Jet Angle Research Articles

Experimental and simulation study on surface material stripping of glass fiber reinforced composites by baking soda abrasive jetting technology

Glass fiber reinforced composites (GFRP) working in a specific environment require regular inspection and maintenance. It is necessary to remove the surface material of fiber reinforced composites to check the fracture of fibers and the damage to matrix that binds fibers in this process. In this paper, the baking soda abrasive jetting was utilized to strip the surface material of glass fiber reinforced epoxy resin (GFREP). The stripping effects of baking soda abrasive jetting technology under different jetting parameters (fiber orientation, jet angle, jet pressure) were explored, and the optimum stripping conditions were determined as parallel to the fiber, 30°, 0.4 MPa. Compared with the chemical stripping method (phenol-dichloromethane), baking soda abrasive jetting can better retain epoxy resin between glass fibers. The LS-DYNA was applied to simulate the erosion process of a single abrasive particle under the optimum stripping condition. The plastic deformation of the matrix and the slight bending deformation of the glass fiber under abrasive impact were observed.

The composition of an atomized slurry fuel jet

Slurry fuels have become increasingly popular over the last decades. The combustion of coal-water slurries does not only help with waste recovery but also produces heat and electricity. Studying the process of slurry atomization for further combustion is high on the research agenda. It is still disputable whether a homogeneous slurry jet can be produced by a twin-fuel atomizer. With split component feeding, fuel premixing will become unnecessary; component storage and transportation is simplified as well. In this research, the composition of an atomized slurry fuel jet is reliably determined using shadowgraphy and laser-induced fluorescence. The results show that an internal-mixing twin-fluid atomizer produces a homogeneous atomized flow. Conditions have been determined in which a fuel slurry jet is formed with an optimal composition of solid particles and droplets with and without particles. It is established that split component feeding leads to a 13–23 % increase in jet angle, a 1–4° reduction in the jet deviation angle from its original path, as well as a considerable reduction (up to twofold) in the droplet velocity in a jet. The results obtained here can be used to optimize the storage and transportation of fuel components.

Experimental and numerical study on liquid film cooling performance under heated wall condition

Liquid film cooling is broadly applied in the thermal protection of liquid rocket engine. An experimental system of liquid film cooling for a heated curved stainless-steel wall is built in this study to investigate the effects of jet mass flow rate, jet angle, and nozzle diameter on the cooling performance. The temperature distribution of the heated wall is demonstrated with infrared thermography technology and the flow spreading shape of the liquid film is captured with high-speed camera. A numerical liquid film cooling model based on the volume of fluid (VOF) coupled Level-set method is established to calculate the evaporative heat absorption and spreading shape of liquid film. The experimental study indicates that the peak film thickness in the hydraulic jump region increases with the jet mass flow rate, such as the peak film thickness increases from 265.15 to 632.25 μm at Q = 100–600 mL·min−1. Besides, a jet angle of 35 degree can maintain the maximum wall temperature drop of 29.4 °C. In addition, the simulated peak film thickness presents a minimum deviation of 5.2 % from the experimental data. The numerical model provides important reference for the study of liquid film cooling performance of the liquid rocket engine.

Effect of leakage source condition on the unignited hydrogen released issuing through a horizontal realistic pipeline geometry

An unignited gas release experiment system for the schlieren visualization and concentration quantitative measurement is designed and built to investigate the diffusion and concentration distribution features of turbulent hydrogen jets issuing from a realistic pipeline geometry. Helium is used in place of hydrogen for safety reasons. The spatial and temporal evolution of the asymmetry of turbulent helium jets was studied. The influence mechanisms of the volumetric flow rate (Q), the ratio of orifice diameter to the inner diameter of pipeline (R), and the angle between the normal of the leakage orifice and the opposite direction of gravity (θ) on the asymmetric concentration distribution are revealed. The experimental results show that the diffusion angle (α) and the inclination angle (β) of the turbulent helium jet are the largest when Q is 15 SLPM, R is 0.3, and θ is 0°, and the asymmetric feature of the turbulent helium jet is obvious. As the Q increased, the slope k of the inverse helium concentration (1/volume fraction) and a scaled distance L (L = (x/d)·(ρa/ρ0)1/2) became small. The increase of Q aggravated the concentration attenuation caused by the volumetric flow rate and the asymmetry jet. As R increased, the slope k of the inverse helium concentration and a scaled distance L first decreased and then increased. The slope k got the minimum value when R was 0.3. The downward movement of the leakage orifice position increased the turbulent intensity near the leakage orifice. This work can provide theoretical support for accident prevention and emergency treatment of hydrogen leakage accidents in long-distance pipeline low-pressure hydrogen transportation.

