Lateral Jet Research Articles

Influence of surface curvature on the impact force of water droplet

Although the global market for wind energy is growing rapidly, leading-edge erosion is a critical issue hindering the development of wind power. The impact force of a droplet colliding with flat surfaces has been investigated in previous studies. However, the impact force exerted on curved surfaces, such as that experienced by eroded wind turbine blades, is not well understood. This study discusses the relationship between the impact force generated on a solid surface by a water droplet and the radius of curvature of the impacting surface. The impact force by a droplet was measured using a force sensor mounted on semi-cylindrical caps with different radii of curvature. The measurement results showed that the impact force decreased as the radius of curvature decreased. A computational fluid dynamics model solving incompressible flows showed that, unlike the case of a curved surface, the initial momentum of the droplet was mostly transferred to the flat surface. This resulted in a high impulse for an impact with a flat surface. The falling droplet was blocked by the surface, and the lateral jet was accelerated sideward. This acceleration was moderate for curved surfaces. When colliding with a flat surface, a higher impact force was generated owing to the wider area of the excited surface pressure compared with that of the curved surface. Finally, the relationship between the peak of the impact force and the surface curvature was derived, suggesting that the force peak is inversely proportional to the curvature.

Preparation of protective coatings for the leading edge of wind turbine blades and investigation of their water droplet erosion behavior

The damage caused by rain droplet erosion to the leading edge of wind turbine blades is extremely severe. To reduce this issue, in this study, hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI) were used as the polyurethane (PU) polyol and curing agent, respectively, to prepare a PU coating with a high resistance to water droplet erosion (WDE) for the protection of the leading edge of wind turbine blades. The effect of n (–NCO):n (–OH) (R-value, n is the molar ratio) on the mechanical properties and WDE resistance of PU coatings, the relationship between the two performances, and the influence of the erosion conditions on the WDE behavior were investigated for the first time. The results show the existence of a correlation between the mechanical properties (hardness, impact, flexibility, and tensile strength) and WDE resistance of the coating. While, a better abrasion resistance is found not to result in a better WDE resistance. The PU coating with an R-value of 1.2 shows an optimal WDE resistance in both atomization and jet erosion experiments. In atomized droplet erosion (ADE) experiments, the change in erosion velocity accelerates the incubation period of coating erosion damage and increases the erosion rate. In jet droplet erosion (JDE) experiments, the damage to the coating is closely related to the erosion angle, reaching a maximum at an impact angle of 60°. Furthermore, in the ADE experiments, various erosion morphologies, such as pits, grooves, cracks, and stepped texture, are observed on the damaged coating surface. While, regarding the JDE experiments, holes, grooves, and cracks are observed. Such damage is caused by the combined effects of water hammer pressure, lateral jets, and local permeation.

Drag reduction in hypersonic flows with viscous compressible fluid–solid coupling: The role of elastic spikes and lateral jets

This article introduces a novel fluid–solid interaction (FSI) method designed for high-speed flow scenarios, which addresses the intricate interactions between viscous compressible fluids and elastic solids. The proposed method, grounded in the finite volume method, balances computational efficiency and stability while accurately capturing fluid dynamics and structural elasticity. Validation against experimental and numerical data from previous studies confirmed the algorithm's effectiveness. The validated FSI model is applied to study drag reduction in elastic spikes with lateral jets under hypersonic conditions, highlighting significant changes in flow characteristics due to structural deformation and lateral jets. The study extensively examined the effects of jet total pressure, jet orifice position, and spike material density on drag reduction, deformation, and flow field characteristics. Key findings include the influence of compressible FSI on temperature, pressure, and drag distribution, the benefits of increased jet pressure ratio for thermal protection, the impact of jet position on flow characteristics, and the relationship between spike deformation and material density. This study offers valuable perspectives and effective strategies for structure design and minimizing aerodynamic resistance in superspeed fluid situations. Nevertheless, there are still obstacles to overcome, such as non-linear deformation, thermal coupling, and computational precision, highlighting the necessity for further enhancement of FSI techniques.

