Conventional Vortex Generators Research Articles

Effect of aero-shaped vortex generators on NACA 4415 airfoil

A parametric study was carried out to investigate the effect of aero-shaped vortex generators (AsVGs) on NACA 4415 airfoil by comparing conventional vortex generators (CVGs). Force and flow visualization experiments were carried out for the CVGs and AsVGs at Re = 1.4 × 105. Six different configurations were selected for the positioning of the CVGs to investigate the best one. The best configuration was applied to the Aero-shaped VGs type, which is generated with the S1223 airfoil model. The results indicated that even if AsVGs did not show better performance to delay the stall angle when compared with the CVGs, in some positions they produced the same stall performance as the CVGs. Moreover, aero-shaped VGs increased the lift coefficient (CL) more than the conventional ones in the pre-stall region. At x/c = 0.1, CL and CD improve by up to 107.7% and 23.39% compared to baseline, respectively. At α = 18° and Re = 0.8 × 105, AeM5 at x/c = 0.1 increased the CL by 102.45% compared to the baseline model. While the CVGs increased the lift coefficient (CL) and postponed the stall (α) angle up to 4° according to the baseline model, the CVGs also caused an overall increase in the drag coefficient (CD). AsVGs decreased the drag coefficient (CD) more than conventional ones. Lift to drag ratio (L/D) of AsVGs is higher than that of the CVGs. The results of the surface oil flow visualization showed that both CVGs and AsVGs segmented the laminar separation bubble (LSB) and formed attached flow zones on the airfoil surface. As a result, AsVGs can be used as an alternative to CVGs in flow control applications.

Air Interactions of Magnetically Driven Plasma Discharges in Crossflow

Motivated by the use of magnetohydrodynamic devices in fluid dynamic flow control research, the current work experimentally studied the actuation mechanism and the resulting aerodynamic interactions of magnetically driven low-current arc-plasma discharges. The investigation was conducted in the context of boundary-layer interactions in low-speed crossflow conditions through the use of coaxial and v-shaped geometries. Time-averaged velocity field measurements showed that the toroidal region of vorticity induced by the coaxial geometry in quiescent air resulted in the formation of a horseshoe vortex in crossflow. Similarly, the v-shaped actuator resulted in the formation of streamwise vortices. The resulting boundary layers had s-shaped streamwise velocity profiles as measured in the wall-normal direction characteristic for the flow downstream of a conventional vortex generator pair, due to the three-dimensional mixing induced by coherent vortex structures. A simplified model based on intermolecular momentum transfer through collisions is proposed to explain the fundamental discharge–air interactions and the induced flowfields. These results inform the applications of various magnetically driven discharges in the field of aerodynamic flow control.

Manipulation of the aerodynamic behavior of the DrivAer model using dimple patterns

Societies rising environmental awareness in the context of advancing climate change is continuously shifting the focus of automotive development to vehicle efficiency and thus also to aerodynamic resistance. However, customers favor the familiar vehicle aesthetics, so research and development must find new solutions to reduce drag based on a given body shape. Dimple patterns extruded outward from the vehicle skin are considered in this study with the aim of reducing flow separation and thus lowering drag. They are applied to the realistic and already optimized notchback DrivAer vehicle model. Delayed detached-eddy simulations validated by experiments are used to assess the potential of this concept. In order to see the dependence of the concept on essential parameters, the location, size as well as height of the dimple pattern are varied in this study. All applied patterns on the rear window of the DrivAer model reduce drag and lift by up to 1.9% and 19.2%, respectively, compared to the reference geometry without dimple pattern. A large-scale dimple pattern is less sensitive with respect to the dimple height, whereas a smaller pattern exhibits more significant variations with respect to drag and downforce as the dimple height is varied. Compared to conventional vortex generators, the dimple pattern approach shows less potential to increase downforce, but allows a significant reduction in drag compared to the classical approach, with the consequence of increasing efficiency and reducing emissions.

