Counter-rotating Vortex Generators Research Articles

The effect of vortex generators having Clark-Y airfoil on tapered swept-back wing

In the experimental study, the effects of vortex generators (VGs) having Clark-Y airfoil and triangular VGs are investigated. The tests were carried out on a tapered swept-back wing at Re = 6.0×104 using counter-rotating vortex generators having Clark-Y airfoil at five different locations that are x/c= 0.1, 0.2, 0.3, 0.4, and 0.5 and triangular VGs at x/c=0.1 location. A load cell is used to measure forces at angles of attack (AoA) ranging from 0° to 30°. It is observed that the maximum lift coefficient (CLmax) and aerodynamic performance of VGs having Clark-Y airfoil decrease when the position of the vortex generators changes from 0.1 to 0.5. The optimal results obtained from the study show that the tapered swept-back wing with the VGs having Clark-Y airfoil exhibits a significant increase of 37.5% in the CLmax and approximately 55% in the lift to drag ratio (L/D) at x/c=0.1 compared to the baseline. At low AoA, the VGs having Clark-Y airfoil provided better lift, whereas at high AoA, the triangular VGs provided better lift.

Numerical study on the Effect of Rectangular and Triangular Counter-Rotating Vortex Generators on the H-Rotor Wind Turbine Performance

Numerical study on the Effect of Rectangular and Triangular Counter-Rotating Vortex Generators on the H-Rotor Wind Turbine Performance

Effect of vortex generator orientation on wind turbines considering the three-dimensional rotational effect

A three-dimensional rotational effect (TDRE) is created in the rotating wind turbines. A TDRE generates a spanwise velocity on the blade surface and changes the inflow angle of vortex generators (VGs) mounted on the blades. The optimal design of VGs should consider the TDRE to improve the aerodynamic performance of a wind turbine. This study analyzes the physical mechanisms of counter-rotating (CtR) and co-rotating (CoR) VGs on a flat plane at different incoming wind directions. Then, the behaviors of CtR and CoR VGs affected by the TDRE were examined on a National Renewable Energy Laboratory (NREL) phase VI wind turbine to find the fit spacing. The computational fluid dynamics studies were validated by experimental data. The results showed that VGs can improve the output power of the wind turbine and delay airflow separation on the blade section. Due to the inclined inflow generated by the TDRE, CtR VGs produced asymmetric vortices pairs behind them, and the effect of CtR VGs was weakened due the substantially decreased strength of one VG. In contrast, CoR VGs formed the same inflow angles under the spanwise velocity, generated more steady shedding vortices, and were relatively more advantageous than CtR VGs. In addition, when the spacing of CoR VGs was z = 3h, the attached flow area on the blade surface was about 10% larger than that when z = 2h.

Controlling the Flow Separation in Heart Valves Using Vortex Generators

A comprehensive computational study is performed to investigate the effectiveness of vortex generators (VGs) applied to mechanical bi-leaflet heart valves. Co-rotating and counter-rotating VG configurations are compared to a control valve without VGs. Detailed flow fields are obtained and used to elucidate the underlying flow physics. It was found that VGs reduce flow separation over the leaflets and hence reduce the Reynolds shear stress (RSS) in the vicinity regions of heart valve. The co-rotating VG configuration demonstrates a better performance compared with the counter-rotating configuration in terms of the RSS, turbulent kinetic energy production and velocity distributions, especially in the peripheral jet flows. The fraction of blood damage in the co-rotating configuration shows a 4.7% reduction in comparison to the control case, while a 3.7% increase is observed in the counter-rotating configuration. The passive flow control technique of applying co-rotating VG illustrates a great potential to help mitigate the hemodynamic factors leading to potential blood damage risk.

Research on the Parametric Modelling Approach of Vortex Generator on Wind Turbine Airfoil

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.

Performance improvements of helicopter basic fuselage model by passive vortex generators

Wind-tunnel tests of a heavy-class helicopter model were carried out to evaluate the effectiveness of a passive flow control system in alleviating fuselage parasite drag. An array of counter-rotating vortex generators was installed to reduce/remove the flow separation occurring on the rear-loading ramp responsible for the high-pressure drag. Novel technical solutions for the VGs’ design and location were selected compared to the previous work. A geometrically scaled 1:7 basic fuselage of a heavy-class helicopter was investigated with and without a passive flow control system using various measurement techniques. In particular, pressure measurements and stereo particle image velocimetry surveys were performed to obtain physical insights into load measurements. This paper reports promising results from wind-tunnel experiments, including the observation of significant drag reduction for a wide range of fuselage angles of attack and side slip angles without a negative impact on other aerodynamic characteristics.

