Crossflow Speed Research Articles

Experimental study of downstream local heat flux of pool fires under relatively strong cross flows

Pool fire is the common form of combustion posing hazard to surroundings by thermal heat transfer. The local heat flux of pool fire under relatively small cross flow has been widely studied. However, none work investigates the influence of relatively strong cross flow to the local heat flux of pool fires. In this study, experiments are carried out to reveal the effect of strong cross flow on the downstream heat flux distributions of pool fires. Four square quartz sand boxes with the side lengths of 8 cm, 10 cm, 15 cm, and 20 cm are applied to simulate the pool fires. The cross flow speed ranges from 0 to 5.0 m/s. Eight local heat flux gauges are aligned downstream with 6 cm interval. In still air or when the flame base drag is smaller than the distance (6 cm) between the closest heat gauge and downstream pool rim, the heat flux decreases monotonically with the downstream distance. For other conditions, the local heat flux firstly increases then decreases with the downstream distance. And the location of peak local heat flux is the same as the flame base drag length. For a given pool size and heat release rate, the evolution of local heat flux with cross flow speed is complicated and shows three trends. Local heat flux is determined by the flame base drag representing the influence of pool dimension, cross flow speed, heat release rate and side entrainment, as well as downstream distance. Two regions of local heat flux are observed based on the different physics of heat transfer. Correlations are obtained for the two regions respectively and agree well with the experimental data.

On particle fountains in a crossflow

We present new experiments of particle-laden turbulent fountains in a uniform horizontal crossflow, $u_a$ , with momentum flux, $M_0$ , and buoyancy flux, $B_0$ . We use the ratio, $P$ , of the crossflow speed to the characteristic fountain speed, $M_0^{-1/4}|B_0|^{1/2}$ , and the ratio $U$ , of the Stokes fall speed of the particles, $v_s$ , to the characteristic fountain speed, to characterise the dynamics of a particle fountain in a crossflow. We find that the dynamics of these particle fountains can be categorised into three distinct regimes. In regime I when the fall speed of the particles is small in comparison with the characteristic fountain speed ( $U\ll 1$ ), the particles remain well-coupled to the fountain fluid and the flow essentially behaves as a single-phase fountain in a crossflow. In the transitional regime II ( $0.1< U<1$ ), when the fall speed of particles is comparable to the characteristic fountain speed, we observe some particles separating from the fountain fluid during the descent of the flow which leaves some fluid neutrally buoyant. As $U>1$ (regime III), we observe particles separating from the fountain as it rises from the source. We measure the average dispersal distance of the particles and the speed of the descending particles as a function of $U$ and $P$ and compare these results with models of a single-phase fountain in a crossflow. We build a regime diagram to describe the effect of $U$ and $P$ on the flow dynamics and consider our work in the context of deep-submarine volcanic eruptions.

Effects of gas flow speed on bead geometry and optical emissions during laser powder bed fusion additive manufacturing

PurposePowder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.Design/methodology/approachA filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.FindingsThe results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.Originality/valueTo the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

Flame detachment of jet fires at windward and leeward sides in crossflow: Experiment and a Damköhler number based model

Flame detachment of jet fires are important in practical application such as elevated flares, where flame detachment is used to minimize damage on nozzle and the attendant fire safety problem. In this work, detachment behavior of a jet flame under crossflow was studied, especially focused on the difference in critical crossflow speeds for flame detachments at the windward and leeward sides of the nozzle exit, such problem has not been quantified previously. Experiments were conducted in a wind tunnel using propane as the fuel by adopting jet nozzles with inner diameters of 3, 5, 8, and 10 mm and an outer diameter of 15 mm; together with inner diameters of 13 and 15 mm and an outer diameter of 20 mm. The results showed that the critical crossflow speeds for flame detachments both at the windward and leeward sides decreased as the jet velocity increased. The critical crossflow speed for flame detachment at the windward side was weakly dependent on nozzle diameter, while that at the leeward side increased with the increase in nozzle diameter. A model was proposed to characterize this difference on the basis of a Damköhler number, which is defined as the ratio of the characteristic mixing time to chemical reaction time. A satisfactory correlation was achieved for the difference in critical crossflow speeds for flame detachments at the windward and leeward sides as a function of fuel jet velocity and nozzle dimensions of inner diameter and wall thickness.

