Jet Flow Research Articles

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.

Numerical method analysis of the multi-nozzle distributor hydraulic performance for a Pelton turbine

Abstract The distributor hydraulic efficiency is very important for a Pelton turbine. In order to improve the turbine efficiency and the jet flow stability from the injector, it’s necessary to optimize the design of the distributor. In this paper, the flow behaviors and the hydraulic efficiency of a model Pelton turbine distributor with and without six-nozzle domain were conducted numerically. Comparison of numerical simulation results of different cases with different boundary condition settings and domain was analyzed. The predicted results show that the results of the distributor with six-nozzle domain are agree well with the measured results and the hydraulic performances is quite different from other cases.

A review of the experimental techniques research progress of the Pelton turbine

Abstract The Pelton turbine internal flow is by far the most complex of all hydraulic turbo-machinery, which consists of confined flow, free jet flow, free-surface water sheet flow and dispersed flow. The efficiency of Pelton turbine is closely related to these flow phenomena, thus knowing the dynamic behaviour of these flow patterns is of high interest to the optimization of Pelton turbine hydraulic flow parts. The experimental techniques were used to analyse the relationship between the connect of the turbine performance and flow patterns for the earlier researches. The present paper reviewed the development of experimental techniques of Pelton turbines, summarized the emerging test means and discussed the internal flow mechanism.

Flow structure and heat transfer characteristics of sweeping and steady impingement jets with/without chevrons on a semi-circular concave surface

Striving for improved gas turbine performance requires operating at higher gas flow temperatures, posing challenges in preserving the structural integrity of the gas turbine. To respond to these challenges, gas turbine manufacturers have turned to internal cooling and jet impingement to provide an effective solution for cooling the leading edge of the gas turbine blades. Fluidic oscillator is known for its sweeping behavior and expansive coverage of targeted surface and, thus, it can efficiently remove heat. In this study, the author numerically simulated the cooling performance of the leading edge of the gas turbine blades under constant heat flux while using four different configurations of jet impingement: a sweeping jet, a sweeping jet with chevrons, a steady jet, and a steady jet with chevrons. The results showed that the sweeping jet configuration with chevrons outperformed the steady jet configurations owing to oscillating jet impingement and a higher intensity of turbulence that increased the entrainment of jet flow. Under the configuration of a sweeping jet with chevrons, the targeted surface recorded an average Nusselt number that is 19.2% higher than the one with a steady jet without chevrons, along with a more uniform distribution of the surface temperature. The outstanding behavior of the sweeping jet with chevrons is due to the its internal flow behavior, i.e., oscillating flow nature of the sweeping jet with augmented turbulence at the exit of the chevron's nozzle.

Numerical Investigation of an Innovative Windbreak Design with Jet Flow Generated by an Air Curtain for Half-pipe Skiing

Numerical Investigation of an Innovative Windbreak Design with Jet Flow Generated by an Air Curtain for Half-pipe Skiing

A review on free miscible buoyant jets

Buoyant jets have been a topic of interest due to their presence in various natural and industrial phenomena, as well as in our daily lives. Covering extensive literature, our focus in this review article is on free, miscible buoyant jets with small-density differences (under the Boussinesq approximation) within uniform and stagnant environments. We examine the latest research on Newtonian jet flows and expand our scope to their viscoplastic counterparts, reflecting a burgeoning trend in contemporary literature. Our analysis covers negatively buoyant, pure, and positively buoyant jets, via delving into their dynamics. This includes regime classifications and key jet characteristics, such as laminar length, penetration length, mixing behavior, velocity profiles, and turbulence parameters. In particular, the effects of the key governing dimensionless parameters, including the Reynolds number, the Froude number, the Bingham number, the viscosity ratio, and the injection angle, on these characteristics are explored.

