Jet In Crossflow Research Articles

Vortex structure and growth process formed by a sweeping jet and a main flow

Sweeping jet is a jet that oscillates at high velocity and is known to have a higher mixing effect. Therefore, it is attracting attention especially from the viewpoint of flow control. In fact, although reports have been made that contribute to control, the flow characteristics that directly contribute to control have not been clarified, and optimization and practical application have not progressed. Moreover, it has been shown that the flow splits in the wake and that a vortex structure similar to a single Jet in cross flow is emitted to the left and right near the exit of the sweeping jet, but the formation and decay processes that link them have not yet been clarified. In this study, we focus on the temporal changes of the flow structure generated near the exit of the inclined sweeping jet and elucidate them. In addition, numerical simulations are used to capture changes in spatial and temporal phenomena in detail.

DROPLET CHARACTERISTICS OF A JET IN CROSSFLOW INSIDE THE PRIMARY BREAKUP ZONE: EFFECTS OF NOZZLE SHAPE AND SIZE

DROPLET CHARACTERISTICS OF A JET IN CROSSFLOW INSIDE THE PRIMARY BREAKUP ZONE: EFFECTS OF NOZZLE SHAPE AND SIZE

A computational fluid dynamics study of flame gas sampling in horizontal dilution tubes

The performance of horizontal dilution tubes is investigated by Reynolds-averaged Navier–Stokes and large-eddy simulations. The flame gas enters the dilution tube through a pinhole. The orifice flow and the dilution process inside the tube are studied. The volume flow through the orifice is shown to be proportional to the square root of the pressure drop. The discharge coefficient is 0.9 ± 0.3 in the cold air (calibration) case and drops to 0.35 under hot (flame) conditions. The resulting dilution ratio is roughly a factor of five below typical literature data. The gas sample remains in the wall boundary layer and the mixing process is not complete at the end of the dilution tube. Turbulence decays rapidly behind the tube inlet, which shifts the flow into the laminar to turbulent transition regime. Turbulence increases significantly in the outlet section which has much smaller pipe cross-sections. Despite its relatively low Reynolds number, the outlet flow to the particle sizer (or to the gas analyzer) is clearly turbulent, and interactions with the wall are probable. The results are in agreement with previous findings from laminar jets in cross-flow. Guidelines for optimization of the sampling conditions are suggested.

オイラー・ラグランジュ法を用いたクロスフロー型液体噴流の微粒化・蒸発に関する数値解析

This study investigates the atomization and evaporation process of liquid fuel jets in crossflow by considering the evaporation from not only Lagrangian droplets but also the liquid column and Eulerian droplets which are generated from the primary breakup of the column. The evaporations from the liquid column and Eulerian droplets are calculated using the heat and mass transfer model, while the evaporation of Lagrangian droplets is calculated by a non-equilibrium Langmuir-Knudsen model. The results show that the evaporation occurs actively at the gas-liquid interface of the liquid column tip and droplets torn from the jet. In addition, in comparison to the evaporation of Lagrangian droplets, the Eulerian part of the evaporation is marked. Moreover, regarding fuel vapor distributions on a downstream plane, fuel vapor from the gas-liquid interface is greatly influenced by the liquid column trajectory and is distributed mostly at the same height as the column tip. In contrast, fuel vapor from Lagrangian droplets is also highly distributed near the wall.

Numerical investigation of impingement heat transfer on the crossflow channel with vortex generators

• A new vortex generator with downstream common-flow-down configuration is obtained. • The counter rotating vortex pair is extruded by a recirculation behind the jet. • The maximum enhancement of area averaged Nusselt number can reach up to 69.7%. • The additional increase of friction coefficient is lower than 10%. Vortex generators (VGs), as novel measures for suppressing a crossflow, have been used for the promotion of jet impingement heat transfer. In this study, to explore more VGs’ benefits, numerical simulations are investigated for the comparisons of a jet in crossflow with four VGs, considering the heat transfer performances and the flow interaction mechanisms. VGs with common-flow-up or common-flow-down configurations are arranged in the upstream or downstream of the jet hole. Parameter studies are carried out by varying the crossflow-to-jet ratio from 0.19 to 0.32, VG heights from 1/8 H to 1/2 H ( H is the jet-to-wall distance), and spacings between the jet and the VGs from 0 d to 2 d ( d is the jet hole diameter). Results show that a new VGs with downstream common-flow-down configuration (DCFD) is obtained with favorable enhancement of heat transfer, which is competitive to the upstream common-flow-up configuration (UCFU) studied in previous work. With the DCFD configuration, the extrusion of the counter rotating vortex pair is caused by a recirculation region generated behind the jet, which gives more blockage to the crossflow. In addition, the heat transfer for the DCFD case is promoted with the increasing height of the VGs, and decreasing the spacing between the VGs and the jet. The maximum enhancement in area averaged Nusselt number for DCFD case can reach up to 69.7% with a small increase in the friction coefficient of lower than 10%. This study will present much more possibilities for the heat transfer enhancement in more complex system, such as jet array system and nonuniform crossflow system.

