Plume Behavior Research Articles

Plume Rise from a Stack Based on the Volkov Formula

Plume rise from most sources is an important factor in determining ground-level concentration of air pollutants. Various attempts have been done to compute plume rise from stationary sources. Volkov (1979) proposed a formula for calculation of plume dimensions (height and length) from a stack, while most of the well-known plume rise equations can only compute plume rise or plume height. Both plume height and plume length should be determined in some cases, for example in study of stack and cooling tower plume mergence, plume behavior (lofting, fanning, coning, looping, trapping and fumigation) etc. Because there are little studies in the world regarding the accuracy of the Volkov equation, the aim of the present work is to investigate the validity of the Volkov formula based on 5 statistical tests including the relative error, mean square error, root mean square error, coefficient of determination and Nash-Sutcliffe coefficient. The results revealed that (1) the Volkov equation better predicts plume rise at the distance of 60 m than 30 m from a typical stack, (2) considering the value of 0.5 instead of 0.4 or 0.65 for n in the Volkov formula will lead to more accurate results and (3) plume dispersion pattern was categorized as lofting. Overall, the Volkov equation can be an acceptable method to study of plume rise; nevertheless more studies must be conducted in the future with regard to the accuracy of the Volkov formula.

Eruption style and dynamics of the ~ 87 ka Baricha peralkaline rhyolite eruption in Ethiopia

Peralkaline rhyolites are a rare magma type, typically associated with continental rift settings, and characterised by excess alkalis relative to alumina and a moderate-low viscosity compared to calc-alkaline equivalents. Despite their prevalence in extensional rift settings, such as the Main Ethiopian Rift, eruption dynamics of peralkaline magmas are poorly understood and have never been directly observed. To address the knowledge gap, this study investigates the style and dynamics of the ~ 87 ka explosive eruption at Baricha volcano as a case study. This eruption deposited widespread pumice lapilli fall and pyroclastic density currents, which provide valuable information on pre- and syn-eruptive magmatic processes. By examining the physical and textural features of the eruption products at different stratigraphic levels, we reconstruct eruption dynamics over time. Our analysis reveals that the eruption had three distinct phases, each characterised by different types of tephra fall deposits and associated with different plume and vent conditions. Specifically, deposits of phases 1 and 3 were characterised by massive and well-sorted tephra falls indicative of sustained plume behaviour, while phase 2 deposits were bedded, lithic-rich (i.e. non-juvenile fragments) tephra falls, and pyroclastic density current deposit associated with an unsteady plume and vent-widening phase. The pumice (8–16 mm size fraction) from this eruption is microlite-free, with a bulk density of 400–700 kg m−3 and > 60% total vesicularity. The vesicle size distribution is polymodal, with the most frequent size ranging from 0.001 to 2.4 mm and an estimated vesicle number density of 0.07*107 to 1.6*107 mm−3. The textural observations suggest rapid nucleation occurred during the late phases of magma ascent. Calculated decompression rates of the ascending magma were 0.07–5.6 MPa/s and show a variation between the eruption phases. We conclude that the shift in eruption dynamics alternating between steady to unsteady plume behaviour during the eruption was likely driven by changes in conduit geometry, lithic abundance of the eruptive mixture, decompression rate, and fresh magma injection.

Study on the diffusion and blocking behavior of bubble plumes in Cross-Flow

Abstract With the deepening of the concept of environmental protection, environmental problems in dredging engineering have attracted more and more attention. The diffusion of suspended particulate matter is inevitable in the process of dredging. A bubble plume, as a multiphase linear plume, has been widely studied because it can block the diffusion of suspended particulate matter in water. To explore the formation characteristics of the bubble plume, we evaluate the formation quality of the bubble plume qualitatively and quantitatively, analyze the effect of the bubble plume on blocking the diffusion of suspended particulates under different operating conditions (the type of bubble plume generation device, the number of bubble plume rows, and the ventilation flow rate) and environmental conditions (water flow velocity), and study the movement trajectory of blocked particles and blocked failed particles. A series of experiments on bubble plume characteristics and bubble plume blocking the diffusion of suspended particles were conducted to analyze the particle distribution characteristics and bubble plume blocking effect under the interaction of transverse flow and bubble plume. The results show that the better the quality of the bubble plume is, the lower the transverse flow intensity is, and the better the barrier effect of the bubble plume is.