Numerical investigations on film cooling effectiveness and heat transfer performance of inclined film hole on the turbine blade squealer tip with plasma actuation

The turbine blade tip frequently encounters elevated thermal loads, necessitating effective protection measures. Conventional film cooling techniques, while employed to mitigate erosion, face challenges in achieving optimal performance due to intricate tip leakage flow dynamics. Thus, the development of advanced film cooling methodologies becomes imperative to ensure the optimal operation of blade tips. In this study, a novel film cooling approach is proposed, leveraging a combination of dielectric barrier discharge (DBD) plasma actuators and inclined film holes. This strategy aims to direct cooling jets towards the tip wall surface, enhancing film cooling efficacy on highly-loaded turbine squealer tips. Numerical investigations are conducted to assess film cooling effectiveness, heat transfer coefficients, and coolant jet flow characteristics across varying actuation strengths (0, 0.6, 0.8, and 1.0) by integrating plasma actuation forces into the Reynolds-Averaged Navier-Stokes equations. Additionally, the impact of different blow ratios (0.5, 1.0, and 1.5) on plasma flow control is examined. Results demonstrate that plasma actuation improves film cooling performance and effectively mitigates tip heat transfer, even in the presence of interfering tip leakage flow. Specifically, at an actuation strength of 1.0, the average blade tip film cooling effectiveness increases by 7.1%, accompanied by a 12.3% reduction in average heat transfer coefficient compared to scenarios without plasma actuation. Furthermore, the blow ratio influences plasma actuation performance, with minimal disparity observed between configurations with and without plasma devices under extreme blow ratio conditions.

Contrail Polarization Scattering Characteristics Simulation Based on Jet Flow Field

Contrail Polarization Scattering Characteristics Simulation Based on Jet Flow Field

Mass transfer enhancement for simultaneous desulfurization and denitrification by a venturi reactor

Interphase mass transfer is acknowledged as the rate-limiting step of simultaneous desulfurization and denitrification by wet oxidation. For this issue, this study established a venturi reactor to facilitate interphase mass transfer between flue gas and absorbent (NaClO2 solution), and to improve the efficiency of simultaneous desulfurization and denitrification. The effects of flow rate of jet, NaClO2 concentration, initial pH of solution, SO2 and NO volume concentration on the efficiency of desulfurization and denitrification were investigated. The results showed that SO2 can be completely removed at all experimental conditions. The denitrification efficiency decreased as jet flow rate increased from 8.38 L/ min to 12.87 L/min. The denitrification efficiency and overall mass transfer coefficient increased as the NaClO2 concentration increased from 0.01 wt% to 0.025 wt%. When the pH of the absorbent decreased from 9 to 3, the denitrification efficiency was improved significantly. An increasing SO2 volume concentration promoted NO removal efficiency, while SO2 and NO competed to inhibit denitrification at NaClO2 deficiency. The denitrification efficiency firstly increased and then decreased, with an increasing NO volume concentration from 500 to 1700 ppm. This study provides an important theoretical basis for the industrial application of simultaneous desulfurization and denitrification in venturi reactors.

Analisis Tenaga Pesentakan Jet Aliran Pekeliling Terbalik (PJAPT) Ke Atas Pengumpul Fotovolta Terma Suria (PVT) Modul Dwimuka

Although photovoltaic thermal (PVT) offers ascertain of benefits, it also has its own limitations. The efficiency of PVT is diminished due to heat gain experienced by its photovoltaic module when subjected to solar radiation. Jet impingement has been recognised as a highly successful technique for the purpose of cooling solar modules, particularly in the context of bifacial module applications. An energy analysis of a reversed circular flow jet impingement on a bifacial PVT collector was perform through an indoor experiment utilizing a solar simulator. The jet plate outlet was varied into four different configurations: one hole (1h), three holes (3h), four holes (4h) and five holes (5h) to identify the jet plate outlet configuration that contributes to the best energy efficiency. The experiment was carried out using a constant solar irradiance of 900 W/m2 and mass flow rate between 0.01 kg/s to 0.14 kg/s. The study’s findings indicate that configuration 1h exhibited the best photovoltaic efficiency of 11.09%. Additionally, the highest thermal efficiency recorded was 63.2%. In summary, it can be concluded that configuration 1h exhibits an overall photovoltaic thermal efficiency of 74.28% when subjected to a mass flow rate of 0.14 kg/s. This configuration outperforms other jet plate outlet configuration in terms of energy performance.