Experimental and Numerical Investigation on Flow Condensation Process of Oxygen Jet in Crossflow of Liquid Oxygen

Experimental and Numerical Investigation on Flow Condensation Process of Oxygen Jet in Crossflow of Liquid Oxygen

Mixing augmentation induced by the combination of the oblique shock wave and secondary recirculation jet in a supersonic crossflow

The mixing process of fuel-air in the supersonic crossflow is a pivotal technology for the scramjet engine. In this paper, numerical simulation of the transverse sonic hydrogen jet into a supersonic Mach 3 crossflow with the mixing augmentation strategy induced by the combination of the oblique shock wave and secondary recirculation jet has been carried out. Detailed flow field structures, hydrogen mass fraction distributions, vortex structures, heat flux and some parameters have been explored in order to investigate its mixing enhancement mechanism. Results of the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two-equation shear stress transport (SST) κ-ω turbulence model show that the combined strategy of the oblique shock wave and secondary recirculation jet device can effectively improve the mixing speed and mixing efficiency with little total pressure loss. Also, the secondary recirculation jet device can reduce the peak of the heat flux effectively. In this study, the case with the single bleed hole owns the best effect with improving the mixing efficiency by 82.75% locally and reducing the maximum heat flux by 15.24% respectively。

Numerical simulation of single/double liquid jets in supersonic crossflows

This study investigates the mixing processes of liquid jets in supersonic crossflows at a Mach number of 2.1 by using numerical simulations that employ the Coupled Level-Set/Volume-of-Fluid (CLSVOF) method, which is based on the Delayed Detached Eddy Simulation (DDES). The instantaneous spray morphology from the simulations agreed well with the experimental data. The spray presents the ‘Ω’ shape when viewed from the front, and the maximum error in the penetration depth was 15% from a side perspective. The direction of the air movement determined the shape of the liquid column shearing and breaking. In turn, the breaking process of the liquid jet significantly affects the structure of the air flow. Three-dimensional flow around the liquid column occurred when the supersonic incoming flow impinged on the liquid column, ultimately forming counter-rotating vortex pairs (CVP) in the inner region of the spray. Evolution of the reverse vortex pair accelerated the mixing process of the spray. Single liquid jet was used as a basis to further study double jets in Mach 2.1 airflow. The results show that the breaking length and penetration depth of the downstream jet are significantly improved.

Modal Analysis of Breakup Mechanisms for a Liquid Jet in Crossflow

Abstract Liquid fuel jet in crossflow (LJIC) is a vital atomization technique significant to the aviation industry. The hydrodynamic instability mechanisms that drive a primary breakup of a transverse jet are investigated using modal and traveling wavelength analysis. This study highlights the primary breakup mechanisms for aviation fuel Jet-A, utilizing a method that could be applied to any liquid fuel. Mathematical decomposition techniques known as POD (proper orthogonal decomposition) and Robust MrDMD (multiresolution dynamic mode decomposition) are used together to identify dominant instability flow dynamics associated with the primary breakup mechanism. Implementation of the Robust MrDMD method deconstructs the nonlinear dynamical systems into multiresolution time-scaled components to capture the intermittent coherent structures. The Robust MrDMD, in conjunction with the POD method, is applied to data points taken across the entire spray breakup regimes: enhanced capillary breakup, bag breakup, multimode breakup, and shear breakup. The dominant frequencies of breakup mechanisms are extracted and identified. These coherent structures are classified with an associated time scale and Strouhal number. Three primary breakup mechanisms, namely, ligament shedding, bag breakup, and shear breakup, were identified and associated with the four breakup regimes outlined above. Further investigation portrays these breakup mechanisms to occur in conjunction with each other in each breakup regime, excluding the low Weber number enhanced capillary breakup regime. Spectral analysis of the Robust MrDMD modes’ entire temporal window reveals that while multiple breakup mechanisms are convolved, there is a dominant breakup route for each breakup regime. An associated particular traveling wavelength analysis further investigates each breakup mechanism. Lastly, this study explores the effects of an increased momentum flux ratio on each breakup mechanism associated with a breakup regime.