Drag and Thermal Reduction of Spiked Hypersonic Vehicle in Thermochemical Nonequilibrium

This study utilizes the in-house parallel direct simulation Monte Carlo–quantum dynamics method to model the aerodynamic flowfield of a spiked reentry vehicle within a rarefied high-altitude atmosphere. Investigating the flight of spiked aircraft under various flight conditions and spike sizes and considering both the real gas effect and the rarefied gas effect, the aerodynamic characteristic of the aircraft is evaluated. Performance evaluation for effectiveness in drag reduction and thermal protection is based on drag and the maximum stagnation heat flux coefficient at the vehicle’s shoulder. Findings indicate that, in the rarefied atmosphere, the distinction between the characteristic shock intensities of spiked and unspiked vehicles is not pronounced, which results in a drag reduction of approximately 5%, accompanied by a more than 100% increase in thermal effect on the vehicle’s shoulder, obviously poor in effectiveness. Subsequently, this study examines the spiked vehicle equipped with a lateral jet, and this augmented approach achieves a marked reduction in the intensity of the shock wave impacting the vehicle’s shoulder with a drag reduction exceeding 10% and attenuates the thermal impact by over 50% in comparison to the implementation of spiking alone, thereby demonstrating superior performance in terms of effectiveness.

Mechanism of active flow control using a novel spike aerodome-channel concept in the hypersonic flow: A numerical study

Among the design requirements of hypersonic vehicles, reducing aerodynamic heating and drag force simultaneously is the main challenge. This paper proposes a novel spike aerodome-channel combination concept to realize the flow field reconstruction around the hypersonic blunt body. The novel configuration is investigated in the axisymmetric flow at a Mach number of 6 at zero angle of attack. The two-dimensional Reynold-averaged Navier–Stokes equations are numerically solved, and the shear-stress transport k–ω model is the turbulence model implemented in this study. Parameters such as spike length and lateral jet location are investigated to explore the drag and heat reduction performance and the flow control features. The obtained results show that the application of the novel spike aerodome-channel concept alters the flow field by eliminating or replacing the strong bow shock wave, and the design of hypersonic vehicles can benefit from the application of the proposed concept. The blunt body coupled with a frustum of cone-tipped spike-channel configuration provides a remarkable drag reduction effect of 20.71% with respect to the case without channel. Considering the effect of lateral jet location, the drag reduction performance of the case with LR = 0.75 is superior to that of the root jet case at the same spike length, and a considerable drag reduction of 28.93% is obtained with L/D = 2.4. In addition, longer spike length is beneficial for improving drag reduction performance, while excellent efficiency of heat protection is obtained in a certain spike length range. For the case of L/D = 1.6 with root jet, the peak Stanton number is significantly decreased by 33.51%.

Surrogate multi-objective optimization of missile RCS performance in hypersonic rarefied flow of the near space

This study focuses on optimizing the lateral jet efficiency of THAAD-like (Terminal High Altitude Area Defense) missiles operating under hypersonic rarefied flow conditions. We employ the DSMC-QK algorithm to simulate the three-dimensional lateral jet flow field, accounting for thermochemical non-equilibrium effects. The analysis investigates how the force/momentum amplification coefficient varies with the angle of attack, jet pressure ratio, jet Mach number, and jet gas composition. Subsequently, we develop an artificial neural network (ANN) proxy model using the pyrenn toolbox, achieving an average prediction error of 0.866% and a maximum error of 1.60%. Utilizing this ANN model, we perform single- and multi-objective optimizations with a genetic algorithm to determine the optimal jet parameters. The results reveal that in multi-objective optimization, the proportion of helium in the jet gas composition increases, leading to a slight reduction in the force amplification coefficient but a substantial 61.4% decrease in the mass flow rate. This demonstrates that a judicious selection of jet gas composition can significantly reduce mass flow while maintaining high jet efficiency, thus achieving efficient lateral jet control.