Estimation of overall droplet size distribution from a local droplet size distribution for a jet in crossflow: Experiment and multiphase large eddy simulations

• Experiment and multiphase large eddy simulations (LES) of oil jet in crossflow. • LES was coupled with the population balance model to compute local droplet size. • Maximum energy dissipation rate after 16 pipe diameters distance from the orifice was not sufficient to break the droplets injected at the orifice. • Plume DSD changed slightly after 15 pipe diameters distance from the orifice. • Overall plume DSD can be estimated from the measurement at a single point in the plume. A local droplet size distribution (DSD) from a jet in crossflow can overestimate or underestimate the overall DSD in the plume based on the measurement location. The overall DSD is crucial to evaluate the fate of oil droplets in the water column for a proper countermeasure following an oil spill. We present experimental results of a vertical oil jet in crossflow with a jet velocity of 2.4 m/s and a crossflow speed of 0.31 m/s, resulting jet-to-crossflow velocity ratio of 7.7 and a jet Reynolds number of 13,400. We measured the droplet size near the top and bottom boundaries of the plume while filming the whole plume. We conducted multiphase large eddy simulations coupled with a population balance model considering the relative velocity among the phases in the momentum and volume fraction equations. The computed plume boundaries and the DSD from the simulations agreed well with the measurements. The Sauter mean diameter and DSD considering all droplets across the plume cross-sections were found to be changing slightly beyond s/D ≈ 15. By considering different plume cross-sections for s/D> 15 and different droplet breakage rates, the overall DSD in a plume cross-section can be obtained locally near thevertical centerline of the plume cross-section (y/D = 0) at (58.8 ± 6.2)% of the plume cross-section height from the bottom boundary of the plume. The trajectory of the local DSD representing the overall DSD was found slightly below the plume trajectory.

Study of Flame Kernel Development at High EGR and High Flow Speed Using Conventional Spark Igniter and Non-Thermal Plasma Under Gasoline Engine Relevant Conditions

ABSTRACT As a novel ignition approach, nanosecond repetitively pulsed discharge (NRPD)-based non-thermal plasma offers significant benefits such as low energy consumption, and lean operating conditions. However, there is no investigation conducted on the early flame kernel formation and development induced by non-thermal plasma. Therefore, in this paper, experiments of conventional spark and non-thermal plasma ignition systems in constant volume combustion chamber (CVCC) are conducted under gasoline engine relevant conditions: wide initial ambient pressures (6.5, 8.3, 11.3 bar), a range of equivalence ratios (0.7–1.0), EGR rates (10−25%), and cross flow speeds (0–30 m/s). The discharge energy of non-thermal plasma is of around 210 mJ, while a single spark event can generate energy from 65 mJ to 83 mJ depending on ambient conditions. A consecutive spark strategy is adopted to guarantee comparable total input energy to non-thermal plasma. The ignition delay and combustion phase obtained from the chamber pressure history are calculated. In the meanwhile, flame kernel radius, flame propagation rate, and flame front length ratio via schlieren images are quantified and analyzed. Results showed that the flame initiated by non-thermal plasma can maintain a robust flame kernel and propagates fast. Under high-speed cross flow and high EGR rate conditions, non-thermal plasma can maintain a robust flame kernel at early stage supporting the initial flame kernel to survive and improve its ignition probability. Considering the effects of the EGR ratio and high-speed cross flow on flame kernel development, non-thermal plasma ignition can efficiently enhance the flame propagation and ignition probability. It is also concluded that non-thermal plasma can successfully ignite under lean (equivalence ratio between 0.7–1.0), high-diluted mixture (25% EGR), and high-speed cross flow of 30 m/s within the range of current study.

Study of the hydraulic performance of PID bits based on a discrete phase model

Particle impact drill bit is the key component for the particle impact drilling technology. In order to optimize the hydraulic structural parameters on the hydraulic performance of bit, a three-dimensional field model of bit was established. The CFD-based discrete particle model (DPM) was used to track the movement of the solid phase. The impact pressure on bottom hole and the cross flow speed were used to evaluate the hydraulic performance of PID bits. Sixteen models were built to analyze the effect of nozzle angle on the flow field. The results of numerical simulation showed that the impact pressure on the bottom hole increased firstly and then declined with the increase of nozzle angle. The cross-speed increased continuously. The optimal combination of radial distance and layout of the nozzles could produce an integrated bottom hole efficiently. Based on the simulation results, the layout of model 3-2 was the optimal. The results could provide a theoretical basis for the design of PID bit.

