Co-flow Jet Research Articles

Numerical Investigation of Performance Enhancement of the S809 Airfoil and Phase VI Wind Turbine Blade Using Co-Flow Jet Technology

Making full use of wind energy can effectively alleviate the global energy shortage and environment contamination problems. Nevertheless, how to significantly improve the performance of the wind turbine airfoil and blade is a crucial issue. As the novel flow control method, the co-flow jet (CFJ) technology is one of the most potential methods to solve this problem. Thus, the effects of the CFJ technology on the performance enhancement of the S809 airfoil and Phase VI wind turbine blade are explored in this study. Furthermore, the effects of the injection location and jet momentum coefficient are studied, and an adaptive jet momentum coefficient strategy of the CFJ technology is proposed. Results demonstrate that the CFJ technology can significantly improve the maximum lift coefficient and maximum corrected lift-to-drag ratio of the S809 airfoil. Moreover, the power coefficient of the Phase VI wind turbine blade at the low tip speed ratio is greatly enhanced as well. In particular, the maximum lift coefficient and maximum corrected lift-to-drag ratio of the typical S809 CFJ airfoil with adaptive Cμ are improved by 119.7% and 36.2%, respectively. The maximum power coefficient of CFJ blade can be increased by 4.5%, and the power coefficient of CFJ blade can be boosted by 226.7% when the tip speed ratio is 1.52.

Flow Separation Control over an Airfoil Using Plasma Co-Flow Jet

A NACA0025 coflow jet airfoil model, including the inner and outer airfoils, was designed and manufactured through 3D printing technology. Using the duct connecting the leading- and trailing-edge slots formed by the inner and outer airfoils, eight plasma actuators are arranged in the duct and synchronously driven by two high-voltage alternating-current sources to realize the plasma coflow jet (PCFJ) flow control technique. The test angle of attack range is 8–30°, and the Reynolds number is 68,000. The induced airflow characteristics were studied, and the flow control mechanism of the PCFJ airfoil was explored using the detailed two-component particle image velocimetry technique. The results in the quiescent air show that in addition to the injection at the leading-edge slot and the suction at the trailing-edge slot, the actuators on the upper surface of the inner airfoil provide local flow acceleration and momentum injection. The results in the wind tunnel show that the PCFJ airfoil has a better performance in delaying flow separation, and its time-averaged flow separation position is delayed by 46% compared with the baseline airfoil. The mixing shear layer that becomes turbulent in advance and the subsequent coherent vortex structures, the injection at the leading edge and suction at the trailing edge, and local flow acceleration and momentum injection of the plasma actuators are the key factors for the mechanism of separation delaying of the PCFJ flow control technique.

Experimental Investigation of Lift Enhancement and Drag Reduction of Discrete Co-Flow Jet Rotor Airfoil

Rotor airfoil design involves multi-point and multi-objective complex constraints. How to significantly improve the maximum lift coefficient and lift-to-drag ratio of rotor airfoil is a fundamental problem, which should be solved urgently in the development of high-performance helicopter rotor blades. To address this, discrete co-flow jet (DCFJ) technology is one methods with the most potential that can be harnessed to improve the performance of the rotor airfoil. In this study, wind tunnel experiments are conducted to study the effect of DCFJ technology on lift enhancement and drag reduction of OA312 airfoil. Furthermore, the performance improvement effects of the open co-flow jet (CFJ) and DCFJ technologies are studied. In addition, the influence of fundamental parameters, such as the obstruction factor and relative unit length, are analyzed. Results demonstrate that DCFJ technology is better than CFJ technology on the performance enhancement of the OA312 airfoil. Moreover, the DCFJ rotor airfoil can significantly reduce the drag coefficient and increase the maximum lift coefficient and the stall angle of attack. The maximum lift coefficient can be increased by nearly 67.3%, and the stall angle of attack can be delayed by about 12°. The DCFJ rotor airfoil can achieve the optimal performance when the obstruction factor is 1/2 and the relative unit length is 0.025.