Computational and experimental study of an oil jet in crossflow: coupling population balance model with multifluid large eddy simulation

Understanding the size of oil droplets released from a jet in crossflow is crucial for estimating the trajectory of hydrocarbons and the rates of oil biodegradation/dissolution in the water column. We present experimental results of an oil jet with a jet-to-crossflow velocity ratio of 9.3. The oil was released from a vertical pipe 25 mm in diameter with a Reynolds number of 25 000. We measured the size of oil droplets near the top and bottom boundaries of the plume using shadowgraph cameras and we also filmed the whole plume. In parallel, we developed a multifluid large eddy simulation model to simulate the plume and coupled it with our VDROP population balance model to compute the local droplet size. We accounted for the slip velocity of oil droplets in the momentum equation and in the volume fraction equation of oil through the local, mass-weighted average droplet rise velocity. The top and bottom boundaries of the plume were captured well in the simulation. Larger droplets shaped the upper boundary of the plume, and the mean droplet size increased with elevation across the plume, most likely due to the individual rise velocity of droplets. At the same elevation across the plume, the droplet size was smaller at the centre axis as compared with the side boundaries of the plume due to the formation of the counter-rotating vortex pair, which induced upward velocity at the centre axis and downward velocity near the sides of the plume.

Penetration of vertical pulsed jets in crossflow at low velocity ratio

Using the visualization method, the initial rise and penetration of a circular turbulent pulsed jet into a transverse air flow are studied at the ratio of jet velocities to the transverse flow r = u j /u f = 0.67–2.33. A comparative assessment of the penetration of a pulsating jet into a transverse flow for frequencies from 0 to 20 Hz is carried out. The cases of both stationary and oscillating jet flows are analyzed. The penetration of a pulsating jet into a transverse flow is shown to be more significant than for a stationary one and depends on an increase in the ratio of velocities and frequency: it increases linearly at a fixed frequency and passes through a minimum at a fixed ratio of velocities.

Submerged gas jet in liquid cross flow: Modeling and flow structures analysis

The influence of the liquid cross flow is important to the flow structure of submerged natural gas jet release from underwater pipelines. In the present study, the development of a submerged gas jet subjected to liquid cross flow is experimentally and numerically investigated to evaluate the effects of the cross flow on the underwater gas jet evolution. Experimentally, a full-scale experimental setup is designed and developed for submerged gas jet release and dispersion in the liquid flow with different cross velocities. The interaction between the gas jet and liquid cross flow and the jet morphology are captured by shadow photography combined with a high speed video camera, and the images are processed to extract the jet parameters and perform Proper Orthogonal Decomposition (POD) analysis to reveal the characteristics of different modes which refer to different flow structures. Numerically, a computation fluid dynamics model tested and verified by the experimental results is used to analyze the submerged gas jet in more detail. A modified integral model considering the jet entrainment and the effects from the liquid cross flow is proposed to predict the jet evolution. It turns out that the modified integral model is able to predict the jet development accurately, including trajectory, jet inclination angles and penetration length, which will provide convincing assessment and opportunity to take prompt response to control potential accidents caused by the submerged natural gas jet release in liquid cross flow.

