Parametric Studies of Vortex Generators Using Source Term Modelling

Today, Vortex Generators (VGs) are becoming an integral part of a Wind Turbine blade design. However, the challenges that are involved in the computation of the flow around VGs are yet to be dealt with in a satisfactory manner. A large number of VG models for flow solvers have been proposed and among them, the BAY model is one of the most popular for its ease of use and relatively low requirements for user input. In the present paper, a thorough investigation on the performance and application of the BAY model for aerodynamic Vortex Generator flows is presented. A Fully Resolved Reynolds Averaged Navier Stokes simulation is validated against experiments and then used as the benchmark for the BAY model simulations. The Benchmark case is the flow past a wind turbine airfoil at Reynolds number 0.87e6. When the grid related errors are excluded, it is found that in the model simulations, the generated vortices are weaker than in the fully resolved computation. The latter finding is linked to an inherent deficiency of the model, which is explained in detail. As the vortex generation mechanism is different between the fully resolved and the BAY model simulation, so is the vortex evolution and interaction, even on the same numerical mesh. With regards to grid dependence, the integral BAY force depends on both grid density and grid architecture.

Flows around vortex generators (VGs), which serve as one of the important flow control methods, are investigated by solving Reynolds-averaged Navier–Stokes (RANS) equations. The influences on the main flow of VGs are intended to explore. Firstly, the flow around a single VG on a flat plane is computed to validate the schemes and to acquire basic knowledge of this kind of flow. Secondly, the effects of a row of VGs mounted about 25% local chord on a supercritical wing are analyzed in transonic condition with strong SWBLI. Lastly, VGs are mounted more upwind (about 3.5% local chord) to explore the effects at low speed and high incidence condition. The numerical results show that seven VGs can effectively suppress the separations behind the strong SWBLI and decrease spanwise flow and wing-tip vortex in transonic condition. VGs also can decrease the large scope of separation over the wing at low speed with high angle of attack.

This paper describes flow visualization results from a continuing Cooperative Research and Development Agreement (CRADA) project between Siemens and the National Renewable Energy Laboratory (NREL) - National Wind Technology Center (NWTC). The cooperative research project was established for the purpose of advancing the understanding of wind turbine aerodynamics in the field environment with complex inflows resulting from atmospheric boundary layer conditions. The research includes extensive measurements to characterize the inflow to the turbine, blade aerodynamics, and loading on the blades, tower, and foundation of the turbine. Together in combination with regular turbine parameters such as power and generator speed the measurements will serve to provide a complete dataset for analyzing complete system performance as well as validation for improving rotor design models developed by Siemens and the NWTC. As a part of the overall research goals of the project, oil-flow visualization tests were conducted for the purpose of evaluating surface flow conditions and the effect of different vortex generators (VGs) at various blade pitch settings. The resulting flow patterns are used to correlate the flow separation on the blade surface to the estimated local angles of attack. Additionally, the results clearly indicate the effectiveness of vortex generators (VG) in delaying the occurrence of stall, compared to regions on the blade where no VG’s are used.

PurposeThe purpose of this paper is to describe numerical investigations focused on the reduction of separation and the aerodynamic enhancement of wind turbine blades by a rod vortex generator (RVG).Design/methodology/approachA flow modelling approach through the use of a Reynolds-averaged Navier–Stokes solver is used. The numerical tools are validated with experimental data for the NREL Phase VI rotor and the S809 aerofoil. The effect of rod vortex generator’s (RVG) configuration on aerofoil aerodynamic performance, flow structure and separation is analysed. RVGs’ chordwise locations and spanwise distance are considered, and the optimum configuration of the RVG is applied to the wind turbine rotor.FindingsResults show that streamwise vortices created by RVGs lead to modification of flow structure in boundary layer. As a result, the implementation of RVGs on aerofoil has proven to decrease the flow separation and enhance the aerodynamic performance of aerofoils. The effect on flow structure and aerodynamic performance has shown to be dependent on dimensions, chordwise location and spanwise distribution of rods. The implementation of devices with the optimum configuration has shown to increase aerodynamic performance and to significantly reduce separation for selected conditions. Application of rods to the wind turbine rotor has proven to avoid the spanwise penetration of flow separation where applied, leading to reduction of flow separation and to aerodynamic enhancement.Originality/valueThe proposed RVGs have shown potential to enhance the aerodynamic performance of wind turbine rotors and profiles, making devices an alternative solution to the classical vortex generators for wind turbine applications.

