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Copyright of Acta Scientiarum Naturalium Universitatis Sunyatseni / Zhongshan Daxue Xuebao is the property of Sun-Yat-Sen University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigates the dynamic internal flow structure, and its outlet jets, of the fluidic oscillator. The objective of this numerical study is to provide a better understanding of this type of jet for a research domain aimed at improving various aspects of fluid flow control. The present work focuses on the two-output fluidic oscillator, which involves no moving parts in direct contact with the flow. An analysis of the internal and external dynamics of the two-output fluidic oscillator using numerical simulations for compressible air flow was investigated by employing the SST turbulence model. The study highlights the periodic oscillation of the jet inside the fluidic oscillator between the two branches driven by the Coanda effect, which characterizes the oscillatory behavior of the fluidic oscillator. Furthermore, it reveals the importance of controlling the inlet pressure to maintain the oscillatory behavior. The results demonstrate that the outlet velocity is influenced by the inlet conditions as well as the system's geometry. In conclusion, the article provides essential insights into the dynamics of the two-output fluidic oscillator, emphasizing the impact of physical and geometrical control parameters on flow behavior.

This study addressed the challenges of vortex formation and dead air zones in traditional long-pressure short suction ventilation and dust removal systems. By leveraging the Coanda effect, the system's structure was optimized through the nesting of the exhaust and pressure ducts. This design enhanced airflow in the negative pressure duct, promoting adherence to the tunnel walls, reducing dust dispersion, and significantly lowering energy consumption. Simulations utilizing flow field analysis and discrete phase model (DPM) revealed an optimal pressure-extraction ratio of 2∶3. Under this ratio, results indicated that the optimized system reduced dust concentrations at the driver's position and downwind side by 5.56% and 55.41%, respectively, compared to traditional systems. With the structure and pressure-extraction ratio established, further improvements in dust removal efficiency were achievable through parameter regulation. Key parameters included the distance between the duct and the dust-producing surface, the distance from the duct's central axis to the ground, and the distance between the pressure and extraction ducts. Convolutional neural network (CNN) was employed for intelligent parameter control, enabling the identification of optimal parameters for varying initial dust concentrations. Experiments conducted on 45 parameter regulation schemes using a scaled-down experimental platform demonstrated that the CNN model outperformed BP neural networks in accuracy and stability for dust concentration predictions. When initial dust concentrations at the driver's position and downwind side ranged from 300 to 900 mg/m3, the optimized system achieved an average dust concentration reduction of 51.49% to 83.88%, thereby validating the effectiveness of parameter control.

Supersonic sweeping jets (SWJs) have demonstrated their effectiveness across a variety of scenarios, particularly in aeronautic applications (e.g., lift enhancement). An experimental study is conducted to investigate the characteristics of SWJs emitted from actuators with different spreading angle θ and exit length θ. Schlieren visualization is used to capture the near- and far-field SWJs at nozzle pressure ratios (NPRs) ranging from 1.6 to 6.9. The results show that as NPR increases the SWJs become underexpanded when θ≠0. Different θ have an impact on the shock structure and the law of the spreading angle of jet control area θ changing with NPR. When θ is approximately 100 deg, θ increases at first and then decreases with increasing NPR, reaching up to 90 deg at high NPRs. When θ is about 50 deg, θ remains roughly constant and equal to θ. Internal flow measurements reveal that flow attachment caused by the Coanda effect plays a significant role in the mechanism that leads to a change in θ. Proper orthogonal decomposition is applied to analyze the spatial and temporal patterns. Far-field measurements show multiple sound waves propagating upstream and downstream, which generated by the supersonic SWJs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

Ore collection devices are important for the collection of deep-sea polymetallic nodules. Based on the CFD-DEM solid–liquid two-phase flow coupling calculation method, this paper simulated the rise and transport phases of polymetallic nodules using the Coanda effect ore collection device. The validity of the numerical simulation method was confirmed through experimental testing. On this basis, the effects of different working and structural parameters on the collection rate were studied. The results indicate that the flow rate of the collection jet and the bottom clearance were the primary factors affecting the collection rate of the polymetallic nodules. An increase in the collection jet flow rate leads to a substantial rise in the collection rate of polymetallic nodules. Conversely, an increase in bottom clearance results in a decrease in the collection rate. A collection rate exceeding 90% can be achieved in both scenarios: a 10 mm bottom clearance with an 8 m/s collection jet flow rate, and a 30 mm bottom clearance with a 10 m/s collection jet flow rate. The collection nozzle slant angle has no substantial impact on the collection rate, and the recommended collection nozzle slant angle is 35° to reduce energy loss. [ABSTRACT FROM AUTHOR]

