Dual Jet Research Articles

CFD Investigation of Dual Synthetic Jets on an Optimized Aerofoil's Trailing Edge

In fluid dynamics, a flow control device is used to control, manage, or modify the behavior of a fluid flow. Jet actuators work by releasing high-velocity jets of fluid, usually air or gas, into the surrounding environment to control or manipulate the flow of fluids. In this study, the flow control device, which was a dual synthetic jet actuator (DSJA), acted as a lift enhancement device over an optimized NACA 0012 aerofoil with a rounded trailing edge (TE) (Coanda surface approximately 9% of the trailing edge was modified) to enhance the lift at various angles of attack (AOAs). Fluctuating pressure inlets were introduced in two slots. When the dual synthetic jets were in control, the out-of-phase jets from the upper and lower trailing edge jets helped to boost the lift coefficient. The suction stroke from the lower half of the jet made the Coanda effect stronger in the upper half. The upper trailing edge jet deflected downwards merged with the lower one and helped to deflect the flow field closer to the bottom half. An unsteady CFD analysis was performed on optimized airfoils with and without a DSJ, with a driving frequency of 40.6 and a reduced frequency of 0.025 at a Reynolds number of 25000. The results obtained at different angles indicated that the L/D ratio was improved by 13.5% at higher angles of attack in the presence of the DSJA.

Study on dynamic stall control strategy based on dual synthetic jets

Study on dynamic stall control strategy based on dual synthetic jets

Effects of offset jet width on periodic flow in a dual jet

The primary aim of this work is to investigate the impact of the offset jet width on the unsteady flow characteristics of a turbulent dual jet, which consists of a wall jet and an offset jet. A computational fluid dynamics code is developed to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) equations. The width of the offset jet is varied while keeping the width of the wall jet constant at the separation distance between the two jets. When the ratio of the offset jet width (w) to the separation distance (d) is w/d=0.5, the flow field exhibits a periodic vortex shedding phenomenon. Conversely, when w/d=0.4, the flow field remains steady. The shedding phenomenon is discernible even when w/d=2. The instantaneous velocity components display sinusoidal oscillations at 0.5≤w/d≤2. Applying the fast Fourier transform to these sinusoidal signals yields a distinct frequency peak at the vortex shedding frequency. Within the range of 0.5≤w/d≤2, the shedding frequency decreases as the width of the offset jet increases. This trend continues until it reaches a constant value at w/d=1.4. This indicates that the width of the offset jet has a notable influence on the shedding phenomenon within the range of 0.5≤w/d≤1.4. For 1.4<w/d≤2, the shedding frequency remains unaffected by the offset jet width variation. Depending on the value of w/d, the shedding phenomenon is characterized by three flow regimes: a steady flow regime (forw/d≤0.4), an outer share layer-influenced shedding regime (for w/d=0.5−1.4), and an outer shear layer-free shedding regime (for w/d>1.4).

PERFORMANCE ANALYSIS OF AISI 4340 HARDENED STEEL IN DUAL JET MQL TURNING SYSTEM: A COMPARISON STUDY BETWEEN CVD AND PVD-COATED CARBIDE TOOLS

The hard part turning process used to finish the cylindrical surfaces has some critical machining responses like tool wear with the lower quality of the machined surfaces. Minimum quantity lubrication (MQL)-based machining environment is currently considered an advanced cooling and lubrication technique. Cutting speed, feed rate, and cutting depth are considered input parameters, and the TaguchiL27 orthogonal array (OA) has been adopted as the design of the experiment. In this context, average surface roughness ([Formula: see text]), tool flank wear (VBc), cutting temperature ([Formula: see text]C), and chip morphology have been selected as measured outputs. To improve the machining performance of hardened steel, a sustainable MQL ([Formula: see text] directions) cooling system has been employed at the cutting zone. Iron–aluminum LRT 30 was considered as the base fluid for the hard turning of AISI 4340 steel by PVD (AlTiN) and CVD (TiN/TiCN/Al2O3) coating cutting inserts. The primary effects of process parameters and their influences on the measured outputs have been discussed. The dual jet MQL-based hard turning was performed at three levels of cutting speeds (80, 170, and 260[Formula: see text]m/min), feed rate (0.5, 0.1, and 0.15[Formula: see text]mm/rev), and cutting depth (0.2, 0.3, and 0.4[Formula: see text]mm) with an air pressure of 5[Formula: see text]bar and mist flow rate 50[Formula: see text]ml/h. The findings showed that PVD-coated carbide tools outperformed CVD-coated tools. The model of the measured outputs of both tools has been developed using second-order regression analysis. Utilizing ANOVA analysis, all the predictive models were observed to be significant and acceptable with larger than 90% of [Formula: see text] value.