Improving the machined surface in electrochemical mill-grinding by particle tracking fluid simulation and experimental research

The hybrid machining method called electrochemical mill-grinding is an advanced machining technology, which can achieve high-quality processing of various difficult-to-cut materials. However, achieving rapid transportation and removal of processed products within a small machining gap is a key challenge, which directly affects the final machined surface quality. In this paper, the product transport under different flushing modes was studied through numerical simulation of the flow field. By using the particle tracking method, the time required for the removal of machining products from the machining gap was dynamically simulated. The analysis results indicated that the removal speed of machining products could be significantly improved when the flushing pressure was 0.8 MPa and the electrolyte jet angle was 30°. In addition, machining experiments were conducted. The machining experiment results showed that the machined surface had a metallic luster with clear edge contours. The grinding marks on the machined surface indicated the grinding effect. The continuous machining of complex patterns demonstrated the reliability of this hybrid machining process.

Experimental investigation of hydrogen jet flame inhibition by nitrogen jet

With the rapid development of hydrogen energy and the increase of the risk of hydrogen jet fires, a reliable fire protection technology is required to extinguish hydrogen jet flame efficiently. An experimental investigation was carried out to study the inhibition of a hydrogen jet flame by a nitrogen jet. The impact angle, nozzle diameter and nozzle position of the nitrogen jet were the variables. The flame characteristic parameters were analyzed, including the flame length, deflection height and deflection angle. The results show that the inhibited flame length was always positively correlated with the vertical distance between the nozzles. The increase of the impact angle had a significant inhibitory effect on the flame length. Besides, the explanatory factor was used to describe the influence of various initial release conditions on flame inhibition and was calculated by the combination of the explanatory variables, such as impact angle, impact stroke and impact height. The flame length reduction ratio, deflection height reduction ratio and dimensionless deflection angle are positively correlated with the explanatory factor. It means that the jet flame is more easily extinguished under a larger explanatory factor. The critical parameter of the explanatory factor for extinguishing the hydrogen jet flame was verified experimentally.

Experimental Investigation of a Micro Turbojet Engine Chevrons Nozzle by Means of the Schlieren Technique

In connection with subsonic jet noise production, especially regarding the hot jet from a micro turbojet engine, we encountered a lack of recent high-resolution data in the literature describing the flow field using experimental validation through optical diagnoses. The objective of this paper is to examine and compare the influence on shear layers of the exhaust plug nozzle of a micro turbojet engine with and without chevrons mounted, using a high-speed camera used in Schlieren-type optical system diagnosis. Three different operating regimes are examined for both the baseline configuration and the configuration with 16 triangular-shaped chevrons. In conjunction with the image captures, the sound pressure level was recorded with the help of a microphone placed perpendicular to the flow, 0.4 m from the exhaust of the nozzle which was further processed. In quantitative terms, we found that the OASPL decreases by more than 1% when the engine is operating at higher regimes. Moreover, we found that the average exhaust jet angle, which is a measure of the quality of the fluid mixing layer is increased by 5% with respect to the baseline nozzle. By using the “darkest pixel” technique in Schlieren imaging, we can verify experimentally, for all working regimes, the theory that asserts that subsonic jet noise is a consequence of fine-scale homogeneous turbulence. Additionally, the potential novelty lies in the specific observations related to consistent dispersion of fine-scale eddies and how the presence of chevrons amplifies this uniformity within the turbulent field.

