Dual Jet Research Articles

The Effect of Dual Water Jet on Discharge Coefficient of Vertical Spillway

The water intakes is one of the important hydraulic installations that is built with the dam and is used to control the water level in the dam's lake. The vertical spillway is a type of intakes used in dams to control floods and as on intakes to change the river stream in mountainous areas. One of the most important problems that occur at vertical intakes is the vortex of water which occurs when the depth of submerge is less than the critical depth, dual water jet applied to the vertical spillway was used with different vertical and horizontal distances, the effect of dual water spillway was tested on six discharges entering the vertical spillway and the three diameters. The results shown that the dual water jet has a clear effect in dissipating the energy of the vortices formed at the vertical spillway, especially in the case of orifice flow, and it is effective in the large diameters of the vertical spillway.

Enhancing the Heat Transfer Rate Through Surface Manipulation

In the present paper, the flow characteristics and the heat transfer rate of turbulent dual jet impinging on a sinusoidal wavy surface are numerically studied. Finite-volume-based two-dimensional Reynolds-averaged Navier–Stokes equations are used to handle the complex behavior of the turbulent dual. The offset ratio is varied from 3 to 15 with an interval of 2. To evaluate the role of sinusoidal wavy surface on flow and heat transfer characteristics, the amplitude and number of cycle are varied from 0.1 to 0.7 m and from 4 to 12 with an interval of 0.1 m and 1, respectively. In the present numerical work, the Reynolds number and Prandtl number are set to 15,000 and 0.71, respectively. The bottom wall is maintained at a constant temperature. The results show that the sinusoidal wavy surface affects both the flow characteristics and heat transfer rate, and that it also enhances the heat transfer rate significantly. Approximately, a maximum of 23.27% enhancement in heat transfer rate is achieved with respect to the plane wall surface. It is also found that the average Nusselt number depends on both amplitude and number of cycle of the sinusoidal wavy surface.

Effect of trailing edge dual synthesis jets actuator on aerodynamic characteristics of a straight-bladed vertical axis wind turbine

Based on the improved effect of synthetic jet (SJ) on airfoil aerodynamic characteristics and the configuration characteristics of dual synthesis jets actuator (DSJ), the effects of DSJ actuators arranged at the trailing edge on the aerodynamic efficiency of straight-blade vertical axis wind turbine (SB-VAWT) were studied. By comparing with the experimental results, the accuracy of the numerical simulation results of clean SB-VAWT power coefficient is verified. In order to consider the control effect of the arrangement, the actuation frequency and the momentum coefficient, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) and the SST k-ω turbulence model were used to simulate the SB-VAWT with different types and parameters. The simulation results show that the three arrangement modes of the trailing edge DSJ actuator proposed in this paper can effectively improve the power capacity of VAWT. Among them, Juxtaposition-type is the best. Through periodic “blowing” and “sucking”, the trailing edge vortex is induced to fall off in advance and delay the occurrence of stall. When λ = 2.05, f = 360 Hz, Cμ = 1.975 × 10−2, the power coefficient can be increased by 58.87%.

On dual jet N-linear connections in the time-dependent Hamilton geometry

In this paper we study the local adapted components of the N-linear connections on the dual 1-jet space J^{1∗}(R,M), together with its local adapted torsion and curvature d-tensors.

Numerical study on mean flow field of turbulent dual offset jet

A numerical investigation on the mean flow and turbulence characteristics of dual offset jet for various separation distances between the two jets with a fixed offset height of the lower jet from the bottom wall is reported in this study. The numerical simulations have been performed by solving the Reynolds-averaged Navier-Stokes equations (RANS) with two-equation standard [Formula: see text] turbulence model. The Reynolds number based on the jet width and the inlet turbulence intensity are considered as 15,000 and 5%, respectively. The computational results for the mean flow reveal that after issuing from the nozzles, the adjacent shear layers of the offset jets meet together at the merging point and then the merged jets reattaches on the bottom wall at the reattachment point before they combine together at the combined point forming a single jet flow. In the far downstream, the flow field behaves like a classical single wall jet flow. The self-similarity of mean flow field is achieved at far down stream of combined point. An increase in separation distance between the two jets [Formula: see text] results in a decrease in magnitude of the streamwise maximum velocity of the combined jet but with same rate of decay. The converging region of the jets has depicted considerable growth of turbulence as the jet centrelines bend towards the merging point. According to the mean flow results, the distances of the reattachment point and the combined point from the nozzle exit gradually increase with the progressive increase in separation distance between the two jets within the range d/ w = 3–8.

