Jet In Crossflow Research Articles

Characterization of the turbulent field behavior of an elevated jet-in crossflow investigated using direct numerical simulation

Direct numerical simulation (DNS) of a turbulent flow in an elevated jet in crossflow has been carried out at a Reynolds number (Re) of 3500 based on the outer width of the stack and crossflow velocity. The jet to crossflow velocity ratio is kept constant at VR=2. Second order spatial and temporal discretization have been used to solve the Navier–Stokes equations employing a high-resolution grid to determine the essential characteristics of the coherent and the incoherent flow fields accurately. The large-scale coherent and small-scale incoherent flow fields are extracted using a reference signal-based phase-averaged method that uses a reference signal against which the phases are identified in each cycle to minimize the phase jitter. The rate of decay of circulation of the stack-wake vortices is observed to be more than that of the jet-wake which has a lower circulation value. The contribution of the incoherent fluctuations to the total turbulent kinetic energy is more compared to its coherent counterpart in the wake as well as jet region, except for the near-wake of the stack. The normal and shear stresses of both coherent and incoherent fields reveal a relatively higher contribution in the near-wake of both stack-wake and jet-wake, while the far-wake shows the opposite trend. The anisotropy factor of both the large-scale coherent and the small-scale fluctuating fields provides the evidence of total anisotropy of the stack-wake. The characterization of both types of fluctuating fields is also carried out using the anisotropy-invariant-map which displays the one-component limit for the coherent fluctuating field in most of the regions, but the anisotropy state of the incoherent fluctuating field is found to switch among various limits, namely, the axisymmetric contraction, the axisymmetric expansion, and isotropic limits.

Investigation of reacting fuel jets in hot vitiated crossflow

Near-wall reacting jets can occur in different engineering applications, such as rocket combustion chambers and in gas turbine combustors and turbines. This work presents results of experimental investigations of reacting gaseous fuel jets (hydrogen, methane, propane) injected normally into a hot oxygen-rich cross-flow using OH laser-induced fluorescence and OH* chemiluminescence diagnostics. RANS CFD simulations with EDC combustion model are performed for comparison. To determine the surface heat fluxes, the inverse heat conduction method was applied using measured wall temperature data as input. It was observed, that hydrogen jets ignite directly at the injection location and caused a higher surface heat flux than the hydrocarbon jets, where jet-like diffusion flames emerged. With the latter fuels, a significant ignition delay length was observed. Operation with methane fuel showed the least stability, least reactivity and the lowest surface heat flux. Increasing the jet momentum ratio led to a reduced ignition delay length due to enhanced jet-crossflow interaction, and to a reduction of surface heat flux as the reacting jet detached more from the surface. CFD results using the Eddy-Dissipation Concept (EDC) combustion model predicted ignition delay lengths and reaction zone shapes in qualitative agreement with the experiment but with a trend of overestimating combustion temperatures.

Investigation on frequency influence on the transverse pulsed jet in a supersonic crossflow

AbstractThe pulsed jet is a novel and effective active mixing enhancement approach. For the transverse pulsed jet in the supersonic crossflow, the frequency influence is investigated using the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with the SST k-ω turbulence model. The averaged flow field properties of the pulsed jet are better than those of the steady jet when considering mixing efficiency and jet penetration depth, especially for the case with the pulsed frequency being 50kHz. The flow field structures of the pulsed jet are connected with the time, with periodic wave structures generating in the flow field and moving downstream. The size of the wave structures and its distance are related to the frequency, namely the size and flow distance are relatively small at 50kHz, and it takes some time for the pulsed jet to establish its influence in the full flow field. At low frequencies, the flow field produces large fluctuations, and this may be detrimental to the stable operation of the engine.