Water droplet transport on superhydrophobic surfaces induced by the dual synthetic jets

Droplet transport is very essential in many industrial applications. This article proposed the concept of employing dual synthetic jets in conjunction with superhydrophobic materials to facilitate the long-distance directional transport of water droplets. Experiments showed that the droplet transport speed could reach approximately 90 mm/s. In addition to linear transport, dual synthetic jets were also capable of achieving curved transport of droplets on superhydrophobic surfaces. High-speed photography captured the details of the droplet transport process. Additionally, simulations analyzed the water droplet's aerodynamic forces and the deformation and breakup mechanisms at the actuator's outlet. The research in this paper was anticipated to contribute to new methods for directed droplet transport on superhydrophobic surfaces. It is eliminated the need for pre-processing the surface to create a path, and there was also no need to incorporate conductive or magnetic substances within the droplets.

Effect of Kerosene Dual-Jet Spacing on the Mixing and Combustion Characteristics of a Scramjet Combustor.

As the core of a hypersonic propulsion system, the effective mixing efficiency of fuel and air in a supersonic combustor is crucial for its performance. This study focuses on a cold supersonic flow and employs computational fluid dynamics (CFD) techniques combined with Euler-Lagrange method's discrete-phase model (DPM) for multiphase flows, K-H and R-T (Kelvin-Helmholtz and Rayleigh-Taylor) mixing and atomization models, turbulence models, and surface evaporation models to investigate the injection, atomization, and mixing characteristics of kerosene in supersonic airflow. In order to enhance the mixing efficiency between kerosene and air while reducing flow losses, this study examines a staggered dual-jet injection scheme, with the dual jets arranged at the center of the cavity and having a dual-jet spacing of 10 and 20 mm, respectively. Starting from the interaction mechanism between jets, the impact of different staggered dual-jet spacings on the kerosene jet penetration height, span expansion area, angle of the shock wave, and Sauter mean diameter distribution was analyzed. The results show that a short dual-jet spacing (10 mm) leads to greater penetration height, wider span expansion, and a larger angle of the shock wave. When the dual-jet spacing is shorter, the interaction between the fuel jet and the cavity shear layer is stronger, resulting in an improved fuel mixing efficiency. The achievements of this study are consistent with previous experimental measurements and the literature, demonstrating a strong theoretical foundation for optimizing the design of hypersonic engines by deepening the understanding of the fundamental atomization mechanisms of kerosene jets in cold-state supersonic flows. Moreover, these results hold practical significance in improving the efficiency of kerosene combustion and enhancing the performance of flame stabilization devices.

Experimental study on a dual synthetic jets liquid cooling device

To address the growing heat dissipation requirements of high heat flux electronic devices, this work presents experimental research on a dual synthetic jets (DSJ) liquid cooling device. The effects of different heat flux, channel inlet flow rates, driving frequencies, and other parameters on the device ability have been explored. The experimental results indicate that the wall temperature increases by increasing the heat flux. Raising the channel inlet flow rate will reduce wall temperature. When DSJ is off, increasing the inlet flow rate from 0.16 L/min to 0.40 L/min results in a maximum temperature decrease of 6.30 °C and a pressure drop increase of 2.20 kPa. There is essentially no change in the pressure drop when DSJ is operating. When the inlet flow rate is 0.16 L/min, the maximum wall temperature at DSJ on is reduced by 6.83 °C compared with DSJ off. The convective heat transfer coefficient was raised by 40.55%. The vibrating diaphragm exhibits better low-frequency characteristics when working underwater. The convective heat transfer coefficient increases by 36.46% when the driving frequency is 20 Hz. Increasing the driving voltage, the device cooling performance increased. By increasing the driving voltage to 240 V, the wall temperature decreased by 6.30 °C, a decrease of 13.82%, and the convective heat transfer coefficient raised by 28.51%. The device overall performance increased by a maximum of 39.55% after DSJ on compared with DSJ off.