The Coanda effect is a fluid dynamics phenomenon in which a fluid jet adheres to a convex or flat surface. This effect occurs when a liquid or gas jet emerging from an orifice clings to an adjacent surface and entrains the surrounding fluid, creating a lower-pressure region along its path that maintains its attachment to the surface. The Coanda effect accounts for the behavior of blood flow in the fetal right atrium and the dispersion of eccentric mitral regurgitation jets along atrial walls. This series of interesting images depicting a large 4 × 3.75 cm saccular intracranial aneurysm suggests that the Coanda effect may play a role in the pathophysiology of intracranial aneurysms and could be an underlying factor in their formation, progression, or rupture. [ABSTRACT FROM AUTHOR]

Seabed mining is a potential solution for diversifying the supply chains of various raw materials required for zero-emission industrial products. The design of a nodule-lifting apparatus in a seabed mining electric vehicle is a crucial step because it significantly affects the mining efficiency of the entire system. Although the physical properties of polymetallic nodules are vital external parameters, little attention has been paid to their effect on the design of nodule-lifting apparatuses. This study aims to analyze and model the physical properties of the polymetallic nodules, expand the conventional numerical model to deal with more diverse physical properties of the nodules, apply probabilistic analysis to evaluate the harvesting rate, and establish a design methodology to efficiently determine the best feasible design. The advantages of the proposed framework are that it enables: (1) quantification of the physical properties of the seabed polymetallic nodules, (2) consideration of these physical properties in the computational simulation of the nodule-lifting apparatus, (3) efficient evaluation of the harvesting performance of the nodule-lifting apparatus through an information criterion-based probabilistic analysis, and (4) effective design of the nodule-lifting apparatus with an orthogonal array and rule-based decision-making strategy. [ABSTRACT FROM AUTHOR]

Coandă-effect-based collection stands out as the foremost technology in polymetallic-nodule mining due to the absence of direct contact between the collector and the ocean floor. Yet, this collection method disturbs the ocean floor, and minimizing such disturbance is crucial from an environmental viewpoint. To this end, a solid understanding of the interplay between the collector and the sediment bed is required. Therefore, we carried out a series of small-scale experiments, where a collector drives over a subaqueous clayey bed. These experiments provide the very first quantitative data on cohesive sediment erosion caused by a moving Coandă-effect-based collector, as well as on turbidity currents generated behind the collector head. This paper discusses the observations and findings derived from these experiments. Our findings reveal a logarithmic relationship between erosion depth and the flow impinging force applied on the clayey bed. An increased flow rate in the collection duct results in a slower turbidity current generated behind the collector head. This study enhances the ability to forecast sediment erosion caused by Coandă-effect-based collectors, offering the possibility to optimize the collector operational conditions and minimize the magnitude of the resulting sediment plumes.

This work investigates the effects of a jet issued from the trailing edge of the wing on to the suction surface of a slotted flap, working at high angles of deflection, 30 ∘ to 50 ∘ . The deflection angle of the flap, the jet velocity, and the jet temperature affects the aerodynamic performance of the wing. Three different jet velocities at the same jet temperature, three different jet temperatures at the same jet velocity, and three different flap deflection angles at the same jet inlet parameters are used to study these effects. The effect of the jet is analyzed using pressure, temperature, and wall shear stress profiles on the surfaces of the wing and the flap. Deviations in lift and drag of the wing and the flap are analyzed. It was found that the jet flushes out the flow separation over the flap, resulting in increased lift. Due to the Coandă effect, the jet attaches itself to the suction surface of the flap. At very high deflection angles, the jet cannot completely remove the flow separation. The ventilated flow from the slot effectively insulates the flap surface from the high temperatures of the trailing edge jet. [ABSTRACT FROM AUTHOR]

The characteristics and control of supersonic jet are hot issues in propulsion system, especially the rectangular underexpanded supersonic jet. In this research, we developed a passive fluidic thrust vectoring nozzle, the characteristics of the shock structure varying with nozzle pressure ratio (NPR) under three working modes were captured by schlieren flow visualization, and the flow topological structures were summarized. The results indicated: when the nozzle was working under the fist mode, the main wave system was "induced shock wave—separated shock wave". When the the nozzle was working under the second mode, the typical structure "oblique shock wave—compression wave" can be separately observed during NPR 3.0–3.8. When the the nozzle was working under the third mode, the non-symmetric expansion appeared on both sides of the jet, then the jet achieved deflection, the maximum vector deflection angle was 10.5° under NPR 3.0. The deflection of the supersonic jet can be realized by switching of the nozzle mode. [ABSTRACT FROM AUTHOR]

