Local Acceleration Research Articles

Comment on “Determining the difference between local acceleration and local gravity: Applications of the equivalence principle to relativistic trajectories” [Am. J. Phys. 92(6), 444–449 (2024)]

Comment on “Determining the difference between local acceleration and local gravity: Applications of the equivalence principle to relativistic trajectories” [Am. J. Phys. <b>92</b>(6), 444–449 (2024)]

Transient behavior of thermocapillary convection in thin liquid film exposed to step laser heating

Temporally developing thermocapillary convection induced by step laser heating of a thin liquid film has been studied numerically. Computations are performed using the commercial software STAR CCM+ version 2022.1. The liquid film of silicone oil (high Prandtl number fluid) is 60 mm in diameter and 3 mm in thickness. Flow characteristics related to surface velocity and surface temperature have been studied. Validation of the computations is achieved for the surface velocity, the velocity along thickness and the surface temperature through comparison with PIV and IR camera measurements. The laser-beam with a carbon dioxide gas laser (10.4 μm in wavelength) is used for heating. It is found that the temporally developing profile of surface velocity shows two local velocity peaks (uS1 and uS2) at two radial locations (rS1 and rS2) respectively. The first peak, uS1, appearing due to the steep temperature gradient generated by laser-beam heating and its radial position, rS1, do not change noticeably with time. On the other hand, the second peak, uS2, travels radially outwards with decreasing magnitude in a self-propelling manner until its radial position, rS2, approaches an asymptotic maximum. Detailed analysis of the coupling among radial temperature gradient, local pressure variation and local convective acceleration near the second peak reveals that hydrothermal mechanisms are responsible for self-propelling travel of uS2. The transient behaviors of both primary and secondary velocity peaks are found to depend on the fluid viscosity and the laser-beam settings

Modeling the rupture dynamics of strong ground motion (> 1 g) in fault stepovers

Following the July 2019 Ridgecrest, California earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their position in the desert pavement within a stepover along the right-lateral strike-slip M7.1 rupture trace, without evidence of dragging or shearing. This implies localized ground motions in excess of 1 g, in contrast to the instrumentally recorded peak of 0.57 g. Similar rock displacement occurred in a stepover in the predominantly strike-slip 2010 M7.2 El Mayor-Cucapah earthquake. Together, these examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration. Here, we use the 3D finite element method to investigate how rupture through a variety of strike-slip stepover geometries influences strong ground acceleration. For subshear ruptures, we find that the presence of a stepover in general matters more than its dimensions; the strongest ground acceleration always occurs at the end of the first fault. For supershear ruptures, the stepover is effectively irrelevant, since the strongest particle acceleration occurs at the point of the supershear transition on the first fault. Our model subshear and supershear ruptures alike do produce horizontal particle acceleration above 1 g, but over a region so close to the fault (< 1 km) that a seismic network may not catch it. We suggest that the physics of rupture through a fault stepover could have been responsible for the displaced rocks in the Ridgecrest and El Mayor-Cucapah earthquakes, and that stepover regions may have particularly high ground motion hazard. Our study suggests that ground motion predictions and local hazard assessments should account for much stronger accelerations in the immediate near field of active faults, especially around stepovers and other geometrical discontinuities.

How does landscape vegetation configuration regulate local channel initiation in a rapidly expanding micro-tidal system?

Tidal channels are essential morphological structures that mediate hydrological connectivity and maintain coastal resilience. Previous studies on vegetation-induced channel development primarily focused on the stages of initial establishment or later elaboration, characterized by slow and localized changes. However, the impact of rapid shifts in landscape vegetation on the initiation of tidal channels, such as main or tributary channels, remains poorly understood, particularly in micro-tidal system. In this study, we investigated this relationship through satellite imagery analysis and biogeomorphic modeling of a rapidly expanding micro-tidal marsh in the Yellow River Delta, China, which has experienced an invasion by Spartina alterniflora over the past decade. The satellite imagery demonstrated that Spartina alterniflora invasion has increased drainage density and reduced overland flow path length. Our modeling results showed that local flow acceleration between vegetation patches was insufficient to rapidly initiate channels under micro-tidal conditions. As the patchy marsh coalesced and expanded into a contiguously vegetated marsh, it altered landscape-scale flow patterns, diverting from homogenous platform flow to concentrated channel flow. This shift prominently promoted the initiation of tributary channels in the landward marsh zone. The simulated scenarios of vegetation removal highlighted a marked increase in flow divergence from adjacent platforms due to changes in landscape-scale vegetation configuration. This alteration in flow pattern amplified local hydrodynamics, consequently intensifying local channel incision. Our findings emphasize that the channel initiation is significantly influenced by landscape-scale vegetation configuration under micro-tidal conditions, beyond the localized interactions between plants and flow.