Numerical optimisation of a ship wind-assisted propulsion system using blowing and suction over a range of wind conditions

A Kriging surrogate model and a genetic algorithm are used to optimise the geometry of a ship wind assisted propulsion system (SWAP). The SWAP device is an actively controlled aerofoil mounted vertically on the deck of a ship in order to produce a forward propulsive force from the wind. The SWAP concept uses a circulation control system which employs both blowing from the leading edge and suction from the trailing edge. The aerodynamic parameters of the sail are found using a computational fluid dynamics (CFD) model validated against experimental data for a similar system, the coflow jet aerofoil. Further application of Kriging models is used to predict maximum lift coefficients for multiple freestream velocities, ensuring that the optimised device offers robust performance and low sensitivity to expected variations in wind speed. The maximum achievable lift coefficient was found to be 13.17% greater than for the baseline aerofoil over a range of wind speeds from 8–12 m/s.

EFFECT OF COFLOW ON SONIC JET

The sonic coflow effect on the core length of sonic primary jet was experimentally investigated in this research work. A circular convergent nozzle was used for both core and coflow jet studies. The 1mm annular gap was maintained between the coflow and core nozzles. The nozzle pressure ratio (NPR) was varied from 3 to 5, insteps of 1 for both the nozzles. For each primary NPR, the NPR of coflow was varied, and the shadowgraph flow visualization was carried out. From the shadowgraph visualization results it was observed that the sonic primary jet core length increases with increasing pressure ratio without coflow. With sonic coflow, the primary jet core length started to increase further with increasing coflow NPR. That is, the increase of sonic coflow NPR at each sonic primary jet NPR resulted in the elongation of core. Therefore, the introduction of coflow has resulted in core length elongation at all the levels of underexpansion. The primary jet core elongation due to the presence of coflow resulted in the weakening of shock strength in the primary jet core.

Numerical analysis of supersonic co-flow jet with varying lip thickness

PurposeThis study aims to present the numerical study on supersonic jet mixing characteristics of the co-flow jet by varying lip thickness (LT). The LT chosen for the study is 2 mm, 7.75 mm and 15 mm.Design/methodology/approachThe primary nozzle is designed for delivering Mach 2.0 jet, whereas the secondary nozzle is designed for delivering Mach 1.6 jet. The Nozzle pressure ratio chosen for the study is 3 and 5. To study the mixing characteristics of the co-flow jet, total pressure and Mach number measurements were taken along and normal to the jet axis. To validate the numerical results, the numerical total pressure values were also compared with the experimental result and it is proven to have a good agreement.FindingsThe results exhibit that, the 2 mm lip is shear dominant. The 7.75 mm and 15 mm lip is wake dominant. The jet interaction along the jet axis was also studied using the contours of total pressure, Mach number, turbulent kinetic energy and density gradient. The radial Mach number contours at the various axial location of the jet was also studied.Practical implicationsThe effect of varying LT in exhaust nozzle plays a vital role in supersonic turbofan aircraft.Originality/valueSupersonic co-flowing jet mixing effectiveness by varying the LT between the primary supersonic nozzle and the secondary supersonic nozzle has not been analyzed in the past.

Rotating co-flow jets with horizontal lip and shape transition

Purpose Control over large-scale coherent structures and stream-wise vortices lead to enhanced entrainment/conservation of the jet which is desirable for most free jet applications such as design of combustion chamber in jet engines and flame length elongation of welding torch used for metal cutting. Design/methodology/approach A co-flow nozzle with lip thickness of 2 mm, between the primary (inner) and secondary (outer) flow, is selected. Three nozzle combinations are used, i.e. C–C (circle–circle), C–E (circle–ellipse) and C–S (circle–square) for acquiring comparative data. For these nozzle combinations, inner nozzle exit plane is kept as a circle, whereas the outer nozzle exit planes are varied to circle, ellipse and square. The exit plane area of outer nozzle for the nozzle combinations has equivalent diameter, De. The nozzles are fabricated in a way that the outer nozzle can be rotated along the longitudinal axis, keeping the inner nozzle intact. Findings The C–C nozzle combination is effective in low Mach number regime in decaying the jet, when the rotational component is introduced. Around 30% reduction in the jet core length is observed for the C–C nozzle combinations without any lip. The C–E nozzle shows sedative result in decaying or preserving the jet. The C–S nozzle combination shows interesting phenomenon, whereby the low subsonic case tends to conserve the jet by 15% and the higher subsonic case tends to decay the jet by 10%. Originality/value The developed nozzle systems show both conservative and destructive effect on the jet, which is desirable for the mentioned applications.