Risk assessment of gas plume dispersion in bunkering of alternative fuel through validated computational fluid dynamics approach

Abstract Maritime decarbonization is crucial in fighting climate change. Adopting low-carbon alternative fuels could help reduce greenhouse gas (GHG) emissions by 50% by 2050 compared to 2008. While liquified natural gas (LNG) has gained a strong foothold in the maritime sector over the past decades, the trend is shifting toward adopting lower and zero-carbon hydrogen and its carriers, such as methanol and ammonia, as alternative fuels. Quantifying risks from accidental leakages during storage and transfer of these alternative fuels using numerical models is required and commonly adopted in industries. The process leverages multiple models and tools for risk assessments with different accuracy levels and costs ranging from integral models to Lagrangian techniques and Eulerian approaches such as computational fluid dynamics (CFD). Increasingly, CFD approaches are employed for near-field dispersion analysis to assess the risk of accidental leakages. Despite their high computational cost, CFD models offer better accuracy than integral and Lagrangian models. In this work, we developed a CFD-based framework as a quantitative tool for risk assessment purposes. Our framework aims to (1) offer finer gas dispersion resolution with a detailed representation of surrounding structures and geometries, (2) minimize reliance on assumptions and empirical models to capture flow dynamics and gas dispersions accurately, and (3) mitigate conservative estimates and over-design of safety measures. The framework was validated using experimental data from various field tests, including a recent one involving releasing cryogenic liquids into the atmosphere. After successfully validating and comparing with experiments and other available tools, the proposed framework investigated gas plume dispersion from accidental leakages during fuel bunkering operations in ship-to-ship and shore-to-ship scenarios. The data obtained from CFD simulations was subsequently utilized to construct a surrogate model for fast prediction of gas plume behavior under varying environmental conditions. This facilitated the development of an effective emergency response plan.

Long-term observations of the turbid outflow plume from the Russian River, California

Understanding the mechanisms that spread freshwater away from small river systems and form turbid, low-salinity coastal plumes is crucial for assessing water quality in coastal waters. We present an analysis of 15 years (January 2004 to December 2018) of daily MODIS Aqua satellite data and in situ instrument data on the turbid freshwater plume that forms off the Russian River (California, USA), a prototypical Mediterranean-climate, small mountainous river system (SMRS). We present per-pixel statistical metrics and regression analyses to identify and quantify the controls on the extent and configuration of the plume exerted by river discharge, waves, winds, and tides. While freshwater outflow exhibits a persistent signal in nearshore waters, a large-scale plume only extends offshore into coastal waters during high river flow, when plume turbidity can be detected more than 10 km offshore from the river mouth. Our results show times when wave radiation stress exceeds outflow inertia, confining the plume within the surf zone and leading to an absence of detectable plume turbidity in coastal waters. Although tidal currents significantly influence the plume near the inlet, wind forcing is the primary control on plume shape and extent in coastal waters, deflecting the turbid outflow more than 30 km upcoast or downcoast of the river mouth with respective wind directions. Coriolis forcing is also significant and observed most clearly during periods of high river discharge and low wind forcing. In addition to introducing novel remote sensing methodology for SMRS plume analyses, these findings highlight the complex interplay of forcing related to tides, river discharge, winds, and waves in shaping the behavior of SMRS plumes. New insights include the impact of tides on larger discharges, the role of Coriolis forcing in SMRS plumes, and the effect of cross-shore winds on plume compression. Further, by considering the Russian River as a model for SMRS, this study can be used to ground-truth existing numerical models of small river plumes and to contribute to understanding critical for managing coastal water quality and nearshore ecosystems.

Simulating the near-field dynamic plume behavior of disposed fine sediments

Projections of the effects of fine sediment disposals, relevant for managed estuaries and tidally influenced coastal areas, are typically based on numerical far-field models. For an accurate consideration of the disposal itself, near-field models are often needed. The open source near-field model, PROVER-M, simulates the relevant processes of the physics based, dynamic behavior of disposed fine sediments in coastal waters and is applied in this study. First, new small scale laboratory experiments of instantaneous disposals are presented, documenting the dynamic behavior of fine material disposed in shallow waters. Second, results of the PROVER-M model are shown for disposals in three different settings: (1) a field-scaled study complementary to the laboratory set-up, (2) a parametric study of sequentially varied model input and (3) a far-field model coupling for estimation of the PROVER-M impact. By comparing results of the laboratory experiments to the PROVER-M model, the physical behavior of PROVER-M is successfully validated. The impact of the ambient setting and dredged material parameters is evaluated by the PROVER-M simulations, where the results show non-linear, complex interdependencies of the input parameters on disposal properties in dependence of ambient site conditions and material composition. In this context, limits of the model application are assessed and critically discussed. Finally, an exemplary coupling to a far-field model based on a real set of disposals in the tidally influenced Weser estuary (Germany) illustrates the potential impact of PROVER-M for assessing far-field suspended sediment concentration (SSC), with increased maximum SSC values of up to 10%.