Flame characteristics of backward-inclined pulsating combusting jet in crossflow

The flame appearances, thermal characteristics, and combustion product concentrations of a backward-inclined pulsating combusting jet in crossflow were experimentally studied. The time-averaged and streak instantaneous flame images were acquired using a still camera and a high-speed camera, respectively. The flame extinguishment processes were captured and analysed on the basis of streak instantaneous images. The flame temperatures and combustion product concentrations were measured using a homemade fine-wire thermocouple and a gas analyser, respectively. Three characteristic flame modes (crossflow dominated, transitional, and jet-dominated) were found when the backward-inclined jet flame in crossflow was subject to acoustic excitation. These characteristic flame modes were observed in different regimes of pulsation intensity and jet backward inclination angle. Discrete flame puffs with a frequency equal to the acoustic excitation frequency appeared in the jet-dominated flame. Periodic flame puffing became unstable when the pulsation intensity was increased to values near the instability limit. When the pulsation intensity was beyond the instability limit, a strong stretching effect caused the recirculation flame, which played the role of a flame ignitor, to almost vanish (misfire). The flame extinguishment then occurred from the area around the lee side of the burner tube tip. The temperature and gas concentration measurement results showed the significant improvement of combustion performance in low inclination angle even at small pulsation intensity in the regime of the crossflow dominated flame. To enhance combustion performance at a large jet backward inclination angle, the pulsation intensity must be large enough to push the flame in the regime of the jet-dominated flame.

Experimental investigation into the flow structure of plasma induced Jet in a 2-D Cross-Flow

This study is focused on the flow physics in the condition of employing the active flow control methods and DBD plasma actuators as a transverse jet. In the current research, a single DBD plasma actuator is added to the Trailing Edge of a flat plate model and several wind tunnel experiments are conducted to study the flow structures. The salient goal of this work is to investigate the flow physics of Plasma Jet in Cross-Flow. Wind tunnel experiments results in two different free stream velocities of U∞=10m/sandU∞=20m/s and several model’s angles of attack show that the flow domain consists of two different counter rotating vortices at St=0.1886 and 0.1725 and a secondary vortex with St=0.5842. The manner of these vortices in the different AoA and free stream velocities, and also the shape of the velocity profile in the near wake and far-field wake of the plasma jet prove that the flow domain around the Plasma Jet in Cross-Flow is very similar to the flow around an airfoil equipped with Gurney Flap.

Numerical simulation of bubbly jets in crossflow using OpenFOAM

This paper conducted a computational fluid dynamics study of bubbly jets (not bubble plumes due to pure gas injection) in crossflow to explore the hydrodynamics that are still unknown. A three-dimensional model was developed, calibrated, and validated by coupling the Euler–Euler two-fluid model with unsteady Reynolds-averaged Navier–Stokes approach in OpenFOAM. The results showed that the modeled gas void fraction, bubble velocity, water jet centerline trajectory, and jet expansion agree well with the experimental data. The vertical distribution of turbulent kinetic energy evolves from mono-peak to dual-peaks as the jet penetrates farther for the bubbly jet due to the interactions between bubbles and ambient water flow. Water velocity distribution was examined at cross sections of both the air- and water-phases of bubbly jets in crossflow, and counter-rotating vortex pairs can be clearly observed for both phases. Generally, the center-plane maximum concentration decreases in the crossflow direction. Compared to pure water jets, bubbly jets are stretched wider in the vertical direction due to the lift of bubbles, and thus, dilution is larger. Interestingly, the vorticity at water jet cross sections of bubbly jets evolves from two vertical “kidney-shapes” to two axisymmetric “thumb-up-shapes.” Moreover, effects of ambient crossflow on bubbly jet behaviors were systematically examined. As the crossflow velocity increases, the locations of maximum concentration, maximum velocity magnitude, maximum vorticity magnitude, as well as water jet centerline, all tend to be lower for bubbly jets.

Liquid film formation: prediction accuracy of different numerical approaches

In counteracting fouling phenomenon in gas turbines, which leads to system inefficiencies and performance degradation, water washing technique is very often adopted. Water droplets sprays are injected and, hitting the solid surfaces, remove the dirt deposition. Among the collateral undesirable phenomena related to water washing, blades erosion and liquid film formation are the most remarkable. Despite the former issue was extensively assessed by the authors in previous works, up to the authors’ knowledge the risk of liquid film formation due to water washing was scarcely investigated. Liquid film formation and spreading on a solid surface is a complex phenomenon involving a large number of physical events, such as: droplets impact on a solid surface, splashing phenomena, liquid film dragging under the effect of the carrier phase and droplets separation from the film in proximity of geometry discontinuities. In this paper, an extensively used experimental test case involving all these phenomena was used to test different numerical wall film models available in literature. The test case consists in the injection of a liquid jet in a high velocity crossflow. Some of the liquid jet mass impacts on the opposite solid surface generating a wall film which develops under the dragging effect of the crossflow. A Lagrangian approach was used to track the suspended droplets within the flow field by also considering the turbulent dispersion by means of a Random Walk model. Droplets-wall interaction is considered according to the Stanton-Rutland model, which provides the outcome of a collision (deposit, rebound or splashing), depending on the local impact conditions. If a droplet sticks on a solid boundary, a liquid film generates. Droplets atomization is also accounted for by using the Madabhushi model while Friederich separation model was selected to take into account the detachment of droplets from the film at the geometry edge. Three different numerical simulations have been performed based on different approaches used to solve the liquid film evolution, namely Eulerian one-way coupling, Eulerian two-way coupling and Lagrangian two-way coupling. Numerical results have been compared with the experimental ones from both a qualitative and a quantitative point of view. The wall film shape, its spatial distribution and the variation of the film thickness of the wall centreline have been compared between experimental and numerical simulations proving that the Lagrangian 2-way coupling approach better reproduces the liquid film dynamics observed in the experiments.