A study of the effect of serration shape and flexibility on trailing edge noise

In this study, we investigated the performance of flexible trailing edge serrations of various shapes for airfoil self-noise reduction through anechoic wind tunnel experiments. A flat plate model was tested at zero angle of attack. The chord-based Reynolds number was between 1.6 × 105 and 4 × 105. The boundary layers were fully tripped near the leading edge. Add-on type trailing edge serrations were cut from flexible polyethylene terephthalate sheets. It is observed that compared with rigid serrations, flexible serrations can achieve an additional broadband noise reduction up to 2 dB–3 dB at high frequencies, and the effect also depends on the geometry of the serrations. Complementary deformation measurement and aerodynamic force measurement show that flexible serrations can align better with the flow and are expected to reduce the crossflow intensity near the serration roots, which has been related to the extraneous high-frequency noise generated by serrations in previous studies. An inviscid model is proposed to predict the wake structure and the loadings for serrations of various shapes. Although the model over-predicts the crossflow speed due to the omission of the viscous effect, the relative intensity corresponding to different serration geometry is consistent with experimental observations. Last, we show that the recent analytical noise prediction model [B. Lyu and L. J. Ayton, “Rapid noise prediction models for serrated leading and trailing edges,” J. Sound Vib. 469, 115136 (2020)] for a serrated trailing edge still significantly overpredicts the noise reduction capacity by serrations and does not reveal the role of serration shape properly. This indicates the necessity to include the non-frozen turbulent properties near serrations in the future prediction models.

Experimental study of pool fire behaviors with nearby inclined surface under cross flow

Few studies have been done on the flame behavior of pool fires, as a typical fire incident in process industry, with a nearby inclined surface, i.e., in hilly area or with obstacle. This work studied the influence of the nearby inclined surface on flame height and air entrainment of pool fires in still air and under cross flow with various pool sizes and regression rates. The inclined angles of the nearby surface were 0°, 20°, 30° and 40° from horizontal direction and cross flow speed ranged within 0−3 m/s. Experimental results show that the flame height increases with increasing inclined angle of nearby surface. Fire Dynamics Simulator (FDS) was adopt to interpret the air entrainment flow field. The nearby inclined surface restricts air entrainment and introduces a negative pressure zone in the upwind part and stretches the flame along the nearby inclined surface. Cross flow supplies additional air while enhancing the negative pressure. Formulas are proposed based on overall buoyancy led by pool fire, cross flow momentum and a deduced characteristic global nearby inclined surface factor, showing good correlation with the experimental results.

Single-layered GO/LDH hybrid nanoporous membranes with improved stability for salt and organic molecules rejection

Graphene oxide (GO) has been intensively adopted as the building block of separation membranes due to its excellent mechanical strength and atomic scale interlayer spacing. However, the practical application of GO nanosheet-based membranes are limited by the swelling and disintegration of GO membranes in water owing to hydration and electrostatic repulsion. In this work, we firstly fabricated a type of layered double hydroxide (LDH) nanosheets, Co(OH)2 nanosheets, by in-situ growth on the surface of GO nanosheets, followed by coating such GO/Co(OH)2 hybrid nanosheets on a microporous substrate through vacuum suction to form a single-layered GO/Co(OH)2 hybrid thin membrane. The electrostatic and coordination interactions between GO and Co(OH)2 nanosheets are found to stabilize the GO/Co(OH)2 hybrid membrane in water, and the hybrid membrane shows good resistance to shear force in a pressurized crossflow nanofiltration system with crossflow speed as high as 0.5 m s−1. With permeation flux up to 17.0 L m−2 h−1, >91% rejection to inorganic salts like Na2SO4 and >98% rejection to various organic dyes (transmembrane pressure: 6 bar, crossflow speed: 0.27 m s−1), the hybrid membrane also survives the challenges of different pH environments, elevated transmembrane pressure and a 60 h continuous crossflow test. Such significantly improved stability from pure GO membranes is expected to enable the 2D nanomaterial based membranes for practical filtration applications in the water industry.