Interaction between lateral jet and hypersonic rarefied flow

Reaction control systems (RCS) are commonly utilized in a variety of air vehicles, and they give rise to complex flow phenomena. For flows dominated by shock waves and expansion, such as lateral jets, a significant gradient is formed in the local region of the flow field, resulting in a high local Knudsen number, and the continuum hypothesis is no longer applicable, even if the freestream belongs to near-continuum flow. As a result, multi-scale simulation approaches should be used to capture the interactions between these multi-scale structures and appropriately determine aerodynamic forces. Our earlier work, which used the conserved discrete unified gas kinetic scheme (CDUGKS) for monatomic gas, studied the flow field features of lateral jets and aerodynamic forces on blunt bodies under various rarefied freestream conditions. In this research, the Rykov model is used to expand the CDUGKS suit for diatomic gas flow while taking into account the excitation of molecular rotational energy. The impact on the flow field and aerodynamic forces from four parameters, namely freestream Mach number, jet Mach number, jet pressure ratio, and nozzle position, is thoroughly investigated. The results show that even if the incoming Mach number is different, the flow field structure and aerodynamic properties don't change much when the jet momentum ratio stays the same. The solid wall stagnation point value and local peak also show some linear relationships. The jet pressure ratio mainly affects the expansion characteristics of the jet, such as the influence range on the solid wall. In addition, with an increase in the distance between the nozzle position and the torque reference point, higher control efficiency can be obtained. The study of these aspects will help us comprehend lateral jet flow and provide reference for the design of an air vehicle's RCS.

Numerical Study on the Influence of Separation Time Sequence on the Initial Thermal Separation

The process of separating stages is crucial for multistage rockets, directly influencing the success of the launch plan. Different separation timing methods alter the flow field structure within the interlevel zone at separation, influencing the separation of the two-stage rockets. This paper employs the SST k-ω turbulence model to investigate the structure of the flow field and its aerodynamic and motion characteristics under different nozzle baffle opening and separation times, taking into account variable properties, supersonic compressibility, and the upstream–downstream interference. First, we examined the standard flow field structure, considering the engine jet, the lateral jet between stages, and the disturbance from the external supersonic inflow. Then, we discussed the displacement characteristics and axial force coefficient curves of the first and second steps of the separation process. Finally, we explored the impact of baffle opening and separation times on the flow field structure and axial force coefficients of the two stages at the onset of separation. For the flow field structure, a delay in the baffle opening and separation moment led to a gradual increase in downstream and separation regions until they stabilized after a certain range. However, the axial force coefficients displayed different behavior before and after the design point.

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Seasonal variability of Red Sea mixed layer depth: the influence of atmospheric buoyancy and momentum forcing

The seasonal and spatial evolution of the mixed layer (ML) in the Red Sea (RS) and the influence of atmospheric buoyancy and momentum forcing are analyzed for the 2001–2015 period using a high-resolution (1/100°, 50 vertical layers) ocean circulation model. The simulation reveals a strong spatiotemporal variability reflecting the complex patterns associated with the air–sea buoyancy flux and wind forcing, as well as the significant impact of the basin’s general and mesoscale circulation. During the spring and summer months, buoyancy forcing intensifies stratification, resulting in a generally shallow ML throughout the basin. Nevertheless, the results reveal local maxima associated with the influence of mesoscale circulation and regular wind induced mixing. Under the influence of surface buoyancy loss, the process of deepening of the ML commences in early September, reaching its maximum depth in January and February. The northern Gulf of Aqaba and the western parts of the northern RS, exhibit the deepest ML, with a gradual shoaling toward the south, primarily due to the surface advection of relatively fresh water that enters the basin from the Gulf of Aden. The mixed layer depth (MLD) variability is primarily driven by atmospheric buoyancy forcing, especially its heat flux component. Although evaporative fluxes dominate the annually averaged surface buoyancy forcing, they exhibit weak seasonal and spatial variability. Wind induced mixing exerts a significant impact on the MLD only locally, especially during summer. Of particular importance are strong winds channeled by topography, such as those in the vicinity of the Strait of Bab-Al-Mandeb and the straits connecting the two gulfs in the north, as well as lateral jets venting through mountain gaps, such as the Tokar Jet in the central RS. The analysis highlights the complex patterns of air-sea interactions, thermohaline circulation, and mesoscale activity, all of them strongly imprinted on the MLD distribution.