Study on ignition mode transition of methanol pre-chamber jet ignition system controlled by boundary condition parameters

Optimizing boundary condition parameters is an effective means to substantially improve the combustion performance of methanol pre-chamber turbulent jet ignition systems. In this study, an optically accessible constant-volume combustion chamber was employed to delve deeply into the impacts of critical boundary condition parameters on the combustion performance of the pre-chamber jet ignition system. The findings suggest that adjusting the pre-chamber boundary condition parameters can lead to various jet ignition modes, including jet flame ignition, jet direct ignition, jet delayed ignition, jet wake ignition, and dual jet ignition. Different jet ignition modes result in variations in ignition timing, ignition location, combustion rate, and lean burn limits. Under identical initial temperature and pressure conditions, compared to jet flame ignition with the lowest combustion velocity and jet wake ignition with almost no lean burn capability, dual jet ignition can reduce the combustion duration by about 50% and elevate the lean burn limit by more than double. Unlike the patterns observed in traditional spark ignition systems, within the range of experimental tests, lowering the temperature and increasing the pressure significantly improved the lean combustion limit of the pre-chamber system and reduced the probability of jet wake ignition. This performance enhancement is attributed to the increase in the density of the mixture in the main combustion chamber.

Non-thermal radiation from dual jet interactions in supermassive black hole binaries

ABSTRACT Supermassive black hole binaries (SMBHBs) are natural by-products of galaxy mergers and are expected to be powerful multimessenger sources. They can be powered by the accretion of matter and then radiate across the electromagnetic spectrum, much like normal active galactic nuclei (AGNs). Current electromagnetic observatories have a good chance of detecting and identifying these systems in the near future. However, precise observational indicators are needed to distinguish individual AGNs from SMBHBs. In this paper, we propose a novel electromagnetic signature from SMBHBs: non-thermal emission produced by the interaction between the jets ejected by the black holes. We study close SMBHBs, which accrete matter from a circumbinary disc and the mini-discs formed around each hole. Each black hole ejects a magnetically dominated jet in the direction of its spin through the Blandford–Znajek mechanism. We argue that in such a situation, the interaction between the jets can trigger strong magnetic reconnection events, where particles are accelerated and emit non-thermal radiation. Depending on whether the jets are aligned or misaligned, this radiation can have different periodicities. We model the evolution of the particles accelerated during the dual jet interaction and calculate their radiative output, obtaining spectra and providing estimates for the variability time-scales. We finally discuss how this emission compares with that of normal AGNs.

Computational study of thermal and fluid mixing behaviour of a dual jet flow using LES approach

The primary goal of any thermal system which demands efficient cooling is to improve heat transmission. For a turbulent jet, this condition becomes far more significant. The present work has employed large-eddy simulation (LES) for an offset ratio of 2.0 to investigate the transfer in heat and flow characteristics of a dual jet. An isothermal boundary wall condition is considered for a Reynolds number of 7500. The present findings are evaluated by comparing with the published experimental and numerical studies on wall jets. A comparative analysis here exhibits the profiles of Reynolds normal stresses, Reynolds shear stresses, turbulence kinetic energy, Nusselt number and turbulent heat fluxes. A comprehensive investigation of the mixing and flow properties of the dual jet is presented by using the Q-criterion of the iso-surface for mean velocity, pressure and vorticity. The present outcomes show that an efficient thermal transmission from the wall occurs in the recirculation region. The magnitudes of the profiles of Reynolds normal stresses, Reynolds shear stresses, r.m.s. temperature and turbulent heat fluxes are observed to be low in the combined region. Roller-like structure formation and near-wall eddies are noticed which spread in the combined region indicating large heat loss due to the turbulent flow.