In the realm of aviation, jet propulsion systems serve to provide enhanced maneuverability and to make sure that the aircraft thrust is accurately and precisely regulated during take-off and landing operations. The movement of aerodynamic control surfaces (flaps, slats, elevators, ailerons, spoilers, wing attachments) determines the mobility of practically all aircraft types. Recognized as dependable components in the aviation world for take-off and landing tasks, these control surfaces are being replaced by fluidic thrust vectoring (FTV) systems, especially in small unmanned aerial vehicles (UAVs) and short or vertical take-off and landing aircraft. The FTV system is capable of directing thrust in any preferred direction without the need for any movable components. This paper numerically examines the FTV system by utilizing computational fluid dynamics (CFD) and an optimization technique based on gradients of the system components to understand the physics of the Coanda effect in FTV systems. This research employs gradient-based optimization for nozzle design in order to optimize the parameter space for different velocity ratios (VR) by calculating the moment around the upper Coanda surface, which is used to represent the jet deflection angle. In that context, four different Coanda surface-pintle pair designs for four different VRs are produced. The parameter space shows significant improvement in all four configurations, and results reveal that all output parameters successfully delay separation on the thrust vectoring system's upper Coanda surface. Finally, four optimum design suggestions are tested at various VRs, and the most efficient and proper design is recommended based on output parameters.

Fluidic thrust vectoring (FTV) control is a cutting-edge method used to manipulate the motion of an unmanned air vehicle when traditional control surfaces like elevators are not available. The primary purpose of employing FTV is to make the aircraft less detectable. This research centers around the exploration of the co-flow variation of the FTV concept. In this approach, a secondary jet with a significant velocity is injected into the boundary layer of the primary jet. As a consequence, the primary jet is diverted, leading to the formation of a pitch moment. Numerical simulations were conducted to analyze different ratios of secondary and primary jet velocities, providing valuable insights into the effectiveness of the proposed technique. The test rig, designed with a pitch-constraint dynamic setup, utilized electric ducted fans to generate primary and secondary flows. At 19 m/s primary velocity, the experimental testing shows a maximum vertical force of 0.4 N, producing a deflection of 25°, which is deemed adequate for thrust vectoring. This research builds upon the authors' previous work on characterizing a static co-flow FTV rig. The comparison between the computational fluid dynamics analyses and the experimental results demonstrates agreement in the behavior of the vectored jet. This validation further strengthens the findings presented in this paper. [ABSTRACT FROM AUTHOR]

An internal unsteady compressible flowfield of a pulsed jet actuator (PJA) is simulated by unsteady Reynolds-averaged Navier-Stokes (URANS) and large-eddy simulation (LES) frameworks. The PJA's feedback loops are short enough to have non-negligible jet switching time compared to the oscillation period. The results show that within a range of inlet pressure (which is the only control parameter) where the jet goes from subsonic to supersonic regime, the oscillation frequencies and the exit velocity waveform predicted by LES are in better agreement with the measured data than those predicted by URANS. Although URANS is able to capture the flowfield inside the feedback loops, it fails to predict the exit jet dynamics, unlike LES. This indicates the importance of a proper resolution of turbulence in the interaction region where jet switching occurs. Using LES data, it is found that the total jet switching time remains constant as the inlet pressure changes. It is also found that only the part of the jet switching period that ends at the first moment when the jet attaches to the opposite wall is involved in the oscillation period. Therefore, a new lumped model is proposed to estimate the oscillation frequency, which also explains the trend observed for the low inlet pressure values. [ABSTRACT FROM AUTHOR]