Flow analysis for lateral synthetic jets to remove contaminants from the outer surface of an automobile camera module

A test facility was constructed to investigate the flow characteristics of lateral synthetic jets generated by an actuator composed of a cavity, an orifice and a vibrating piezoelectric disc. Subsequently, 3D unsteady numerical simulations were conducted to analyze the formation of the synthetic jets and their dependence on the height of the orifice exit from the outer surface of the cavity. The time-averaged axial velocity was measured and used to validate the numerical results, and the maximum velocity reached approximately 8 m/s. In this work, it was found that the interaction of the vortex tube generated at the edge of the orifice exit and the outer surface of the cavity has a significant impact on the axial velocity distribution and characteristics of the lateral synthetic jets. Based on the experimental data and the numerical results, an attempt has been made to understand the formation of the synthetic jets and their interaction with the outer surface.

Low-frequency large-scale unsteadiness analysis of lateral jet interactions on a slender cylinder in hypersonic flows using fast-responding pressure-sensitive paint

Lateral jet interactions, commonly encountered in high-speed vehicles, are typical complex three-dimensional (3D) shock wave/boundary layer interactions. The spatiotemporal features of surface pressure are crucial for understanding such complex interactions. In this study, fast-responding pressure-sensitive paint measurements are implemented at a sampling rate of 3000 Hz and a spatial resolution of 0.35 mm/pixel to investigate global pressure fields in lateral jet interactions on a slender cylinder under hypersonic flow conditions. Tests are conducted at three angles of attack (0°, 5°, and 10°) and two sideslip angles (0° and 2.5°) at Mach 6 and a Reynolds number of 1.35 × 107/m. The mean pressure results indicate the presence of a 3D high-pressure region beneath the bow shock feet, the area and pressure level of which depend on the cylinder attitude. Moreover, significant low-frequency broadband unsteadiness associated with the large-scale motion of bow shock is found in the high-pressure region. Statistical, coherence, and modal analyses are performed to clarify the characteristics of the large-scale unsteadiness. The results indicate that the dominant pressure mode is induced by streamwise oscillation of the bow shock, which exhibits two subregions with opposite pressure-fluctuation variations. Furthermore, the effects of the cylinder attitude on the unsteadiness extent and intensity are discussed.

Effect of a Control Mechanism on the Interaction between a Rectangular Jet and a Slotted Plate: Experimental Study of the Aeroacoustic Field

The aeroacoustic field of a rectangular subsonic jet impinging on a slotted plate was investigated experimentally using microphones and stereoscopic particle image velocimetry (S-PIV). The study was carried out with a Reynolds number of 6700 and an impact distance of 4 cm. The current configuration represents a benchmark standpoint, featuring high levels of generated noise. A control mechanism consisting of a thin rod was introduced downstream from the jet exit to suppress the self-sustained tones. A total of 1085 positions of the rod between the jet exit and impinging plate were tested to identify positions of optimal noise reduction. Two zones were distinguished in terms of control efficacy: a zone where the sound pressure level (SPL) dropped by up to 19 dB and another zone where the SPL increased by up to 14 dB. The velocity fields show that the presence of the rod divides the jet into two lateral secondary jets on both sides of the main jet axis. The outer part of the secondary jets expanded radially with less interaction with the plate compared to the case without the control. This behavior affected the deformation of vortices against the slot. Proper orthogonal decomposition was applied to the velocity field for a better understanding of the turbulence dynamics with and without the control rod.

Drag Reduction and Thermal Protection of the Combination of Aero Disk, Lateral Jet, and Rear Jet for Hypersonic Vehicle

This study proposes a combined scheme based on a spike-aero-disk, a lateral jet, and a rear jet to enhance hypersonic vehicles’ drag reduction and thermal protection performance. Numerical simulations were conducted using CFD methods to validate the scheme’s capabilities. The results demonstrate a significant improvement in drag reduction and thermal protection compared to the basic scheme with only a spike-aero disk. Furthermore, under the same mass flow rate conditions, the combined scheme with an extra rear jet is compared to a scheme with a spike-aero-disk-lateral jet, revealing a reduction of approximately 23.4% in the peak Stanton number, indicating a remarkable enhancement in drag reduction and thermal protection performance. The simulation results show that the use of lateral jet and rear jet improves the overall thermal protection ability and drag reduction ability of the vehicle.