Comparison of flow structures for vane and rod type vortex generators on a wind turbine airfoil

PurposeThe purpose of this paper is to investigate and compare the effects of rod and vane-type vortex generators for wind turbine applications. In large wind turbine rotors, an attached flow at all sections along the span direction is difficult to achieve which leads to an increase in aerodynamic losses, noise generation, and fatigue stress. Therefore, flow control strategies such as vortex generators (VGs) are beneficial to improve performance.Design/methodology/approachThe benefits of the application of rod-type vortex generators (RVGs) to control flow separation on a wind turbine airfoil are assessed numerically using computational fluid dynamics (CFD). The validation of the computational model is conducted against the experimental data available for the DU96-W-180 wind turbine airfoil equipped with 44 RVGs. In addition, a revised wind tunnel angle of attack (AoA) calibration procedure (based on CFD) is proposed that is applicable for separated flows. A comparison of the RVGs to the conventional vane-type vortex generators (VVGs) is presented for inflow velocity of 30 m/s and AoA leading to significant flow separation. A parametric evaluation of the geometric characteristics of both types of VGs is conducted to quantify the generated streamwise vortices.FindingsThe comparison of the induced flow structures and aerodynamic efficiency enhancements proves that RVGs may be used as an alternative to the more conventional VVGs applied on wind turbine blades for boundary layer separation control.Originality/valueA new type of VG (rod) has been investigated and compared against conventional VG (vanes) for wind turbine applications.

Separation and flow unsteadiness control in a compression corner induced interaction using mechanical vortex generators: Effects of vane size and inter-device spacing

An experimental investigation was conducted to control separation characteristics of a 24° compression corner induced interaction in a Mach 2.0 flow using an array of mechanical vortex generators (VGs) with rectangular vanes (RRV) placed 6.8δ upstream of the interaction. The objective was to study the effect of (i) inter-VG spacing (s/h = 12, 9.5, 8.0, 6.1, 5.7, 5.5, 4.9, and 4.7), (ii) vane chord length (c/h = 7.2, 4.2, and 3.0), and (iii) vane angle (α = 24°, 20°, 18°, and 16°) in controlling the interaction and on the surface flow topology. These modifications reduce the projected area of VGs in the array from the conventional VG design of RRV2 (c/h = 7.2 and s/h = 9.5) to RRV8 (c/h = 3.0 and s/h = 4.7) by 41%. Reducing s/h also reduces the inter-VG region of the separation significantly that helps to achieve maximum reduction in the streamwise extent of separation up to 83% and in the peak rms value up to 80%. The former improves the overall pressure recovery from 3.0 to 3.4, thereby moving closer toward the inviscid value of 3.8. Surface flow topology shows that the VG array splits a single large spanwise separation bubble for no control into multiple smaller scale individual separation cells placed side-by-side all along the span of the interaction. This helps to reduce the magnitude of mass exchange imbalance across each individual separation cell and, hence, stabilizes the overall interaction relative to no control. The best VG configuration of RRV8 shifts the dominant frequency of fluctuations to approximately 2 kHz or St = 0.19, which is nearly an order of magnitude higher than that for no control.

Numerical investigation of double sided plasma vortex generator in separation control

Control of flow separation is a great issue to deal with a moving body to ensure its proper aerodynamic characteristics. To achieve this, various methods including active and passive control are suggested depends upon the flow characteristics and the surface in which control is necessary. To make the better use of both active and passive method of flow control this article proposed a new type of double sided plasma actuator (DSPVG) to overcome the drag penalty of conventional vortex generators (VGs) that commonly used in controlling flow and to use actively control. In this regard, the effectiveness of DSPVG has been numerically and experimentally investigated in a separated flow region of a 20° diffuser of an open type tunnel. DSPVG is placed at the upstream of separation location normal to the surface as like as conventional VG except zero angle with flow direction. Both numerical and experimental results of DSPVG are compared with that of VG and baseline flow and better agreements are found. Moreover, DSPVG has shown better separation suppression ability than conventional VGs due to its dual vortices. It is found that DSPVG significantly delay the separation. A freestream flow of 4 m s−1 is used for experiments and numerical computations.

