Jet Mixing Research Articles

Jet mixing enhancement with Bayesian optimization, deep learning and persistent data topology

We optimize jet mixing using large eddy simulations (LES) at a Reynolds number of $3000$ . Key methodological enablers consist of Bayesian optimization, a surrogate model enhanced by deep learning and persistent data topology for physical interpretation. The mixing performance is characterized by an equivalent jet radius ( $R_{eq}$ ) derived from the streamwise velocity in a plane located $8$ diameters downstream. The optimization is performed in a 22-dimensional actuation space that comprises most known excitations. This search space parameterizes the distributed actuation imposed on the bulk flow and at the periphery of the nozzle in the streamwise and radial directions. The momentum flux measures the energy input of the actuation. The optimization quadruples the jet radius $R_{eq}$ with a $7$ -armed blooming jet after around $570$ evaluations. The control input requires $2\,\%$ momentum flux of the main flow, which is one order of magnitude lower than an ad hoc dual-mode excitation. Intriguingly, a pronounced suboptimum in the search space is associated with a double-helix jet, a new flow pattern. This jet pattern results in a mixing improvement comparable to the blooming jet. A state-of-the-art Bayesian optimization converges towards this double-helix solution. The learning is accelerated and converges to another better optimum by including a deep-learning-enhanced surrogate model trained along the optimization. Persistent data topology extracts the global and many local minima in the actuation space. These minima can be identified with flow patterns beneficial to the mixing.

Integrated Assessment of Bearing Capacity and GHG Emissions for Foundation Treatment Piles Considering Stratum Variability

Foundation treatment piles are crucial for enhancing the bearing capacity and stability of weak foundations and are widely utilized in construction projects. However, owing to the complexity of geological conditions, traditional construction methods fail to meet the demand for low-carbon development. To address these challenges, this study introduced a comprehensive decision-making approach that considers the impact of stratum variability on greenhouse gas (GHG) emissions and pile bearing capacity from the design phase. During the design process, the GHG emissions and bearing capacities of deep cement mixing (DCM) and high-pressure jet grouting (HPJG) piles were quantitatively assessed by analyzing the environmental and performance impacts of foundation treatment piles related to materials, transportation, and equipment usage. The results suggest that the bearing capacity of piles in shallow strata is highly susceptible to stratum variability. Using piles with a diameter of 800 mm and a length of 20 m as an example, compared with DCM piles, HPJG piles demonstrated a superior bearing capacity; however, their total GHG emissions were 6.58% higher, primarily because of the extensive use of machinery during HPJG pile construction. The GHG emissions of foundation treatment piles in shallow strata were influenced more by geological variability than those in deep strata. Sensitivity analysis revealed that the pile diameter is a critical determinant of GHG emissions and bearing capacity. Based on the bearing capacity–GHG emission optimization framework, a foundation treatment strategy that integrates overlapping and spaced pile arrangements was introduced. This innovative construction method reduced the total GHG emissions by 22.7% compared with conventional methods. These research findings contribute to low-carbon design in the construction industry.

Numerical investigation gaseous ammonia basic jet and mixing characteristics in the constant volume vessel

Ammonia is considered a promising zero-carbon fuel under the dual-carbon targets. Systematically understanding ammonia's basic jet and mixing characteristics can promote its practical application in the engine field. Thus, a three-dimensional computational fluid dynamics (CFD) model of constant volume vessel (CVV) is established in this paper, and the forecasting abilities of the Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) models for the gaseous ammonia jet process are compared based on the experimental data. Then, the ammonia jet development rule and mixing characteristics under different ambient temperatures, ambient pressures, and fuel temperatures are investigated. The variation laws of key data such as penetration distance, jet area, ammonia mass concentration distribution, equivalence ratio, and turbulent kinetic energy are obtained and analyzed. The results show that during the injection process, the airflow on the left and right sides of the jet rotates in opposite directions. A higher temperature and lower pressure within the CVV lead to a larger flammable range for ammonia jets. Moreover, the distribution of ammonia mass concentration on the radial plane shows a dynamic development law with time, meaning that it first increases to a maximum value, then gradually decreases, and finally remains stable. The farther the radial plane is from the nozzle outlet position, the lower the ammonia mass concentration. In addition, the ammonia jet's turbulent kinetic energy has a large core region and symmetrical distribution along the central axis. At the beginning of the injection, the core length is small, gradually increasing with time and finally stabilizing.

