Forced Jet Research Articles

Retrofitting stoves with forced jets of primary air improves speed, emissions, and efficiency: Evidence from six types of biomass cookstoves

Incorporating jets of forced air into biomass cookstove combustion has been shown to potentially decrease harmful emissions, leading to a variety of designs in recent years. These have shown mixed success in terms of real-world performance, usability, and durability. The Jet-Flame forced draft retrofit accessory was recently developed to implement forced jets of primary air at a low cost into a wide range of types of cookstoves using a small 1.5-W fan housed in a low-cost cast iron body to be inserted beneath the fuel bed of a biomass cooking fire. This research sought to quantify the potential efficiency and emissions performance impacts of the Jet-Flame when installed in six different types of biomass cookstoves (three open or shielded fires and three rocket stoves) versus the natural draft performance of each. The effect of the operating fan voltage was also measured. A series of tests following a modified ISO 19867-1:2018 protocol were performed in the laboratory using the Aprovecho Laboratory Emissions Measurement System (LEMS) equipped with additional oxygen and temperature sensors. Results for each stove carefully tended with a single layer of sticks showed that the global average PM2.5 reduction with the Jet-Flame was 89 % relative to the natural draft cases, with larger relative improvements seen in the most rudimentary stoves. CO was reduced by a global average of 74 %, reaching tier 4 or 5 for all stoves. Thermal efficiency was also improved by 34 % when calculated without taking into account the energy content of the remaining char (or 21 % with char), illustrating the value of burning char to provide cooking energy rather than leaving it unburned in the combustion chamber as is common in many natural draft stoves. Time to boil was also reduced by 8 %. In addition, adjusting the voltage of the jet-flame assisted in modulating firepower, improving the usability of the stove. These results indicate a strong potential for the Jet-Flame to help reduce emissions and fuel consumption in a wide range of cookstove designs at a relatively low cost or need for changes in behavior, fuel, or cooking device. The unit also provides enhanced usability in terms of ease of startup, cooking speed, low PM emissions at high power, and burning char. Additional studies are needed to measure performance in the field and under a variety of operational conditions.

Hydrodynamic response of an annular swirling liquid sheet surrounding a forced gas jet

Gas–liquid coaxial injectors invariably involve a shear layer between a fast-moving gas stream and a slow-moving liquid stream. This shear layer within the confinement of a recess has a region of absolute instability beyond a critical momentum flux ratio. This causes the spray to exhibit self-pulsation at discrete natural frequencies. We apply sinusoidal acoustic forcing to the gas jet over a range of frequencies and amplitudes to explore the frequency response of the spray. The fluctuating spray width near the injector orifice is measured as a time-resolved tracer characteristic, and its power spectral density is used to determine the spectral response of the spray. The non-pulsating spray that involves a primarily convectively unstable shear layer responds unconditionally to all the forcing frequencies. However, for a self-pulsating spray, when the forcing frequency is far from the natural frequency and both are incommensurate, the spectral response involves both the frequencies, their linear combinations and harmonics representing a state of quasi-periodicity. When the forcing frequency is close enough or the amplitude is high enough, 1 : 1 lock-in is observed where the natural mode is suppressed completely and the spray behaves just like the unforced flow with the peak shifted to the forcing frequency. Combining the experimental observations and application of the van der Pol oscillator model, we could demonstrate the analogous behaviour of this multiphase system with other hydrodynamically self-excited systems with external forcing. The results presented here can prove significant in understanding the dynamics of the atomization process in thermoacoustic coupling and possible control of it.

Unsteady test technique of jet control with multi-parameter coupling

In this paper, the jet control effect of air vehicle is studied, and a new multi parameter coupling unsteady test technique is established, which can ensure that the test model is consistent with the real air vehicle, and the jet is carried out under the condition of complete freedom and no support constraints, so that the wind tunnel test can better simulate the jet control effect of real air vehicle. The new technique overcomes the shortcoming that the previous jet test can only carry out unsteady flow field or unsteady aerodynamic force research, and can ensure that in the whole process of jet flow, the interference flow field at the nozzle, the aerodynamic force of the air vehicle, especially the movement of the air vehicle, are coupled with each other all the time, so as to achieve the same effect as the real air vehicle. The establishment of the new technique overcomes many problems, including the total length of the model is 167 mm, no support for the model, storage of small volume/high-pressure gas in free state, on-time unlocking of sealed gas source in free state of the model, and connection of gas source and nozzle in the model. The test results show that when no jet, the revolution body is head up, which affected by the cavity shock wave. When jet on, the jet force continues to act on the revolution body, resulting in the revolution body lowering its head until it diverges. The new technique can achieve more advanced technical indicators, including: ensuring jet Mach number >1; Ensure that the static pressure ratio of the jet is more than 10 (the static pressure ratio can be greater at hypersonic speed). After the establishment of the new technique, the supersonic wind tunnel test is carried out, and the ideal test results are obtained, which shows that the new technique is reliable.