Atomization of composite liquid fuels in experimental setup with variated gas temperature and pressure

The efficiency of slurry fuel combustion can be improved by developing a predictive mechanism to estimate fuel atomization characteristics. However, no data are available on slurry fuel atomization behavior under near-real conditions. This paper presents the experimental research findings on the combined and separate effect of gas temperature and pressure on slurry fuel atomization characteristics. The experiments involved composite liquid fuels based on water and filter cake (typical coal processing waste) in variable concentrations. These conditions are the same as in advanced fuel slurry preparation units involving pre-combustors, swirlers, and other elements. In this research we have recorded such spray characteristics as droplet sizes and velocities, volume fraction of droplets with given sizes, jet angle, as well as the angle its deviation from the original trajectory. As has been observed, an increase in the ambient gas temperature leads to a 30% increase in the jet velocity and a 40–60% increase in the volume fraction of small droplets, whereas a pressure increase, on the contrary, reduces these parameters by 11–32% and 100%, respectively). Combined effects of chamber gas pressure and temperature on atomization characteristics have been identified: the variation of atomization characteristics did not exceed 18%. Mathematical expressions have been obtained to predict the atomization characteristics of composite liquid fuels in power-generating units with the known gas temperature and pressure. Maps have been plotted using a set of dimensionless parameters that can help control droplet size, velocity, jet angles, and angles of its deviation from its original path.

Numerical Investigations of Synthetic Jet Control Effects on Iced Airfoils

Based on the numerical method, the effects of synthetic jet control (SJC) on the aerodynamic characteristics of iced airfoils are systematically analyzed for the first time. First, an analysis method for the airfoil flowfield under SJC in icing conditions is developed, which contains the CFD method, the icing prediction method, and the boundary conditions of the synthetic jet. Then, the variation in the aerodynamic characteristics of different iced airfoils under the SJC are analyzed, and the flow separation near the ice shape is discussed in detail. Finally, parameters, such as the jet position and angle, are quantified, and conclusions are obtained. The synthetic jet can reduce the separation area on the upper surface induced by the ice accretion. When the energy of the jet is sufficient, it interacts with the mainstream, reducing the separation vortex downstream of the jet orifice and greatly improving the aerodynamic characteristics of the iced airfoil. These results provide valuable insights for the application of synthetic jet technology in mitigating the adverse effects of ice accretion on the airfoil’s aerodynamic characteristics.

Thermal-mixing flow characteristics of mixing valve

Mixing valves play an important role in fluid transmission pipeline systems and fluid heat mixing in the chemical-energy industry. To limit thermal fatigue cracking failure of cross-combination pipelines and thermal-mixing equipment, this study investigated the effect of plunger strokes on the internal flow and temperature fluctuation of a mixing valve. A large eddy simulation method was used to study the temperature distribution and fluctuation mechanism of a fluid during hot mixing using a mixing valve with different plunger strokes. For mixing valves, the centroid of the effective jet section of the branch pipe moves to the negative Y-axis during plunger stroke operations, resulting in a jet angle change in the branch pipe. As the effective jet area of the branch pipe decreases, the vortex structure of the branch pipe also changes. When the plunger stroke is small, there is a higher and stronger temperature fluctuation in the 90° circumferential area of the wingspan section, whereas when the plunger stroke is large, there is a higher and stronger temperature fluctuation in the 270° circumferential area of the wingspan section. The results showed that valve operation should be avoided at these plunger strokes and monitoring at these positions is required during operation. The study results provide an industry reference for the internal hot-mixing flow characteristics of mixing equipment with adjustable flow channels.