A novel flow channel inspired by classical mathematical function: Enhancing output performance and low-grade heat recovery efficiency of thermal regeneration ammonia-based flow battery

Thermal Regeneration Ammonia-based Flow Battery (TRAFB) faces significant challenges in enhancing its output performance and low-grade waste heat recovery efficiency due to limitations in mass transfer and an incomplete understanding of the mass transfer mechanism. To address these issues, this study innovatively introduces a novel sinusoidal wave flow channel (SWFC), which is inspired by the classic mathematical function. The impact of the SWFC on TRAFB performance is thoroughly discussed and compared in detail with the conventional straight flow channel (SFC). Most importantly, this work unveils for the first time the distribution mechanism of the three mass transfer modes in TRAFB, which are convection, diffusion, and electrophoretic mass transfer. The main findings reveal that the mass transfer performance of TRAFB is primarily governed by convection and diffusion, with electrophoretic mass transfer playing a minimal role, and there is a threshold of current density beyond which the dominant mass transfer mechanism transitions from convection to diffusion. The unique design of the SWFC, which induces the Venturi effect, significantly enhances the overall mass transfer performance of the TRAFB due to the distinct local acceleration, achieving a remarkable enhancement in flux of up to 118.48 times. By optimizing the amplitude and period, the battery's output performance can be further enhanced, with the maximum peak power achieved by the SWFC with an amplitude of 0.8 mm and a period of 0.5π, which is 95.63 % over the SFC. Notably, the SWFC also excels in improving the thermoelectric conversion efficiency, particularly at high current densities, achieving an enhancement of up to 9.81 times.

An Improved Combinatorial Benders Decomposition Algorithm for the Human-Robot Collaborative Assembly Line Balancing Problem

As an emerging technology, human-robot collaboration (HRC) has been implemented to enhance the performance of assembly lines and improve the safety of human workers. By integrating the advantages of human workers and collaborative robots (cobots), HRC enables production systems to process tasks consecutively, concurrently, or collaboratively. However, the introduction of cobots also makes the corresponding human-robot collaborative assembly line balancing problem more complex and difficult to solve. To solve this problem, we first propose an enhanced mixed integer program (EMIP) with various enhancement techniques and tighter bounds, and then, we develop an improved combinatorial Benders decomposition algorithm (Algorithm ICBD) with new local search strategies, Benders cuts, and acceleration procedures. To verify the effectiveness of our proposed model and algorithms, we conduct extensive computational experiments, and the results show that our proposed EMIP model is significantly better than the existing mixed integer program model; the percentages of instances that can obtain feasible and optimal solutions are increased from 82.42% to 100% and from 29.17% to 43.5%, respectively, whereas the average gap is decreased from 19.81% to 5.64%. In addition, our proposed Algorithm ICBD can get 100% of feasible solutions and 65.92% of optimal solutions for all of the test instances, and the average gap is only 1.49%. Moreover, compared with existing Benders decomposition methods for this problem, our approach yields comparatively better solutions in notably shorter average computational time when run in the same computational environment. History: Accepted by Andrea Lodi, Area Editor for Design &amp; Analysis of Algorithms–Discrete. Funding: This research was supported by the National Natural Science Foundation Council of China [Grants 72401214, 92167206, 7221101377, 72471169, and 72231005], the Ministry of Education of China [Grant 24YJC630078], and Computation and Analytics of Complex Management Systems (Tianjin University). This research was also supported by the Tianjin Natural Science Foundation Project [Grant 23JCQNJC01900] and the Tianjin Philosophy and Social Science Planning Project [Grant TJGL21-016]. Supplemental Material: The software that supports the findings of this study is available within the paper and its Supplemental Information ( https://pubsonline.informs.org/doi/suppl/10.1287/ijoc.2023.0279 ) as well as from the IJOC GitHub software repository ( https://github.com/INFORMSJoC/2023.0279 ). The complete IJOC Software and Data Repository is available at https://informsjoc.github.io/ .