Impingement-Induced Stability Analysis of Intake Manifold Air Jets Using High Speed PIV and POD

The flow stability induced by the impingement of gas jets exiting from the intake manifold affects the in-cylinder flow characteristics of internal combustion engine. Using high-speed planar particle image velocimetry (PIV) with proper orthogonal decomposition (POD) analysis, an investigation was conducted to reveal the spatio-temporal characteristics of annular gas jets impinging in a region between the exits of two intake valves. Unique flow behaviors are identified where strong initial interaction of impinging jets appears near the valve exit as a result of fierce flow vorticity competition in both clockwise and counter-clockwise directions. This mixing zone exhibits strong fluctuations in the angle of the merged gas jet. Flow vorticity and merged jet angle are highly correlated with each other, and the quasi-periodical behavior of the jet impingement is linked to the kinetic energy dissipation. In addition, using POD, the underlying flow structures show large-scale rotating structures with translation which are responsible for the quasi-periodical behavior. In summary, three types of flow stability can be identified resulting from different levels of induced impingement: one-way interaction of single jet flow case, two-way interaction of dual impinging jets with equal flow magnitude, and transitional one-way interaction of dual impinging jets with unequal flow magnitude.

Experimental Characterization of Supersonic Single- and Dual-Impinging Jets

Supersonic single-impinging jet flows are known to exhibit strong unsteadiness levels and acoustic signatures due to large-scale resonant motions. However, the flowfield characteristics of two such jets operating in tandem, where properties are influenced by jet–jet interaction and coupling, are relatively unknown. The present study reports on the experimental investigation of the flowfield associated with two underexpanded, impinging jets operating at a nozzle pressure ratio of 2.65 and discharged from identical converging nozzles with exit diameters of 25.4 mm. Comparisons with a single-impinging jet operating at the same conditions are provided through flow visualizations, near-field acoustics, and surface pressure measurements. Fountain flow produced by the interaction of wall jets (a unique feature of dual-impinging jets) is found to be relatively strong at short impingement heights and contributes to additional loads on the ground surface. Unsteadiness in dual jets is weaker than that in a single jet at conditions involving resonance, and the fountain upwash plays an important role in the process. Although the feedback mechanism that drives the resonance in both impinging jet configurations is similar and the corresponding instability mode shapes are retained, there are differences in the strengths of the instability modes between the two configurations.

Eulerian–Lagrangian CFD-microphysics modeling of a near-field contrail from a realistic turbofan

Aircraft contrails contribute to climate change through global radiative forcing. As part of the general effort aimed at developing reliable decision-making tools, this paper demonstrates the feasibility of implementing a Lagrangian ice microphysical module in a commercial CFD code to characterize the early development of near-field contrails. While engine jets are highly parameterized in most existing models in a way that neglects the nozzle exit-related aspects, our model accounts for the geometric complexity of modern turbofan exhausts. The modeling strategy is based on three-dimensional URANS simulations of an aircraft nozzle exit involving a bypass and a core jet (Eulerian gas phase). Solid soot and ice particles (dispersed phase) are individually tracked using a Lagrangian approach. The implemented microphysical module accounts for the main process of water-vapor condensation on pre-activated soot particles known as heterogeneous condensation. The predictive capabilities of the proposed model are demonstrated through a comprehensive validation set based on the jet-flow dynamics and turbulence statistics in the case of compressible, turbulent coaxial jets. Simulations of contrail formation from a realistic nozzle-exit geometry of the CFM56-3 engine (short-cowl nozzle delivering a dual stream jet with a bypass rate of 5.3) were also carried out in typical cruise flight conditions ensuring contrail formation. The model provides reliable predictions in terms of the plume dilution and ice-particle properties as compared to available in-flight and numerical data. Such a model can then be used to characterize the impact of nozzle-exit parameters on the optical and microphysical properties of near-field contrails.

