Vortex rings can maintain their structure during motion and achieve long-distance transport with low energy consumption, which is a fluid transport method with great energy-saving potential. In this paper, a reciprocating Vortex ring generator structure is designed, which can generate two Vortex rings during the reciprocating motion of one piston, making full use of the thrust in the reciprocating motion period of the piston and improving the Vortex ring generation frequency compared with traditional Vortex ring generators. For the characteristics of long-distance transport of Vortex rings, an experimental platform is designed and built, and 277 sets of experiments are carried out with different geometric parameters. The results show that the effect of generating two Vortex rings could be achieved under other parameter conditions, except for some parameter conditions where the diameter ratio D1/D2 = 4. By analyzing the influence of baffle width ratio, length ratio, and diameter ratio on the moving distance of Vortex rings, the performance of the Vortex ring generator is preliminarily studied. In 277 sets of experiments, the maximum moving distance ratio x1 of Vortex ring 1 is 13. 7 when L1/L2 = 2. 4, D1/D2 = 2, and w1 = 0. 2. And the maximum moving distance ratio x2 of Vortex ring 2 is 20 when L1/L2 = 2, D1/D2 = 2. 5, and w2 = 0. 2.

This paper presents an original concept of using a composite flexible flapping Vortex generator mounted on a heat sink fin for air side heat transfer augmentation. The main aim is to combine the advantages of hard and soft winglets in a composite one for having the highest possible enhancement. The proposed composite Vortex generator, which is made with a thin elastic sheet is responsible for enhancing heat transfer and mixing quality performances in laminar convection air flow in a heat sink. The merged vortical structures due to oscillation by winglet swept out the thermal boundary layer and enhance thermal mixing between the fluid near the heated fin and the channel core flow. This novel concept is demonstrated using numerical simulation of the flow field with considering a two-way strongly coupled fluid-solid interaction approach in transient condition. The set of governing equations including, the continuity, momentum, and energy for a 2-D forced convection air flow are solved by the finite element method using the COMSOL Multi-Physics. The present findings show 148%, 116%, and 121% increases in the cooling rate by the composite and the two hard and soft homogeneous winglets, respectively. Numerical results are validated against the numerical data reported in the literature.

Experiments were carried out for the numerical investigation of heat transfer enhancement in a solar air collector using different types of baffles and Vortex generators. In this study, the Vortex generator was implemented to increase the efficiency of the solar air collector. The variations in Nusselt number, pressure drop, friction coefficient, and thermal and exergy efficiency in four collectors with different baffles arrangement (type A, B, C, D) were investigated. Type A was chosen as the optimum collector for implementing the Vortex generator on the absorber surface. In the solar air collector the effects of using a novel Vortex generator-the Perforated Delta Wing Vortex generator (PDWVG), in comparison with a flat one-the Flat Delta Wing Vortex generator (FDWVG), were considered. In order to determine the maximum efficiency of the solar air collector, four different pitch ratios of Vortex generators were studied. The Nusselt number and pressure drop increased with the Reynolds number but the friction coefficient decreased with Reynolds, the experimental and numerical results revealed that the thermal and exergy efficiency decreased from a specific range. The comparison of PDWVG and FDWVG showed that the presence of holes on the novel Vortex generator led to reduced pressure drop and increased heat transfer between the airflow and the absorber surface. Increasing the number of Vortex generator rows had a slight effect on increasing the studied parameters. The results showed that collector type A with ep=0. 55 of PDWVG improves the energy and exergy efficiency 4. 43% and 5. 29% respectively.

This article presents a comprehensive approach to enhance heat transfer rates in a 3D channel using Ferrofluids. The study investigates the individual and combined impacts of rectangular winglet Vortex generators and magnetic fields on flow characteristics, heat transfer enhancement, and entropy generation. Numerical solutions are derived for the governing partial differential equations using the finite volume technique and the SIMPLE algorithm. The investigation assesses the influence of key parameters, including the type of rectangular winglet Vortex generator (simple, concave, and convex), Reynolds number, and magnetic field strength. Optimal operational conditions are identified based on thermodynamics' first and second laws. This study has been conducted in three steps, and the interaction of created vortices and their effect on heat transfer, pressure drop, and entropy production were investigated. In the first step, the effect of the Vortex generator in different Reynolds has been investigated. In the next step, the impact of applying a magnetic field at different intensities by a current-carrying wire has been studied in a channel without Vortex generators. Finally, the application of Vortex generators and magnetic fields has been investigated simultaneously. The results showed that using the concave Vortex generator in the absence of a magnetic field increased the heat transfer by 50% and pressure drop by 60%. Applying a magnetic field in the channel without Vortex generators has increased heat transfer and pressure drop by 70% and 118%, respectively. Moreover, it is observed that the magnetic field induces a greater pressure drop penalty than the Vortex generator for achieving the same heat transfer augmentation. The simultaneous application of magnetic field and Vortex generator has also increased the heat transfer and pressure drop by 200% and 269%, respectively, for simple Vortex generators.

In the current research, four different configurations of plasma streamwise Vortex generators (PSVGs) for compressible flow control have been experimentally investigated to analyze their capabilities in controlling compressible flow (M=0. 428) at the different excitation voltages and frequencies. The impacts of electrical parameters on the performance and efficiency of plasma actuators have been studied. Power spectrum analysis of pressure fluctuations in the boundary layer has been employed to determine the unsteady forcing frequencies of PSVGs. The presence of a dominant frequency in power spectrum diagrams is a strong indication of flow separation in the region from which the pressure signal has been extracted. As such, it was observed that the separation bubble was created in front of the comb-type PSVG when it starts its operation,however, using the T-type configuration diminished the separation bubble. T-type and mesh-type PSVGs, in similar experimental conditions, were observed to be more efficient than the comb-type and saw-type geometries in controlling compressible flow.