A study emphasizing the effects of passive vortex generators (VGs) on aerodynamic characteristics of a NACA 4415 airfoil is presented. Both experimental and numerical works have been carried out on an array of VGs attached to a NACA 4415 airfoil. Lift and drag measurements are made at various angles of attack by using three‐axis component balance system. On the numerical side, Reynolds‐averaged Navier‐Stokes (RANS) equations have been solved with ANSYS FLUENT 14.5 commercial code with fully structured mesh and three turbulence models (realizable k‐ε, k‐ω shear stress transport [SST] and the Spalart‐Allmaras model) at Reynolds number Re = 2 × 105. Parametric studies have been conducted to find out optimal configurations with respect to span‐wise separation distance between VGs, along with their location along the chord. A very good agreement has been obtained between experimental and computational results indicating that this optimized configuration is robust for the considered parameters. It turns out that increasing the span‐wise separation length increases the aerodynamic performances (lift‐to‐drag ratio) at low attack angles for which low parasitic drag is achieved but conversely degrades it at higher ones. For the stream‐wise location along the chord, upstream position of VGs degrades the lift‐to‐drag ratio at low attack angles and conversely improves it at higher ones.

Bi-leaflet Mechanical Heart Valve (BMHV) is widely used in surgically heart valve replacement in worldwide. The main complication of the BMHV is that BMHV leaded to the formation of blood clotting known as thrombosis. Vortex Generator (VG) is used to improve the performance of the BMHV by delaying the turbulence that activated the platelet and hemolysis. This paper presents various configuration of VG to enhance the performance of BMHV. In this Computational Fluid Dynamic (CFD) approach, a simplified prosthetic heart valve is used to investigate the performance of BMHV with different orientation of VG. As a result, the fluid is passed through the leaflets with VG. The pressure drop is decreased between the position of after leaflets and before leaflets. In the present study, four different configurations of VG are reviewed, which are without VG, Co-counter Equally Spaced VG, Straight Equally Spaced VG and Counter-rotating Far Spaced VG. In the other hand, this present study also investigates the pulsatile turbulent transient flow in simplified prosthetic heart valve with no VG and the best configuration of VG in the previous study. In the present study, Co-counter Equally Spaced VG is the best configuration and it contributed 42.62% of improvement in pressure drop across the leaflets. Besides that, Co-counter Equally Spaced provided 52.96% and 7.82% reduction in Turbulence Shear Stress and Turbulence Kinetic Energy respectively. In the summary, the pressure drop, turbulence kinetic energy and turbulence shear stress are significantly reduced due to the existence of VG. VG is a crucial device to enhance the performance of BMHV by delaying early separation and thus turbulence reduced.

Effects of vortex generator (VG) on the flow field in a flush-intake duct for waterjet propulsion are investigated numerically under various navigation conditions. Flow’s Reynolds-averaged Navier-Stokes equations (RANS) are solved with the SST-Kω turbulence model. Four VG blades are installed at the ship bottom ahead of the intake entrance. The VG blade is rectangular shaped with a height of 0.1D, a length of 0.3D, and an angle of attack of 20°. Results show that under the forward moving condition, VG device effectively restrains the flow separation on the duct ramp side and improves the section uniformity at intake exit under low inflow velocity ratio (IVR) condition. The duct efficiency gets improved over a wide IVR range. Under the oblique moving condition, there is no separation region on the duct ramp side at low IVR, but significant vortex appears on the lip side. VG device does not introduce any obvious extra negative effects on the hydraulic performance.

Counter-rotating vortex generators (VGs) are typically employed to delay airflow separation on wind turbine blades. Large-size wind turbine blades equipped with small size VGs make the computational fluid dynamics (CFD) researches require a great deal of computational resources. Parametric models of VGs can effectively improve the numerical research efficiency of wind turbine blades with VGs. In order to improve the accuracy of such parametric models, this study proposed a series of modeling approaches to determine the positions of the adding source term in Cartesian coordinates, the VG vortex core radius, etc., on the wind turbine airfoils. These techniques are integrated with a maximum circulation algorithm by considering the interactions between VG pairs to predict the performance of a DU91-W2-250 blade section with VGs. The proposed parametric model and an entity model at different angles of attack (AoAs) are implemented on the blade section. Our approach is validated using experimental data. Comparisons demonstrate a strong agreement between the modelled and experimental results, proving the high accuracy of the two models. The numerical results of the models are then compared and analyzed at different incoming flow velocities and AoAs to verify the universality of the proposed parametric approaches. The results reveal a high consistency between the vortex structure, the velocity profile above the blade surface and the distribution of the pressure coefficient calculated by the two models. This proves the high universality of the proposed approaches and demonstrates the potential of the parametric model in replacing the VG entity model. The VG parametric model expresses VG parameters by program, which can improve the research efficiency of VG arrangement on wind turbine blades.