Ultra-relativistic electron flux enhancement under persistent high speed solar wind stream

The physical mechanisms usually applied to explain the relativistic electron enhancement have been delved into to elucidate non-adiabatic electron acceleration resulting in the ultra-relativistic electron population observed in the outer radiation belt. We considered multisatellite observations of the solar wind parameters, magnetospheric waves, and particle flux to report an unusual local acceleration of ultra-relativistic electrons under a prolonged high-speed solar wind stream (HSS). A corotating interaction region reaches the Earth’s bowshock on August 3, 2016, causing a minor geomagnetic storm. Following this, the magnetosphere was driven for 72 h by a long-term HSS propagating at 600 km/s. During this period, the magnetosphere sustained both ultra-low frequency (ULF) and very-low frequency (VLF) waves in the outer radiation belt region. Besides the waves, the relativistic and ultra-relativistic electron fluxes were enhanced with different time lags regarding the magnetic storm main phase. The efficiency of wave-particle interaction in enhancing ultrarelativistic electrons is evaluated by the diffusion coefficient rates, considering both ULF and VLF waves together with phase space density analyses. Results show that local acceleration by whistler mode chorus waves can occur in a time scale of 2–4 h, whereas ULF waves take around 10’s of hours and magnetosonic waves take a time scale of days. This result is confirmed by the phase space density analysis. Accordingly, it shows that peaks of local acceleration of 1 MeV electrons are consistent with the observation of the highest chorus wave amplitude at the same L-shell and MLT. Thus, we argue that whistler mode chorus waves interacting with relativistic electrons are the main physical mechanisms leading to ultra-relativistic electron enhancement, while ULF and fast magnetosonic waves are found as secondary physical processes. Lastly, our analysis contributes to understanding how whistler and ULF waves can contribute to ultra-relativistic electrons showing up in the inner magnetosphere under the HSS driver.

Thermohydraulic Performance and Flow Structures of Diamond Pyramid Arrays

Abstract Surface features are a common heat transfer enhancement method used in a myriad of applications including gas turbines and heat exchangers. One such style of surface features are diamond pyramids, which offer significant heat transfer augmentation for moderate increases in overall pressure losses. This study investigated a suite of additively manufactured pyramids in a variety of sizes and arrangements at relevant scale contained in test coupons. Designs were printed with low surface roughness relative to typical additive components (Ra &amp;lt; 5µm), and pyramids were printed within 100 µm of the design intent. Experimental and computational results indicate that the pressure penalty and heat transfer increased as the pyramids increased in size with aligned pyramids on both channel walls having higher values than staggered pyramids. It was found that implementing the pyramids onto a rough surface had a lesser impact on the friction factor than implementing on a smooth surface, but that the relative increase in heat transfer was the same regardless of the roughness of the endwall. The greatest enhancement to local heat transfer and pressure loss was offset from the location of minimum flow area due to local acceleration around the wake regions. The vortices formed in the wake of the pyramid structures enhanced the endwall heat transfer and shear stress. The performance of the pyramids investigated in this study follows a similar trend to prior studies investigating smooth rib geometries, though certain rib designs had higher heat transfer at lower pressure losses.

Dynamic response of rock landslides and avalanche debris flows impacting flexible barriers based on shaking table tests

Flexible barrier structures are commonly installed in mountainous regions to resist the impact effects of rock avalanches. Without reliable physical data, the study of rock landslide initiation and the impact mechanism of avalanche debris flow under seismic excitation remains poorly understood. In this study, a model of rock slope-flexible barrier system was developed to simulate seismic slope failure behavior and debris flow impact on flexible barriers. Seismic waves in shaking table tests were triaxially loaded to effectively simulate actual seismic responses. The results indicate that the response of the Acceleration Amplification Factor (AAF) is closely associated with seismic damage and deformation within the overlying rock layers and differential propagation of seismic energy on either side of the shear band triggers rockslide initiation. Furthermore, the progressive failure mode of modeled slopes under multiple seismic events is slip-compression cracking failure. Crushing spreading at the intersection of the cracking and slip surfaces is the source of the loose fractured rock mass. Finally, this paper examines the impact patterns and dynamic responses of large individual blocks and loose fractured deposits on flexible barriers. Large blocks cause localized strong acceleration in the steel wire nets, increasing the risk of local damage, whereas loose deposits tend to induce overall seismic deformation and instability of the supporting structure. The natural seismic damage mechanisms of the barrier structure are revealed. It is recommended that flexible barrier structures in earthquake-prone mountainous areas incorporate a reasonable footing design to ensure the columns can deflect out-of-plane in response to seismic activity.