The hydrodynamic behaviour of biologically inspired bristled shark skin vortex generator in submarine

Fluid flow control is vital in submarine operations to prevent drag of crossflow separation and boundary layer separation. This research attempts to use bristled shark skin vortex generator to control the fluid around the submarine and to reduce drag during operation of submarine. The conventional vortex generator is delta wing shaped which unbaled to generate vortices efficiently. The effect of using biologically inspired vortex generator on hydrodynamic behaviour of submarine is studied through Computational Fluid Dynamic analysis. The analysis is carried out for linear movement, 30° yaw movement and 30° pitch movement of the submarine. Further wind tunnel experiments are conducted to validate the numerical simulation results. The numerical analysis and experiments reveal that the use of bristled shark skin vortex generator in the lateral side of submarine reduces the drag drastically in linear, yaw and pitch movements of the submarine. It assists in crossflow separation and moves the fluid away from the body of the submarine. During yaw and pitch movement, it moves the fluid towards the same direction as the submarine turns, which subsequently assists in generating additional torque during the turning.

An Approach to Suppress Flow Separation by Plasma Vortex Generator as a Combined Active and Passive Control Mechanism

Flow control is an important issue in fluid mechanics and aerodynamics as separated flow introduce undesirable impact on overall system performance. Several active and passive techniques have been used to control the flow when necessary. But in passive control techniques, the actuator has to be fixed on the surface so that it can create vortices along streamline to enhance the mixing in the separated region to delay or suppress separation. Among passive flow control system vortex generators (VGs) are generally used but it control the flow with the cost of drag increase. It would be advantageous by combining both active and passive flow techniques together. In this regard plasma actuator (PA, active flow control device) and VGs are combined together with a view to not only suppress the separation but also minimizing the drag that could arise by using conventional passive control techniques. The combination flow control device is named as Plasma Vortex Generator (PVG) which proves its effectiveness to control separation as conventional VGs do but without any drag penalty.

Mitigation of heat transfer deterioration in a circular tube with supercritical CO2 using a novel small-scale multiple vortex generator

Abstracts This paper explores the performance effects of a novel small-scale multiple vortex generators (MVG) on heat transfer deterioration (HTD) mitigation and pressure drop using supercritical CO2 (sCO2) as the working fluid. The HTD mitigation and pressure drop are examined using an overall performance factor, R = ΔHTD/(Δp/Δp0). Numerical calculations are first conducted to investigate the effects of single conventional vortex generator's (VG) configurations (rectangular, triangular and trapezoidal). The results indicate that under the same aspect ratio, rectangular VG has the largest area facing the fluid flow and the largest angle of attack which induces the strongest longitudinal vortices leading to its highest value of R. Then, the morphological properties (density and height) of five pairs of evenly distributed rectangular VGs in an MVG are varied while their uniformity is maintained. With the increase in MVG's height, the channel's heat transfer coefficient (HTC) profiles increase significantly at the locations where MVG is installed while the opposite trend is found for R. The density and nonuniformity of the MVG have the highest performance effects on HTD mitigation, with R of more than 18% and 11% for the density of 2.5 and non-uniform MVG respectively. Analysis reveals that as the density of MVG increases, the fluid recirculation zone behind each VG diminishes correspondingly, causing a greater vortex intensity mixing by swirling flows which enhances the downstream production of turbulence kinetic energy (TKE), thus weakening the buoyancy forces and leading to HTD mitigations. In addition, by further increasing the MVG density beyond 2.5, it was found that the HTC decreases while the pressure drop increases, with the wall temperature peaks stabilizing at 178 °C, which demonstrates the breakdown of Reynold's analogy. Increasing the number of VGs in an MVG increases its delay and broadening effects on the wall temperature peaks by further delaying the boundary layer recovery caused by interaction of longitudinal vortices generated by each VG, but has relatively little effects on R. Also, analysis further reveals the presence of buoyancy-induced flow oscillations near the channel walls, which are attenuated by the VG and MVG effects. Overall, MVG offers superior performance than convectional single VGs in terms of HTD mitigation, and the results presented here can be employed as a reference guide in the design of highly efficient, safe and reliable supercritical heat exchanger systems.