Permuted proper orthogonal decomposition for analysis of advecting structures

Flow data are often decomposed using proper orthogonal decomposition (POD) of the space–time separated form, $\boldsymbol {q}'\left (\boldsymbol {x},t\right )=\sum _j a_j\left (t\right )\boldsymbol {\phi }_j\left (\boldsymbol {x}\right )$ , which targets spatially correlated flow structures in an optimal manner. This paper analyses permuted POD (PPOD), which decomposes data as $\boldsymbol {q}'\left (\boldsymbol {x},t\right )=\sum _j a_j\left (\boldsymbol {n}\right )\boldsymbol {\phi }_j\left (s,t\right )$ , where $\boldsymbol {x}=(s,\boldsymbol {n})$ is a general spatial coordinate system, $s$ is the coordinate along the bulk advection direction and $\boldsymbol {n}=(n_1,n_2)$ are along mutually orthogonal directions normal to the advection characteristic. This separation of variables is associated with a fundamentally different inner product space for which PPOD is optimal and targets correlations in $s,t$ space. This paper presents mathematical features of PPOD, followed by analysis of three experimental datasets from high-Reynolds-number, turbulent shear flows: a wake, a swirling annular jet and a jet in cross-flow. In the wake and swirling jet cases, the leading PPOD and space-only POD modes focus on similar features but differ in convergence rates and fidelity in capturing spatial and temporal information. In contrast, the leading PPOD and space-only POD modes for the jet in cross-flow capture completely different features – advecting shear layer structures and flapping of the jet column, respectively. This example demonstrates how the different inner product spaces, which order the PPOD and space-only POD modes according to different measures of variance, provide unique ‘lenses’ into features of advection-dominated flows, allowing complementary insights.

Simple integral model for trajectories of jet deflection in crossflow

An integration method is developed based on mass and momentum conservation laws to predict trajectories of transverse jets in crossflow. The dominant mechanisms of jet deflections, namely, the jet ingestion and the drag force, are quantified. The evolution of the jet size is determined by modeling the growth of the counter-rotating vortex pair, bringing closure to the equation set. Results are compared with experimental data at different velocity ratios, density ratios, and turbulence intensity. Good agreements between predicted results and experimental data demonstrate the advantages of the proposed model over the commonly adopted correlation in prediction accuracy and generality.

Simultaneous measurements of time-resolved velocity and concentration fields behind a sand dune-inspired jet in crossflow

The flow field and scalar concentration behind a sand dune-inspired jet-in-crossflow were measured to quantify the characteristics of flow and scalar mixing. The velocity was resolved from particle image velocimetry measurements, and the time-resolved concentration was simultaneously captured by planar laser-induced fluorescence. During the experiments, the velocity ratio was set to 0.4, 0.6, 0.8, 1.0, and 1.2. The corresponding jet flow statistics, concentration statistics, and flow-concentration dynamics were comparatively analyzed. Aided by the dune, all jets were found to discharge tangentially into the mainstream, forming an energetic shear layer in the dune upper region that not only affects the jet attachment but also influences the flow mixing dynamics. The measured turbulent flow statistics (vorticity, turbulent kinetic energy, and Reynolds stress), concentration statistics (scalar standard deviation and turbulent scalar flux), and dynamics of the flow-concentration fields (instantaneous evolutions, scalar dissipation, and strain rate) revealed not only the complex nature of the generated shear layer but also the significant correlations between the shear flow and scalar mixing. Proper orthogonal decomposition (POD) analysis successfully decomposed the instantaneous velocity and concentration fields into a series of energetic POD modes, vividly demonstrating the modulating effect of the energetic shear layer on the flow and scalar mixing.

Scale resolving simulations of a high-temperature turbulent jet in a cold crossflow: Comparison of two approaches

A high-temperature turbulent jet in a cold crossflow is investigated with the help of two scale-resolving simulation approaches. This work aims at improving the methodologies used to predict the thermal footprint of exhaust gases issuing from helicopter engines onto the fuselage. Specific attention is brought to the capability of scale resolving simulations to correctly reproduce flow dynamics and turbulent mixing. Mean flow features, turbulent quantities and temperature fields are compared and validated against wind tunnel test measurements. In addition, the present work highlights the importance of synthetic turbulence injection at pipe inlet to obtain a fair prediction of both flow dynamics and temperature field.

Single camera 20 kHz two-color formaldehyde PLIF thermometry using a dual-wavelength-switching burst mode laser.