Study on the window spill fire plume trajectory of over-ventilated intermediate-scale compartment fires

The fire plume behavior of over-ventilated compartment fire is believed to be related with the façade fire. When the fire plume is reattached to the façade wall, the combustible materials over building wall are potential to be ignited soon. To investigate the window spill fire plume trajectory of over-ventilated intermediate-scale compartment fires, a modeling of fire plume trajectory is set up by using the energy conservation equation and spread theory. The temperature history of over-ventilated compartment fire is conducted by using a 1.35 m (L) × 1.35 m (H) × 1.35 m (W) compartment with window opening aspect varied from 1.12 to 4.44 and HRR differed from 200 kW to 1000 kW. The temperature of fire plume is recorded by the thermocouple mesh and the IR camera. It shows that the modelling theory could be used to predict the shape of fire plume. It agrees well with experimental result. The heat release rate of compartment fire is found to impact little influence on the shape of fire plume regarding a fixed opening dimension. It could provide a reasonable method for fire plume trajectory prediction of the intermediate-scale enclosure fire under an over-ventilated condition.

Investigation on the restrain effect of air curtain to the spilled flame and its heat flux of a compartment-facade fire

This paper investigates the restrain effect of air curtain to the spilled flame and its heat flux of a compartment-facade fire. A compartment model of 1.2 m × 0.9 m × 0.9 m is established in this study, and an air curtain is facilized at the compartment opening for fire protection. The air curtain jet velocity, the heat release rate as well as the opening dimension are changed as representative to typical fire scenarios. Flame behavior and heat flux profile of spill plume are captured by CCD cameras and water-cooled heat flux gauge for discussion. Results show that the air curtain jet could have a substantial impact on the flame behavior of spilled plumes from a compartment-facade fire. Compared to that of free condition without air curtain, the flame height becomes 20 % lower as the jet velocity to be 2 m/s, while it becomes 60 % lower as the jet velocity to be 5 m/s. At the meantime, the spilled plume is noticeably influenced by the “restricting effect” of the air curtain and thus flame trajectory is significantly flattened by the inertia force of the air curtain but also pushed farther from the facade wall, resulting in an increasing of flame depth. The decreasing in flame height plus the increasing flame depth would result in the reduction of heat flux intensity upon the facade wall, which is helpful for the fire protection of the facade wall. Then, a normalized factor of Υ is further proposed to the new correlation of flame height under various air curtain jet conditions at the opening. Regarding to different ejected flame behavior at the presence of air curtain jet, the heat flux upon the facade wall is quantitative analyzed to evaluate the thermal impact of spilled plume from the compartment fire. Finally, new correlations of the vertical heat flux upon the facade wall could be well achieved by a function of normalized height factor Z/Zf, v.

Physicochemical behavior and impact of CO2 and CH4 plumes during gas-rich water leakage in a shallow carbonate freshwater aquifer

Carbon capture and storage (CCS) is a promising technology for reducing CO2 emissions. Significant concerns have emerged about the potential leakage of CO2 into shallow aquifers, highlighting the risk to water quality and environmental safety. This underscores the importance of finding monitoring tools suitable for different geological scenarios. If leakage occurs in the context of depleted reservoirs being used for CO2 storage, residual CH4 from the storage complex will likely be entrained together with CO2. However, few studies have addressed the implications of CH4 presence and its potential as a monitoring parameter during CO2 leakage.To address this gap, we simulated a leakage event by injecting water enriched with CO2 and CH4 into a shallow limestone aquifer. The impact of the injection was monitored using a combination of laboratory measurements on water samples and in-situ sensors located downstream from the injection well.All parameters were affected by the simulated leakage. Some monitoring tools allowed us to differentiate the leakage event from natural variations. A key finding of this study was that at 7 m from the injection well, the CH4 breakthrough occurred roughly one day before the CO2 breakthrough, highlighting the potential of CH4 as an early indicator of CO2 leakage and suggesting interesting prospectives for industrial-scale sites. However, further research is needed to confirm the potential of CH4 as a CO2 leakage indicator at industrial scales, due to potential methane oxidation and loss of the signal with longer times and distances.This study contributes to a better understanding of the potential risks and effective monitoring strategies associated with CO2-CH4 leakage in carbonate aquifers.