Numerical Simulation of Horizontal Axis Wind Turbines with Vortex Generators

In the present study, a simulation about the effects of vortex generators on horizontal axis wind turbine rotor blade was numerically conducted using a static coupled CFD–CSD method. A Navier–Stokes CFD flow solver based on unstructured meshes was used to obtain the blade aerodynamic loads. A FEM-based CSD solver employing a nonlinear coupled flap-lag-torsion beam theory was utilized to calculate the blade elastic deformation. The coupling of the CFD and CSD solvers was accomplished in a loosely coupled manner by exchanging the information between the two solvers at infrequent intervals. The static coupled CFD–CSD method was applied to the NREL 5 MW reference wind turbine rotor under steady axial flow conditions. Triangular counter-rotating vortex generators were adopted to control flow separation and radial flow in the inboard section of the NREL 5 MW reference rotor blades. They were installed on the inboard part of the blade from 0.2 to 0.4 R. As a result of the flow analysis considering the counter-rotating vortex generators, strong vortices were generated by counter-rotating vortex generators. It can be seen that the regions where flow separation and radial flow occur in the inboard sections were reduced compared to the baseline wind turbine. For this reason, the maximum power improvement due to counter-rotating vortex generators was 1.04% at the rated wind speed.

Reduction of Pressure Gradient and Turbulence Using Vortex Generators in Prosthetic Heart Valves.

Blood damage and platelet activation are inherent problems with present day bi-leaflet mechanical heart valve designs. Passive flow control through different arrangements of vortex generators (VG) as means of improving pressure gradients and reducing turbulence are investigated. Rectangular VG arrays were mounted on the downstream surfaces of a 23mm 3D printed mechanical valve. The effect of VGs on the resulting flow structures were assessed under pulsatile physiological flow conditions where high resolution particle image velocimetry measurement was performed. The co-rotating VGs showed lower Reynolds shear stresses and improved pressure gradients (PG) compared with the counter-rotating ones and the no-VG control one (that showed higher turbulence). RSS was found 38.13 ± 0.89, 12.95 ± 0.32, 15.75 ± 0.71, 24.54 ± 0.84 and 16.33 ± 0.58Pa for the control, co-rotating VGs, 8 counter-rotating VGs, 4 far-spaced VGs and 4 closely-spaced VGs, respectively. PG of 10.45 ± 0.94mmHg was obtained with co-rotating VGs and the difference was significant compared with the other configurations (control 14.88 ± 0.4mmHg; 8 counter-rotating VGs 13.76 ± 0.51mmHg; 4 far-spaced VGs 13.84 ± 0.09mmHg; and 4 closely-spaced VGs 15.37 ± 0.16mmHg). Co-rotating VGs for this application induce a more delayed flow separation and a more homogenized and streamlined transition of flow compared with the counter-rotating VGs. Passive flow control techniques deployed on BHMVs is potentially beneficial as significant control of flow at small length scales without inducing large-scale design modifications of the valve.

Modeling of wind turbine vortex generators in considering the inter-effects between arrays

Vortex generators (VGs) are commonly placed on wind turbine blades to delay flow separation in the boundary layer. VGs can be parametrically modeled in computational fluid dynamics for effective and efficient simulations of wind blade flow fields. Many researchers have studied the vortex circulation created by VGs and created various parametric models used with the Navier-Stokes equations, but most of them are based on a single winglet of VGs and do not include the inter-effects between the winglets. This paper proposes a parameterized VG array model based on counter-rotating VGs, which properly takes into account the inter-effects between winglets. Two cases, i.e., a plate with a pair of VGs and a DU-W2–250 blade segment with five pairs of VGs, are investigated to validate this model; the array type parametric model is in closer agreement with experimental data than traditional models. Compared to the solid VG model, the array type model has similar streamlines and surface pressure coefficients on the suction surface. The array type VG model can effectively reduce the number of grid points and yield highly accurate predictions of wind turbine blade aerodynamic characteristics.

Characterization of Vortex Generators Induced Flow around Wind Turbine Airfoil

Vortex generators (VGs) are an effective way to control flow separation in wind turbine. To understand the mechanism of VGs controlling flow separation, the flow field around airfoil Du97W300 with VGs was simulated and analyzed with CFD tools, and this numerical method is validated through the comparison between the numerical results and the experimental results. Furthermore, the flow fields around airfoil equipped with four different types of VGs are calculated and analyzed. The results show that the helical vortex induced by counter-rotating VGs develop approximately along streamwise direction; these types of VGs can cause a delay in stall and enhance the maximum airfoil lift coefficient. However the helical induced vortex actuated by the co-rotating VGs develop nearly along vortex generator direction and cannot cause a delay in stall effectively. In the counter-rotating VGs, the Q integration (the character parameter of induced vortex) of rectangular is twice of the triangle, and the Q integration of the forward triangle is almost equal to the backward triangle VGs.