In the realm of aviation, jet propulsion systems serve to provide enhanced maneuverability and to make sure that the aircraft thrust is accurately and precisely regulated during take-off and landing operations. The movement of aerodynamic control surfaces (flaps, slats, elevators, ailerons, spoilers, wing attachments) determines the mobility of practically all aircraft types. Recognized as dependable components in the aviation world for take-off and landing tasks, these control surfaces are being replaced by fluidic thrust vectoring (FTV) systems, especially in small unmanned aerial vehicles (UAVs) and short or vertical take-off and landing aircraft. The FTV system is capable of directing thrust in any preferred direction without the need for any movable components. This paper numerically examines the FTV system by utilizing computational fluid dynamics (CFD) and an optimization technique based on gradients of the system components to understand the physics of the Coanda effect in FTV systems. This research employs gradient-based optimization for nozzle design in order to optimize the parameter space for different velocity ratios (VR) by calculating the moment around the upper Coanda surface, which is used to represent the jet deflection angle. In that context, four different Coanda surface-pintle pair designs for four different VRs are produced. The parameter space shows significant improvement in all four configurations, and results reveal that all output parameters successfully delay separation on the thrust vectoring system's upper Coanda surface. Finally, four optimum design suggestions are tested at various VRs, and the most efficient and proper design is recommended based on output parameters. [ABSTRACT FROM AUTHOR]

Landfill aeration may cause economic problems due to the amount of power consumed by blowers. Thus, this study proposes the use of an air amplifier to reduce the power consumption of air injection into landfills. The developed air amplifier is an aerodynamic device that induces a large amount of airflow using a small quantity of compressed air caused by the Coanda effect. Field experiment results demonstrated that the use of the air amplifier reduced power consumption by at least 90% and showed an air amplification effect of approximately 3.5 times compared with existing in-situ aeration systems. After aeration, the methane (CH4) reduction efficiency was 90.3%. The CH4/CO2 ratio was 0.12 (0.06-0.25) on average, and the CH4/CO2 ratio decreased as the oxygen concentration increased. Thus, the air amplifier is a low-cost solution for landfill aeration systems. In addition, aeration using existing leachate collection and drainage pipes was found to be more economical than air injection using air injection wells. However, despite the air injection, approximately 20% of organic carbon was decomposed anaerobically. The CH4/CO2 ratio range of 0.56-0.90 was presented as a criterion for categorizing a landfill as semi-aerobic. [ABSTRACT FROM AUTHOR]

The Coanda effect is a tendency of flowing fluid to follow the solid surface rather than to separate under the inertial effect. This paper presents the effects of surface curvature on the Coanda angle and jet deflection for a vertical jet impacting a horizontal cylinder (of diameter D) with Froude numbers Fr = 4.74 and 6.33. The penetration depth h of the cylinder in the jet is varied from h/D = 0.01-0.4 while the jet-to-cylinder diameter ratio d/D is varied from 0.11 to 2.0. For Fr = 4.74, the round jet impacting the cylinder evolves into a planar jet for d/D £ 0.40 where the jet deflection is positive, dictated by the Coanda effect. The deflection of the jet is negative for d/D = 0.60 and 0.83 where the bouncing (inertial) effect overwhelms the Coanda effect. Fr = 4.74, the jet deflects in the positive direction, regardless of d/D. With increasing h/D or decreasing d/D, both deflection and Coanda angles monotonically increase. An intermittent switch of the jet from one side of the cylinder to the other is observed for certain curvature of the cylinder, ascribed to the competition between bouncing and Coanda effects.

The flow surrounding a frigate is characterized by high-velocity gradients and flow detachment behind the superstructure of the ship. Therefore, the helicopter pilot's workload during the recovery maneuvers above the flight deck can increase. Different techniques of flow control have been tested for reducing the flow detachment and pilot workload. In this paper, a combined numerical optimization and experimental tests in a wind tunnel are performed to analyze the implementation of the Coanda effect at the back part of the hangar as an active flow control technique to reduce the flow detachment above the flight deck. The numerical optimization is conducted by testing different velocities and geometries of the Coanda hangars tested. The best results show a complete elimination of the flow detachment above the flight deck and an up to 2.85 times reduction of the low-speed area with respect to the base case. The geometries selected from the numerical results were installed in a scaled simple frigate shape 2 (SFS2) and tested in a wind tunnel with particle image velocimetry (PIV). The experimental results also show a drastic reduction of the flow detachment above the flight deck combined with reduced levels of turbulence intensity at the height where the helicopter rotor must operate during the recovery maneuver. [ABSTRACT FROM AUTHOR]