Numerical simulation of single-jet impact cooling and double-jet impact cooling of hot-rolled L-shaped steel based on multiphase flow model

In this paper, numerical simulations of single-jet impingement cooling and double-jet impingement cooling processes of heated L-shaped steel are carried out using the VOF model. The SIMPLEC pressure–velocity coupling algorithm and realizable k-ε model are used for the solution. The effects of jet position, water flow, and jet distance in the single-jet condition are analyzed in the simulations. The distributions of impact pressure, turbulence kinetic energy, and Nusselt number were obtained, as well as the variation of the peak values of these three factors with the jet position, water flow, and jet distance. The water flow rate is 3–11 L/min, and the jet distance is 5–25 cm. The effect of the distance between the two nozzles on the jet cooling uniformity under the dual jet condition was also analyzed. The distance between the two nozzles was 15–45 mm. The results showed that the variation of water flow rate had a greater effect on the ability of jet cooling compared with the jet position and jet distance, and the heat transfer efficiency also increased gradually with the increase of water flow, but the increased rate of heat transfer efficiency decreased gradually. When the flow rate increased from 3 to 11 L/min, the maximum instantaneous cooling rates at 1/4 of the thickness of the short side upper side, long side upper side, short side lower side, and long side lower side positions increased by 38.9%, 48.5%, 48.2%, and 32.9%, respectively. To ensure that the jet does not shift, the jet distance should be less than or equal to 10 cm. In the case of the double jet, the nozzle distance is 1.5 cm, and the cooling uniformity of the cooling area between the two nozzles is better. The peak Nusselt number in the cooling area of each part under the double jet cooling condition increased by 5%, 9.4%, 10.2%, and 13.3%, respectively, compared with the single jet.

Thermal and fluid aspects of dual piezoelectric jet pump of double chambers

The rapid development of electronics has led to a significant reduction in the size of electronic devices, while increasing their power consumption. This has resulted in the need for small-scale thermal management solutions. Piezoelectric pump is one of the efficient devices for local thermal management. This paper presents a novel configuration of a piezoelectric pump, which separates the pump chamber with a rigid wall to create two independent pulsating flows. This configuration aims to reduce eddies within each chamber. Furthermore, the proposed design incorporates two pairs of open-sided channels to guide the pulsating flow towards the hot target. The electrostatics physic of the piezoelectric patches along with energy and momentum equations in three dimensions are manipulating mathematically and solved numerically using the finite element method (FEM) and the Arbitrary Lagrangian-Eulerian (ALE) technique. The implicit Large Eddy Simulation (iLES) turbulence model is adopted for this purpose. Several parameters, including frequency, voltage, and the radius of the piezoelectric patch are investigated to better understanding their influence on both the zero-net volumetric flow rate and the heat transfer process. The findings indicate that by separating the pump chamber, it becomes feasible to obtain a 3D solution with the iLES using a reasonable mesh size. Nusselt number increases with all the examined parameters, where it enhances by 42.48 % at V = 100 Volt when the pump is switched on compared to natural convection mode. The peak-peak volumetric flowrates rises by 50 % and 350 % when the applied voltage is raised from 50 to 100 Volts and the frequency is raised from 20 to 50.50 kHz, respectively.

Numerical Simulation Study of Energy Separation in Jet Shear Layer

In order to investigate the rational utilization of energy in the fluid jet process, a free dual jet of parallel air is used as a research object. Simulation of turbulence was carried out based on the realizable k-epsilon equations with pressure-velocity coupling, PISO method, discrete method with second-order windward format, and first-order implicit transient solution. The energy separation phenomenon within the jet shear layer and its influencing factors were investigated under dual-jet Reynolds number differences of 12,800, 19,200, 25,600, 32,000, 41,500, and 51,100, respectively. The simulation is in transient format and the jet inlet velocity is given by udf. Calculations show that the pressure perturbation in the air shear layer, which gives rise to the pressure work exchange between the jet and the surroundings, is the main reason for the coexistence of high- and low-temperature regions formed within the jet shear layer, and the larger the Reynolds number, the stronger the energy separation effect. The center streamline path of a parallel air free dual jet can be fitted by a circular arc, whose radius of curvature increases with the Reynolds number, and the curvilinear development path of the dual jet can offset the energy separation effect to some extent. This paper confirms the existence of energy separation in the shear layer of a parallel air free double jet, reveals the mechanism of energy separation in the fluid domain, and explores the flow characteristics of two parallel jets.