On the effect of axial inlet angle on the droplet size distribution and mixing uniformity for swirl jet mixer at high phase ratios

The “short pass” problem of liquid-liquid two-phase mixing at high phase ratios limited the development and applications of jet mixer in industrial process. In this study, the effect of the axial inlet angle on the mixing characteristics of a swirl jet mixer was investigated through laser particle size analysis and computational fluid mechanics (CFD) coupled with population balance model (PBM). The result was shown that as the axial inlet angle increased, the dispersed phase droplet sizes decreased, and the droplet size distribution was widened for the fixed mixer configuration. At Re ≤ 3.000×104, tangential inlet was more conducive to improving mixing uniformity. Conversely, the axial inlet angle of 90° was optimal at Re ≥ 3.750×104. Numerical simulations revealed that the tangential inlet effectively intensified liquid-liquid interactions, including streamlines extension, increased vorticity, improved droplet size uniformity. Additionally, the increase of the axial inlet angle resulted in increased turbulence stress and shortened decay period, the reduction in droplet size, and a wide droplet size distribution. The research findings can serve as theoretical basis for the hydraulic design and promoted applications of swirl jet mixers.

Jet Installation Noise Modelling for Round and Chevron Jets

Wall-Modelled Large Eddy Simulations (LES) are conducted using a high-resolution CABARET method, accelerated on Graphics Processing Units (GPUs), for a canonical configuration that includes a flat plate within the linear hydrodynamic region of a single-stream jet. This configuration was previously investigated through experiments at the University of Bristol. The simulations investigate jets at acoustic Mach numbers of 0.5 and 0.9, focusing on two types of nozzle geometries: round and chevron nozzles. These nozzles are scaled-down versions (3:1 scale) of NASA’s SMC000 and SMC006 nozzles. The parameters from the LES, including flow and noise solutions, are validated by comparison with experimental data. Notably, the mean flow velocity and turbulence distribution are compared with NASA’s PIV measurements. Additionally, the near-field and far-field pressure spectra are evaluated in comparison with data from the Bristol experiments. For far-field noise predictions, a range of techniques are employed, ranging from the Ffowcs Williams–Hawkings (FW–H) method in both permeable and impermeable control surface formulations, to the trailing edge scattering model by Lyu and Dowling, which is based on the Amiet trailing edge noise theory. The permeable control surface FW–H solution, incorporating all jet mixing and installation noise sources, is within 2 dB of the experimental data across most frequencies and observer angles for all considered jet cases. Moreover, the impermeable control surface FW–H solution, accounting for some quadrupole noise contributions, proves adequate for accurate noise spectra predictions across all frequencies at larger observer angles. The implemented edge-scattering model successfully captures the mechanism of low-frequency sound amplification, dominant at low frequencies and high observer angles. Furthermore, this mechanism is shown to be effectively consistent for both M=0.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M=0.5$$\\end{document} and M=0.9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M=0.9$$\\end{document}, and for jets from both round and chevron nozzles.

Flow dynamics and mixing of jet in crossflow with cylindrical cavity

The flow dynamics and mixing characteristics of an air jet issued from a cylindrical cavity in an air crossflow are numerically studied using a large-eddy-simulation technique. The cavity, aligned concentrically with the jet, is located beneath the crossflow wall. The jet-to-crossflow velocity ratio is 4, and the Reynolds number for the jet flow is 1.39×104 based on its diameter and centerline velocity. The presence of the cavity significantly influences the early evolution of the jet and its interaction with the crossflow. Complex vortical structures are observed. Notably, windward vortices on the jet surface increase in size, accompanied by a reduction in the Strouhal number. For a deep cavity, these vortices break down and result in small vortical tubes in the jet streamwise direction due to secondary instability. Also examined are leeward shear-layer vortices, hanging vortices, wake vortices, and the recirculating flow within the cavity. Their roles in the mixing between the jet fluid and the crossflow are identified. The cavity enhances mixing. The effect is significant in the near field but diminishes in the far field. By adjusting the cavity radius and depth, it is determined that the cavity depth exercises a more profound impact on jet evolution and mixing than the cavity radius. The most substantial influence occurs when a narrow and deep cavity is implemented. These findings may serve as guidelines for optimizing cavity design for effective modulation of jet behaviors.