Two-temperature modeling of lamellar cathode arc

A three-dimensional, two-temperature (2T) model of a lamellar cathode arc is constructed, drawing upon the conservation equations for mass, momentum, electron energy, and heavy particle energy, in addition to Maxwell’s equations. The model aims to elucidate how the physical properties of electrons and heavy particles affect heat transfer and fluid flow in a lamellar cathode arc. This is achieved by solving and comparing the fields of electron temperature, heavy particle temperature, fluid flow, current density, and Lorentz force distribution under varying welding currents. The results show that the guiding effect of the lamellar cathode on current density, the inertial drag effect of moving arc, and the attraction effect of Lorentz force at the lamellar cathode tip primarily govern the distribution of the arc’s physical fields. The guiding effect localizes the current density to the front end of the lamellar cathode, particularly where the discharge gap is minimal. Both the inertial drag effect and the attraction effect of Lorentz force direct arc flow toward its periphery. Under the influence of the aforementioned factors, the physical fields of the lamellar cathode arc undergo expansion and shift counter to the arc’s direction of motion. A reduction in welding current substantially weakens the guiding effect, causing the arc’s physical fields to deviate further in the direction opposite to the arc motion. In comparison with a cylindrical cathode arc, the physical fields of the lamellar cathode arc are markedly expanded, leading to a reduction in current density, electron temperature, heavy particle temperature, cathode jet flow velocity, and Lorentz force.

Evidence of a toroidal magnetic field in the core of 3C 84

The spatial scales of relativistic radio jets, probed by relativistic magneto-hydrodynamic (RMHD) jet launching simulations and by most very long baseline interferometry (VLBI) observations differ by an order of magnitude. Bridging the gap between these RMHD simulations and VLBI observations requires selecting nearby active galactic nuclei (AGN), the parsec-scale region of which can be resolved. The radio source 3C 84 is a nearby bright AGN fulfilling the necessary requirements: it is launching a powerful, relativistic jet powered by a central supermassive black hole, while also being very bright. Using 22 GHz globe-spanning VLBI measurements of 3C 84 we studied its sub-parsec region in both total intensity and linear polarisation to explore the properties of this jet, with a linear resolution of ∼0.1 parsec. We tested different simulation set-ups by altering the bulk Lorentz factor Γ of the jet, as well as the magnetic field configuration (toroidal, poloidal, helical). We confirm the persistence of a limb brightened structure, which reaches deep into the sub-parsec region. The corresponding electric vector position angles (EVPAs) follow the bulk jet flow inside but tend to be orthogonal to it near the edges. Our state-of-the-art RMHD simulations show that this geometry is consistent with a spine-sheath model, associated with a mildly relativistic flow and a toroidal magnetic field configuration.

Multi-jet impingement cooling in the leading edge of turbine blade using matrix as internal structure

Multi-jet impingement is a competitive cooling scheme for the turbine blade leading edge, due to its strong ability in suppressing thermal boundary layer and quickly releasing the thermal load. However, crossflow is always a challenge if thermal performance is expected to be further improved. This paper proposed to induce jet flow from matrix to enhance cooling capability as well as uniformity of leading edge. A dual-air-paths test rig is built to measure heat transfer distribution and to validate the computational method. The results indicated strong coupling between jet cavity and matrix, implying the potential of enhancing heat transfer on both ends. Comparisons are made between different jet hole locations, among which the “Stagnation” position yields best performance, since superior initial jet condition can be created by matrix sub-channel flow. Increasing jet hole aperture leads to elevated heat transfer of nearly 72% in jet cavity, due to more stable vortex scour on the target wall. Changing jet cavity outflow configuration has significant effect on heat transfer due to thorough reconstruction of thermal field. The most advanced performance is acquired by both-sides outflow configuration, with approximately 34% improvement in heat transfer compared to the single-side cases.

Numerical investigation on the transverse jet into a supersonic crossflow with different pressure ratios

The jet can be applied to the yaw control of a projectile, however, the complex interaction of the jet with the supersonic mainstream makes the flow field complex and yaw force unpredictable. To reveal the evolution of flow structures under different pressure ratios (PRs), or momentum flux ratios, a transverse sonic jet injected into a supersonic laminar crossflow has been studied numerically. Large-eddy simulations are employed to simulate the flow fields and evolution tendency of flow structures under different PRs of 10, 50, 100, 300, and 500. Our results show clearly the shock and flow structures of the jet interaction with crossflow under different PRs. Moreover, we find that, with the increase of PR, a larger upstream recirculation zone (RZ) and jet shock core appear, which accelerates the transformation of the bow shock (BoS) and the instability of the jet shear layer due to its stronger interaction with the crossflow. In addition, a high PR also accelerates RZ instability and produces a strong compressing effect on the major counter-rotating vortex pair in the jet flow, which makes the streamwise vortex tube stronger in the wake. These findings provide important information for applications of jet control of projectiles.