Study on the Bubble Growth and Departure with A Lattice Boltzmann Method

For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain to deal with the no-slip boundary condition. Effects of the viscosity, surface tension, gas inertial force and buoyancy on the characteristics of bubbles when they grow and departure from an orifice in quiescent liquid are studied. The releasing period and departure diameter of the bubble are influenced by the residual gas at the orifice, and the interaction between bubbles is taken into consideration. The relations between the releasing period or departure diameter and the gravity acceleration show fair agreements with previous numerical and theoretical results. And the influence of the gas outflow velocity on bubble formation is discussed as well. For the bubbles growing in cross-flow field, effects of the cross-flow speed and the gas outflow velocity on the bubble formation are discussed, which is related to the application in ship resistance reduction. And optimal choice of the ship speed and gas outflow velocity is studied. Cases in this paper also prove that this high density ratio LBM model has its flexibility and effectiveness on multiphase flow simulations.

An experimental investigation and scaling analysis on flame sag of pool fire in cross flow

Flame sag, a phenomenon observed as flame sinks downwards along the leeward sidewall, occurs for a pool fire having its rim above the ground in cross flows. Few data or investigations of this phenomenon have been reported in the literature. In the present study, the length of flame sag measured from the lowest point of sunk flame to the pool rim; as well as the critical speed of the cross flow under which the lowest point of sunk flame reaches the ground level (namely flame sag length equaling sidewall height), were quantified. Experiments were carried out by employing square quartz sand box pool fires with dimensions in the range of 10–20 cm for various cross flow air speeds, heat release rates and pool rim heights. Propane is used as the fuel. The results showed that the length of the flame sag increased with the increasing of the fire source heat release rate. And it also increased with the increasing of the air speed of the cross flow. However, the flame sag length decreased with increasing pool size. The critical air speed of the cross flow at which the flame sag reached the ground increased with increasing pool size and rim height, meanwhile decreased with increasing heat release rate. A scaling analysis for the interaction physics of the fuel flow near the base with the cross flow, and the total buoyant flow (heat release rate) of the fire with the cross flow, was provided to characterize the flame sag behavior. Two dimensionless quantities(ρa-ρf)gDρaUw2, Q̇/DgρacpTaUw3, namely an inverse Froude number for the base and an inverse Froude number for the interaction of total buoyancy of the fire with cross flow, were derived from the analysis with a new length scale found as ξL=ρaUw2(ρa-ρf)g. The data of flame sag length, as well as the critical value of the cross flow speed for flame sag reaching ground level, were shown to correlate well to the proposed dimensionless quantities.

Flame downwash transition and its maximum length with increasing fuel supply of non-premixed jet in cross flow

The present study experimentally investigated the flame downwash transition and its maximum length that can be reached at leeward side of nozzle with increasing fuel supply of non-premixed jet in cross flows. Experiments were conducted with 8, 10, 13 and 15 mm nozzles, using propane and methane as fuel. The cross flow speed ranges from 0.70 to 3.08 m/s while the fuel jet velocity ranges between 0.04 and 4.26 m/s. Results showed that, with increasing fuel supply at a given cross flow speed, flame downwash length first increased (fuel supply controlled regime) then decreased (leeward side reversing flow rotating strength controlled regime). A function between the jet-to-crossflow momentum flux ratio (Rc) and dimensionless fuel mass flow rate (m˙c∗) was proposed to illuminate the tuning state of above transition. The flame downwash maximum length at the turning state normalized by nozzle diameter was found to have a linear relation with Froude number of fuel jet (Frj=uj/gD) or cross flow (Fra=ua2/gD). These findings contribute to a better understanding of flame downwash evolution process, which could have a basic significance for reducing fuel emission, improving combustion energy efficiency and saving energy by controlling the flame downwash scale.