We propose and demonstrate a two-color formaldehyde planar laser induced fluorescence spectroscopy thermometry scheme using the third-harmonic of injection-seeded Nd:YAG lasers. The 28183.5cm-1 and 28184.5cm-1 peaks of formaldehyde are identified to measure the low-temperature combustion zone. Using a fast dual-wavelength-switching burst mode amplifier and a high-speed camera, high-repetition-rate (20 kHz) temperature field measurement is validated on a laminar coflow diffusion flame and demonstrated on a turbulent reacting jet in hot crossflow. Directly using the 355 nm output has the advantage of large energy and high signal-to-noise ratio. Combined with the fast dual-wavelength-switching method, the proposed scheme can greatly reduce experimental complexity and improve the understanding of practical combustors.

On the generality of tensor basis neural networks for turbulent scalar flux modeling

This study focuses on Reynolds-averaged Navier Stokes (RANS) models for passive scalar transport. A recently developed machine learning turbulence closure, the tensor basis neural network for scalar flux modeling (TBNN-s), is applied on two different datasets, an inclined jet in crossflow and a wall mounted cube in crossflow. The TBNN-s consists of a deep neural network that predicts a turbulent diffusivity matrix after being trained on high fidelity datasets. The present work addresses the generality question (i.e. will a model trained in one turbulent flow perform well in a different turbulent flow?) by training and testing across different classes of flows. We show that when trained and tested in the same class of flow, the TBNN-s obtains significant improvements in the mean scalar field over a common baseline model. When trained and tested across different classes of flows, the TBNN-s has a similar performance to the baseline model, which is encouraging since training set extrapolation does not produce the nonphysical results some fear. Further analysis suggests that varying training sets for the same test case produces similar results in terms of alignment of the scalar flux vector, but different turbulent diffusivity matrix magnitudes.

Numerical investigation of the breakup mode and trajectory of liquid jet in a gaseous crossflow at elevated conditions

ABSTRACTThe commercial Computational Fluid Dynamics (CFD) software STAR-CCM+ was used to simulate the flow and breakup characteristics of a Liquid Jet Injected into the gaseous Crossflow (LJIC) under real engine operating conditions. The reasonable calculation domain geometry and flow boundary conditions were obtained based on a civil aviation engine performance model similar to the Leap-1B engine which was developed using the GasTurb software and the preliminary design results of its low-emission combustor. The Volume of Fluid (VOF) model was applied to simulate the breakup feature of the near field of LJIC. The numerical method was validated and calibrated through comparison with the public test data at atmospheric conditions. The results showed that the numerical method can capture most of the jet breakup structure and predict the jet trajectory with an error not exceeding ±5%. The verified numerical method was applied to simulate the breakup of LJIC at the real engine operating condition. The breakup mode of LJIC was shown to be surface shear breakup at elevated condition. The trajectory of the liquid jet showed good agreement with Ragucci’s empirical correlation.

Preheating and premixing effects on NOx emissions in a high-pressure axially staged combustor

NOx emissions remain a primary concern for modern and future gas turbines, particularly as we progress towards a net-zero carbon future. It is critical to identify novel strategies to mitigate environmental pollutants for both modern turbines operated on natural gas and future turbines projected to use carbon-free fuels (such as hydrogen). In the current study, NOx emissions of a reacting methane-air jet in a vitiated crossflow are experimentally investigated in a model axially staged combustor at 5 atm. The combustion products from the main stage combustor flow into the axial stage at temperatures ranging from 1580 to 1650 °C. The axial stage contains a reacting jet in crossflow, which provides an overall temperature rise ranging from 50 to 220 °C to generate exit temperatures similar to gas turbine engines. The focus of this paper is to explore the effects of flame liftoff and ignition timescales on the NOx contribution of this secondary jet. This is done by varying the premixed level and preheat temperature of the axial jet. The effects are explored at different momentum flux ratios (J), jet equivalence ratios (φjet), exit temperatures (Texit), and main stage (headend) temperatures (THE). High-speed CH* chemiluminescence imaging is employed for each test case to determine the flame stabilization point. For a given temperature rise and combustor exit temperature, an increase in ignition delay was observed with a decrease in jet temperature. This provided a NOx benefit, particularly for jets that are injected at or close to an ignitable mixture fraction. Similarly, the coaxial injector caused a significant ignition delay compared to the fully premixed injector; this also led to a NOx benefit. Overall, the results show that a thermally driven delay in the axial stage provides a greater NOx reduction than a mixing delay.