An efficient propulsion system holds the key to the smooth operation of any aerospace vehicle over different flight regimes. Apart from generating the necessary thrust, emphasis has also been laid on vectoring the direction of thrust. The primitive modes of thrust vectoring chiefly focused on mechanical means such as the use of gimbals or hinges. The current state-of-the-art technologies demand more efficient methods for thrust vectoring, which minimize the use of mechanical components. These methods termed fluidic thrust vector control methods, employ secondary jets for achieving the required attitude, and trajectory of the aerospace vehicles such as aircraft, rockets, and missiles. Such methods have greatly helped in reducing vehicle weight, vehicle maintenance requirements, and enhancement of stealth characteristics of such vehicles. This work presents a review of the various fluidic thrust vectoring systems, starting with a brief overview of traditional thrust vectoring systems, followed by a discussion on the various aspects of fluidic thrust vectoring systems. It also highlights the effect of the various geometrical and operating conditions on the performance parameters of the thrust vectoring system such as the thrust vector angle, system thrust ratio, and thrust vectoring efficiency among others. For ensuring the comprehensive character of this work, synthetic jet vectoring techniques have also been included due to their nonmechanical nature and similarities with purely fluidic thrust vectoring techniques. [ABSTRACT FROM AUTHOR]

• Static gas wave refrigerator (SGWR) realizes gas refrigeration through pulsed shock waves and expansion waves generated by pressure energy. • Full feedback jet oscillator as the pulsed jet trigger. Its switching mechanism is illustrated, and the structure is optimized. • The oscillation frequency can be well estimated through the jet switching frequency simplified equation derived. • The jet frequency control method can make the gas wave tube operate at the refrigeration's peak frequency, thus improving SGWR refrigeration efficiency. Static gas wave refrigeration (SGWR) is a mechanic equipment with no moving parts which realize refrigeration by working on gas through pressure energy. This paper introduces full feedback jet oscillator as the jet distributor of the gas wave refrigerator and shows the switching mechanism of the oscillator in detail through dynamics description. The range of influence of wedge distance (distance between wedge tip and the nozzle) on the pressure retention rate and frequency at the oscillator outlet is discussed, and a SGWR experiment platform is set up to make comparison of the pressure waveform as well as cooling efficiency of the impulse jet from two oscillators with different wedge distance in the gas wave tube. The result shows that jet oscillator performance varies along with the wedge distance, thus influencing the cooling efficiency. To expand the efficient operation range, the principle of jet frequency changing and the impact of narrowing the oscillator structure on jet frequency are discussed in detail, the variation rule equation of the jet switching frequency is derived. Matching experiments of jet oscillator and size of gas wave tube have been conducted under conditions of specific frequency and variable frequency. It is concluded that there exists fluctuation value in gas wave tube refrigeration efficiency versus gas injection frequency curve, which can be up to 15% or more. Based on the present results, the jet frequency control method can make the gas wave tube operate at the refrigeration's peak frequency, thus improving SGWR refrigeration efficiency. [ABSTRACT FROM AUTHOR]

The present study investigates experimentally the flame horizontal lengths of elevated pool fires and compares with those of ground pool fires in cross airflows. This, as a fundamental problem considering air entrainment and combustion structure change due to Coandă effect resulted from ground at leeward side, has not been quantified but is of practical significance. Experiments were performed employing both elevated- and ground square propane pool fires of various heat release rates in cross airflows from 0∼3.0 m/s with 224 test conditions in all. The overall flame horizontal length could be physically divided into two parts: 1) cross flow momentum-dominated length (base-drag part, L m); 2) buoyancy-dominated length (plume-like part, L b). Both the L m and the overall flame horizontal length showed to be significantly larger for a ground pool fire than those of an elevated one, due to the ground constraint effect on air entrainment at leeward side (Coandă effect). L b /(u 2 /g) or L m /(u 2 /g) of elevated fires is proportional to that of ground fires. Large eddy simulations for two representative fire scenarios were further conducted utilizing an in-house version of FireFOAM. The purpose of the simulations was to uncover the underlying physics of combustion and flow structures observed in the experiment. Finally, a model was proposed based on analysis of air entrainment, momentum- and buoyancy effects, which described well the overall flame horizontal lengths of both elevated- and ground pool fires generally as a function of non-dimensional heat release rate, normalized volumetric air entrainment and Froude numbers using L m and L b as length scales. This work provides new observation and basic quantification on elevated- and ground pool fire flame horizontal lengths considering air entrainment change due to Coandă effect in wind. [ABSTRACT FROM AUTHOR]

Inspired by the “water dancing ball” problem proposed in the International Physicists’ Tournament 2019, we study the small-angle oscillations of a cylinder on a plane subject to a thin sheet of water. The interaction between the water flow and the cylinder is modeled using basic physics principles such as Newton’s laws, momentum, and energy conservation. We found that the flux of water around the cylinder applies a force which is responsible for the oscillations of the cylinder. From the motion equation of the cylinder, the period of oscillation is calculated in the harmonic approximation. Our results are contrasted with the period measurements presented recently by Pagaud and Delance, with a good agreement found, showing an error of only 10%.