Shedding of water droplets by the dual synthetic jet

Taking into account the benefits of the dual synthetic jet (DSJ) actuator's simple form, the absence of an air supply, and powerful jet momentum, as well as the low water adhesion force of the superhydrophobic surfaces, it is possible to make droplet shedding happen easily by combining these two methods. This paper studied the motion of water droplets under the action of the DSJ actuator with inclined outlets on three different kinds of surfaces with different wettability, namely, aluminum (hydrophilic), fluorinated silicon (hydrophobic), and superhydrophobic surfaces. Particle image velocimetry measurements were used to describe the flow field of the DSJ actuator. Then, high-speed photography was adopted to compare the critical air velocity for stable motion of the droplet on the three kinds of surfaces. The droplet mobility at three different surfaces when the jet velocity was the same was compared. The displacement and changes of the contact line of water droplets with different volumes on the superhydrophobic surface under the influence of jets were studied. Besides, choosing a typical case, the effect of the dual synthetic jet on the droplet was quantitatively examined, as well as the aerodynamic drag and lift forces. And some of the phenomenon observed in the experiment was explained using the simulation data. It is hoped that this research would lead to the development of a new method of facilitating droplet transport in applications such as anti-icing, drug delivery, self-cleaning surfaces, etc.

Influence of dual purging jets on interferometric measurement of optical path difference

Incompressible large eddy simulations of dual purging jets at three Reynolds numbers of ReL = 1500, 1000, and 500 are performed, providing the database for simulated interferometric measurements subjected to the spatiotemporally varying temperature fields. The temperature is modeled as a passive scalar, and the index-of-refraction field is calculated from the air temperature and pressure using the modified Edlén equation. Based on wave optics, wavefront distortions of laser beams traversing the flow field are computed, and the optical path difference measurement is simulated. Statistical results of the velocity and temperature indicate distinctly different flow patterns at three Reynolds numbers. Spectral proper orthogonal decomposition is adopted to analyze the relationship between coherent flow structures and temperature wavepackets. There is a dominant frequency (St = 0.29) at ReL = 1500 and 1000, which is attributed to the Kelvin–Helmholtz instability, whereas the two jets have notable flapping behaviors at ReL = 500. The wavefront distortions are found to be insensitive to the Reynolds number. The effects of the flow region and tracing distance are examined, and the optical performances of different beam pairs for interferometry are evaluated. The optical beams passing through the outer shear layers of the dual jets and wall jets are distorted severely, resulting in large systematic and random errors in the interferometric measurement.

Flight test of flying wing aircraft controlled by dual synthetic jets at Ma0.2

To explore the application potential of zero-mass-flux dual synthetic jets in flight control of flying wing aircraft (FWA), dual synthetic jet actuators (DSJAs) are integrated into a FWA and flight tests without deflections of rudders are firstly carried out to verify the viability of DSJAs to manipulate three-axis attitudes at a cruising speed of 70 m/s. Two active flow control methods of circulation control and reverse jet control performed by DSJAs are utilized to execute the three-axis control. Novel flight control effectors based on DSJAs are designed and achieve the integration with the FWA. Flight tests show that three-axis flight control is realized by DSJAs distributed in different locations. The maximum roll, pitch and yaw angular velocities are 10.12°/s, 6.17°/s and 8.38°/s respectively. The work initially verifies rudderless flight control ability of DSJAs at a cruising speed of 70 m/s and the control ability will be improved by the further optimization of DSJAs.