Research on the effect of air flow extinguishing arc in double jet non-equilibrium field

A dual-jet arc-extinguishing method is proposed in order to improve the performance of jet-extinguishing gaps for extinguishing large currents and reducing the lightning trip-out rate of power lines. Meanwhile, we studied the arc-extinguishing effect of the dual-jet non-equilibrium field gas flow. Based on this, a Double Jet Arc Extinguishing Gap (DJAEG) is developed. First of all, the jet field arc extinction modeling analysis is carried out by coupling the typical MAYR arc model with the jet field. Then, the COMSOL MUTIPHSICS simulation software is used to simulate the arc extinction of the DJAEG in the balanced flow field and the non-balanced flow field. Finally, the DJAEG extinguishment arc test is carried out through the construction of the power frequency continuous flow interruption test. The simulation results show that the velocity of the high-speed jet emitted by the DJAEG can reach 3000 m/s, and the arc can be extinguished within 4 ms. These results also verified that the dual jet non-equilibrium flow field has the characteristics of long jet sustaining time. The test results show that the DJAEG successfully extinguished the arc within 4 ms, and there was no reignition. This means that the dual-jet non-equilibrium field has an obvious arc extinction effect.

Role of a Sinusoidal Wavy Surface in Enhancement of Heat Transfer Using Turbulent Dual Jet

Abstract In this paper, the role of sinusoidal wavy surface in enhancing the heat transfer is numerically studied. The heat transfer characteristics are studied for two thermal boundary conditions of the wavy wall. To assess the effect of wavy wall, the amplitude is varied between 0.1 and 0.7 and number of cycle from 4 to 12 at an interval of 0.1 and 1, respectively. In order to see the effect of offset ratio, it is varied between 3 and 15 at an interval of 2. The Reynolds number (Re) and Prandtl number (Pr) are set to 15, 000 and 0.71, respectively, for all the numerical simulations. It is found that the maximum average Nusselt number (Nuavg) depends not only on the amplitude and number of cycle but also on the offset ratio. Overall, 23.27% in maximum heat transfer enhancement is achieved with reference to the plane wall surface. An approximately linear decrement in maximum Nuavg is observed when offset ratio increases. The results indicate that Nuavg increases with an increase in the amplitude of sinusoidal wavy surface up to N = 8 and almost follows the linear trend up to N = 7. It is also found that Nux is always on the higher side as compared to the corresponding case of a plane wall surface when N = 4, irrespective of the offset ratio. With an increase in N, Nux fluctuates about the result of plane wall surface after the initial increase because of the obstruction. The amplitude of the fluctuation increases with an increase in the number of cycle N, which indicates that fluid accelerates and decelerates gradually owing to the presence of trough and crest. Also, it is worth noticing that for some cases, there is a decrease in the heat transfer rate as compared to the plane wall case. Therefore, it is concluded that the increase in the surface area does not necessarily result in an increase in the heat transfer rate.

Experimental investigation on active control of flow around a finite-length square cylinder using dual synthetic jet

This paper presents an active flow control method for flow around a finite-length square cylinder using dual synthetic jet (DSJ). A piezoelectric dual synthetic jet actuator (DSJA) was installed at the leading edge of the free end for generating the DSJ. The amplitude and frequency of DSJ can be adjusted through the driving voltage and driving frequency. In our research, the pressure measurements and flow visualization are conducted to test the control effectiveness of dual synthetic jet. According to the aerodynamic results, there is a correlation between the control efficiency and the amplitude and frequency of DSJ, which are determined by jet momentum coefficient and driving frequency. After the application of the free-end DSJ with moderate amplitude and frequency, the maximum reduction of total mean drag coefficients, fluctuating drag coefficients and fluctuating lift coefficients respectively reached 4.3%, 18.0% and 30.8%. Moreover, the smoke-wire and PIV results indicate that there is a remarkable suppression of the free-end separated shear flow and a prominent increase in the TKE in the area near the free end. All results point to that the aerodynamic forces and wakes of a surface-mounted finite-length square cylinder can be effectively controlled using dual synthetic jet at free end.

Dual microwave-excited atmospheric-pressure plasma jets with a single power source

In this paper, we propose dual microwave-excited atmospheric-pressure plasma jets (DME-APPJs) that can be generated with a single power source. A T-junction power divider that evenly distributes the input power to two ports is used, and two coaxial transmission line resonators are used as plasma generators for the DME-APPJs. The power divider distributes the incoming power in port 1 and supplies 46% of this power to port 2 and port 3, respectively. Surface treatments are conducted by exposing the multiple plasma jets to polypropylene (PP) specimens and then confirming the degree of hydrophilic change. Using the proposed DME-APPJs, it is possible to perform surface treatments on areas that are up to 50% larger compared to using two single ME-APPJs with the same power consumption. The DME-APPJs thus show more advanced performance for surface treatments by comparison with the single ME-APPJ.