It is yet unknown how the formation of an aneurysm inside the human body occurs. Thus, understanding and analyzing the Coanda effect will result in a better overview of the overall fluid mechanics that develop inside such a structure, leading not only to better treatment plans, but also to diminished postoperative risks. This paper presents how the fluid behaves in this situation, and takes into consideration how this physical phenomenon influences the hemodynamics inside numerous anatomical regions, located in the central nervous system, where aneurysms usually develop. Analyzing the three main areas in which cerebral aneurysms form, the Coanda effect can potentially lead to the rupture of the aneurysm by changing the blood flow trajectory; this should be taken into consideration when choosing a treatment plan, especially in postoperative care. In addition, there are other factors that can influence the evolution of an aneurysm, such as its shape, size, localization and the patient's health condition. Understanding and analyzing the Coanda effect will result in a better overview of the overall fluid mechanics that develop inside such a structure, leading not only to better treatment plans, but also to diminished postoperative risks. [ABSTRACT FROM AUTHOR]

Pitch control of an unmanned aerial vehicle (UAV) using fluidic thrust vectoring (FTV) is a relatively novel technique requiring no moving control surfaces, such as elevators. In this paper, the authors' previous work on the characterization of a static co-flow FTV rig is further validated using the free to pitch dynamic test bench. The deflection of a primary jet after injection of a high-velocity secondary jet was captured using the tuft flow visualization technique, along with the experimental recording of subsequent normal force impinged on the Coanda surface resulting in the pitching moment. The effect of primary and secondary flow velocities on exhaust jet deflection, as well as on the pitch angle of the aircraft, is examined. Aerodynamic gain as well as the inertia of a delta wing UAV test bench are computed through experiments and fed into the equation of motion (e.o.m). The e.o.m developed aided in the design of a model-based PID controller for pitch motion control using the multi-parameter root locus technique. The root locus tuned controller serves as a benchmark controller for performance evaluation of the genetic algorithm (GA) and particle swarm optimization (PSO) tuned controllers. Furthermore, the frequency domain metric of gain and phase margins were also employed to reach a robust control design. Experiments conducted in a simulation environment reveal that PSO-PID results in a better response of the UAV in comparison to the baseline pitch controller. [ABSTRACT FROM AUTHOR]

The Coanda effect is a tendency of flowing fluid to follow the solid surface rather than to separate under the inertial effect. This paper presents the effects of surface curvature on the Coanda angle and jet deflection for a vertical jet impacting a horizontal cylinder (of diameter D) with Froude numbers Fr = 4.74 and 6.33. The penetration depth h of the cylinder in the jet is varied from h/D = 0.01-0.4 while the jet-to-cylinder diameter ratio d/D is varied from 0.11 to 2.0. For Fr = 4.74, the round jet impacting the cylinder evolves into a planar jet for d/D - 0.40 where the jet deflection is positive, dictated by the Coanda effect. The deflection of the jet is negative for d/D = 0.60 and 0.83 where the bouncing (inertial) effect overwhelms the Coanda effect. Fr = 4.74, the jet deflects in the positive direction, regardless of d/D. With increasing h/D or decreasing d/D, both deflection and Coanda angles monotonically increase. An intermittent switch of the jet from one side of the cylinder to the other is observed for certain curvature of the cylinder, ascribed to the competition between bouncing and Coanda effects. [ABSTRACT FROM AUTHOR]

Abstract Conventional Coanda-based unmanned aerial vehicles (UAV) experience thrust losses in the radial direction. To address these losses, a rectangular, linear arrangement of the Coanda surface was adopted in the proposed novel design. This arrangement minimizes the area change in the radial direction to recover such thrust losses. A prototype of the proposed UAV structure was 3D printed and assembled with a single 9-inch propeller. Performance characteristics of the UAV were evaluated through static testing on a dynamometer under different loading conditions. Experimental results were validated through computational fluid dynamics (CFD) simulations, using the k-ε realizable turbulence model, while the multiple reference frame (MRF) approach was applied in steady state. CFD simulations provided good overall agreement with experimental results having errors less than 8%. Numerical comparison between the novel Coanda design and a conventional Coanda design, having similar radial dimensions, showed that the novel design offered an overall 17% improvement in thrust per the side surface area, thus demonstrating an effective reduction of thrust losses in the radial direction.