Flow characteristic investigation of localized arc filament plasma assisted turbulent jet and Bunsen flame

Localized arc filament plasma actuators (LAFPAs) have shown the capability to alter the entrainment of freestream air into a jet. This paper presents an investigation into the effects of LAFPAs on the air jet and methane/air premixed Bunsen flames at different Reynolds numbers. The flow disturbance covering the laminar to turbulent transient conditions was generated by a high voltage plasma discharge system of LAFPAs. The high speed Z-type Schlieren technique was applied to visualize the instantaneous flow and flame structures, and an optical flow algorithm was used to estimate the velocity distribution and further analyze the turbulent effect induced by the plasma. The results illustrate that, in the presence of LAFPA operation, the turbulence jet was accelerated and the jet mixing enhanced. Meanwhile, with the help of LAFPAs, the global consumption burning velocity increased significantly by the area enhancement via plasma–flame interaction. The flame front response to the flow disturbance consists of more surface stretch and flame separation. Furthermore, turbulence spectra analysis of the images reveals a considerable increase in turbulent fluctuations in both cold flow and reacting flow.

Thermo-chemical nonequilibrium effects on combustion characteristics of a transverse jet in the scramjet

As the Mach number increases, the local static temperature gradually approaches the characteristic gas vibration/dissociation temperature, and significant thermo-chemical relaxation processes occur. The thermo-chemical nonequilibrium phenomenona could affect the mixing and combustion process and become a factor that must be considered for scramjet design. In this paper, a large eddy simulation solver based on the two-temperature model is developed. The transfer terms between vibrational and trans-rotational energy are modeled by the Landau–Teller formulation and the vibrational-dissociation coupling is considered by adopting the Park model. Three sets of simulations based on the Hyshot Ⅱ engine configuration with different models were performed simultaneously to validate numerical methods and analyze results. The results reveal that the shock, cross-injection of fuel, and Prandtl-Meyer flow induce significant nonequilibrium regions. The vibration relaxation process in the jet mixing region is frozen, the vibration temperature is much higher than the trans-rotational temperature, and the extra energy is converted from the vibration mode to the trans-rotational mode, resulting in the increase of the trans-rotational temperature and the advance of auto-ignition in the nonequilibrium condition. Considering the vibration-dissociation coupling, the higher vibration temperature promotes dissociation. It inhibits the generation of active radicals in the ignition process, weakening the enhancement effect of nonequilibrium on auto-ignition. In the expanded nozzle, the concentrations of molecules and trans-rotational temperature in nonequilibrium cases are slightly lower than those in the equilibrium case due to the enhancement of dissociation.

Research on the cooling mechanism of low-temperature liquid jet mixing in high-temperature and high-speed airflow

The multi-stage water spray cooling system of the space launch site involves a complex gas–liquid two-phase mixed cooling problem in the process of spraying water onto the rocket engine gas jet. To investigate the complex multiphase flow field of the interaction between the airflow and liquid water jet, the Mixture multiphase flow model is adopted, which is coupled with the vaporization equation and component transport model of liquid water. The computational fluid dynamics method is used to numerically analyze the mixing and cooling mechanism of low-temperature liquid jet in high-temperature and high-speed gas flow. The results show that mixing low-temperature liquid jets in high-temperature and high-speed airflow can cause the exchange of momentum and energy, resulting in pressure loss and temperature reduction in the gas phase flow field. Due to the acceleration of transverse airflow, the diffusion flow range of the jet is significantly increased, and violent vaporization occurs, which further consume a large amount of airflow energy. The mixing cooling effect of transverse airflow and liquid water jet is directly related to the mass flow rate ratio of the jet to airflow. In addition, directly designing liquid water jet orifices on the solid wall of the guiding device can achieve the effect of improving the gas flow field environment. This conclusion can provide theoretical reference for the thermal protection design of ground launch devices in space launch site.

