers from initial hard scatterings to final-state hadrons. By examining jets that contain heavy-flavor hadrons, this study explores the effects of both perturbative and nonperturbative QCD on jet formation and structure. The angular differences between various jet axes, Δ⁢𝑅 axis , offer insight into the radiation patterns and fragmentation of charm quarks. The first measurement of 𝐷 0 -tagged jet axes differences in pp collisions at $\sqrt{s}$ =5.02 TeV by the ALICE experiment at the LHC is presented for jets with transverse momentum 𝑝$^{ch jet}_{T}$ ≥ 10 GeV/𝑐 and 𝐷 0 mesons with 𝑝$^{D^0}_{T}$ ≥ 5 GeV/𝑐. In this 𝐷 0 -meson-tagged jet measurement, three jet axis definitions, each with different sensitivities to soft, wide-angle radiation, are used: the standard axis, soft drop groomed axis, and winner-takes-all axis. Measurements of the radial distributions of 𝐷 0 mesons with respect to the jet axes, Δ⁢𝑅 axis−D 0 , are reported, along with the angle, Δ⁢𝑅 axis , between the three jet axes. The 𝐷 0 meson emerges as the leading particle in these jets, closely aligning with the winner-takes-all axis and diverging from the standard jet axis. The results also examine how varying the sensitivity to soft radiation with grooming influences the orientation of the soft drop jet axis and uncover that charm-jet structure is more likely to survive grooming when the soft drop axis is further from the 𝐷 0 direction, providing further evidence of the dead-cone effect recently measured by ALICE.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS1979

Experimental investigation of jet-induced loads on a flat plate in hover out-of-ground effect

Effects of varying jet decay rate on jet-induced loads on a flat plate located in the plane of the jet exit perpendicular to the jet axis were investigated using a small-scale laboratory facility. Jet decay rate has been varied through use of two cylindrical centerbodies having either a flat or hemispherical tip, which were submerged various distances below the flat plate jet exit plane. Increased jet decay rate, caused by the presence of a center-body or plug in the jet nozzle, led to an increased jet-induced lift loss on the flat plate. Jet-induced lift losses reached 1 percent of the jet thrust for the quickest jet decay rates for plate areas equal to 100 times the effective jet exit area. The observed lift loss versus jet decay rate trend agreed well with results of previous investigations.

Kuhlman, J. M.↗

NASA NTRS1985

Effects of velocity profile and inclination on dual-jet-induced pressures on a flat plate in a crosswind

An experimental study was conducted to determine surface pressure distributions on a flat plate with dual subsonic, circular jets exhausting from the surface into a crossflow. The jets were arranged in both side-by-side and tandem configurations and were injected at 90 deg and 60 deg angles to the plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective of the study was to determine the effect of a nonuniform (vs uniform) jet velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform jets with a high-velocity outer annulus and a low-velocity core induced stronger negative pressure fields than uniform jets with the same mass flow rate. However, nondimensional lift losses (lift loss/jet thrust lift) due to such nonuniform jets were lower than lift losses due to uniform jets. Changing the injection angle from 90 deg to 60 deg resulted in moderate (for tandem jets) to significant (for side-by-side jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce as the angle decreased. Jets arranged in the side-by-side configuration led to significant jet-induced lift losses exceeding, in some cases, lift losses reported for single jets.

Jakubowski, A. L.↗

NASA NTRS1994

The Aeroacoustics of Supersonic Coaxial Jets

Instability waves have been established as the dominant source of mixing noise radiating into the downstream arc of a supersonic jet when the waves have phase velocities that are supersonic relative to ambient conditions. Recent theories for supersonic jet noise have used the concepts of growing and decaying linear instability waves for predicting radiated noise. This analysis is extended to the prediction of noise radiation from supersonic coaxial jets. Since the analysis requires a known mean flow and the coaxial jet mean flow is not described easily in terms of analytic functions, a numerical prediction is made for its development. The Reynolds averaged, compressible, boundary layer equations are solved using a mixing length turbulence model. Empirical correlations are developed for the effects of velocity and temperature ratios and Mach number. Both normal and inverted velocity profile coaxial jets are considered. Comparisons with measurements for both single and coaxial jets show good agreement. The results from mean flow and stability calculations are used to predict the noise radiation from coaxial jets with different operating conditions. Comparisons are made between different coaxial jets and a single equivalent jet with the same total thrust, mass flow, and exit area. Results indicate that normal velocity profile jets can have noise reductions compared to the single equivalent jet. No noise reductions are found for inverted velocity profile jets operated at the minimum noise condition compared to the single equivalent jet. However, it is inferred that changes in area ratio may provide noise reduction benefits for inverted velocity profile jets.

Dahl, Milo D.↗