Detailed numerical simulation of liquid jet atomization in crossflow of increasing density

Atomization of liquid fuel jets by cross-flowing airstream is critical to the performance of many aerospace combustors. Recent advances in numerical methods and increases in computational power have enabled the first principle, high fidelity simulation of this phenomenon. In the recent past we presented a detailed validation and analysis of such simulations against experimental data at ambient conditions. At combustor operating conditions, however, both temperature and pressure are significantly elevated. In this work we extend the same computational approach to the study of the impact of reduced liquid–gas density ratio due to increased air density associated with operating pressure elevation on the atomization physics. The previously validated ambient condition case is used as the baseline for comparison with three cases with decreasing density ratios. The density ratio is independently varied by adjusting the gas density and velocity together so that the momentum flux ratio and Weber number are maintained constant. The global-scale jet penetration and trajectory are slightly modified as the density ratio varies. The most significant changes are observed for the local processes of liquid breakup and atomization. As the density ratio is independently reduced, a transition of dominance from the Rayleigh–Taylor to the Kelvin–Helmholtz instability mechanisms on the liquid column surface is detected by analyzing the vorticity fields. Such a transition is verified using linear stability analyses and is also shown to be consistent with the simulation results of a non-monotonic variation of surface wavelength with density ratio. Downstream, a counter-rotating vortex pair (CVP) arises as the density ratio is reduced, the physical origins of which are similar to those documented for gaseous jet in cross-flow studies. Atomization effectiveness is reduced downstream with reduced density ratio and this is in agreement with experimental observation. This result is explained in terms of the density-ratio-related velocity-ratio changes that allow for a switch in behavior from a faster to a slower crossflow speed with respect to the liquid. As a result, at low density ratio recoiling of stretched structures and possibility of increased collision result in increasing Sauter Mean Diameter (SMD).

Liquid jet trajectory and droplet path influenced by combined cross flow and electric fields

This study investigates an ethanol liquid jet subjected to combination of an air crossflow and a normal electric field. The results on the liquid jet trajectory and subsequent droplets flight paths are presented. The liquid jet trajectory was found as a function of two non-dimensional quantities; the liquid jet to the crossflow momentum ratio and the electroinertial number. The electroinertial number is defined as the ratio between the liquid jet specific momentum and the electric force. A correlation is introduced for the jet trajectory in low crossflow speeds and electric field intensities. The same two quantities control the detached droplets flight paths. Satellite droplets flight angles are also reported with a correlation for their separation angle, which can be useful in applications where uniform droplet production is important.

A combined numerical-experimental approach to analyze cross flow problems in the entrance channel: A case study of Lanshan Port, China

The present study combines numerical and experimental approaches to investigate cross flow problems in the entrance channel of a harbor. The combined numerical-experimental approach is illustrated by an application to Lanshan Port (Shandong, China) where large tidal ranges and a newly planned harbor layout may give rise to strong cross flow in the entrance channel of the planned harbor. The resulting flow field with the numerical prediction shows that the layout of newly planned harbor has a major impact on the cross flow speeds in the entrance channel. This will affect the navigation safety of ship entering or leaving the harbor. A corresponding protective scheme related to breakwaters was put forward. A series of physical model experiments under the given flow provided by the numerical approach, were conducted to design the length and crest elevation of a previously proposed breakwater. Results from a series of laboratory model tests show a significant reduction of flow velocities across the entrance channel with longer breakwater length and higher crest elevation. However, a longer or higher breakwater obviously can expand the cross flow influenced zone into the entrance channel. The acceptable breakwater length and crest elevation were determined by taking account the maximum cross flow speed and cross flow influenced zone in addition to the construction cost.

Preparation of multifunctional hollow fiber nanofiltration membranes by dynamic assembly of weak polyelectrolyte multilayers

In this work, we investigate the effect of preparation conditions for dynamic layer-by-layer (LbL) coating, to prepare multifunctional hollow fiber nanofiltration (NF) membranes. Dynamic coating was performed at constant pressure and at variable cross flow speeds. In this way, polyelectrolyte multilayers (PEMs) were formed of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), on a negatively charged polyethersulfone ultrafiltration (UF) support. The resulting membrane performance was investigated and compared to membranes prepared by different methods (dip coating and dead end filtration), and it was found to be comparable. It was shown that PAH/PAA multilayers can be fabricated reproducibly and homogenously using optimised dynamic LbL deposition conditions on single fiber module (surface area of 6.2cm2) as well as on a module of 15 fibers (surface area of 67cm2). Moreover, the approach of dynamic coating could be easily up scaled to coat existing UF modules. The prepared membranes reject the solutes on the basis of size exclusion and Donnan exclusion, retaining small organic solutes and divalent ions. Membranes terminated with PAA exhibit a low fouling tendency compared to membranes terminated with PAH and compared to the UF support membrane. Moreover, if severe membrane fouling would occur after prolonged use, the PEM coating, including any attached foulants can be removed by rinsing with a solution that combines a low pH and a high salinity (pH 3, 3M). The surface of bovine serum albumin (BSA) fouled membranes were successfully cleaned at least twice, after which a new PEM coating could be re-applied by active coating.