Jet cross-flow induced vibrations in rod bundles. Part I: Experimental apparatus and stream-wise vibration results

Jet cross-flow induced vibration of fuel assemblies has recently been observed in some reactors that have fail-safe features for pressure release in the event of a loss of coolant accident (LOCA). The generated pressure in the barrel–baffle region during LOCA is mitigated by discharging the flow through LOCA holes and slots normally to the primary axial coolant flow inside the core. However, the jet flow injected through the LOCA holes and slots can induce vibration in the fuel assembly near the baffle before being mixed with the axial flow, and subsequent it can cause grid-to-rod-fretting (GTRF). In this paper, experimental investigations were performed to characterize the jet cross-flow induced vibration of fuel rods by performing fluidelastic instability (FEI) tests on flexible rod bundles. The effect of the stream-wise which is called ”stand-off distance”, is studied by the changing number of rows in the tested bundle. Furthermore, an offset between the centerlines of the jet and the bundle (jet eccentricity) which means the transverse direction on the jet centerline, is changed to show its effect on rod bundle vibration. An experimental test facility was designed to give the capability to study different jet eccentricities to examine their stability effects. The stream-wise results show that varying jet eccentricity excited the rod bundle with different mechanisms. The rods vibrations occurred with the centered jet with rod bundle case had a lock-in/synchronization phenomenon, where the resonant peak is observed. While, the excitation mechanism is switched to turbulence-induced vibrations by moving the jet flow by 0.25 of pitch. However, the aligned jet-rod case showed a fluidelastic instability phenomenon at relatively high jet velocity. On the other hand, the two resonant peaks are obtained when the rod bundle moved away from the jet flow (i.e larger stand-off distance).

Jet cross-flow induced vibrations in rod bundles. Part II: Transverse vibration results and excitation mechanisms

Jet cross-flow in fuel assemblies has recently led to grid-to-rod fretting (GTRF) in reactors with fail-safe features, for the event of a loss of coolant accident (LOCA), including LOCA holes and slots. The findings in Part I of the paper showed that the stream-wise response behavior of the rod bundle was strongly dependent on the jet eccentricity and stand-off distance. These two parameters were defined to identify the location of the rod bundle centerline with respect to the jet centerline.The experimental investigation was extended to identify the direction in which the instability is most critical. The present Part II of the paper discusses the effect of both jet eccentricity and stand-off distance on the stability of transverse rod bundle vibrations and the underlying excitation mechanisms. This is achieved by adjusting the flexible rods to vibrate in the direction normal to the jet flow. The results show that jet cross-flow causes fluidelastic instability in the transverse direction. The rod bundle vibration and instability depends strongly on the jet eccentricity. The transverse vibrations are more dominant than those in the stream-wise direction. The critical velocity decreases with increasing stand-off distance and then reverses. This stand-off distance behavior in the transverse direction is opposite of that found for stream-wise vibrations.