Investigation of mixing characteristics of coflow rectangular nozzle of aspect ratio 2 and 3

PurposeThe purpose of this study is to understand experimentally the mixing characteristics of a two-stream exhaust system with a supersonic Mach 1.5 primary jet that exits the rectangular C-D nozzle surrounded by a sonic secondary jet from a convergent rectangular nozzle by varying the aspect ratio (AR = 2 and 3) similar to those that can be available for future high-speed commercial aircraft.Design/methodology/approachThis paper focuses on the experimental results of effects of AR at various expansion levels of jets issued/delivered from a central rectangular convergent-divergent nozzle of AR 2 and 3 surrounded by a coflow from a convergent rectangular sonic nozzle. The lip thickness of the primary nozzle is 2.2 mm. various nozzle pressure ratios (NPRs) ranging from 2, 3, 3.69 and 4 were chosen for pressure measurements.FindingsFor all the NPRs, AR 3 had a shorter core than AR 2. Also, AR 3 was found to decay faster in the transition and fully developed zones. The lateral plots show that the AR has an influence on the jet spread.Originality/valueThe structure of waves existing in the potential core of the rectangular coflow jet along with the major and minor axis planes was visualized by the shadowgraph technique.

Numerical investigation of critical lip thickness of subsonic co-flowing jet

Purpose The effect of increasing lip thickness (LT) and Mach number on subsonic co-flowing Jet (CFJ) decay at subsonic and correctly expanded sonic Mach numbers has been analysed experimentally and numerically in this study. This study aims to a critical LT below which mixing enhances and above which mixing inhibits. Design/methodology/approach LT is the distance, separating the primary nozzle and the secondary duct, present in the co-flowing nozzle. The CFJ with LT ranging from 2 mm to 150 mm at jet exit Mach numbers of 0.6, 0.8 and 1.0 were studied in detail. The CFJ with 2 mm LT is used for comparison. Centreline total pressure decay, centreline static pressure decay and near field flow behaviour were analysed. Findings The result shows that the mixing enhances until a critical limit and a further increase in the LT does not show any variation in the jet mixing. Beyond this critical limit, the secondary jet has a detrimental effect on the primary jet, which deteriorates the process of mixing. The CFJ within the critical limit experiences a significantly higher mixing. The effect of the increase in the Mach number has marginal variation in the total pressure and significant variation in static pressure along the jet axis. Practical implications In this study, the velocity ratio (VR) is maintained constant and the bypass ratio (BR) was varied from low value to very high values for subsonic and correctly expanded sonic. Presently, commercial aircraft engine operates under these Mach numbers and low to ultra-high BR. Hence, the present study becomes essential. Originality/value This is the first effort to find the critical value of LT for a constant VR for a Mach number range of 0.6 to 1.0, compressible CFJ. The CFJs with constant VR of unity and varying LT, in these Mach number range, have not been studied in the past.