Artificial intelligence-based optimization techniques for optimal reactive power dispatch problem: a contemporary survey, experiments, and analysis

The optimization challenge known as the optimal reactive power dispatch (ORPD) problem is of utmost importance in the electric power system owing to its substantial impact on stability, cost-effectiveness, and security. Several metaheuristic algorithms have been developed to address this challenge, but they all suffer from either being stuck in local minima, having an insufficiently fast convergence rate, or having a prohibitively high computational cost. Therefore, in this study, the performance of four recently published metaheuristic algorithms, namely the mantis search algorithm (MSA), spider wasp optimizer (SWO), nutcracker optimization algorithm (NOA), and artificial gorilla optimizer (GTO), is assessed to solve this problem with the purpose of minimizing power losses and voltage deviation. These algorithms were chosen due to the robustness of their local optimality avoidance and convergence speed acceleration mechanisms. In addition, a modified variant of NOA, known as MNOA, is herein proposed to further improve its performance. This modified variant does not combine the information of the newly generated solution with the current solution to avoid falling into local minima and accelerate the convergence speed. However, MNOA still needs further improvement to strengthen its performance for large-scale problems, so it is integrated with a newly proposed improvement mechanism to promote its exploration and exploitation operators; this hybrid variant was called HNOA. These proposed algorithms are used to estimate potential solutions to the ORPD problem in small-scale, medium-scale, and large-scale systems and are being tested and validated on the IEEE 14-bus, IEEE 39-bus, IEEE 57-bus, IEEE 118-bus, and IEEE 300-bus electrical power systems. In comparison to eight rival optimizers, HNOA is superior for large-scale systems (IEEE 118-bus and 300-bus systems) at optimizing power losses and voltage deviation; MNOA performs better for medium-scale systems (IEEE 57-bus); and MSA excels for small-scale systems (IEEE 14-bus and 39-bus systems).

ELFIN‐GPS Comparison of Energetic Electron Fluxes: Modeling Low‐Altitude Electron Flux Mapping to the Equatorial Magnetosphere

AbstractNear‐equatorial measurements of energetic electron fluxes, in combination with numerical simulation, are widely used for monitoring of the radiation belt dynamics. However, the long orbital periods of near‐equatorial spacecraft constrain the cadence of observations to once per several hours or greater, that is, much longer than the mesoscale injections and rapid local acceleration and losses of energetic electrons of interest. An alternative approach for radiation belt monitoring is to use measurements of low‐altitude spacecraft, which cover, once per hour or faster, the latitudinal range of the entire radiation belt within a few minutes. Such an approach requires, however, a procedure for mapping the flux from low equatorial pitch angles (near the loss cone) as measured at low altitude, to high equatorial pitch angles (far from the loss cone), as necessitated by equatorial flux models. Here we do this using the high energy resolution ELFIN measurements of energetic electrons. Combining those with GPS measurements we develop a model for the electron anisotropy coefficient, , that describes electron flux dependence on equatorial pitch‐angle, , . We then validate this model by comparing its equatorial predictions from ELFIN with in‐situ near‐equatorial measurements from Arase (ERG) in the outer radiation belt.

Zigbee-Based Wireless Sensor Network of MEMS Accelerometers for Pavement Monitoring

In this paper, we propose a wireless sensor network for pavement health monitoring exploiting the Zigbee technology. Accelerometers are adopted to measure local accelerations linked to pavement vibrations, which are then converted into displacements by a signal processing algorithm. Each device consists of an on-board unit buried in the roadway and a roadside unit. The on-board unit comprises a microcontroller, an accelerometer and a Zigbee module that transfers acceleration data wirelessly to the roadside unit. The roadside unit consists of a Raspberry Pi, a Zigbee module and a USB Zigbee adapter. Laboratory tests were conducted using a vibration table and with three different accelerometers, to assess the system capability. A typical displacement signal from a five-axle truck was applied to the vibration table with two different displacement peaks, allowing for two different vehicle speeds. The prototyped system was then encapsulated in PVC packaging, deployed and tested in a real-life road situation with a fatigue carousel featuring rotating truck axles. The laboratory and on-road measurements show that displacements can be estimated with an accuracy equivalent to that of a reference sensor.