Effect of the combustion chamber length in combustion instability of low-toxic hypergolic thruster

In this study, the effect of combustion chamber length on the hypergolic combustion instability of hydrogen peroxide-based propellants was investigated. Twenty-four hot-firing tests were conducted using a combination of 95 wt.% hydrogen peroxide and amine-based fuel with a drop test ignition delay of 5.65 ms and an adjustable length hypergolic thruster. When the chamber length was changed from 80 mm to 120 mm, the root mean square (RMS) combustion instability decreased drastically from 24 % to 9 %. The measured high-frequency instability was considerably consistent with the longitudinal resonance mode of each combustion chamber geometry. Low-frequency instability, that is, the rate of popping, occurred predominantly in all hot-firing tests. Within the 245–418 Hz range, its frequency increased as the chamber length decreased or the chamber pressure increased. The high-speed camera image of the exhaust plume coincided with the period of low-frequency instability, which was confirmed by the periodic popping of the propellant. Combustion instability was analyzed in depth by performing power spectral density (PSD), wavelet synchro squeezed transform (WSST), dynamic mode decomposition (DMD), and image intensity analyses using the chamber pressure and exhaust plume images. DMD decomposed the plume behavior into one expansion mode and three plume decay modes, and it also matched the low-frequency instability of the chamber pressure with an error of less than 5 %.

Time- and angular-distribution of ion current in pulse-laser ablation plume of aluminum

Thrust generation through pulse-laser ablation has been proposed for use in propulsion systems in space. However, to achieve a high thrust performance, the energy efficiency must be improved and it is important to determine the behavior of the ablation plume to identify where energy losses occur. In this study, the ion-current distribution of a plume with aluminum ablation was measured. A neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with a wavelength and pulse width of 1064 nm and 9 ± 2 ns, respectively, was used for the ablation. Experiments were conducted at three different fluences: 10, 15, and 20 J/cm2. The fluence was varied in two ways: changing the beam-spot diameter while maintaining the single-pulse energy and changing the single-pulse energy while maintaining the beam-spot diameter. The ion current was measured at various angles using Faraday probes. The generated impulse and reduction mass were also measured. By combining and analyzing the results, the divergence angle of momentum, mean valence of ablated aluminum, and energy efficiencies of several processes were estimated.

Integration of hydrodynamic and water quality modeling to mitigate the effects of spill pollution into the Nile River, Egypt.

Mitigating spill pollution in the Nile River is crucial to protecting aquatic life, water quality, and public health. Extensive studies focused on the assessment of water quality and hydrodynamics of the Nile River, but there have been relatively few studies that have applied integrated hydrodynamic and water quality modeling approaches to simulate actual accidents in the Nile Fourth Reach. The goal of this study is to develop advanced computational models to simulate accidental spills in the Nile River and track the resulting impacts on water quality. Hydrodynamic and water quality simulations were performed using Delft3D software for 144km of the Nile River, Egypt, from El-Menia to Assuit. Once the hydrodynamic and water quality models were calibrated, two phosphate spill scenarios were modeled under maximum and minimum flow conditions. The spatial distribution of the spill plume along the studied river section was visualized every 12h following the spill occurrence for both scenarios. The results of the research were calibrated and validated against measured field data. In addition, various error and performance indicators were calculated to thoroughly assess the rigor and reliability of the results. The results demonstrated that flow velocity was the main factor influencing the spill plume characteristics and behavior. Initially, advection force plays a significant role after a spill occurs. After that, phosphate becomes mixed and diluted through dispersion. The spill plume took less time to reach downstream areas during the period of maximum flow compared to minimum flow. Additionally, the concentration of phosphate decreased as the water flowed downstream. The spatial distribution of the spill over time can assist water treatment facilities in developing mitigation strategies to address the spill impacts. However, complex Nile River dynamics demand extensive computational power. Therefore, the model was simplified for spill events, using the modeling capabilities to analyze hypothetical spills and contaminant spread in the absence of real data.