Experimental investigation of dual jet flow past a heated surface: Effect of Reynolds number

A dual jet flow comprises a wall jet, discharged immediately parallel to a solid boundary, flowing alongside a parallel jet whose exit is offset from the solid boundary by some distance. Despite the widespread industrial application of dual jet flows, experimental analysis of their flow and heat transfer characteristics is severely underrepresented in the published literature. As a result, the heat transfer capabilities and driving flow mechanisms associated with dual jet flows are not yet fully understood, meaning they cannot be optimised towards specific applications. The present study is thus concerned with characterising the transfer of heat to a dual jet flow for varying Reynolds number through experimental means. Using air as the working fluid, each jet Reynolds number is varied in the range 5500≤Re≤12,000 and the offset ratio and velocity ratio are each maintained at a constant value of 1. A constant heat flux generation of 1670W/m2 is maintained in the bounding wall and the surface Nusselt number distribution is measured using infrared thermography techniques. A distinct Nusselt number profile is observed with respect to downstream distance, which remains consistent regardless of the Reynolds number. The results indicate that increasing Re elevates the Nusselt number proportionally at all downstream locations, where the surface-averaged Nusselt number rises linearly with increasing jet Reynolds number.

Comparison of single nozzle and dual nozzle MQL performance in hardened steel turning: A case study

This study focused on comparing the machining output performance of single and dual jet nozzle assisted MQL (Minimum Quantity Lubrication) in CNC hard turning. Two case studies were conducted using different hardened steels and cutting tools. The cutting parameters including feed rate (0.1 mm/rev), cutting speed (60 m/min) and depth of cut (0.1 mm) were maintained constant. In the first case study, AISI 4340 hardened steel workpiece and CVD-coated carbide cutting tool were used. The results showed that the dual nozzle MQL system achieved lower tool flank wear (30.54 %), cutting power (11.33 %), surface roughness (24.59 %), cutting temperature (22.36 %), and cutting sound (2.35 %) compared to the single nozzle system. The second case study used AISI D2 steel workpiece and PVD-coated carbide tool, and similar findings were observed. Cutting power observed during hard turning operations in a dual nozzle MQL environment was 0.360 kW for AISI 4340 Steel and 0.386 kW for AISI D2 Steel, respectively, which is very low in terms of hard turning concerns. Dual Nozzle Overall, the dual nozzle MQL system consistently demonstrated more efficient machining, regardless of the variations in tool material, workpiece material, and hardness. Therefore, it is suggested for further research in machining applications in the future.

Aero-Propulsive Characterization of a Flight Vehicle with Two Side-Jets

Numerical simulations were carried out to study the aero-propulsive characteristics of a flight vehicle using in-house developed Reynolds Averaged Navier-Stokes code CERANS. The analyses involved subsonic external flow with inclined supersonic dual sustainer jets at various angles of attack, roll orientations and side slip. The control characteristics of the configuration are evaluated for the flow with and without sustainer jets. Numerical simulations indicated that the jet plume exhausting out of the scarf sustainer nozzle grazed and clung to the airframe for a considerable downstream distance causing serious damage to the airframe. This numerical study led to an important design change of the sustainer nozzle shape from ‘scarf’ to ‘conical’ which alleviated plume interference problem with the airframe.

Novel yaw effector of a flying wing aircraft based on reverse dual synthetic jets

For achieving the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft (FWA), a novel yaw effector based on Reverse Dual Synthetic Jets (RDSJ) was proposed without the movement of rudders. Effects on aerodynamic characteristics of a small-sweep FWA and control mechanism were investigated by numerical simulations. Finally, reverse dual synthetic jet actuators were integrated into a real FWA and flight tests were firstly carried out. Numerical results show that RDSJ could make drag coefficient increase and weaken lift coefficient, which generate a yawing moment and a rolling moment in the same direction, realizing control of heading attitudes, but strong coupling with the pitching moment occurs at large angles of attack. For control mechanism, RDSJ could produce two reverse synthetic jets out of phases, improve the reverse pressure gradient and hence form alternate recirculation zones or even early large-area separation, which cause the rise of pressures before exits and the dip of pressures behind exits, achieving improvement of drag and the yawing moment. The results of flight tests support that RDSJ could realize control of heading attitudes without deflections of rudders during the cruise stage and achieve the maximal yaw angular velocity of 10.12(°)/s, verifying the feasibility of this novel yaw effector.