The internally blown flap is of efficient lift enhancement ability,but stall angle of attack drops significantly at a higher jet momentum.In order to improve the stall characteristics,the stall characteristics of the internally blown flap with the droop leading edge is studied.The numerical simulation of flow fields of a subsonic airfoil with droop leading edge combined with seamless flaps under the effect of circulation control are conducted.The influence rules of the blowing momentum coefficient on the stall characteristics are studied.The effects of leading edge rigid deflection,camber and thickness changes on the improvement of stall characteristics are studied.The effects of doop leading edge with different flap angle are also studied.The results show that,with the increase of the blowing momentum coefficient,the stall angle of attack is firstly droped rapidly and then slightly increased.The pressure gradient on the upper surface of the airfoil is reduced by the leading edge droop devices,the trend of the momentum thickness of the foil boundary layer increasing with the angle of attack is delayed,and the stall angle of attack is increased effectively.By gradually changing the curvature of the leading edge surface,the target that the leading edge droop design has the best effect on the improvement of stall characteristics is realized.

Abstract Soft robots have advantages in terms of safety, softness, and compliance compared to traditional robotic systems. However, fluid-driven soft actuators, often employed in soft robots, require a corresponding number of bulky pressure supplies/valves to drive. Here, we consider a valve that can control the flow without mechanical moving parts for simplifying the driving system of soft actuators. We developed a system comprising a pump, a switching valve, and two latex balloons to demonstrate the feasibility of introducing a fluid valve into soft robotics. As the valve, which makes use of the Coanda effect, can switch the flow between two outlets when the pressure difference between the outlets is 3 kPa, we employed a latex balloon connected to each outlet. The system can control the expansion of each balloon by switching the flow from the pump. The experimental results proved that the system could actuate each balloon.

The effect of outlet thickness and outlet angle of the bladeless fan have been an alysed numerically on the aerodynamic performance of the bladeless fan. Five different aerofoil profiles have been considered for the present work is Eppler 479, Eppler169, Eppler 473, S1046 and S1048. The bladeless fan arrangement has been achieved by converting the aerodynamic models listed above. The ANSYS ICEM CFD 16.0 have been used to discretize the enclosure and bladeless fan through finite volume approach. The mesh model is then imported into ANSYS CFX 16.0 pre-processor for applying the required boundary conditions. The governing equations namely continuity and momentum are used to solve the flow physics through and across the bladeless fan and SST k-? turbulence model has been used to predict the turbulence in the bladeless fan. The effect of outlet thicknesses and outlet angles have been varied for all the five aerofoil configurations mentioned and the volumetric flow at inlet have been adjusted from 5 LPS to 80 LPS. Outlet thickness is varied from 0.8, 1.0, 1.3, 1.5 and 2 mm and the slit angle is varied from 20 degrees to 80 degrees in step of 10 degrees. The results predicted that Eppler 473 aerofoil profile showed better performance when the thickness of slit and outlet angle has been fixed constant as 1 mm and 70 degree respectively. Also, the maximum discharge flow ratio is recorded for an inlet volumetric flow rate of 80 LPS and it is found to be 34.37. The present numerical study substantiated that outlet thickness plays a dominant role on the bladeless fan's aerodynamic performance compared to outlet angle and aerodynamic shape considered in this numerical analysis. The contours of velocity, streamline and pressure of the bladeless fan have been discussed. [ABSTRACT FROM AUTHOR]

In this research, a method for direction control of a primary jet with a Coanda surface is investigated as part of a fundamental study of fluidic thrust vectoring. The effect of the velocity amplitude ratio (i.e., ratio of time-averaged velocity to velocity fluctuation amplitude) of the secondary flow on the flow characteristics of the jet was experimentally investigated. It was determined that the jet deflection angle was maximized under the suction condition wherein the secondary flow exhibited velocity fluctuation. The relationship between the jet deflection angle and the momentum ratio between the primary jet and the secondary flow is presented, in which the dimensionless frequency of the secondary flow was used as a parameter. Although the jet deflection angle depended on the dimensionless frequency and the momentum ratio, it was difficult to adjust this parameter using only the momentum ratio in the hypothetical saturated region where this ratio is large. In addition, unsteady characteristics were also discussed for several conditions. [ABSTRACT FROM AUTHOR]

The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics. [ABSTRACT FROM AUTHOR]