Understanding the liquid jet break-up in various regimes at elevated pressure using a compressible VOF-LPT coupled framework

The present work implements a compressible Volume of Fluid (VOF) – Lagrangian Particle Tracking (LPT) coupled solver in OpenFOAM and utilizes it to simulate a liquid jet in crossflow (LJICF) numerically. This methodology helps accurately predict a complex primary breakup in the Eulerian framework and the secondary atomization of spherical droplets using a computationally efficient LPT method. The coupled solver with Adaptive Mesh Refinement (AMR) is rigorously validated for a liquid jet in crossflow at varying operating conditions – pressure, crossflow velocity, and inlet liquid jet velocity. We have further carried out a thorough investigation to study the effect of momentum flux ratio and weber number on the various flow features and liquid jet break-up phenomenon in a crossflow while identifying the stream-wise location of the liquid jet breakup region. At low momentum flux ratios in the bag breakup regime, the predictions reveal that the liquid jet breakup occurs due to the growth of similar instability as usually observed in the high-speed liquid sheet atomization. The short wavelength assumption of the inviscid dispersion relation resembles the Kelvin-Helmholtz type instability observed in this case, as opposed to Rayleigh-Taylor instability at high momentum flux ratio in the surface breakup regime. It is also proposed that the shear breakup along the transverse edges of the liquid column occurs due to the shear layer instability of the air passing around the liquid column. The simulation wavelength closely matches the Williamson correlation for shear layer instability around cylinders – a shape similar to the cross-section of the bottom of the liquid column. The results show a distinct streamer or bifurcation phenomenon at low momentum flux ratios and moderate weber numbers. Further investigation suggests that the internal liquid boundary layer and the three-dimensional flow field behind the liquid jet are responsible for streamer formation.

Lift-off region temperature field and planar flow field of a twin-nozzle reacting jet in hot crossflow

Secondary fuel injection affects the combustion organization and flame dynamic in axial fuel staging gas turbines. Here, we experimentally investigate a front-fuel rear-air twin-nozzle configuration in which the fuel and air can be independently injected to stabilize a lifted flame front, control the jet trajectory and tune the combustion mode in a very flexible way. A high repetition two-line formaldehyde planar laser induced fluorescence thermometry technique is used to measure the lift-off preheat zone temperature field of the flame with different amount of secondary air injection. The combustion flow field and the flame front dynamics are investigated using particle image velocimetry and CH* chemiluminescence. When the air to fuel ratio increases from 0 to 3, the preheat zone temperature, which is affected by the local equivalence ratio and injection air cooling, increases from 1300 K to 1600 K and then slightly declines. The lift-off region temperature and flow field dynamics are related to the variation of lift-off height, heat release rate and stability of the reacting jet in hot crossflow.

Heat transfer enhancement in turbulent boundary layers with a pulsed slot jet in crossflow

The convective heat transfer enhancement in a turbulent boundary layer (TBL) employing a pulsed, slot jet in crossflow is investigated experimentally. A parametric study on actuation frequencies and duty cycles is performed. The actuator is a flush-mounted slot jet that injects fluid into a well-behaved zero-pressure-gradient TBL over a flat plate. A heated-thin-foil sensor measures the time-averaged convective heat transfer coefficient downstream of the actuator location and the flow field is characterised by means of Particle Image Velocimetry. The results show that both the jet penetration in the streamwise direction and the overall Nusselt number increase with increasing duty cycle. The frequency at which the Nusselt number is maximised is independent of the duty cycle. The flow topology is considerably altered by the jet pulsation. A wall-attached jet rises from the slot accompanied by a pair of counter-rotating vortices that promote flow entrainment and mixing. Eventually, a simplified model is proposed which decouples the effect of pulsation frequency and duty cycle in the overall heat transfer enhancement, with a good agreement with experimental data. The cost of actuation is also quantified in terms of the amount of injected fluid during the actuation, leading to conclude that the lowest duty cycle is the most efficient for heat transfer enhancement.

Experimental and numerical investigation on flow condensation process of oxygen jet in crossflow of liquid oxygen

The mixing and condensation process of gaseous oxygen jet in liquid oxygen flow in the outlet pipeline of oxidizer booster pump in liquid rocket engine are studied. In the present study, experiments are performed to investigate oxygen jet condensation in crossflow of liquid oxygen in a vertical pipe. The image of the test section is obtained by visualization device and processed by digital image technology. A computational fluid dynamics (CFD) model is developed to simulate the mixing and condensation process based on multiphase VOF model and Lee phase change model. The experimental results show that, under the current operating conditions, gaseous oxygen forms a crooked jet plume at the outlet of orifices, and then the gas phase gradually condenses, forming discontinuous bubbles downstream. The effects of Reynolds number of liquid oxygen, oxygen mass flux, ambient pressure and liquid oxygen temperature on the gas distribution and axial condensation length are investigated accordingly. The mass transfer coefficient r=10000s−1 which has been verified by the experiment of oxygen jet in liquid oxygen crossflow is obtained and the predicted gas distribution by CFD simulation is in good agreement with the experimental data. The experimental dimensionless axial condensation length is in the rage of 7.3 to 18.2, and a correlation of dimensionless axial condensation length has been modified. Besides, the dimensionless axial condensation length predicted by simulation is less than 13% comparing with experiment. The averaged heat transfer coefficients obtained in experiment and simulation are around 13.89–26.04 kW/(m2K) and 12-67kW/(m2K), which is much lower than the average heat transfer coefficient in the DCC of water. The results of the present investigation will be helpful in designing the pipeline between pumps in liquid rocket engine.