Simulations of Compression Ramp Shock Wave/Turbulent Boundary Layer Interaction Controlled via Steady Jets at High Reynolds Number

Shock wave/turbulent boundary layer interaction (SBLI) is one of the most common physical phenomena in transonic wing and supersonic aircraft. In this study, the compression ramp SBLI (CR-SBLI) was simulated at a 24° corner at Mach 2.84 using the open-source OpenFOAM improved delayed detached eddy simulation (IDDES) turbulence model and the “Rescaling and Recycling” method at high Reynolds number 1.57×106. The results of the control effect of the jet vortex generator on CR-SBLI showed that the jet array can effectively reduce the length of the separation zone. The simulation results of different jet parameters are obtained. With the increasing jet angle, the reduction in the length of the separation zone first increased and then decreased. In this work, when the jet angle was 60°, the location of the separation point was x/δ=−1.48, which was smaller than other jet angles. The different distances of the jet array also had a great influence. When the distance between the jet and the corner djet=70 mm, the location of the separation point x/δ=−1.48 was smaller than that when djet=65/60 mm. A closer distance between the jet hole and the corner caused the vortex structures to squeeze each other, preventing the formation of a complete vortex structure. On the other hand, when the jet was farther away, the vortex structures could separate effectively before reaching the shock wave, resulting in a better inhibition of SBLI. The simulation primarily focused on exploring the effects of the jet angle and distance, and we obtained the jet parameters that provided the best control effect, effectively reducing the length of the CR-SBLI separation zone.

Surface wave and splashing of liquid film by oblique water jet impinging on a vertical plate

Liquid film cooling by jet impingement, known as a common thermal protection technique, is extensively applied in liquid rocket engines. The present work investigates the impact of a water jet onto a vertical plate by high-speed visualization system and laser particle analyzer, with a focus on the characteristics of surface waves and droplets splashing during the formation of liquid film. Depending on whether the jet is broken before impact, two regimes are identified, i.e., droplet or continuous jet impingement regime. The frequency and velocity of the surface wave and the splashing rate are jointly affected by the jet angle and the impingement distance. The splashing is mainly caused by the capillary breakup of the crown film that forms at the edge of the surface wave, and most of the splashing droplets are generated from the top of the crown film. The larger the jet angle, the smaller the wave frequency and velocity, but the higher the splashing rate. A large impingement distance causes a small wave frequency and velocity due to the shift of the impingement regime, further resulting in different tendencies in the splashing rate. A parameter expression for the size distributions of splashing droplets is established by the fitting result of the log-normal distribution and the Rosin-Rammler (R-R) distribution, where the parameters are associated with the jet Weber number.

Effect of a Double-Machine Parallel Air Curtain on Wind Flow in an Underground Roadway of a Coal Mine

In order to study the effect of a double-machine parallel circulation air curtain in intercepting wind flow in a mine roadway, the air curtain jet angle and full fan pressure were analyzed. Taking a metal mine roadway as the engineering background, Fluent numerical simulation technology was used to establish an equi-proportional physical model of the original roadway, and a K45-6 axial flow fan was selected to numerically simulate the flow field inside the original roadway, which was analyzed from three aspects: isolation pressure difference, air leakage volume and wind choke rate. The results show that when the full pressure of the fan is fixed, with an increase in the jet angle of the air curtain, the separation pressure difference and the wind choke rate show a trend of first increasing and then decreasing, and the air leakage volume shows a trend of first decreasing and then increasing. With an increase in the air curtain jet angle, the air curtain convergence gradually forms a complete air curtain, but when the air curtain jet angle continues to increase, the air curtain cannot effectively block the wind flow due to the transverse pressure from the roadway. When the jet angle is too small or the full pressure of the fan is too large, the phenomenon of induced air flow will occur, and the two-machine parallel air curtain will direct the air downstream of the roadway to upstream and no longer intercept the roadway air flow. After comprehensive analysis, the effect of wind control is obvious to set up a double-parallel air curtain in the roadway, and the optimal combination of the roadway air curtain is 30° for the full pressure blade of the fan and 30° for the jet angle.