The impact of converging steady blowing on the global drag past a square back Ahmed bluff body is investigated experimentally. The dynamics of the recirculation bubble are studied for a width to height aspect ratio, w / h of 1.346, with a ground clearance of g / w = 0. 154 , and for a nominal Reynolds number of R e h = 2. 86 × 1 0 5 . When unforced, the bistable wake alternates between a left and right skewed states. Adaptable Coanda devices are used in combination with side air-knife blowers to deflect steady blowing jets into a converging (boat-tail) configuration. Two jet injection angles are investigated: 45 ° and 90 °. Planar PIV and time-history force and pressure measurements indicate that inwards steady blowing reshapes the recirculation bubbles and induces significant variations of the pressure drag. On one hand, bilateral steady blowing leads to the interruption of bistability associated with a removal of the vertical pressure gradient for velocity ratios V R ≈ 0. 35 − 0. 4. This has a favourable impact on the total drag with a reduction up to 3%. On the other hand, the boat-tailing effect shortens the recirculation length which tends to increase drag. This counter-productive effect limits and then outweighs drag reduction for higher velocity ratios. Another symmetry breaking is brought to light for intense highly deflected forcing. [ABSTRACT FROM AUTHOR]

Bladeless fans are more energy efficient, safer due to the hidden blades, easier to clean, and more adjustable than conventional fans. This paper investigates the influence of the airfoil's outlet slit thickness on the discharge ratio by varying the outlet slit thickness of an Eppler 473 airfoil from 1.2 mm to 2 mm in intervals of 0.2 mm by using a k-omega SST turbulence model with an all y + wall treatment used to numerically simulate in CFD. The computational results indicated that smaller slits showed higher discharge ratios. The airfoil with a 1.2 mm slit thickness showed a discharge ratio of 18.78, a 24% increase from the discharge ratio of the 2 mm slit. The effect of outlet angle on the pressure drop across the airfoil was also studied. Outlet angles were varied from 16 ° to 26 ° by an interval of 2 ° . The airfoil profile with a 24 ° outlet angle showed a maximum pressure difference of 965 Pa between the slit and leading edge. In contrast, the 16 ° outlet angle showed the least pressure difference of 355 Pa. Parameters such as average velocity (U), turbulent kinetic energy, the standard deviation of velocity, and outlet velocity magnitude are used to assess the performance of airfoil profiles used in bladeless fan. [ABSTRACT FROM AUTHOR]

This study carried out a simplified baffle filter shape study on the over the range (OTR) filter used in a general kitchen. In order to improve the filter's efficiency, the simulation was performed using ANSYS FLUENT and COMSOL Multiphysics, and a wind tunnel test apparatus was manufactured to minimize the error rate of dust collection efficiency in the experiment. In the case of a physical filter, it was confirmed through a theoretical review that dust is collected in the filter by the inertial collision method, and the flow velocity must be increased to increase the dust collection efficiency. To increase the flow velocity and increase the filter contact area, the use of sub-filters and the Coanda effect was proposed and simulated. When only the Coanda effect was applied, the collection efficiency increased by about 7–15% compared to the original filter, and when the three types of sub-filters were proposed, and among them, a circular sub-filter was applied, it increased by 25%. When applying the sub-filter and the Coanda effect at the same time, it was confirmed that the sub-filter was more efficient than the Coanda effect. However, in the case of a physical filter, since it cannot collect particles less than PM2.5, the electric dust collection method was proposed and a simulation was conducted. The possibility of removing ultrafine dust below PM2.5 was secured by using an electric dust-collection filter simulation, and it is expected that the reliability will be secured by using experimental devices and products in the future. [ABSTRACT FROM AUTHOR]

In this paper, the hydrodynamic characteristics of a piezoelectric micropump operate on the Coanda effect, and the mechanism of bi-directional pumping are analyzed by numerical simulation and experiments. The research focuses on the different positions of the fluid deflector and the influence on the output of the micropump. The results show that a closer fluid deflector to the inlet can produce greater vortices in the suction process due to the Coanda effect, and the backflow diminishing is more significant as well. Moreover, the different positions of the fluid deflector can cause a phenomenon that the micropump will achieve bi-directional pumping. As a finding, vortices arranged in pairs could improve the rectification efficiency of the micropump. The micropump achieves a maximum flow rate of 40.5 ml/min and back pressure of 5.76 cmH2o. In addition, the maximum flow rate per unit area can reach 305.2 µl/(min mm2). [ABSTRACT FROM AUTHOR]