Rupture point is associated with divergent hemodynamics in intracranial aneurysms.

Understanding the risk factors leading to intracranial aneurysm (IA) rupture have still not been fully clarified. They are vital for proper medical guidance of patients harboring unruptured IAs. Clarifying the hemodynamics associated with the point of rupture could help could provide useful information about some of the risk factors. Thus far, few studies have studied this issue with often diverging conclusions. We identified a point of rupture in patients operated for an IAs during surgery, using a combination of preoperative computed tomography (CT) and computed tomography angiography (CTA). Hemodynamic parameters were calculated both for the aneurysm sac as a whole and the point of rupture. In two cases, the results of CFD were compared with those of the experiment using particle image velocimetry (PIV). We were able to identify 6 aneurysms with a well-demarcated point of rupture. In four aneurysms, the rupture point was near the vortex with low wall shear stress (WSS) and high oscillatory shear index (OSI). In one case, the rupture point was in the flow jet with high WSS. In the last case, the rupture point was in the significant bleb and no specific hemodynamic parameters were found. The CFD results were verified in the PIV part of the study. Our study shows that different hemodynamic scenarios are associated with the site of IA rupture. The numerical simulations were confirmed by laboratory models. This study further supports the hypothesis that various pathological pathways may lead to aneurysm wall damage resulting in its rupture.

Experimental investigation of the heat transfer characteristics of a synthetic annular jet impingement on a flat surface

ABSTRACT Annular impinging jets create a more uniform flow on the impact surface compared to circular impinging jets, allowing the surface to cool better. Additionally, periodic flow oscillations significantly increase heat transfer by reducing the thermal resistance on the surface. Therefore, this study experimentally investigated the heat transfer characteristics of a synthetic annular jet impinging on a flat surface with constant heat flux. In the experiments, the jet-target surface distance (H/D), jet Reynolds number (Re j), oscillation amplitude (A o), and Womersley number (Wo) were changed. In contrast, the Prandtl number (Pr) and other geometric parameters were kept constant. The effects of these parameters on heat transfer were analyzed and the results were compared with continuous circular and annular impinging jets. Local temperature values on the target surface were obtained for different parameters and heat transfer from the surface was calculated. Experimental results showed that heat transfer increased with decreasing H/D ratio for all jet types. The highest heat transfer on the surface was achieved in synthetic jet flow. Heat transfer increased as the oscillation amplitude decreased. It was observed that there is a specific value for the Womersley number (Wo = 94) and that the heat transfer decreases after this value. For Re = 50000 and H/D = 2, the annular jet provided 27% higher heat transfer than the circular jet. In synthetic jet flow, heat transfer at H/D = 2 was improved by 21% compared to H/D = 8 for Re = 6000, A o = 1.87 and Wo = 163.

The penetration phenomenon of the expiratory airflow from thermal plume of human body in the microenvironment around people

Understanding the influence of the human body's thermal plume on exhaled airflow is crucial for accurately assessing indoor infection risks. This study employs numerical simulations and a jet integral modeling method to investigate the airflow dispersion patterns of a single thermal manikin during sustained expiration. It was found that the thermal plume formed a two-stage evolution in exhaled airflow. Initially, the airflow was weakened by the thermal plume in the horizontal dispersion, and subsequently it was bent due to the entrainment of the surrounding air in the upward dispersion of the exhaled airflow. The thermal plume changes the trajectory and lateral dispersion distance of exhaled airflow. When the exhalation velocity is 1 m/s, the airflow is fully deflected towards the head plume region. When the exhalation velocity is between 1.5 and 2 m/s, the airflow is partially deflected, with only part of the upper airflow deflected towards the head plume region. In addition, it is interesting to note that the plume changes the dispersion trajectory of the exhaled airflow, while still adhering to the distributions of buoyant jet flow. This study suggests that the thermal effect of the human body is a significant factor in characterizing the dispersion of exhalation airflow and aerosols. Considering the thermal plume in indoor infection risk assessment is expected to yield more reliable data for theoretical modeling of respiratory airflow transport.