Mixing effects of high-speed jets in gas-solid riser and downer reactors

For the high-temperature and short-contact time gas-solid reaction process, riser and downer are considered appropriate reactors. To realize an intensive and complete mixing of reactants with catalysts, the feed raw is always introduced in the form of high-speed jets. In this study, in order to investigate the mixing effects of different types of high-speed jets in riser and downer, traceable ozone is injected with the high-speed feed jets to react with catalyst particles. By detecting the decomposition of ozone, the gas-solid mixing and reaction in riser and downer under the influence of both co-current and counter-current injections are analyzed. The relative ozone concentration is used to reflect the location reaction extent and its radial nonuniformity index is proposed to compare the results in riser and downer. It is found that the jet influence zone in downer provides a relatively better environment for the mixing of feed jets with catalysts. In the riser, introduction of counter-current injections could improve the uniformity of gas-solid mixing in the initial contact region of feed with catalysts.

Effect of parameter optimization on the flow characteristics of venturi-self-excited oscillation mixer based on response surface model and multi-island genetic algorithm

The present study focuses on the development of a novel venturi-based self-excited oscillation mixer that effectively utilizes the venturi effect to facilitate efficient abrasive intake while simultaneously ensuring effective prevention of backflow through the utilization of the systolic section within the venturi tube. It not only ensures uniform mixing of water and abrasive but also transforms the continuous jet into a pulsed one, thereby significantly enhancing exit velocity. The orthogonal experimental design method and single factor experiment method were employed to investigate the effects of inlet water pressure, water nozzle diameter, abrasive inlet angle, aspect ratio of the self-excited oscillation mixer, and abrasive pipe inlet diameter on the inlet pressure of the abrasive pipe and the velocity of the jet exit in the new mixing device. Approximate response surface models for these parameters were constructed using lsight optimization software, combining the results of orthogonal experimental simulation. By employing a multi-island genetic algorithm, we have globally optimized this innovative mixing device to determine its optimal performance parameters. Subsequently, comparative experiments were conducted to validate the performance of different mixing devices in descaling applications. Through experimental verification, it was found that the venturi-self-excited oscillation mixer exhibits excellent rust removal capabilities in steel plate tests compared to traditional self-excited oscillation mixers. These findings provide valuable guidance for the subsequent design and enhancement of abrasive water jet mixers.

The usage of non-aligned multi-circular winding injectors for efficient fuel mixing inside the scramjet engine

The usage of zigzag multi-jet configuration for efficient fuel circulation along the supersonic combustion chamber has been extensively examined in this article. To analyze the flow and fuel jet interactions, computational fluid dynamic is applied as an efficient technique to visualize the flow and fuel jet in the zigzag injection system. Injection via an annular nozzle is compared with coaxial air and fuel jet to find the effective mechanism for well-organized fuel mixing in the combustion chamber of the scramjet engine. The circulation and fuel mixing of the zigzag injection is inspected at a supersonic air stream with Mach = 4. The contour of the Mach value and stream shows that the deflection of the air stream after contact with the core of the upstream jet redirects to the core of the downstream jet and consequently, the fuel mixing is enhanced in the combustion chamber. The usage of an internal air jet expands the performance of fuel mixing of annular jets up to 100 % in the zigzag nozzle arrangement.