Effect of Eccentricity on Co-flow Jet Characteristics

Effect of Eccentricity on Co-flow Jet Characteristics

Assessment of a Method to Enhance the Momentum of Water Mist: Co-Flow Jet Water Mist System

Assessment of a Method to Enhance the Momentum of Water Mist: Co-Flow Jet Water Mist System

Mixing efficiency of hydrogen and air co-flow jets via wedge shock generator in dual-combustor ramjet

Flame stabilization and distribution are highly significant for fuel combustion in supersonic vehicles. In this investigation, the effects of wedge shock generator on co-flow of air and hydrogen jet are studied by the computational method. The main emphasis of this work is to disclose the structure of the fuel jet in presence of wedge shock produced in the middle of the air and fuel injector. The impacts of wedge angle and total pressure of the air and fuel jets are also investigated. RANS equations are solved with the SST turbulence model for the modeling of high compressible flow inside the combustor. Our results that produced vortices behind the splitter fluctuated more intense total pressure of air and fuel jet increases instantaneously. It is also found that a lower wedge angle is more effective than a higher one for destabilization of the flam propagation inside the combustor of the DCR engine.

Two-Dimensional Numerical Study of the Pulsed Co-Flow Jet

Two-Dimensional Numerical Study of the Pulsed Co-Flow Jet

Large Eddy simulation of a supersonic lifted hydrogen flame with perfectly stirred reactor model

Large Eddy Simulation with a Perfectly Stirred Reactor model (LES−PSR) is developed to simulate supersonic combustion with high-enthalpy flow conditions. The PSR model considers the viscous heating and compressibility effects on the thermo-chemical state, through correcting the chemical source term for progress variable and incorporating absolute enthalpy as the control variable for the look-up table. It is firstly validated by using a priori analysis of the viscous heating and compressibility effects. Then an auto-igniting hydrogen flame stabilized in supersonic vitiated co-flowing jet is simulated with LES−PSR method. The results show that the shock wave structure, overall flame characteristics, flame−shock interaction and lift-off height are accurately captured. Good agreements of the velocity and mixture fraction statistics with the experimental data are observed. The results also show that the LES−PSR model can predict the mean temperature and mole fractions of major species quite well in both flame induction and stabilization zones. However, there are some under-predictions of temperature RMS by about 100−150 K, which may be due to the chemical non-equilibrium in the H2/O2-enriched combustion product of the co-flowing jet. The scatter plots of two probe locations respectively from induction and flame zones show that the respective flame structures in mixture fraction space are captured well. However, the flucturations of the temperature and species mole fractions are under-predicted in the flame zone. The shock-induced auto-igniting spots are captured by the PSR model. These spots are highly unsteady and play an important role in flame stabilization. It is also shown that the intense reactions are initiated at mixture fractions around the stoichiometry or fuel-lean values, corresponding to local elevated pressure (1.5−2.0 atm) due to shock compression. The results also demonstrate that the pressure elevation is shown to have significant effects on the most reactive mixture fraction and shortest ignition delay time.

Effects of an annular plasma actuator on a co-flow jet downstream of a bluff-body

The present study is to experimentally investigate flow interactions downstream of a bluff-body incorporated with an annular plasma actuator, potentially for flame stabilization application. The dielectric-barrier discharge (DBD) actuator, flush with the bluff-body, is operated with AC in both sine and square waves, creating an inward flow and facilitating air entrainment to the jet. Electrical measurements show the larger peak current and the higher dissipation power in square wave, in which the high variation rate of voltage favors the electron escape from the dielectric surface, resulting in a stronger discharge. In addition, a more diffusive discharge accompanied with a larger peak current is observed in the negative half-cycle while filament discharges are present in the positive half-cycle. The plasma-induced flow is confirmed to be positively charged due to the flow deflection in a lateral DC electric field. Schlieren imaging and particle image velocimetry (PIV) show that as the actuator is activated, the jet at low Reynolds number is more susceptible to develop into turbulence and a vortex ring, due to the secondary low-pressure region induced by the actuator, is formed downstream of the bluff-body. The vortex ring is advantageous to active flow control, and is shown to enhance flame stabilization.