Effect of Arc Behaviour and Metal Transfer Process on Aluminium Welds during Ultrasonic Frequency Pulsed GMAW

In order to study the influence of a novel current waveform control method of ultrasonic-frequency pulse (UFP) on arc behaviour, metal transfer process and the welds formation, monitoring system and image processing algorithms were employed for extracting the welding characters. Mechanics, defect, microstructure and mechanical property analysis based on pulsed GMAW was carried out. The results showed that, compared with the conventional pulsed GMAW, the ultrasonic-frequency pulse not only increased axial arc plasma jet force, arc force and droplet falling acceleration, but also suppressed the welded porosity formation, decelerated the microstructure regional element segregations, refined the grain and increased the microhardness property of welded joint. The study helped to reveal the mechanism for improving welding quality of ultrasonic-frequency pulsed GMAW.

Wave cancellation in jets with laminar and turbulent boundary layers: The effect of nonlinearity

In this work we perform real-time control of forced jets based on a wave-cancellation scheme. Building on previous work on control of stochastic disturbances, here we carefully characterize the performance and limits of this control approach with the onset of nonlinearities. The breakdown of linearity and its impact on control performance are illustrated through a thorough comparison between jets with laminar and turbulent boundary layers.

Aerodynamic characteristics of co-flow jet wing with simple high-lift devices

Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet (CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift, reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one, which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.

High-efficiency casing perforation oil and gas wells

The energetic capabilities of a high-speed jet of an aqueous solution of polyethylene oxide (PEO) with varying concentration and different outflow pressures from a jetforming nozzle were investigated using the length of the forming channel in the model of the casing of an oil and gas well, cement sheath and rock layer, as well as impact of the jet force on a metal plate fixed on a physical pendulum. The experimental data made it possible to obtain a calculated dependence in a dimensionless form to determine the quality (initial sections) of jets of aqueous solutions with different concentrations and molecular weights of PEO, considering the real parameters of the jet-forming nozzles of the hydroperforator. A comprehensive study of the perforation process made it possible to substantiate the mechanism of the high destructive capacity of a high-speed jet of polymer solution. It has been established that the mechanism of the high destructive capacity of the polymer water jet is not due to the Toms effect, but caused by the destructive action of the dynamic pressure of the polymer water jet «reinforced» by strongly unfolded macromolecular chains under the action of a tensile flow in the inlet area of the jet forming nozzle of the hydroperforator. Keywords: perforator; jet nozzle; jet quality; casing; cement sheath; rock; Toms effect.

Analysis of geometric and non-geometric parameters in a Coanda device for marine applications

This numerical study comprises the geometric evaluation of turbulent, steady-state, two-dimensional, and incompressible flows over the Coanda effect-based H.O.M.E.R. (High-Speed Orienting Momentum with Enhanced Reversibility) nozzle. The main purpose is to evaluate the influence of the central septum insertion (P) and change in dimensionless mass flow rate between two inlets (m*) over the deflection angle of the mixed jet (α), velocity fields (V), and thrust forces per unit length (F) at the nozzle exit. The time-averaged conservation equations of mass and momentum have been solved using the Finite Volume Method for all simulations. Turbulence closure is solved using RANS (Reynolds-Averaged Navier–Stokes) and standard k-ε modeling. Results show the septum insertion associated with the mass flow rate difference as possible important parameters for controlling the exit jets and forces generated in the device. Moreover, higher magnitudes of m* associated with a high intruded septum (P = 11 mm) in the device led to the highest magnitudes of forces in the y-direction, while intermediate configurations of m* and P are best for maximizing forces in the x-direction. For the present conditions, the forces generated in the y-direction are almost four times higher than that generated in the x-direction, indicating that this device can be suitable for maneuverability purposes.

Simulation of the turbulent axisymmetric bluff body wake with pulsed jet forcing

A turbulent axisymmetric bluff body wake is investigated using large eddy simulation to uncover key flow dynamics and structures. The effect of low-frequency and high-frequency pulsed jet forcing at the point of separation is studied to reveal the underlying mechanisms involved in the base pressure changes, which provide a reference for bluff body drag reduction and active flow control.

Real-time reactive control of stochastic disturbances in forced turbulent jets

In this work we perform reactive control of axisymmetric disturbances in turbulent jets. The disturbances are produced by an external forcing and possess stochastic phases and amplitudes, akin to turbulent fluctuations found in unforced jets. The control law is based on an existing inverse feedforward scheme developed for transition control. Here we apply it to control convective growth mechanisms in fully turbulent jets and we build on previous works that considered control of harmonic disturbances. We demonstrate the successful implementation of real-time reactive control of the disturbances and achieve order-of-magnitude attenuations of velocity fluctuations.