Characteristics of wake morphology during debris flow when passing a cylindrical obstacle

Predicting wake morphology during debris flow when passing a cylindrical obstacle is vital for disaster assessment, early warning, evacuation planning, engineering design, and ecologic conservation. It can provide a scientific foundation for pertinent decision-making processes, diminishing the risks and impacts of debris flow disasters. This study extracts the morphological characteristics of debris flow cylindrical flow traces through the steady-state motion of debris flow observed in a flume during cyclical tests. It introduces a theoretical prediction formula and compares it to empirical data. The results indicated that the morphology of debris flow cylindrical flow traces can be described as a wall-jet-like bow wave (a bow wave formed by an upward wall jet on the obstacle upstream face). The primary upstream inflow is predominantly discharged through the wall and lateral jets. Formulas for three crucial parameters that determine the morphology of the traces are derived by combining the aerodynamics theory and extant literature. The predicted outcomes strongly align with the experimental data, underscoring their high predictive precision.

Computational study of lateral jet interaction in hypersonic thermochemical non-equilibrium flows using nonlinear coupled constitutive relations

The present study reports the numerical analyses of lateral jet interaction around a Terminal High Altitude Area Defense-type (THAAD-type) model in hypersonic rarefied flows, with the real gas effect incorporated. The computation approach employed is the recently developed thermochemical non-equilibrium nonlinear coupled constitutive relations (NCCR) model. Regarding the simulation conditions, the flight velocity and height are set to 20 Ma and 80 km, respectively. To disclose the flow mechanism of lateral jet interaction, the complex flowfield characteristics and surface pressure distributions are discussed at length. Additionally, the research explores the impact of two key factors, namely, the jet pressure ratio and the jet Mach number, on the control performance of an in-flight vehicle's reaction control system (RCS). The results demonstrate that the complicated flowfield structures in lateral jet interaction are successfully reproduced by the NCCR model. With an increase in either the jet pressure ratio or the jet Mach number, the force and moment amplification factors decrease, while the absolute value of the normal force coefficient increases. Notably, it is found that the rarefied gas effect captured by the NCCR model against the Navier–Stokes–Fourier solution affects the lateral jet interaction flowfield, e.g., weakening the compressibility of the barrel shock and the expansibility of the Prandtl–Meyer expansion fan, as well as strengthening the jet wraparound effect. Importantly, the rarefied gas effect also exerts a prominent influence on the performance of RCS, with the degree of influence diminishing as the jet Mach number or the jet pressure ratio increases.

Direct numerical simulation of turbulent jet in regular waves: A comparison between circular and non-circular cross-sections

Direct numerical simulations of circular and non-circular jets (square and rectangular) when released into regular waves are performed and reported in this article. In case of a rectangular jet, two different orientations of the nozzle have been simulated i.e major axis parallel (case 1) and perpendicular (case 2) to wave advancement direction. An analysis of the leading vortex ring reveals that axis switching in a rectangular jet takes place irrespective of nozzle orientation with respect to wave advancement direction. The axis switching is absent in the square jet. Further, the roll-up frequency of the non-circular jets is found less than the circular jet. Also, the roll-up frequency is independent of the orientation of the rectangular jet with respect to the wave direction. The braid region shows that the number of counter-rotating pairs are four for all the cases, however, the lateral jets are three for circular, square and case 1 of rectangular jets. The lateral jets in case 2 of the rectangular jet remain four due to change in orientation of the lateral jets owing to change in the nozzle orientation. The time-averaged quantities suggest increased mixing and entrainment in the rectangular jet as compared to circular jet. The highest mixing and shortest potential core are observed in case 2 of the rectangular jet. Therefore, for better mixing, the rectangular nozzle should be placed in the ocean outfall such that its major axis remains perpendicular to the direction of wave advancement.