Computational modelling of TRIANGULAR sub-boundary-layer vortex generators

Vortex generators (VGs) are used increasingly more by the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. The VG height is usually designed with equal thickness of the local boundary layer at the VG position. Nevertheless, these conventional VGs may produce excess residual drag in some applications. The so-called sub boundary layer VGs can provide enough momentum transfer over a region several times their own height for effective flow-separation control with much lower drag. The main objective is to investigate how well the simulations can reproduce the physics of the flow of the primary vortex generated by a triangular VG mounted on a flat plate with negligible pressure gradient with the angle of attack of the vane to the oncoming flow β= 18. Three different device heights H= 5mm, H1= 6,25mm, H2= 4,16mm have been studied and compared both qualitatively and quantitatively. To that end, computational simulations have been carried out using RANS method and at Reynolds number Re = 2600 based on the boundary layer momentum thickness θ= 2.4 mm at the VG position. The computational results show good agreement with the experimental data available in AVATAR project.

Numerical Simulation of Flow behind Vortex Generators

In this study, flow behind rectangular vane type vortex generators mounted on a flat plate, is numerically simulated using the immersed boundary (IB) method. In the present work, the direct forcing IB method is employed because of its simplicity and high efficiency. Vortex generators of two different heights are numerically investigated. The height of vanes in the first case is close to the definition of submerged/low-profile vortex generators while the other case is closer to the definition of a conventional vortex generator. The resultant highly three-dimensional flow and its transition to turbulence have been studied. Counter-rotating vortices generated by these passive rectangular vortex generators are characterized. Streamwise evolution of non-dimensionalised maximum values of vorticity, vortex strength, streamwise velocity and wall-normal velocity are studied. The simulations show that the IB method in conjunction with DNS effectively simulates the time-dependent flow behind an array of passive vortex generators placed in an initially laminar boundary layer.

Numerical Investigation of Passive Vortex Generators on a Wind Turbine Airfoil Undergoing Pitch Oscillations

Passive vortex generators (VGs) are widely used to suppress the flow separation of wind turbine blades, and hence, to improve rotor performance. VGs have been extensively investigated on stationary airfoils; however, their influence on unsteady airfoil flow remains unclear. Thus, we evaluated the unsteady aerodynamic responses of the DU-97-W300 airfoil with and without VGs undergoing pitch oscillations, which is a typical motion of the turbine unsteady operating conditions. The airfoil flow is simulated by numerically solving the unsteady Reynolds-averaged Navier-Stokes equations with fully resolved VGs. Numerical modelling is validated by good agreement between the calculated and experimental data with respect to the unsteady-uncontrolled flow under pitch oscillations, and the steady-controlled flow with VGs. The dynamic stall of the airfoil was found to be effectively suppressed by VGs. The lift hysteresis intensity is greatly decreased, i.e., by 72.7%, at moderate unsteadiness, and its sensitivity to the reduced frequency is favorably reduced. The influences of vane height and chordwise installation are investigated on the unsteady aerodynamic responses as well. In a no-stall flow regime, decreasing vane height and positioning VGs further downstream can lead to relatively high effectiveness. Compared with the baseline VG geometry, the smaller VGs can decrease the decay exponent of nondimensionalized peak vorticity by almost 0.02, and installation further downstream can increase the aerodynamic pitch damping by 0.0278. The obtained results are helpful to understand the dynamic stall control by means of conventional VGs and to develop more effective VG designs for both steady and unsteady wind turbine airfoil flow.

Source Term Modelling of Vane-Type Vortex Generators under Adverse Pressure Gradient in OpenFOAM

An analysis of the generation of vortices and their effects by vane-type vortex generators (VGs) positioned on a three-dimensional flat plate with a backward-facing ramp and adverse gradient pressure is carried out. The effects of a conventional vortex generator and a sub-boundary layer vortex generator are implemented by using a source term in the corresponding Navier-Stokes equations of momentum and energy according to the so-called jBAY Source Term Model. The influence of the vortex generator onto the computational domain flow is modelled through this source term in the Computational Fluid Dynamics (CFD) simulations using the open-source code OpenFOAM. The Source Term Model seems to simulate relatively well the streamwise pressure coefficient distributions all along the flat plate floor as well as certain parameters studied for vortex characterization such as vortex path, decay and size for the two vane-type vortex generators of different heights studied. Consequently, the implementation of the Source Term Model represents an advantage over a fully Mesh-Resolved Vortex Generator Model for certain applications as a result of a meaningful decrease in the cell number of the computational domain which implies saving computational time and resources.