Momentum Coefficient Governing Discrete Jet Actuation for Separation Control

Amplitude scaling laws for active control of boundary layer separation using discrete jet forcing are not fully established. Momentum coefficient is the most widely accepted scaling parameter, but accurate measurement and assessment of the employed assumptions are often not documented or even attempted. This work discusses various methods for experimentally determining the momentum coefficient produced by fluidic oscillators. Complementary simulations of the actuator are performed using delayed detached eddy simulations to validate the methods and offer explanations for shortcomings in the experiments. Scaling methods are applied to the experimental study of separation control on the suction side of a type II Glauert airfoil, otherwise known as the NASA hump model. An array of fluidic oscillators is located at and used to control separation over a range of Reynolds numbers () for various actuator sizes and spacings . Integrated surface pressure measurements are used to determine the suitability of various momentum coefficient definitions for scaling the flow control efficacy. It is found that the momentum coefficients obtained using direct measurements of actuator plenum or throat pressure govern scaling with respect to both Reynolds number and actuator size. This is independent of the sweeping frequency in the range surveyed.

Vorticity transports in turbulent channels under large-scale control via spanwise wall jet forcing

Vorticity transport in turbulent channels under large-scale active drag control (i.e., spanwise opposed jet forcing) is investigated via direct numerical simulation of the Navier–Stokes equation. The skin-friction coefficient is newly expressed by the volume integration average of the mean flow dissipation expressed in terms of the spanwise vorticity (Ωz), and the turbulent transports of the spanwsie vorticity fluctuation (−v′ω′z) and of the wall-normal vorticity fluctuation (w′ω′y). Three Reynolds number cases (i.e., Reτ=180,395, and 550) with notable drag reductions (i.e., 18%, 16%, and 15%, respectively) are examined, following the setup in Yao et al. [Phys. Rev. Fluids 2, 062601(R) (2017)]. The transports of vorticity fluctuations dominate the contributions to the frictional drag, consistent with previous results for the passive drag reduction strategy of slip-wall [Yoon et al., Phys. Fluids. 28, 081702 (2016)]. Specifically, the effect of −v′ω′z is to increase drag (due to sweeping −v′), while w′ω′y decreases the drag. A triple decomposition (mean, coherent, and random) reveals the random −v″ω′′z as the only term adding to drag, while the random w″ω′′y and the coherent −ṽω̃z and w̃ω̃y transports all decrease the drag. Weighted joint probability distribution function (p.d.f.) of v″ and ω′′z shows a transition from the first–third quadrant dominance (hence positive-correlated) near the wall to the second–fourth quadrant dominance (hence negative-correlated) away from wall. In contrast, w″ and ω′′y are negatively correlated in the entire region. The analysis here suggests that the suppression of random spanwise-vorticity transport (v″ω′′z) is the target for more effective drag reduction under the current method.

Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

Direct numerical simulation of forced turbulent round jet: Effect of flow confinement and varicose excitation

Direct numerical simulation of a turbulent round jet subjected to varicose excitation has been carried out. The effect of domain size and waveform used for providing varicose excitation have been studied with the help of time-averaged mean, fluctuating quantities, and instantaneous isosurfaces of the Q-criterion. Initial evolution of the jet suggests that the secondary instability is delayed in time with an increase in the domain size irrespective of the waveform. It has also been observed that the secondary instability manifests stronger for the square wave based excitation as compared to sinusoidal excitation for the smaller and medium domains. In addition, simulations demonstrate that the aforementioned secondary instability is sustained in the long term for small and medium domains. In the case of a confined domain, simulations indicate that square wave based excitation leads to greater enhancement in mixing and entrainment characteristics of the jet when compared to sinusoidal excitation. We demonstrate that sine pulsing at the inlet excites energy up to the second harmonic of the preferred mode while square pulsing excites energy (at least) up to the fifth harmonic which results in more energetic small-scales structures in the far field which in turn augment the mixing characteristics of jet. Qualitative assessment of vortical structures indicates that differently excited jets gradually become similar in the far field of large domains owing to the availability of sufficient amounts of fluid for entrainment. This behavior has also been quantitatively established by means of axial and lateral profiles of both time-averaged as well as fluctuating quantities characterizing the pulsed jet.