Damage behavior and assessment of aeronautical PMMA subjected to high-velocity water-jet impact

Rain erosion of forward-facing aircraft components such as windshields can lead to a significant reduction in performance, hence a potential hazard to air safety, especially for supersonic fighters exposed to precipitation. To understand such threats, the damage behavior of two types of most commonly used aeronautical PMMA, i.e., oriented and non-oriented, under water droplet impact is investigated. A single-impact jet apparatus based on the one-stage gas gun was established to simulate the rain droplet impact. Two critical variables were evaluated, including water-jet velocities and incident angles. Typical damage characteristic features including annular depression and circumferential cracks were observed on non-oriented PMMA targets. In contrast, on oriented PMMA targets, massive subsurface craze delamination was observed without any sign of surface cracks. The distinct damage features are determined by the different damage behavior of the oriented and non-oriented PMMA targets during the initial stage of the impingement and the shearing effect of the lateral jet. Increasing impact velocity leads to surface peeling and bulk removal, escalating the damage severity. The damage mechanism of subsurface failure was revealed by observing stress wave interaction and the FEM simulation. An impulse method was developed to quantify each impact event and assess the damaged area. A linear relationship between the damaged area and the initial impact stage impulse was established, which can be applied for preliminary evaluation and prediction of the damage caused by high-velocity water droplet impact on aeronautical PMMA.

It’s About Time: Jet Interactions in an Asymmetrical Plenum

Hybrid Reynolds-Averaged Navier-Stokes–Large Eddy Simulation was used to reveal detailed flow information and timescales in an isothermal reactor cavity cooling system plenum four-jet configuration. Plenum asymmetry and nonuniformity work together to cause premature jet merging. Bulk stirring in the plenum causes lateral jet vortex shedding, strong jet-jet interactions, swirl, and premature confluence. Two dominant transient modes exist: a jet flow timescale and then a plenum circulation timescale that is nearly three orders of magnitude larger. A primary consequence is that frequencies far less than the presumed 10 Hz threshold for thermal striping are pervasive. A second result is that scale-resolved computational fluid dynamics (CFD) models (as well as experimental rigs) need hundreds of seconds of statistically stationary flow time (tens of thousands of jet timescales) to produce stationary time averages. Fluid typically arrives at positions on the laser sheet in less time than it spends at those positions fluctuating in the streamwise and lateral directions. Also, a previously undocumented, but experimentally confirmed, vortex trap was identified via CFD. Finally, two-point velocity correlation analyses demonstrated a few dozen strong correlations across positions on the laser sheet. Expected close-proximity correlations emerged, but others across larger spaces also were connected. Most of these correlated at timescales close to that of the jet.

Uncertainty and Sensitivity Study on Lateral Jet Interaction for Hypersonic Missile

The demanding working environment of hypersonic missiles imposes high requirements on the reliability and stability of the reaction control system. This work aims to investigate the impact of uncertainties in freestream and jet parameters on the flowfield and aerodynamic performance of a missile with a lateral jet. Initially, the influence of angle of attack and Mach number on aerodynamic characteristics is evaluated. The findings indicate that the lateral jet control effect is enhanced as the Mach number increases. Moreover, the interference force/moment does not vary linearly with the angle of attack, and there are notable differences in the flow characteristics when the jet is on the windward and leeward sides. Subsequently, six parameters are selected as input variables. The uncertainties of the output results are analyzed using a stochastic expansion based on the nonintrusive polynomial chaos method. Sensitivity analysis is performed using Sobol indices to estimate the relative contributions of each parameter to the overall uncertainty. Within the given uncertainty interval, the surface pressure of the missile exhibits significant variation, with a maximum uncertainty of approximately 480%. The uncertainty of the recirculation zone range is 50.14%, while the pitch moment amplification factor has an uncertainty of 52.44%. The freestream Mach number, angle of attack, and jet pressure ratio are identified as key factors affecting the aerodynamic performance, surface pressure coefficient, and jet penetration height. Conversely, the contribution of other parameters can be considered negligible.