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.

Experimentally validated high-fidelity simulations of a liquid jet in supersonic crossflow

Utilizing recent advancements in computational schemes for compressible, multiphase flows , this work features a parametric study of a pure liquid jet in supersonic crossflow that involves simulating the atomization process for four values of momentum-flux ratio. These simulations are validated against experimental results measured with high-speed X-ray imaging, which confirm the accuracy of the numerical approach. Also, the effect of numerical resolution on some flow behavior is investigated, revealing convergence of the jet shape and surface instability wavelength. Analysis of the resulting sprays includes statistical descriptions of the liquid distribution, liquid structures created through breakup, interfacial instabilities, and dominant flow features. As the flowrate increases, the spray penetrates further, it becomes more disperse, and less liquid impacts the wall, but the droplet size distribution changes little. The wavelength of instabilities on the windward side of the jet diverges from measured trends in subsonic crossflows. In a visualization of the time-averaged flow, counter-rotating vortices are observed along the jet core and in the wake, affecting the process of primary atomization and early droplet trajectories. • Large Eddy Simulations of liquid jet in supersonic crossflow at high Weber number. • Quantitative validation against experimental results using equivalent path length. • Shear-driven instability wavelengths differ from subsonic crossflow analogy. • Analysis of spray statistics and mean flow features.

Numerical and Experimental Study on Jet Trajectory and Fuel Concentration Distribution Characteristics of Kerosene Jet in Air Crossflow

The fuel concentration distribution in an afterburner is a critical factor that affects its ignition, flameout, stability, and combustion efficiency. Additionally, the trajectory of the fuel jet directly affects the distribution of the downstream fuel. Hence, this paper studied the factors that affect a jet’s trajectory and fuel concentration distribution through numerical calculations. The change law of the fuel jet trajectory under various parameters was studied, and the jet penetration depth change rate was analyzed. Moreover, the empirical formula of the spanwise distribution range of the liquid fuel in front of the stabilizer was fitted. Furthermore, this study investigated fuel concentration distribution experimentally in the afterburner under normal temperature and pressure. The paper obtained the variation law of fuel concentration in the spanwise and radial directions, and the proportion of the gaseous fuel in the flow section under the influence of different parameters. Additionally, the spatial distribution of the droplet concentration was obtained, revealing that it increased initially, and then decreased in the flow direction, reaching a peak at the end of the recirculation zone. In the radial direction, two concentration peaks were found in the boundary of the recirculation zone and in the main flow region.

Improving Detonability in a Small-Scale Rotating Detonation Engine Using Partial Premixing

Small-scale rotating detonation engines (RDEs) with low mass flows and high frequency have potential as small thrusters, robust flame holders, and research tools that can be quickly and cheaply modified. However, the necessarily small channel geometry and low mass flow force the detonation wave to propagate near the limits of detonability. Previous success in a small-scale, 28-mm-diameter micro-RDE, operating on nitrous oxide () and ethylene (), exhibited unstable wave behavior with propagation velocities between 47 and 56% the Chapman–Jouguet speed. These results were observed at mass flows from 25 to using an in-chamber jets-in-crossflow (JIC) injection scheme with spark plug initiation. Building upon this work, the current investigation looked to improve the detonation behavior in the micro-RDE without changing the channel geometry or resultant operability and better understand the nature of mechanisms governing the design limitations in RDEs. To improve the wave behavior, a new partially premixed JIC injection scheme was used along with a predetonator ignition device. With these changes, tighter windows of operable mass flows () and equivalence ratios () were observed, between 35 and and 0.6 and 1.3, respectively. Maps of versus before and after detonation showed that the space of conditions conducive to ignition was not isomorphic with the space of conditions that sustained operation. Increases to the injection pressure to chamber pressure ratios improved the probability of detonation but resulted in greater pressure losses than were seen in the original JIC injection scheme. Single wave detonation was achieved for the first time in this RDE and had a peak frequency of 16.6 kHz, or 66% Chapman–Jouguet speed. Increases in fill height drove increases in wave frequency. Decreased fill height estimates compared to the previous design showed that partial premixing decreased the required fill time. These results support that the limits of detonability in small RDEs can be expanded without significantly compromising the characteristic low-mass-flow and high-frequency operation inherent to their geometry.