Vortex generators (VGs) are applied to a two-stage highly-loaded transonic fan using the full blended blade and endwall (F-BBEW) method to assess their effects on fan performance. In the last stage stator, VGs were arranged on the hub and shroud within the blade passages. Numerical simulations are conducted to explore the effects of VGs on performance of the highly loaded transonic fan and the VGs action mechanism. The results demonstrate that the implementation of VGs led to an increase in fan aerodynamic performance, improving the fan pressure ratio margin by 2.25% while maintaining efficiency. The total pressure loss of the last stage stator decreased, with the loss coefficient reduced from 5.33% to 4.58% at 1.15 times the design pressure ratio. Furthermore, the VGs improve the flow field of the last stage stator. While the VGs on the hub suppressed local secondary flows, they do not provide significant benefits due to interaction with shock waves. In contrast, the VGs on the shroud reduce secondary flows and mitigate separation induced by upstream VGs, improving corner flow and overall flow quality of the last stage stator.

A low-speed wind-tunnel investigation is presented detailing the effects of vortex generators on an airfoil at low Reynolds numbers (80,000 and 160,000). Six different static vortex generator layouts were tested. In addition, an oscillatory (or active) vortex generator was designed and tested. Force balance measurements were recorded and interpreted with the aid of surface flow visualization. The data suggest that the static vortex generators function similarly to those at higher Reynolds numbers; increasing the maximum lift coefficient and increasing the stall angle. Different static vortex generator configurations appear preferable at the two tested Reynolds number ranges. The oscillating vortex generator did not appear effective in its present configuration.

Flow over a conventional delta wing has been studied experimentally at a subsonic flow of 20 m/sec and the flow field developed at higher angle of attack varying from 10° to 20° has been captured. A vortex generator is mounted on the leeward surface of the delta wing and its effect on the flow field is studied. The set of wing tip vortices generated over the delta wing is captured by the oil flow visualization and the streamline over the delta wing surface captured with and without a vortex generator are compared. Based on the qualitative results, the effect of the vortex generator on the lift coefficient is anticipated. Further, force measurement is carried out to quantitatively analyze the effect of vortex generator on the lift and drag coefficient experienced by the delta wing and justify the anticipation made out of the qualitative oil flow visualization tests. In the present study, the effect of mounting of a vortex generator is found to be minimal on the lift coefficient experienced by the delta wing. However, a significant reduction in the drag coefficient with increase in angle of attack was observed by mounting a typical vortex generator.

This paper deals with an adjoint-based design optimization of vortex generators for the performance improvement of an S-shaped subsonic inlet, the Royal Aircraft Establishment intake model 2129. To enhance the flow quality entering the engine face maximally, the vortex generators are independently optimized with five design parameters per each vortex generator (a total of 55 design variables). To increase the design efficiency, the source term model of the vortex generator is employed. The original source term model, which does not reflect a small change in position and thus has difficulties in differentiation for sensitivity analysis, is modified into a differentiable source term model. To deal with a large number of design variables, the gradient-based design optimization method using the discrete adjoint approach is employed to minimize the distortion coefficient while maintaining the baseline total pressure recovery ratio. A total of five design cases are conducted to validate the proposed design approach, to obtain the optimized vortex generators, and to confirm their enhanced performance. Through the proposed design process,theperformanceofthetargetinletisremarkablyimproved,showingthatthedistortioncoefficientdecreases well over 70% while maintaining the total pressure recovery ratio.

An empirical model which simulates the effects of vane-type vortex generators in ducts was incorporated into the Wind-US Navier-Stokes computational fluid dynamics code. The model enables the effects of the vortex generators to be simulated without defining the details of the geometry within the grid, and makes it practical for researchers to evaluate multiple combinations of vortex generator arrangements. The model determines the strength of each vortex based on the generator geometry and the local flow conditions. Validation results are presented for flow in a straight pipe with a counter-rotating vortex generator arrangement, and the results are compared with experimental data and computational simulations using a gridded vane generator. Results are also presented for vortex generator arrays in two S-duct diffusers, along with accompanying experimental data. The effects of grid resolution and turbulence model are also examined.

Aeroelasticity of modern wind turbines is a critical issue which can significantly affect the structural integrity and lifetime of the wind turbine blades. However, previous aeroelastic or aerodynamic studies were mostly concentrated on low-fidelity numerical methods, and the details of flow separation and vortex generation over wind turbine airfoils cannot be detected with these methods. In this study, a high-fidelity direct numerical model is used to investigate the details of flow separations and laminar separation bubbles (LSB) over a NACA-0012 wind turbine airfoil under oscillation. The simulations are conducted at Reynolds number of Re = 1.3 × 105 and the blade has harmonic pitch-wise oscillations at Mach number of Ma∞ = 0.4. Strong fluctuations are observed in the wake region of the vibrating wind turbine blade. The results show that the blade vibrations have a significant influence on vortex generation and separation point over wind turbine blades. details of flow structure over wind turbine blades compared to previously proposed models.

Simulation of an innovative internal design of a plate solar receiver: Comparison between RANS and LES results