A Development and Assessment of Variable-Incidence Angle Vortex Generator at Low Reynolds Number of ~ 5×104

The aerodynamic benefit for conventional vortex generator (VG) is often counterbalanced by the appearance of parasite drag. An immovable installation similar to a fixture also limited its application. To overcome those issues, this paper proposes a variable-incidence-angle vortex generator (VIVG). Counter-rotated miniature gears with a single rack-pinion system adjust the incidence angle of the VIVG, thereby precisely control mixing flux at boundary layer interface with minimizing the parasite drag. The variable incidence angle of the VIVG was then examined to evaluate the applicability of the VIVG at low Reynolds number. The VIVG was mounted on a NACA 0015 airfoil, and a low-turbulence blowing type wind tunnel was employed. We found that the VIVG effectively eliminated laminar separation bubbles, and suppressed separation at Reynolds number of 5.4 × 104; excessive lift production at low Reynolds number became similar to a theoretical value of potential flow (CL = 2πα). It was also found that the VIVG can reduce the drag in the pre-stall region at the low Re with small incidence angles, providing a noticeable increment of the lift-to-drag ratio. The large incidence angle of VIVG was also useful both to extend the stall point and to produce higher lift force with reasonable efficiency. These clearly indicate that the VIVG is applicable for performance improvement of aerodynamic devices operated in low Reynolds number flow fields.

Computational Modelling of Rectangular Sub-Boundary Layer Vortex Generators

Vortex generators (VGs) are increasingly used in the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. Nevertheless, VGs may produce excess residual drag in some applications. The so-called sub-boundary layer VGs can provide an effective flow-separation control with lower drag than the conventional VGs. The main objective of this study is to investigate how well the simulations can reproduce the physics of the flow of the primary vortex generated by rectangular sub-boundary layer VGs mounted on a flat plate with a negligible pressure gradient with an angle of attack of the vane to the oncoming flow of β = 18°. Three devices with aspect ratio values of 2, 2.5 and 3 are qualitatively and quantitatively compared. To that end, computational simulations have been carried out using the RANS (Reynolds averaged Navier–Stokes) method and at Reynolds number Re = 2600 based on the boundary layer momentum thickness θ at the VG position. The computational results show good agreement with the experimental data provided by the Advanced Aerodynamic Tools of Large Rotors (AVATAR) European project for the development and validation of aerodynamic models. Finally, the results indicate that the highest VG seems to be more suitable for separation control applications.

Effects of leading-edge rod on dynamic stall performance of a wind turbine airfoil

A cylindrical rod placed at the leading edge of the S809 airfoil is used as an alternative for the conventional vortex generators. In this paper, extensive numerical investigations have been conducted on the effects of the rod on the static and dynamic stall performance of the S809 airfoil. The flows around the stationary and sinusoidally oscillating S809 airfoils at Re = 106 are simulated by solving the unsteady two-dimensional Reynolds-averaged Navier–Stokes equations with the Shear Stress Transport k–ω model. For the stationary airfoil, the leading edge rod can effectively enhance the aerodynamic characteristics of the airfoil and delay the stall angle, with the maximum lift–drag ratio increased by 30.7%. For the airfoil undergoing deep dynamic stall, the rod shows the capacity of eliminating the dynamic stall vortex at the leading edge and suppressing the flow separation at the tailing edge. It also reduces the peak of the negative pitching moment and the hysteresis effects substantially, and eliminates the negative damping sub-loop of the moment coefficient. Moreover, the distance between the rod and the airfoil has a strong influence on the lift forces but little effect on drag and moment coefficients of airfoil under deep dynamic stall.

Parametric study of low-profile vortex generators

Vortex generators (VGs) are flow control devices employed to avoid or delay flow separation. In most cases, the VG is calculated with the same height as the boundary layer (BL) thickness at the device position. However, these so-called conventional VGs may produce overload drag in some applications. The low-profile VGs can decrease the residual drag linked to this kind of passive flow control actuators. The main goal of the present work is to investigate the trajectory and size of the primary vortex produced by low-profile VGs on a flat plate with a height to length ratio of ½ and a vane incident angle of 18.5°. Hence, numerical simulations have been performed using Navier–Stokes equations at Re = 1350 based on the local boundary layer thickness where the VG was placed. Additionally, a prediction model has been developed to describe the progression of the vortex size behind the passive vanes.