Effect of Trailing Edge Dual Synthesis Jets Actuator on Aerodynamic Characteristics of a Straight-Bladed Vertical Axis Wind Turbine

Based on the improved effect of synthetic jet(SJ) on airfoil aerodynamic characteristics and the configuration characteristics of dual synthesis jets actuator (DSJ), the effects of DSJ actuators arranged at the trailing edge on the aerodynamic efficiency of straight-blade vertical axis wind turbine (SB-VAWT) were studied. By comparing with the experimental results, the accuracy of the numerical simulation results of clean SB-VAWT power coefficient is verified. In order to consider the control effect of the arrangement, the actuation frequency and the momentum coefficient, the Unsteady Reynolds-Averaged Navier-Stokes(URANS) and the SST k-ω turbulence model were used to simulate the SB-VAWT with different types and parameters. The simulation results show that the three arrangement modes of the trailing edge DSJ actuator proposed in this paper can effectively improve the power capacity of VAWT. Among them, Juxtaposition-type is the best. Through periodic blowing and sucking, the trailing edge vortex is induced to fall off in advance and delay the occurrence of stall. When λ =2.05, f =360 Hz, C μ =1.975×10 -2 , the power coefficient can be increased by 58.87%.

Flow and mixing characteristics of dual parallel plane jets subject to acoustic excitation

The effects of jet pulsation intensity and excitation Strouhal number on the flow and dispersion characteristics of dual parallel plane jets at a low Reynolds number of 200 were experimentally studied so that the transition from laminar to turbulence was focused. A hot-wire anemometer was used to record the jet velocities. The flow patterns were obtained using the laser-light sheet assisted smoke flow visualization technique. Jet spread widths were derived from the long-exposure images using the binary edge detection method. The jet fluid dispersion characteristics were examined using the tracer-gas concentration detection technique. Four characteristic flow modes (discrete coherent vortices, contiguous coherent vortices, early vortex breakup, and lateral dispersion) were identified in the domain of the jet pulsation intensity and excitation Strouhal number. At small jet pulsation intensities, discrete and contiguous coherent vortices appeared at low and high excitation Strouhal numbers, respectively. The vortices appearing in the jet shear layers broke up slowly and caused small jet expansions and turbulent intensities, thus inducing a low efficiency of jet fluid dispersion. The early vortex breakup mode was induced by the low-frequency back-and-forth flow motions in the near region at large jet pulsation intensities and low excitation Strouhal numbers. Large turbulence fluctuations caused by the early vortex breakup increased the jet dispersion significantly. At large jet pulsation intensities and excitation Strouhal numbers, high-frequency back-and-forth flow motions in the region near the jet exits significantly reduced the time-averaged axial momentum and induced large lateral jet expansion and jet fluid dispersions.

Effects of pulsation intensity on the flow and dispersion of pulsed dual plane jets

The effects of jet pulsation intensity on the flow and dispersion characteristics of dual parallel plane jets were experimentally studied. The jet pulsations were generated by acoustic excitations. The laser-light-sheet-assisted smoke flow visualization method was used to study the flow evolution processes. The lateral spreading characteristics of the jets were measured using the binary edge detection method. A hotwire anemometer was used to measure the velocity pulsations, mean velocities, turbulence intensities, and Lagrangian turbulent length and time scales. The dispersion characteristics of the jet fluids were measured by the tracer-gas concentration detection method. The jet Reynolds number and excitation Strouhal number were fixed at 600 and 0.106, respectively. The jet pulsation intensities were varied from 0 to 1.6. As the jets were pulsed, the turbulence intensity, lateral spread width, and jet fluid dispersion capability markedly increased compared with those of the non-pulsed jets. The larger the pulsation intensity was, the higher the turbulence intensity, lateral spread width, and jet fluid dispersion. The Lagrangian time and length scales of the turbulent eddies decreased as the jet pulsation intensity increased because the mushroom-shaped structures generated by the jet pulsations broke up into small turbulent eddies caused by the strong vortex-stretching effect.