Nonlinear dynamics of a fluid-conveying pipe under the combined action of cross-flow and top-end excitations

We report a theoretical investigation of an elastic and slender fluid-conveying pipe with a top-end excitation subjected to uniform cross flows. Considering the mean drag force and the time varying vortex-induced lift force which is modeled using a nonlinear van der Pol oscillator, the nonlinear partial differential equations of the motion of coupled fluid-structure system are constructed and simplified to a reduced-order model through the Galerkin-type discretization. By virtue of quasi-static displacement conditions, the characteristics of vortex-induced vibration of the pipe are evaluated for the first two lock-in modes. The results show that the top-end excitation can increase the vibration amplitude of the pipe when the cross-flow speed is out of the lock-in regions. When the cross-flow speed is within the lock-in region, however, the top-end oscillation causes a transition between quasi-periodic and periodic in the responses of the pipe, significantly reducing or increasing the vibration amplitudes depending on the excitation acceleration and frequency. This finding has an important guidance in suppressing vortex-induced vibrations by balancing the internal fluid velocity and the top-end excitation.

Modeling and nonlinear dynamics of fluid-conveying risers under hybrid excitations

The nonlinear dynamical responses of a vertical riser concurrently subjected to hybrid excitations, namely, vortex-induced vibrations (VIVs) and base excitations are investigated. The riser conveying fluid is placed in a uniform cross-flow and subjected to direct harmonic excitations. A van der Pol wake oscillator is used to model the fluctuating lift coefficient. The extended Hamilton’s principle and the Galerkin procedure are used to derive a nonlinear distributed-parameter model for a vertical riser under a combination of vibratory base excitations and vortex-induced vibrations. Linear and nonlinear analyses are performed to investigate the effects of internal fluid velocity, cross-flow speed, and base acceleration on the coupled frequency, onset speed of synchronization, and vibration amplitudes of the riser. The results show that when the cross-flow speed becomes in the synchronization region, vibration behaviors of the riser change from aperiodic to periodic motions, with a jumping phenomenon between these two kinds of motions. It is also demonstrated that the amplitude of the riser can be increased or decreased under combined effects of vortex-induced vibrations and base excitations compared to the separate effect of vortex-induced vibrations or base excitations. The results also show that an increase of the base acceleration results in a wider synchronization region and a significant effect associated with the quenching phenomenon.

A turbulent convection model with an observational context for a deep-sea hydrothermal plume in a time-variable cross flow

[1] A turbulent convection model for a hydrothermal fluid discharging into a tidally modulated, stratified cross flow is used to investigate time-variable conditions in plumes, such as the one rising from Dante, a sulfide mound at ∼2175 m depth on the Endeavour segment of the Juan de Fuca Ridge. That plume is the consequence of the coalescence of 10 or more small, individual plumes from chimneys discharging hot, salt-diminished fluid into the near-bottom ocean. At Dante, the discharge encounters ambient horizontal currents with speeds oscillating from near zero to a maximum of ∼7 cm s−1, speeds which can bend a plume more than 45° from the vertical. Model results are compatible with field measurements of the plume footprint size and vertical velocity both 20 m above the source when earlier estimates for Dante's heat flux of ∼50 MW drive the convection. The small-scale short period variability of velocities and properties distributions observed in the field is mimicked in model results. Plumes pool above a source during periods of weak cross flows but stream away from the source, with more diluted concentrations and lower rise heights, at other times. Plume distributions, at identical cross-flow speeds, differ whether the flow is accelerating or decelerating. Small changes in background hydrographic profiles create differences in rise heights comparable to those caused by large changes in source buoyancy flux. If put into an entrainment context, results suggest an entrainment coefficient (αEFF) that varies from ∼0.11 to ∼0.025 with increasing height (2–76 m) above the source.