A process-led approach to framing uncertainty and risk in CO 2 storage in the subsurface

Carbon capture and storage (CCS) requires the safe, long-term storage of CO 2 in the subsurface. This challenges subsurface practitioners to build on and adapt many of the techniques and processes developed for hydrocarbon exploration and production to create innovative approaches to assessing CO 2 storage risk and uncertainty. A wide-ranging and integrated understanding of the processes controlling CO 2 behaviour in the subsurface is required to facilitate effective risk identification and characterization. In this paper we explore the different physical processes acting within storage formations and their evolution throughout the injection project life cycle to illustrate key controls on CO 2 plume behaviour and frame risk identification and characterization. An approach applying wide-reaching premortem risk identification coupled with evidence-led uncertainty characterization is described to frame inputs for detailed risk characterization and management activity during early screening of prospects for CO 2 storage.

A physics-based model of thermodynamically varying fuel moisture content for fire behavior prediction

Fuel moisture content (FMC) is a critical parameter in fire and plume behaviors, showing diurnal and spatial variations influenced by local meteorological conditions, soil characteristics, and fuel properties. In low-intensity fires, small-scale FMC variations intensify, leading to an amplification of their effects on fire physics. In an effort to capture these variations, this paper presents the development of a physics-based model that couples a thermodynamic-based FMC prediction model for dead fuels with the Fire Dynamics Simulator of the National Institute of Standards and Technology. The model accuracy is validated against several existing experimental data, showing improvements over the baseline model which uses the kinetic-based Arrhenius drying approach. A case study of flame propagation in a small fuel bed is also presented, indicating the improved performance of the new model and its novel capabilities in capturing complex processes of fuel drying and moisture flux exchanges between the fuel and ambient atmosphere.

An enhanced fourier neural operator surrogate for radioactive plume transport forecasting

Accurate real-time forecasts of atmospheric plume behavior are crucial for effective management of environmental release incidents. However, the computational demands of weather simulations and particle transport codes limit their applicability during emergencies. In this study, we employ a U-Net enhanced Fourier Neural Operator (U-FNO) to statistically emulate the calculations of the WSPEEDI dose forecasting numerical simulator, using pre-calculated ensemble simulations. The developed emulator is capable of effectively simulating any radioactive-release scenario and generating the time series of dose distribution in the environment 4000 times faster than the numerical simulator, while still maintaining high accuracy. It predicts the plume direction, extent, and dose-rate magnitudes using initial- and boundary-condition meteorological data as input. The speed and efficiency of this framework offers a powerful tool for swift decision-making during emergencies, facilitating risk-informed protective actions, evacuation execution, and zone delineation. Its application extends to various contaminant release and transport problems, and can be instrumental in engineering tasks requiring uncertainty quantification (UQ) for environmental risk assessment.

Modelling CO2 storage in oil and gas reservoirs in the Gippsland Basin

The Gippsland Basin has world class geology for carbon capture and storage (CCS) and a long history of oil and gas production. Depleted oil and gas fields within the Gippsland Basin that are candidates for carbon dioxide (CO2) storage are in close proximity to existing infrastructure that could be repurposed as part of a CCS project. Modelling of CO2 storage in the depleted Bream oil and gas reservoir is being progressed. Bream reservoir properties are very well understood due to extensive geological and geophysical data sets available from wells and seismic data. Additionally, the field has been through three key phases of development during its production history; oil production and gas re-injection in 1988, gas cap blowdown started in 2002, and seasonal gas storage and withdrawal started in 2012 through to field shut-in in 2020. This provides a wealth of dynamic data that is used to calibrate the reservoir models to improve our confidence in the CO2 plume prediction. However, there are also challenges in modelling CO2 storage in depleted fields. Unlike saline aquifers, CO2 can be injected into a three-phase depleted reservoir that contains residual oil and gas saturation. The key aspects of our workflow to evaluate the plume behaviour are presented in this paper.

Particle dynamic behaviors in bubble curtain barriers blocking the diffusion of sediment

Bubble curtains are linear multiphase plumes that are used in industry and engineering to reduce diffusive flows between two zones. The circulating shear flow generated by the bubble plume can effectively create a particle barrier in the water; thus, it is also widely used to suppress the diffusion of suspended particles during dredging operations. To clarify the interaction mechanism between the bubble curtain and suspended particles under pressure-driven flow, experimental studies and numerical simulations were conducted to investigate the particle dynamics in the flow field around the bubble curtain. In this study, we established a formal analogy between a bubble curtain and an air curtain and qualitatively identified four typical distribution zones of the particles in the flow field. Based on the quantitative measurements and theoretical considerations, the optimal operating conditions and the upper limit of effectiveness of the bubble curtain were determined. In addition, the blocking behavior and efficiency of bubble plumes on particles with different ReU and FrUgnumbers and different particle properties were simulated via the computational fluid dynamicsdiscrete element method (CFDDEM) numerical simulation method.