(Non)Equilibrium of OH and Differential Transport in MILD Combustion: Measured and Computed OH Fractions in a Laminar Methane/Nitrogen Jet in Hot Coflow

Spatial distributions of temperature, major species, and OH mole fractions under moderate or intense low-oxygen-dilution (MILD) conditions in a laminar-jet-in-hot-coflow configuration were measured using spontaneous Raman and laser-induced-fluorescence methods. A preheated mixture of 18% CH4/82% N2 at 1100 K was used as fuel, while the products of a laminar, flat, premixed burner-stabilized flame with an equivalence ratio of 0.8 at 1550 K were used as the oxidizer. For comparison, experiments replacing the fuel by pure N2 were also performed. The measurements are compared with the results of numerical simulations performed using the GRI-Mech 3.0 chemical mechanism and a multicomponent mixture-averaged transport model. Analysis of the data shows that the maximum axial and radial temperature and OH mole fraction occur on the lean side of the stoichiometric mixture fraction. MILD combustion generates maximum OH mole fractions of ∼700 ppm in the radial profiles close to the burner exit and ∼300 ppm along the centerline, more than five times lower than those measured in equivalent methane/air diffusion flames. Overall, good qualitative and quantitative agreement is found between the results of detailed computations and experiments, with the maximum differences observed in the axial OH profiles, which are just outside the estimated experimental uncertainty. Analysis of the computational results shows that differential diffusion hinders the use of the mixture fraction to estimate the equilibrium temperature and species fractions, causing an overestimation of the stoichiometric temperature by ∼200 K. Calculating the equilibrium quantities based on the local (computed) species fractions shows an axial temperature profile that differs from that experimentally/computationally determined by less than 25 K. The analysis further shows that the measured OH mole fractions are roughly three times higher than the (locally determined) equilibrium value.

Aerodynamic performance enhancement of co-flow jet airfoil with simple high-lift device

The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet (CFJ) airfoil with simple high-lift device configuration, with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing. Computations have been accomplished by an in-house-programmed Reynolds-averaged Navier-Stokes solver enclosed by k-ω shear stress transport turbulence model. Three crucial geometric parameters, viz., injection slot location, suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift, drag, power consumption and equivalent lift-to-drag ratio. Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack. The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle. The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio. Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain, meanwhile, carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.

An integrated microfluidic platform to fabricate single-micrometer asymmetric giant unilamellar vesicles (GUVs) using dielectrophoretic separation of microemulsions.

We present a microfluidic technique that generates asymmetric giant unilamellar vesicles (GUVs) in the size range of 2-14 μm. In our method, we (i) create water-in-oil emulsions as the precursors to build synthetic vesicles, (ii) deflect the emulsions across two oil streams containing different phospholipids at high throughput to establish an asymmetric architecture in the lipid bilayer membranes, and (iii) direct the water-in-oil emulsions across the oil-water interface of an oscillating oil jet in a co-flowing confined geometry to encapsulate the inner aqueous phase inside a lipid bilayer and complete the fabrication of GUVs. In the first step, we utilize a flow-focusing geometry with precisely controlled pneumatic pressures to form monodisperse water-in-oil emulsions. We observed different regimes in forming water-in-oil multiphase flows by changing the applied pressures and discovered a hysteretic behavior in jet breakup and droplet generation. In the second step of GUV fabrication, an oil stream containing phospholipids carries the emulsions into a separation region where we steer the emulsions across two parallel oil streams using active dielectrophoretic and pinched-flow fractionation separations. We explore the effect of applied DC voltage magnitude and carrier oil stream flow rate on the separation efficiency. We develop an image processing code that measures the degree of mixing between the two oil streams as the water-in-oil emulsions travel across them under dielectrophoretic steering to find the ideal operational conditions. Finally, we utilize an oscillating co-flowing jet to complete the formation of asymmetric giant unilamellar vesicles and transfer them to an aqueous phase. We investigate the effect of flow rates on properties of the co-flowing jet oscillating in the whipping mode (i.e., wavelength and amplitude) and define the phase diagram for the oil-in-water jet. Assays used to probe the lipid bilayer membrane of fabricated GUVs showed that membranes were unilamellar, minimal residual oil remained trapped between the two lipid leaflets, and 83% asymmetry was achieved across the lipid bilayers of GUVs.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.