Heat transfer processes are widely used in many industrial applications, therefore many studies have been conducted in this field. so in this research, the effect of the active vibrations of a piezoelectric Vortex generator on the displacement heat transfer rate in a microchannel is investigated. The assumed Vortex generators consist of square pins having a flexible splitter plates on their lee side. These plates will be deformed under fluid structure interactions. The Reynolds number, based on the channel’s hydraulic diameter,is set to 1000 to ensure laminar flow. The heat transfer performance, the hydrodynamic friction factor and the overall hydrothermal efficiency for different number of VGs and splitter’s flexural rigidity are investigated. The results showed that softer splitters provide better heat transfer capability and the higher hydrothermal performance. The results also indicated that, by selecting proper configuration, in the expense of 33% decrease in total hydrothermal efficiency with respect to clean channel, 140% increase in the rejected heat, compared to clean channel, can be achieved.

Flow separation is mostly an undesirable phenomenon and boundary layer control is an important technique for flow separation problems on airfoils and in diffusers. Longitudinal (streamwise) vortices are produced by the interaction between jets and a freestream. This technique is known as the Vortex generator jet method of separation, or stall control. The Vortex generator jet method is an active control technique that provides a time-varying control action to optimize performance under a wide range of flow conditions because the strength of longitudinal vortices can be adjusted by varying the jet speed. In the present study, an active separation control system using Vortex generator jets with rectangular orifices has been developed. The active separation control system can be practically applied to the flow separation control of a two-dimensional diffuser. It was confirmed that the proposed active separation control system could adaptively suppress flow separation for the flow fields caused by some changes in freestream velocity and the divergence angle of the diffuser.

Today, the effects of three-dimensional flow near the blade and wing tip in the turbomachinery industry, such as rotor helicopters, turbine, as well as wings optimization in the airline industry, for safe flight with high maneuverability, are the focus of the industry in this area. Stall can be considered an influential phenomenon in this field. In the present study, the flow separation control was investigated by a Vortex generator on a wing of a radar invader UAV, including a Naca64a210 airfoil with a 5° washout angle at the wing tip and integrated wings and attached to the body with a 47° sweep angle in the subsonic flow. The turbulent flow was solved by the kw-sst method for attack angles ranging from 5-20° and speeds of 30 and 60 m/ sec. The results show a good fit with numerical and experimental results, so that the pressure distribution curves indicate the growth of pressure in the Vortex generating regions and also the areas near the tip of the wing, which results in the flow remain in the wing surface in these areas. Therefore, by examining the pitching moment and velocity contours, it can be seen that the flow separation from the 15° angle of attack, has been delayed to 20° , and also the ability to control the separation of flow along with the growth of velocities has been achieved.

The compressor cascade performance is significantly restricted by the secondary flow mainly presented as the trailing edge separation and corner stall. This paper develops a synthetic flow control approach in a high turning cascade using the Vortex generator and slot jet approach. Numerical simulations were conducted to assess the flow control benefits and illustrate the flow control mechanisms. Four configurations, the baseline, the two individual approaches and the synthetic approach, were simulated to compare the separation control effects. The simulations show that all the three configurations achieve considerable improvements of the cascade performance and the cascade sensitivity to incidence angle is greatly decreased. The synthetic approach improves the most among them which is almost the superposition of the two individual ones. In the synthetic approach, the trailing Vortex induced by the Vortex generator suppresses the end wall cross flow and deflects the passage Vortex, and then prevents the production of corner stall; at the same time, the slot jet speeds up the trailing edge separation caused by the cascade high camber. Owing to the combination of the two aspects, the synthetic approach restricts the developments of secondary flow and vortices in the cascade, and improves the outflow uniformity. The synthetic approach nicely utilizes the advantages of the two individual approach while avoids the shortages by the complementation, so it can achieve more powerful flow control effects. At the end, vortices models are established to illustrate the secondary flow structure and the flow control mechanisms.

The receptivity of a smooth flat plate to localized disturbances in freestream is investigated experimentally and numerically. The disturbances are generated outside a nominally-zero-pressure-gradient laminar boundary layer by a collision of two identical Vortex rings with opposite signs. The Vortex rings are generated by intermittent ejections of short duration jets from nozzles facing each other in the spanwise direction. A pair of rolled up Vortex rings is given as the initial disturbances in the direct numerical simulation, and the growth of a boundary layer is simulated for a range of the Reynolds number based on the displacement thickness of boundary layer, 704£ Re * £ 844. In the experimental results, high- and low-speed regions aligned in the streamwise direction are observed in the boundary layer before the external disturbances in the freestream reach the outer-edge of the boundary layer. Although velocity fluctuations inside both regions become stronger downstream, a transition to turbulence takes place only in the high-speed region at approximately Re *=844. In the numerical results, vortical fluctuations similar to the experiment appear near the wall immediately after the Vortex-ring-type disturbances are added in the freestream, but it is found that the vortical fluctuations do not directly grow into strong vortical structures. On the contrary, the development of strong vortical structures that leads to transition is triggered by the external disturbances directly intruding the boundary layer.