Effect of increasing bypass ratio on supersonic co-flowing jet with finite lip thickness

The article presents the investigation on the effect of increasing bypass ratio on a supersonic co-flowing jet with finite lip thickness for a jet exit Mach number of 2.0. Co-flowing jets of differing bypass ratios (BR = ms/mp, where ms and mp are the mass flow rate of secondary and primary jets, respectively) 3.69, 9.0, and 16.0 were employed to explore the impact of high bypass secondary jets on the primary jet. A single-jet BR 0 is used for comparison. The supersonic core lengths of the single jet and the co-flow jet for BR 3.69, BR 9.0, and BR 16.0 were metrics for quantifying the mixing. The surrounding jet enhances the wake dominance in the nozzle lip, and the supersonic core length shortens. High bypass co-flowing jets are extremely efficient at shortening the supersonic core length compared to the low bypass counterpart, and hence, the jet mixing increases. The radial Mach number profiles quantitatively represent different zones in the co-flowing jet. The variation of these zones with bypass ratios highlights the dynamic interaction between the primary and secondary jets. The physical reason for apparent jet mixing and flow categories has been discussed based on considerations about changes in the flow field and shock structure.

Mixing of Hydrogen-Steam Buoyancy Jets Released into the Upper Atmosphere of the Containment Building

This study evaluates the spatial dilution of hydrogen concentration caused by steam-hydrogen buoyancy jets rising through the open top of the steam generator compartment during a loss-of-coolant accident in the OPR1000, the Korean Standard Nuclear Power Plant. The correlation of the concentration decay rate in the plume with relatively high buoyant flux was applied to estimate the hydrogen concentration in the rise distance of the buoyant jet. The MELCOR code was used to calculate the gas composition and discharge flow rate in the ruptured cold leg during the rapid cladding oxidation to determine the volume and buoyant fluxes that affect the mixing behavior. The concentration decay rate at the plume’s center decreases as the steam-hydrogen binary buoyant jet rises. Despite the assumed initial volume flux and simplified jet nozzle geometry, the decay rate correlation can assess conservatively the diluted hydrogen in a severe accident.

Air tab location effect on supersonic jet mixing

Abstract Mixing of Mach 2.1 circular, jet issuing from a straight convergent-divergent circular nozzle, in the presence of sonic air tabs at exit and shifted locations along the jet axis was investigated experimentally at nozzle pressure ratios (NPR) 3–6, insteps of 1. Two constant area tubes of 1 mm diameter positioned diametrically opposite, at 0 D, 0.25 D, 0.5 D and 0.75 D (where D is the nozzle exit diameter), were used for fluidic injection. The injection pressure ratio (IPR) of air tabs was maintained at 6. The Mach 2.1 jet operated at nozzle pressure ratio (NPR) in the range of overexpanded states corresponding to NPR 3–6 was controlled with the sonic air tabs operating at the underexpanded state corresponding to IPR 6. The impact of air tabs on jet mixing was studied from the measured Pitot pressure along the jet centerline. The centerline pressure decay of the jet confirms that the air tab promotes jet mixing with the entrained air mass, and the mixing promotion caused by the air tab is dependent on tab location as well as the NPR. In the presence of air tabs, the jet possesses shorter core and experiences faster decay than the uncontrolled jet. Also, the air tabs were effective in reducing the number of shock cells and rendering the waves weaker in the jet core. Among the tab locations, the mixing promoting effectiveness of air tabs at 0 D is better than the tabs at shifted locations. The jet core length reduction caused by the air tab at 0 D increases from 25.4 % to 77.2 %, with increasing NPR from 3 to 6. The same trend was noticed for tab location 0.75 D, but not for 0.25 D and 0.5 D locations. The core length reduction for 0.75 D tab location is about 61.4 %, at NPR 6, and 62.1 % and 55.8 %, for NPR 5 and 4 for tab locations 0.25 D and 0.5 D, respectively. Shadowgraph images of the waves present in the jet core confirms the findings of centerline pressure decay results.