Liquid jet injection in supersonic crossflow: Self-induced jet oscillations and its effects

Liquid jet injection into supersonic crossflow is one of the conceptually simple ways of fuel atomization in Scramjet engines. In the present work, we experimentally investigate the flow and spray formed due to the injection of a liquid jet in supersonic crossflow with free stream Mach number of M∞ = 2.5. The main focus of the work is on the unsteady aspects of the flow and spray, which are found to be self-induced and occur naturally in the flow. High speed shadowgraphy shows large variations in the windward spray edge and penetration with time. Unsteady pressure measurements in the liquid injection line show that in the presence of a supersonic crossflow, there exist significant self-generated mass flow fluctuations that occur in the injection line. The frequency of these oscillations is seen to be close to a Strouhal number, St = fδ /U∞ ≈ 0.007, close to the typical low frequencies seen in Shock-Wave Boundary Layer Interaction studies (δ = boundary layer thickness). The variations in mass flow rate within the injection line leads to significant fluctuations of the spray penetration and shocks. In particular, the variations in spray penetration with time is observed to lead to significant variations in both the droplet numbers and size at a given location in the generated spray, which can have significant implications for applications where such configurations are used.

Numerical investigation on mixing process of a sonic fuel jet into a supersonic crossflow

The mixing process of a fuel jet in a supersonic crossflow is one of the significant issues for the design of the scramjet combustor. In this paper, the orthogonal analysis was employed to investigate the influences of the parameters of the supersonic mainstream and the fuel jet on the mixing process. Eight variables were considered and 27 cases were performed by the three-dimensional Reynolds-averaged Navier-Stokes (RANS) coupled with the shear stress transport (SST) turbulence model. The results show that the jet patterns can be divided into three categories by calculating the velocity ratio, named attachment pattern, transition pattern, and separation pattern, respectively. The extreme difference analysis indicates that the total pressure and Mach number of the mainstream, the total pressure of the fuel jet, and the diameter of the jet hole have a remarkable impact on the penetration depth and total pressure recovery. Additionally, a new dimensionless number named BS was proposed. And the penetration depth and total pressure recovery can be fitted to different functions of the BS. The fitted curves show that the larger penetration depth and smaller total pressure loss are generated as the BS increases. Finally, another new dimensionless number named LJ was proposed. And a positive correlation between the LJ and mixing efficiency has been elaborated based on analyzing the influence mechanism of the streamwise vortexes and the shockwaves on the mixing process. These correlations can provide help for primary optimization of supersonic combustor.

Film Cooling Performance Prediction for Air and Supercritical CO2

Abstract The current study explores the possibility of cooling the vanes and blades of a direct-fired sCO2 turbine using film cooling. The operating conditions of a direct-fired sCO2 cycle and thermophysical properties of the fluid at those conditions can alter the flow field characteristics of the coolant jet and its mixing with the mainstream. Very little information is present in the literature regarding the performance of film cooling geometries employing supercritical CO2. The objective of this study is to estimate the resulting film cooling effectiveness while also capturing the effects of the crossflow-to-mainstream velocity ratio on the coolant jet. A computational fluid dynamic model is used to study the coolant jet exiting a cylindrical hole located on a flat plate, with the coolant fed by an internal channel. Steady-state Reynolds-averaged Navier–Stokes equations were solved along with the (shear-stress transport) SST k–ω model to provide the turbulence closure. The operating conditions for the direct-fired sCO2 turbine are obtained using an in-house Cooled Turbine Model. Numerical predictions revealed that the crossflow effects and jet lift-off were more pronounced in the case of sCO2 when compared to air. Spatial distribution of flow field and cooling effectiveness are presented at different operating conditions.