Optimal configuration of oblique air curtains for heat loss suppression from vertical solar-thermal receiver surfaces

An external solar-thermal receiver is critical to the operation of a solar-thermal power plant because it converts concentrated solar radiation into useful heat. However, as these receivers are surrounded by relatively cold air, they suffer from significant convective heat loss that is detrimental to their thermal performance. Air curtains, in the form of air jets directed obliquely from the top of the receiver surface, have been shown to provide significant local reductions in receiver heat loss. This study presents, for the first time, a rigorous optimisation of air curtain operation to increase the mitigation of overall convective heat loss. Two-dimensional computational fluid dynamics simulations in OpenFOAM were used to optimise jet speed, angle, position, and thickness. Performance was measured based on global effectiveness, with a maximum of over 18% achieved for a jet with speed Uac=5.5ms−1, angle α=45°, thickness b=30mm, and gap G=30mm. Increasing jet thickness yielded the greatest gains in overall effectiveness. An equivalent air curtain effectiveness was defined, with the optimal case having an effectiveness of around 14%. The effect of jet outlet temperatures on effectiveness was also examined, with effectiveness gradually decreasing with increasing jet outlet temperature.

Experimental and numerical investigation of an S-shaped duct using pulsed jet actuators with multiple angles

The complexity and twistiness of the ultra-compact S-shaped ducts with high curvature aggravate the internal flow separation, which affects the intake efficiency. An advanced flow control technology, pulsed jet actuators (PJAs), was implemented to improve the flow condition in the S-shaped duct at a Mach number of 0.4. Based on the considerable control effect obtained from the experimental studies, the influence of the pulsed jet angles on the S-shaped duct was further investigated by utilizing the unsteady Reynolds-averaged Navier–Stokes equations (URANS). The jet angles as a research parameter were set to 15°, 30°, 45°, 60° and 75°, respectively. Moreover, steady jet schemes were adopted to reveal the unsteady flow control mechanism of the pulsed jet. The results showed that the overall performance of the S-shaped duct with the pulsed jet was improved, mainly attributed to the additional kinetic energy and dispersion. The total pressure loss coefficient and distortion index at the aerodynamic interface plane (AIP) were decreased by 7 % and 2.9 % when the pulsed jet angle was 30°. Furthermore, the temperature distortion was significantly improved, with a maximum temperature rise rate of −87.59 K/s. It is concluded that the suitable penetration of the mainstream is the prerequisite for achieving the best flow control effect.

Effect of jet angle and jet pitch on the Thermo-Hydraulic performance of solar air heater having absorber plate with jet impingement

This numerical investigation focuses on enhancing the heat transfer characteristics and thermo-hydraulic performance of a solar air heater by employing jet impingement over the absorber plate. The study explores the influence of two geometrical parameters, namely jet pitch ratio (P/Dh) and jet angle ratio (α/90), on the heat transfer, frictional losses, and overall performance of the solar air heater with jet impingement (SAHJI) under various flow conditions, represented by Reynolds numbers (Re) ranging from 3500 to 17500. The simulations are conducted using the RNG k-ɛ model with second-order upwind discretization. A comparative analysis is performed between the SAHJI system and a conventional smooth solar air heater (SPSAH) configuration, revealing a significant enhancement in thermal–hydraulic performance with the use of jet impingement. The investigation identifies the maximum thermo-hydraulic performance parameter, reaching a value of 4.12. This peak performance is achieved at specific values of jet pitch ratio (P/Dh) of 1.30 and jet angle ratio (α/90) of 0.094, respectively, at a Reynolds number of 7500. These findings demonstrate the potential of jet impingement as a heat transfer enhancement technique in solar air heaters, contributing to improved overall system efficiency.

Novel wall-attached multidirectional jets: Mathematical formulation, CFD modeling and experimental validation

Achieving a healthy and comfortable indoor air environment has long been an objective of human endeavors. For a novel ventilation system, the wall-attached multidirectional jet pattern, the mathematical model describing the jet trajectory, temperature and velocity changes was first proposed to predict airflow attachment and separation moments from walls, covering a densimetric Froude number range from 0.5 to 4.0. Subsequently, this mathematical model was solved using a comprehensive numerical methodology and validated by full-scale experiments, which demonstrated that this established model could accurately depict the wall-attached multidirectional jet flow, with controllable errors — 16.4% for jet trajectory and 8.2% errors for jet axis temperature — when maintaining a supply velocity of 0.2 m/s. Also, the flow characteristics within a room featuring internal heat sources were analyzed, varying air supply velocities from 0.1 to 0.8 m/s and jet angles from 0° to 60°. Finally, this flow pattern of the wall-attached multidirectional jet was further confirmed and reproduced through CFD modelling which illustrated temperature stratification ranging from 18.1 °C to 25.2 °C, similar to the pattern observed in displacement ventilation. Present research could be valuable for the development of wall-attached multidirectional jet and the establishment of a healthy indoor air environment in practical applications.