Experimental study on the effect of adjacent near-wall heat sources on the particle deposition

Adjacent near-wall heat sources are widely used in indoor environments. It is important to investigate the particle deposition under the influence of coupled thermal plumes arising from adjacent near-wall heat sources to improve indoor air quality and control harmful particle deposition. Thus, this study scrutinizes the behavior of thermal plumes emanating from adjacent near-wall heat sources, focusing on the deposition of particles with diameters of 0.3 μm, 0.5 μm, 1.0 μm and 3.0 μm on the wall behind the heat sources. These findings are juxtaposed with the pattern of particles with varying sizes situated above the single near-wall heat source and away from the heat sources. The study delves into the impact of varying surface temperatures and the distance from the wall behind the heat sources, as well as the top surface of the heat source, on particle deposition in 29 distinct cases. The results indicate that the deposition velocity of particles with the same size is highest above the adjacent near-wall heat sources, followed by that of a single near-wall heat source, and finally, locations away from the near-wall heat source. Also, the decay rate loss coefficient of particles with the same size above the adjacent near-wall heat sources increases with a decrease in the distance of the heat sources from the wall behind them, an increase in the temperature of the heat sources, and a reduction in distance from the top surface of heat sources.

Factors influencing the variation of the Sepik-Ramu River system's sediment plume off the north coast of New Guinea

The Sepik-Ramu River system (SRRs) is a principal contributor of terrestrial materials to the pelagic waters of the tropical Western Pacific, boasting the highest sediment discharge in New Guinea. However, this system's sediment outflow and dispersal patterns are not well-documented. This study seeks to address this gap by analyzing the estuarine sediment plumes, which are the key indicators of the marine dispersion of terrestrial materials. Utilizing Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2010 to 2020 and applying the Novoa17 algorithm, we examined the distribution and temporal evolution of the sediment plume of the SRRs estuary. The sediment plume was categorized into two distinct zones: core and diffuse, based on suspended sediment concentration (SSC) levels. Our findings reveal significant seasonal variations of these sediment plumes in the nearshore. The plume area expands during the wet season and contracts during the dry season, respectively, with core and diffuse plumes sharing similar change characteristics. The diffuse plume primarily extends northeast in the wet season and subsequently shifts northwest in the dry season, and the core plume consistently points to the northeast. The study further explores the driving factors and mechanisms behind these patterns, identifying river discharge as the primary influence on the core plume and sea surface winds and coastal currents as determinants of the diffuse plume's behavior. Interannual variations in the plume characteristics were found to be influenced by the El Niño-Southern Oscillation (ENSO), which indirectly affects plume dynamics through its impact on regional precipitation. During El Niño events, characterized by drier conditions and reduced discharge, the plume SSC and area typically decrease. During La Niña events, the plume's SSC and area typically increase, except for the 2011 super La Niña's negative anomaly, caused by the rain belt's excessive westward shift.

The investigation of laser beam interaction with aluminum/titanium overlap joint

In-situ analysis of dissimilar laser welding in overlap configuration, which finds the most frequent application in industry, attracts an increasing attention of the research community. In the present work, emission spectroscopy and high-speed imaging were used to investigate the vapor plume behavior during a Yb:YAG laser pulse on the overlap joint between pure titanium and aluminum alloy A5754. A 15 ms long laser pulse was applied to the overlap joints, where titanium and then A5754 were placed on the top. Correlation of the obtained results with post-mortem observation of the impact zones and with a finite-element model of the keyhole evolution was performed. The combination of these approaches facilitated the development of a comprehensive phenomenological timelines of the processes, along with an evaluation of the efficacy of the employed online methods to discern the involvement of the bottom material with the melted zone. The considered configurations showed very different behavior: with reflective A5754 placed on top, the use of high laser power produced an intense keyhole propagation in bottom titanium plate, inducing rapid mix between the elements, while with titanium on top, the use of lower laser power produced prolongated keyhole stagnation at the interface with reflective A5754. High-speed imaging showed very fluctuating behavior of the plume, where the involvement of the bottom material was traduced either by a drastic drop of thermal and atomic emission after the keyhole tip enters the bottom A5754 plate, or by strong periodic bursts of Ti-rich jet after the keyhole reaches the bottom titanium plate. The results of emission spectroscopy were found in adequation with the involvement of bottom material into the melted zone, however, they are affected by plume fluctuations and by the pollution of the top plate by volatile elements.