Generating and Separating Twisted Light by gradient-rotation Split-Ring Antenna Metasurfaces.

Nanoscale compact optical vortex generators promise substantially significant prospects in modern optics and photonics, leading to many advances in sensing, imaging, quantum communication, and optical manipulation. However, conventional vortex generators often suffer from bulky size, low vortex mode purity in the converted beam, or limited operation bandwidth. Here, we design and demonstrate gradient-rotation split-ring antenna metasurfaces as unique spin-to-orbital angular momentum beam converters to simultaneously generate and separate pure optical vortices in a broad wavelength range. Our proposed design has the potential for realizing miniaturized on-chip OAM-multiplexers, as well as enabling new types of metasurface devices for the manipulation of complex structured light beams.

Micro vortex generator control of axisymmetric high-speed laminar boundary layer separation

Interest in the development of micro vortex generators (MVGs) to control high-speed flow separation has grown in the last decade. In contrast to conventional vortex generators, MVGs are fully submerged in the boundary layer and have the potential of inducing surface flow mixing with marginal drag penalty when suitably designed. Also, they do not result in undesired reduced mass flow such as with suction methods. The flow mechanisms at the location of MVGs are not yet fully understood, and optimal designs are difficult to establish given that both numerical predictions and experiments are particularly challenged for short element heights, yet optimal MVGs are generally expected to be at least shorter than half the local boundary layer thickness. The present work aims at investigating experimentally the fundamental flow physics concerning an individual MVG element (of ‘canonical’ or simplified geometry) at a range of near-wall heights. A fully laminar base flow is considered so as to isolate the effect of incoming turbulence as well as the more complex physics that may occur when specific and/or multiple elements are used. Tests were performed in a gun tunnel at a freestream Mach number of 8.9 and Reynolds number of $$47.4\times 10^{6}$$ /m, and the basic test model consisted of a blunt-nosed cylinder which produced an axisymmetric laminar boundary layer with an edge Mach number of 3.4 and Reynolds number of $$3.2\times 10^{6}$$ /m at the MVG location. A laminar shock-wave/boundary layer interaction with separation was induced by a flare located further downstream on the model. Measurements consisted of time-resolved surface heat transfer obtained in the axial direction immediately downstream of the MVG and along the interaction, together with simultaneous high-speed schlieren imaging. The height ( $$h$$ ) of the MVG element used in a ‘diamond’ configuration (square planform with one vertex facing the flow) was adjusted between tests ranging from $$h/\delta $$ = 0.03 to 0.58, where the local undisturbed boundary layer thickness was $$\delta $$ = 1.75 mm. The effect of planform geometry was further assessed by performing tests with the MVG used in a ‘square’ configuration (one edge normal to the incoming flow). Results show that MVG height drives the intensification of heat transfer fluctuations in the wake of the element. The optimal MVG operating conditions, where downstream boundary layer separation is avoided and minimal flow interference is produced, based here on heat transfer unsteadiness, are $$h/\delta \approx 0.3$$ with a ‘diamond’ arrangement.

Computational study of the vortex path variation with the VG height

An extensive range of conventional, vane-type, passive vortex generators (VGs) are in use for successful applications of flow separation control. In most cases, the VG height is designed with the same thickness as the local boundary layer at the VG position. However, in some applications, these conventional VGs may produce excess residual drag. The so-called low-profile VGs can reduce the parasitic drag associated to this kind of passive control devices. As suggested by many authors, low-profile VGs can provide enough momentum transfer over a region several times their own height for effective flow-separation control with much lower drag. The main objective of this work is to study the variation of the path and the development of the primary vortex generated by a rectangular VG mounted on a flat plate with five different device heights h = δ, h1 = 0.8δ, h2 = 0.6δ, h3 = 0.4δ and h4 = 0.25m, where 5 is the local boundary layer thickness. For this purpose, computational simulations have been carried out at Reynolds number Re = 1350 based on the height of the conventional VG h = 0.25m with the angle of attack of the vane to the oncoming flow β = 18.5°. The results show that the VG scaling significantly affects the vortex trajectory and the peak vorticity generated by the primary vortex.