Visualization of boundary layer separation and passive flow control on airfoils and bodies in wind-tunnel and in-flight experiments

Infrared camera, Particle Image Velocimetry, smoke-wire, tuft filaments and oil-flow visualization techniques were used for wind-tunnel and in-flight investigation of boundary layer separation, both stall and separation bubbles, related to the low-Reynolds numbers transition mechanism. Airfoils of Wortmann FX66 series and FX66 series wing-fuselage interaction, as well as modern airfoils and their wing-fuselage geometry were subject to study. The presence of previously identified structures in the CFD modelling, such as horse-shoe vortices, was confirmed in the flow. Wind-tunnels and in-flight measurements on sailplanes were carried out and effect of passive flow control devices - vortex generators - was surveyed; namely counter-rotating vortex generators and Zig-zag type turbulators were applied. Separation suppression and consequent drag coefficient reduction of test aircrafts was reached. PIV investigation was further extended by Time-Resolved

Multifidelity Surrogate Modeling of Experimental and Computational Aerodynamic Data Sets

This study presents a multifidelity surrogate modeling approach, combining experimental and computational aerodynamic data sets. A multifidelity cokriging regression surrogate model is used. This study highlights how lowfidelity data from computations contribute to improving surrogate models built with limited high-fidelity data from experiments. Various types of sampling design for low fidelity data are also examined to study the impact of characteristics of the sampling design on the final surrogate models. Replication, blocking, and randomization techniques originally developed for design of experiments are used to minimize random and systematic errors. Surrogate models representing the performance of an inverted wing with counter-rotating vortex generators in ground effect are constructed, where design variables of the wing ride height and incidence and the response of sectional downforce are examined. A cokriging regression containing 12 experimental and 25 computational data points sampled with a Latin hypercube design shows the best performance here, capturing general characteristics of the target map well.

Flow Separation Control on a Race Car Wing With Vortex Generators in Ground Effect

Flow separation control using vortex generators on an inverted wing in ground effect is experimentally investigated, and its performance is characterized in terms of forces and pressure distributions over a range of incidence and ride height. Counter-rotating and co-rotating rectangular-vane type vortex generators are tested on the suction surface of the wing. The effect of device height and spacing is investigated. The counter-rotating sub-boundary layer vortex generators and counter-rotating large-scale vortex generators on the wing deliver 23% and 10% improvements in the maximum downforce, respectively, compared with the clean wing, at an incidence of one degree, and delay the onset of the downforce reduction phenomenon. The counter-rotating sub-boundary layer vortex generators exhibit up to 26% improvement in downforce and 10% improvement in aerodynamic efficiency at low ride heights. Chordwise pressure measurement confirms that both counter-rotating vortex generator configurations suppress flow separation, while the co-rotating vortex generators exhibit negligible effectiveness. This work shows that a use of vortex generators, notably of the counter-rotating sub-boundary layer vortex generator type, can be effective at controlling flow separation, with a resultant improvement in downforce for relatively low drag penalty.

Experimental and numerical investigation of the performance of vortex generators on separation control

An experimental wind tunnel study of the flow past a row of counter-rotating vortex generators mounted on top of a bump has been performed. All three velocity components are measured in spanwise planes downstream of the vortex generators using Stereoscopic Particle Image Velocimetry, SPIV. The objective of this study is to investigate the effect of vortex generators in a separating, low Reynolds number, turbulent boundary layer over a geometry which is generating an adverse pressure gradient. The flow behaves as expected, in the sense that the vortices transport high momentum fluid into the boundary layer, making it thinner and more resistant to the adverse pressure gradient with respect to separation. The idea behind the experiments is that the results will be offered for validation of modeling of the effect of vortex generators using various numerical codes. Steady-state RANS computations have been carried out in parallel to the experiments. The computations are able to capture the overall flow structure, but has difficulties predicting the flow in the separation region and the large scale convection due to the vortex generators.

Empirical Model for Vane-Type Vortex Generators in a Navier-Stokes Code

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.

Reducing Inter-Chip Temperature Differences in Computers Using Vortex Generators in Forced Convection

Experiments were conducted to investigate methods of reducing inter-chip temperature differences in forced convective direct immersion cooling of semiconductor chips using a dielectric liquid (FC-77) as coolant. The experiments were conducted in a closed-loop flow facility with a 5 × 15 array of chips mounted on the bottom wall of a horizontal channel and with vortex generators installed on the opposite wall, upstream of the heated chip. Single, half delta-wing vortex generators of two heights, as well as a pair of counter-rotating vortex generators, were tested at different placement locations with respect to the heated chip. The channel height-based Reynolds number was varied from 1000 to 7500. Heat transfer coefficients and pressure drop measurements were obtained. The taller vortex generator placed 2.5 chip heights upstream of the heated chip was found to yield the best results. The increase in pressure drop due to each of the individual vortex generators was found to be negligible. The greatest enhancement in heat transfer of 17 percent was obtained at Reynolds numbers in the transitional flow regime.