Hollow fiber membrane governed microjet flow regime for confined crystallization of large‐sized crystal aggregates

AbstractConfined crystallization can realize controllable nucleation and growth of crystals with targeted morphologies in a restricted region. Here, we achieved confined reactive crystallization within a novel micro columnar jet flow regime constructed by the hollow fiber membrane. The interface of the jet flow corresponds as the restricted region for reactive crystallization, and the large‐sized calcium carbonate (CaCO3) crystals aggregates with millimeter length can ordered and self‐assembly grow along the boundary of this region. Formation mechanism of the jet flow was systematically investigated by real‐time observation and force analysis. The detected detachment‐regrowth cycle during the experiments furtherly uncovered the potential for continuous operation. Linear (diameter: 0.12–0.3 mm; length: 1.5–3.1 mm) and lamellar crystals (thickness of 200–300 nm and average area of 0.21 mm2) were obtained by effectively manipulating the diameter and effective length of jet flow.

External Jet Nebulization and Measured Ventilator Performance.

During invasive ventilation, external flow jet nebulization results in increases in displayed exhaled tidal volumes (VT). We hypothesized that the magnitude of the increase is inaccurate. An ASL 5000 simulator measured ventilatory parameters over a wide range of adult settings: actual VT, peak inspiratory pressure (PIP), and time to minimum pressure. Ventilators with internal and external flow sensors were tested by using a variety of volume and pressure control modes (the target VT was 420 mL). Patient conditions (normal, COPD, ARDS) defined on the ASL 5000 were assessed at baseline and with 3.5 or 8 L/min of added external flow. Patient-triggering was assessed by reducing muscle effort to the level that resulted in backup ventilation and by changing ventilator sensitivity to the point of auto-triggering. Results are reported as percentage change from baseline after addition of 3.5 or 8 L/min external flow. For ventilators with internal flow sensors, changes in displayed exhaled VT ranged from 10% to 118%, however, when using volume control, actual increases in actual VT and PIP were only 4%-21% (P = .063, .031) and 6%-24% (P = .25, .031), respectively. Changes in actual VT correlated closely with changes in PIP (P < .001; R2 = 0.68). For pressure control, actual VT decreased by 3%-5% (P = .031) and 4%-9% (P = .031) with 3.5 and 8 L/min respectively, PIP was unchanged. With external flow sensors at the distal Y-piece junction, volume and pressure changes were statistically insignificant. The time to minimum pressure increased at most by 8% (P = .02) across all modes and ventilators. The effects on muscle pressure were minimal (∼1 cm H2O), and ventilator sensitivity effects were nearly undetectable. External flow jet nebulization resulted in much smaller changes in volume than indicated by the ventilator display. Statistically significant effects were confined primarily to machines with internal flow sensors. Differences approached the manufacturer-reported variation in ventilator baseline performance. During nebulizer therapy, effects on VT can be estimated at the bedside by monitoring PIP.

LES of the upper plenum of the liquid metal fast reactor under the forced flow conditions

A Large Eddy Simulation (LES) of the upper plenum of the E-SCAPE (European SCAled Pool Experiment) facility under the normal operations has been conducted to gain deeper insights into the thermal hydraulics phenomena in liquid metal fast reactors (LMFRs). The results unravel the overall flow features in the upper plenum, the thermal instability in the above core structure region and the impact of the jets from the barrel holes on the large flow circulation and thermal mixing.The above core structure region is represented using a homogeneous porous model. It is shown that during the normal operations, most of the hot stream of the lead bismuth eutectic (LBE) from the core center rises to the top and disperses from the upper barrel holes. Conversely, the cold LBE spread out from the lower barrel holes. Mixing between the two streams only affect the fluids leaving from the middle heights demonstrating limited mixing. These jets help to create a large circulation in the upper plenum region which prevents any thermal stratification. At the interface between the hotter and colder streams, there are unsteady large-scale structures resulting in a mixing layer in the thermal field. This strong mixing is not conventional turbulence and potentially cannot be captured by Reynolds Averaged Navier Stokes average (RANS) modelling.The flow in the upper plenum is dominated by the influences of the different types of jets, which include some free jets issued horizontally or angled upwards and some jets impinging onto the structures in the plenum. The jets overall behave similar to ‘standard’ jets, though significant interactions between the top and bottom jets and the background circulations have strong influences at later stages of the jets, typically after four jet diameters leading to the jets not reaching self-similarity. In addition, the turbulence that is observed in the upper plenum is largely generated by the jet flows and hence the distribution of turbulence is very non-uniform. Away from the jets, turbulence is minimal with the mixing largely driven by the large-scale circulation.