Correlation of Local Flow Acceleration in a Narrow Channel and Anomalous Intensification of Separated Laminar Flow in Two-Row Grooves on Its Wall

Correlation of Local Flow Acceleration in a Narrow Channel and Anomalous Intensification of Separated Laminar Flow in Two-Row Grooves on Its Wall

Characterizing the evolution of the Daguangbao landslide nearly 15 years after the 2008 Wenchuan earthquake by InSAR observations

The Daguangbao landslide (DGBL), the largest landslide triggered by the 2008 Ms 8.0 Wenchuan earthquake, has received much attention, but its long-term post-earthquake evolution and driving force of activity are still poorly understood. As the evolutionary behavior of the DGBL is complicated by the influence of mainshock, aftershocks and rainfall, it is of great significance to study the dynamics of the landslide. In this study, a systematic and comprehensive framework for assessing the long-term stability and risk of co-seismic landslides was proposed. Based on ALOS-1 and Sentinel-1 data, time-series InSAR technology was used to reveal the nearly 15-year post-seismic evolution characteristics of the DGBL at different stages, followed by the prediction of the stabilization time, the estimation of the landslide thickness and risk assessment. The first stage was identified as three years after the earthquake (2008–2011). During this stage, ALOS-1 results show that the deformation of DGBL was intense (300 mm/year) with uneven spatial distribution, and an aftershock (Ms 5.3), along with increased rainfall, triggered its acceleration in 2009. The second stage was the period from 2014 to 2022. For this stage, we used the mass conservation approach to invert the thickness of the DGBL, revealing that a new sliding surface and thickness center had formed following the co-seismic failure in 2008. Sentinel-1 time series results indicated that the DGBL remains active even 15 years after the Wenchuan earthquake, but the deformation of DGBL has significantly slowed down (50 mm/year). The stabilization time for different segments of DGBL was predicted to range from 2027 to 2040 according to an exponential model. Beyond the overall trend of recovery, seasonal movements (including localized acceleration in 2021) closely related to rainfall remained evident, but the impact of aftershocks on the DGBL was severely weakened over time. UAV and field survey results suggested that the risk of localized debris flows at DGBL still exists. Our study improves our understanding of the long-term evolutionary pattern of DGBL and provides an important reference for post-earthquake landslide risk assessment and disaster prevention.

Rapid Transport of Energetic Electrons to Low L $L$‐Shells: The Key Role of Electric Fields

AbstractThe dynamics of the outer radiation belt are traditionally associated with wave‐particle resonant interactions, which provide local electron acceleration and losses through very low‐frequency waves, and electron radial transport by ultra‐low frequency waves. However, these processes cannot explain observations of rapid radial transport of energetic electrons (on a time‐scale of a couple of hours), deep into the inner magnetosphere (down to , mapping to magnetic latitude in the ionosphere). This transport is likely associated with strong convection electric fields forming around the plasmapause. To investigate these rapid, low‐latitude electron transport, we combine low‐altitude observations of energetic electron fluxes by the ELFIN CubeSats and DMSP satellites, SuperDARN measurements of ionospheric plasma flows (electric fields), and equatorial measurements of energetic electrons and electric fields by THEMIS. Our findings demonstrate that the rapid filling of the slot region by keV electrons is directly associated with electric field penetration to low latitudes (down to ). The proposed electron transport scenario, the direct penetration of energetic electrons by strong, localized electric fields, underscores the importance of ionosphere‐magnetosphere coupling in radiation belt dynamics.

One‐Step Local Acceleration Process of Ultra‐Relativistic Electrons in the Center of the Outer Radiation Belt: Observations