Turbulent Eulerian–Eulerian simulation and Taguchi optimization of twin oblique nanofluid jets injecting into a water cross-flow

In this work, a turbulent Eulerian–Eulerian description is utilised to simulate the injection of twin oblique jets of alumina–water nanofluid into a water cross-flow. This technique can be considered as a heat transfer enhancement strategy in cooling technologies. A Taguchi optimization study is undertaken to determine the optimal combination of the involved control factors to achieve the highest heat transfer rate and to explore the contribution ratio of each factor. Inspection of the simulation results demonstrates that about 70% of the contribution on the final response belongs to the velocity and the angle of the first jet. Meanwhile, it is elucidated that the presence of the nanoparticles in the injected jets may not alter the heat transfer rate more than 6%. This indicates that with proper selection of the velocity and the angle of the jets (especially the first one), the need to utilise nanofluids will be eliminated.

Machine learning-based optimization of a pitching airfoil performance in dynamic stall conditions using a suction controller

Flow separation control on oscillating airfoils is crucial for enhancing the efficiency of turbine blades. In this study, a genetic algorithm was employed to optimize the configuration of a pure suction jet actuator on an oscillating airfoil at a Reynolds number of 1.35×105. Neural networks based on multilayer perceptrons were used to train the aerodynamic coefficients as functions of the control parameters and reduce the number of simulations. The objective function was the mean performance coefficient, defined as the ratio of the average lift to the average drag during an oscillation period. The control parameters were location, velocity, opening length, and suction jet angle relative to the airfoil surface. The optimal jet had the maximum velocity and opening length and was normal to the airfoil surface. The optimal jet location was near the leading edge vortex (LEV) (between 3% and 6% of the chord). The optimum jet can increase the average performance coefficient (average ratio of lift to drag during a period) by about 24 times. The major part of this improvement is related to reducing drag force. The average lift coefficient increases from about 0.58 to about 0.92 using this jet, while the average drag coefficient decreases from about 0.23 to about 0.02. The optimal jet suppressed the dynamic stall vortex, which resulted from the combination of two clockwise vortices: LEV and turbulent separation vortex. Suppressing this vortex prevented the counterclockwise trailing edge vortex from growing at the end of the airfoil.

Rock-Breaking Characteristics of High-Pressure, Dual-Stranded Water Jets

Because of the unclear understanding of the characteristics associated with coupled rock breaking using multiple water jets, a numerical model combining smoothed particle hydrodynamics (SPH) and the finite element method (FEM) was established to investigate the rock-breaking capacity of a high-pressure, double-stranded water jet structure. The effectiveness of this model was verified through field experiments. The study further examined the specific energy required for rock breaking using the high-pressure double water jets and analyzed the effects of jet pressure, nozzle diameter, jet impact angle, and impact point spacing on rock-breaking volume. The results demonstrate that the rock-breaking ability of a high-pressure double water jets is better than that of a single water jet. When the impact angle of the high-pressure double water jets was 15° and the distance between impact points was 2.0 d, the rock damage effect was the best. By comparing the specific energies for rock breaking of a single water jet and a double water jet, it was concluded that the best rock-breaking nozzle diameter is 1.6 mm. Furthermore, an orthogonal testing approach was employed to determine the main and secondary factors influencing the rock-breaking energy of the high-pressure double water jet. The order of significance was found to be jet pressure > impact angle > impact point spacing > nozzle diameter. These findings provide valuable guidance and reference for application in the coal mining industry.