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Reduced-Order Model for Supersonic Transport Takeoff Noise Scaling with Cruise Mach Number

The recent interest in the development of supersonic transport raises concerns about an increase in community noise around airports. As noise certification standards for supersonic transport other than Concorde have not yet been developed by the International Civil Aviation Organization, there is a need for a physics-based scaling rule for supersonic transport takeoff noise performance. Assuming supersonic transport takeoff noise levels are dominated by the engine mixed jet velocity and the aircraft-to-microphone propagation distance, this paper presents a reduced-order model for supersonic transport takeoff noise levels as a function of four scaling groups: cruise Mach number, takeoff aerodynamic efficiency, takeoff speed, and number of installed engines. This paper finds that, as cruise Mach number increases, supersonic transport takeoff noise levels increase while their thrust cutback noise reduction potential decreases. Assuming constant aerodynamic efficiency, takeoff speed, and number of installed engines, the takeoff noise levels and noise reduction potential of a Mach 2.2 aircraft are found to be ∼15.3 dB higher and ∼19.2 dB less compared to a Mach 1.4 aircraft, respectively. This scaling rule can potentially yield a simple guideline for estimating an approximate noise limit for supersonic transport, depending on their cruise Mach number.

Experimental study on control of transverse jet mixing by arrayed plasma energy deposition

The efficient and prompt mixing of fuel is crucial in the operation of scramjet engines. This paper presents the findings from wind tunnel experiments that examined the influence of plasma energy deposition on transverse jets at a Mach number of 6.13. The study took into account various inlet flow total pressures and momentum flux ratios between the jet and the main flow. Utilizing a database containing time-resolved intensities from instantaneous schlieren images, we perform turbulence analysis employing various techniques such as the root mean square, fast Fourier transform, proper orthogonal decomposition, and the two-point correlation method. Specifically, we aim to compare and analyze the pulsation characteristics and spatial self-organization of the jet flow field, both with and without energy deposition control. The findings reveal that intermittent “hot bubbles” created by plasma energy deposition interact with the bow shock induced by the jet, resulting in the formation of an array of large-scale vortices. These vortices emerge as the dominant structures within the jet, effectively amplifying its pulsations. At low inlet flow pressures, energy deposition primarily disrupts the jet, causing large-scale vortices to propagate primarily within the jet plume region. However, at high inlet flow pressures, the impact of energy deposition extends to both the jet and the turbulent boundary layer, encompassing their respective disturbance ranges. Increasing the inlet flow pressure constraints the evolution of large-scale vortices, thus limiting the efficacy of energy deposition in governing the mixing process.

Computational study of thermal and fluid mixing behaviour of a dual jet flow using LES approach

The primary goal of any thermal system which demands efficient cooling is to improve heat transmission. For a turbulent jet, this condition becomes far more significant. The present work has employed large-eddy simulation (LES) for an offset ratio of 2.0 to investigate the transfer in heat and flow characteristics of a dual jet. An isothermal boundary wall condition is considered for a Reynolds number of 7500. The present findings are evaluated by comparing with the published experimental and numerical studies on wall jets. A comparative analysis here exhibits the profiles of Reynolds normal stresses, Reynolds shear stresses, turbulence kinetic energy, Nusselt number and turbulent heat fluxes. A comprehensive investigation of the mixing and flow properties of the dual jet is presented by using the Q-criterion of the iso-surface for mean velocity, pressure and vorticity. The present outcomes show that an efficient thermal transmission from the wall occurs in the recirculation region. The magnitudes of the profiles of Reynolds normal stresses, Reynolds shear stresses, r.m.s. temperature and turbulent heat fluxes are observed to be low in the combined region. Roller-like structure formation and near-wall eddies are noticed which spread in the combined region indicating large heat loss due to the turbulent flow.

Usage of multi-extruded nozzles for hydrogen fuel mixing in the double cavity flame holder in the existence of the shock generator

Improvement of the fuel mixing inside the cavity flame-holder is important for the development of this injection system in scramjet engines. This article presents significant flow results on the mixing role of multi-extruded nozzles inside dual cavity flame holders with a single shock generator. A three-dimensional model of the dual cavity with injectors located on the inclined rear wall is produced to simulate real flow physics associated with proposed jet configurations. The impression of air injection from the inclined rear wall is also examined by computational modeling of the compressible flow inside the dual cavity. Based on the achieved results, the injection of multiple extruded nozzles enhances fuel diffusion in the cavity when the shock generator is applied. Our findings disclose that the injection of the fuel from the inclined rear wall results in more efficient fuel mixing inside the dual cavity flame holder. Mixing of the annular jet is increased about 14% via backward air jet inside the cavity.