A Note on Leakage Jet Forces: Application in the Modelling of Digital Twins of Hydraulic Valves

The proper modelling of fluid flow through annular gaps is of great interest in leakage calculations for many applications in fluid power technology. However, while detailed numerical simulations are certainly possible, they are very time consuming, in various cases prone to numerical instabilities and may not even include all physically relevant effects. This is an issue especially in system simulations, where a large set of computations is needed in order to prepare the lookup-tables for the required input fields. In this work, an analytical approximation for the shear force, which is induced by viscous flow between two eccentric cylinders, is presented. This relation, and its derivation, mimics and enhances the well-known Piercy-relation for the corresponding volume flow that is utilized in state-of-the-art system simulation tools. To determine its range of validity, the analytical relation for the shear force is compared to 3D-simulations. Additionally, an application of this approximation for creating digital twins of hydraulic valves is also discussed in this work.

Research on Anti-reflection Measures of Hydraulic Reaming of Low Permeability Soft Coal Seam in Goutou Coal Mine

According to the C5 coal seam of gully head coal mine complex geological conditions Poor permeability gas pressure is big Coal seam gas content is high Soft coal extraction from standard time is long, etc., combined with high pressure water jet force reaming technology principle and characteristics of the gully head coal mine is put forward using the method of integration of bottom hole drill wear layer expansion technical measures to increase coal seam permeability, and within the scope of the field to carry out the experimental study. In soft coal seam through field experiment research shows that the drilling construction process, through the integration of enlarging anti-reflection technology measures, can effectively improve the exposed area of a single layer of bore, change of coal seam and the stress distribution state of joints, thus improve the wear layer drilling drainage concentration and smoke volume, shorten the wear layer drilling extraction from standard time to the success of the test for the mine and similar mine to improve coal seam permeability is to provide the basis.

A simplified dynamic model and control for a multiple launch rocket system

Multiple launch rocket system, a type of launching platform used to launch kinetic load to hit the target, is an extremely complicated mechanical system with strong vibration because of the jet force. In this study, a nonlinear dynamic model and vibration control of a multiple launch rocket system are presented to reduce vibration and improve position accuracy. A simplified dynamic model of the multiple launch rocket system is derived using the Newton–Euler method, which facilitates the controller design considering the strong complexity of the multiple launch rocket system. On this basis, the feedback linearization technique is introduced to design a nonlinear controller based on the deduced dynamic model. The simulated and experimental results show that the simplified dynamic model–based control effectively can reduce vibration level of the launching system and make the azimuth and elevation angles reach the desired values with smaller error despite of each rocket’s jet force.

Impulse mode of physical and technical gases parameters control based on the jet force action effect

This paper presents the results of research on the use of the jet force action effect for physical and technical gases parameters monitoring systems and devices. Authors considered and proposed the impulse mode of physical and technical gases parameters control based on the jet force action effect, which provides high accuracy and sensitivity measurements, and presented possible control devices based on the use the impulse mode of physical and technical gases parameters control: the density sensor used for single-component gases parameters control and the sealing capacity control sensor used for binary mixtures parameters control. For each device were determined static characteristics and the physical, technical and design parameters, which ensure a high level of sensors accuracy and sensitivity.

Inner–outer interactions in a forced plane wall jet

A plane wall jet (PWJ) is used as the model flow field to study the interactions within complex wall-bounded flows. The PWJ is subject to large-scale, large-amplitude forcing, and the subsequent scale interactions, in the forced flow, are characterized using time-resolved particle image velocimetry. These interactions are contrasted with those of the unforced flow. It is observed that the energy of the large-scale structures in the wall region is significantly increased by the forcing. It is unambiguously shown that the PWJ encapsulates an inner–outer interaction in the form of an amplitude and frequency modulation of the finer scales, by the outer representative large scale. In addition, this amplitude and frequency modulation effect is enhanced by the forcing over most of the wall-normal extent of the flow. This is particularly true in the near-wall region. Considering a structural perspective of the flow suggests that the flow scales responsible for the increased modulating effect are the forward-leaning boundary-layer-like structures of the flow.

Датчики быстроизменяющегося давления на основе силового действия струи

Static and dynamic characteristics of rapid response pneumatic digital systems are determined with the help of pneumatic-galvanometric sensors that consist of pneumatic optical converters, electrical bridge circuits and magnetoelectric galvanometers. This paper presents theoretical and experimental studies of the pneumatic optical converter whose mode of operation is based on the jet force effect on a plate of limited dimensions commensurate with the dimensions of the contact area between the jet and the plate. The investigations are based on the equality of moments of the jet force and the counter-moment of the rod that the plate is fixed on. The sensitivity and other static characteristics of the converter (linearity, measurement rage) as well as other parameters necessary for interpreting the readings, calculating errors and calibrating the scale are determined. The natural frequency is sufficient to control dynamic processes controlled by pneumatic systems. For the design of converters, it is proposed to use the aggregate criterion of the quality factor that equals the product of the sensitivity and the natural frequency squared. The performed calculations are verified by experiments.