Vortical structures and density fluctuations analysis of supersonic forward-facing step controlled by self-sustaining dual synthetic jets

Shock wave/boundary layer interaction (SWBLI) is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles. Supersonic forward-facing step (FFS), an extreme case of compression ramp, often occurs severe SWBLIs with a large separation bubble. In this paper, experimental investigations on vortical structures and density fluctuations characteristics of supersonic FFS controlled by self-sustaining dual synthetic jets (SDSJ) are carried out in a Mach number 2.95 wind tunnel. High spatial–temporal resolution flowfield images of FFS without/with active flow control are captured by adopting nano-particle-based planar laser scattering technique. The control effects of the distance between the actuator and the step are mainly compared. The paper finds that the SDSJ can effectively change the feature of flowfield, eliminate the separation shock and the reattachment shock, compel the original shock induced by the step leading edge to distort and reduce its intensity finally. Density fluctuations analysis demonstrates that the whole flows seem to move upstream with the increase of distance (dS-J). Discrete Fourier transformation spectrums results reveal that the fluctuations are mainly located in the low-frequency region at first. High-frequency components and frequency bandwidth increase slightly after the SDSJ are applied.

Experimental Study on Oxygen Mass Transfer Characteristics by Plunging Hollow Jets

Aeration by plunging water jets is an effective and economical method of transferring oxygen into the receiving pool of water. A dispersion of air bubbles occurs underneath the pool surface as a high-velocity liquid jet plunges on the water surface after being ejected from a particular fall height. The present study aims to investigate the impact of jet velocity, jet length, water depth and jet thickness of plunging hollow jets in oxygenating the water in the aeration tank. Empirical correlations are proposed for the determination of volumetric oxygen transfer coefficient based on jet velocities and jet kinetic powers. Moreover, the oxygen transfer capacity of single hollow jet, double hollow jet and a dual jet (combined hollow and solid) is tested by keeping a nearly constant jet flow area through the jet openings. The observations recorded from the experimental analysis lead to the development of predictive relationships for estimating the values of volumetric oxygen transfer coefficient in terms of basic jet variables.

Theoretical modeling of vectoring dual synthetic jet based on regression analysis

The excellent vectoring characteristic of Dual Synthetic Jet (DSJ) provides a new control strategy for the active flow control, such as thrust vectoring control, large area cooling, separated flow control and so on. For incompressible flow, the influence relation of source variables, such as structure parameters of actuators, driving parameters and material attributes of piezoelectric vibrating diaphragm, on the vectoring DSJ and a theoretical model are established based on theoretical and regression analysis, which are all verified by numerical simulations. The two synthetic jets can be deemed as a main flow with a higher jet velocity and a disturbing flow with a lower jet velocity. The results indicate that the influence factors contain the low-pressure area formed at the exit of the disturbing flow, which could promote the vectoring deflection, and the impact effect of the disturbing flow and the suppressive effect of the main flow with the effect of restraining the vectoring deflection. The vectoring angle is a complex parameter coupled by all source variables. The detailed theoretical model, whose error is controlled within 3.6 degrees, can be used to quantitatively assess the vectoring feature of DSJ and thus to provide a guidance for designing the control law applied in the active flow control.

Influence of Non-Structural Parameters on Dual Parallel Jet Characteristics of Porous Nozzles.

As an important actuator of the dual parallel jet, the porous nozzle has some non-structural parameters (such as inlet pressure, nozzle spacing ratio, etc.) which have a significant influence on energy transport, chemical combustion and pollutant generation. The research on the microfluidic state of the porous nozzle dual parallel jet, however, remains insufficient because of its microjet pattern and complex intersection process. In this paper, the authors used numerical simulation and an experimental method to clarify the influence of porous nozzles’ non-structural parameters on dual parallel jet characteristics. The results show that the inlet pressure only changes the pressure peak value on the parallel jet axis; the starting point (SP) and peak point (PP) on the parallel jet axis, which are located at Xsp = 22 mm and Xpp = 75 mm, respectively, are not changed; and with the increase in the nozzle spacing ratio, the merging points (MPs) on the parallel jet axis are Xmp = 25 mm, 32 mm and 59 mm, respectively. The merging point and the combined point move to a farther distance and the inner deflection angle of the jet is weakened.

Impingement Cooling with Dual Synthetic Jet Based on Improvement of Exit Configuration

Impingement Cooling with Dual Synthetic Jet Based on Improvement of Exit Configuration