AbstractUltra‐relativistic (&gt;3 MeV) electrons are considered as a novel, separate population in the Earth's radiation belts since their loss and acceleration features are distinct from relativistic (∼MeV) electrons. The dominant acceleration mechanism of ultra‐relativistic electrons remains a subject of ongoing debate. Some studies suggest that the acceleration mechanism of ultra‐relativistic electrons is energy‐dependent: local acceleration dominants the enhancement of ∼3–5 MeV electrons while two‐step acceleration process leading by radial diffusion effects for ∼7 MeV electrons. However, a recent study (https://doi.org/10.1126/sciadv.abc0380) theoretically demonstrated that local acceleration could accelerate electrons up to &gt;7 MeV directly under the extreme plasma depletion. In this study, we report four enhancement events of ultra‐relativistic electrons that occurred in September and October 2017. Analysis of phase space density (PSD) radial profiles and contours demonstrate that local acceleration plays the dominant role in the enhancements of ∼7 MeV electrons in mid‐September and mid‐October, supported by persistently growing peaks in electron PSD. While enhancements of ultra‐relativistic electrons in other two events still show energy‐dependent phenomenon, our results provide the observation evidence that one‐step local acceleration process can lead to the enhancement of ∼7 MeV electrons in some events. We suggest that the acceleration process of ultra‐relativistic electrons may be subject to the efficiency of local acceleration.

Computational fluid dynamics simulation of cryogenic vertical upflow boiling under Earth gravity

This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer phenomena important to space applications. The computational fluid dynamics (CFD) model utilized the coupled level set volume of fluid (CLSVOF) method, incorporating additional source terms for bubble collision dispersion force and shear lift force in the momentum conservation equation to enhance simulation accuracy. The simulations were conducted for two mass velocities (G = 526 and 804 kg/m2s) and three different heat flux levels (approximately 10%, 30%, and 70% of critical heat flux (CHF) under Earth gravity. The model was validated against measured wall temperature data acquired from the authors’ previous experimental studies, demonstrating average deviations of less than 2.8 K across all operating conditions. The simulated two-phase flow contours illustrated various flow patterns, including bubbly, slug, churn, and annular. Both mass velocity and heat flux were observed to impact the onset of nucleate boiling (ONB), bubble nucleation, growth, and coalescence, and overall vapor structure. The simulations also offered insight into axial and radial void fraction and velocity profiles, revealing local flow acceleration trends synchronized with void fraction development. A comparison between predicted and measured bulk fluid temperature profiles showed excellent agreement, further validating the CFD model’s accuracy and practical usefulness for two-phase cryogenic flow boiling simulations in space applications.

Causal Inference in the Outer Radiation Belt: Evidence for Local Acceleration

AbstractCurrently, there is no clear understanding of the comprehensive set of variables that controls fluxes of relativistic electrons within the outer radiation belt. Herein, the methodology based on causal inference is applied for identification of factors that control fluxes of relativistic electrons in the outer belt. The patterns of interactions between the solar wind, geomagnetic activity and belt electrons have been investigated. We found a significant information transfer from solar wind, geomagnetic activity and fluxes of very low energy electrons (54 keV), into fluxes of relativistic (470 keV) and ultra‐relativistic (2.23 MeV) electrons. We present evidence of a direct causal relationship from relativistic into ultra‐relativistic electrons, which points to a local acceleration mechanism for electrons energization. It is demonstrated that the observed information transfer from low energy electrons at 54 keV into energetic electrons at 470 keV is due to the presence of common external drivers such as substorm activity.

Interrelation between the Local Acceleration of Laminar Flow in a Channel and the Anomalous Heat Transfer Enhancement in Inclined Two-Row Grooves

Interrelation between the Local Acceleration of Laminar Flow in a Channel and the Anomalous Heat Transfer Enhancement in Inclined Two-Row Grooves

PIV And Schlieren Measurements Of A Linear Plug Nozzle Jet Interacting With External Flow

Plug nozzles represent a promising concept as part of a propulsion system for space launchers. The ability to adapt the nozzle jet to the ambient pressure level improves thrust performance in overexpanded operating conditions compared to conventional bell nozzles. In this study, the dynamics of a jet flow of a cold air plug nozzle model are investigated by means of PIV and high-speed schlieren measurements. For a fixed nozzle pressure ratio, the jet flow is studied in an externalouter flow environment with sub-, trans-, and supersonic Mach numbers. The effect of plug truncation is analyzed as well. It is found that the outer Mach number strongly influences the flow pattern, local velocity magnitudes and aerodynamic modes. The frequency and dominance of vortex shedding and jet screeching modes are found to be highly dependent on the Mach number of the surrounding flow. A truncated plug introduces local accelerations in its base wake region, causing an increased shock strength in the jet structure. In addition,it causes severe periodic fluctuations in the flow that are transmitted to the shear layer and induce acoustic wave emissions. The impact of the plug length on the flow dynamics has been seen to decrease with increasing outer Mach number.