Co-rotating Vortex Generators Research Articles

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.

低速平板境界層における2つのCo-rotating Vortex Generatorsの設置間隔による渦干渉流れへの影響

低速平板境界層における2つのCo-rotating Vortex Generatorsの設置間隔による渦干渉流れへの影響

Parametric studying of low-profile vortex generators flow control in an aggressive inter-turbine duct

This paper presents a study of low-profile vortex generators flow control on the effect of casing boundary layer separation in an aggressive inter-turbine duct. Counter-rotating and co-rotating vortex generators configurations were tested parametrically to obtain the optimum low-profile vortex generators’ setup within the aggressive inter-turbine duct, in terms of the axial location, height, angle of attack and streamwise vortices per swirl vane pitch. Surface oil flow visualization was used to qualitatively examine the low-profile vortex generators eliminating the casing separation and subsequently the detailed seven-hole probe measurements were carried out to evaluate the loss reduction quantitatively. The inter-turbine duct examined for this study was more aggressive compared with the geometries found in the most current modern engine designs. Measurements were made inside the aggressive inter-turbine duct annulus at Reynolds number of 150,000. The flow structures within the aggressive inter-turbine duct were found to be dominated by counter-rotating vortices evolved by the swirl vanes and boundary layer separation in both casing and hub regions. A massive casing boundary layer separation extending from the duct first bend to the second bend was found within the aggressive inter-turbine duct. The primary source of pressure loss in the aggressive inter-turbine ducts was the result of the extensive casing boundary layer separation. Flow control by utilizing the low-profile vortex generators installed on the casing was conducted to eliminate the casing separation. Regardless of the vortex generator mitigating the casing separation associated with consequential loss reduction, a pair of casing counter-rotating vortices was always evident at the duct second bend in all cases. Among the tested low-profile vortex generator configurations, two of the most effective low-profile vortex generator configurations, one counter-rotating and one co-rotating low-profile vortex generator configurations, were acquired as a result of successfully eliminating the casing separation. Despite that the inter-turbine duct is aggressively designed, it is concluded that this duct associated with proper flow control techniques is considered as a potential candidate for weight saving in a high bypass ratio engine.

Direct Simulation and RANS Modelling of a Vortex Generator Flow

An array of co-rotating vortex generators (VG) is placed in a supersonic boundary layer, similar to that on an airliner wing. Direct numerical simulations (DNS) are conducted, with unsteady turbulent content in the incoming boundary layer obtained from the synthetic-turbulence approach of Shur et al. (Flow Turbul. Combust. 93, 63–92, 2014). The RANS models are tested in two ways: with a straightforward application to the problem, but also by solving the turbulence equations in the “frozen” average flow field of the DNS and therefore in “passive” mode, which appears to be a powerful procedure, similar to that of Parneix et al. (J. Fluids Eng. 120(1), 40–47, 1998). Side-by-side comparisons become clearer. The model Reynolds stresses are compared with the Reynolds stresses of the DNS. A plausible definition of an effective scalar eddy viscosity extracted from the DNS is also used for comparison, providing a target value. The models are the k- ω Shear Stress Transport model of Menter (1993) (SST) and the curvature-corrected version of Smirnov and Menter (J. Turbomach. 131(4), 041010, 2009) which we will denote by SST-RC, the eddy-viscosity transport model of Spalart and Allmaras (1992) (SA), and the SA model with Rotation and Curvature correction of Spalart and Shur (Aerosp. Sci. Technol. 1(5), 297–302, 1997) (SARC). As expected, SST and especially SA return an excessive decay of the peak vorticity, and both SST-RC and SARC perform better, but the flow is too complex for RANS to near perfection. This decay is very detrimental in practice, since their persistence is the key property of vortices used for separation control.

Flow Control in an Aggressive Interturbine Transition Duct Using Low Profile Vortex Generators

This paper presents an experimental investigation of the flow mechanisms in an aggressive interturbine transition duct with and without low-profile vortex generators flow control. The interturbine duct had an area ratio of 1.53 and a mean rise angle of 35 deg. Measurements were made inside the annulus at a Reynolds number of 150,000. At the duct inlet, the background turbulence intensity was raised to 2.3% and a uniform swirl angle of 20 deg was established with a 48-airfoil vane ring. Results for the baseline case (no vortex generators) showed the flow structures within the duct were dominated by counter-rotating vortices and boundary layer separation in both the casing and hub regions. The combination of the adverse pressure gradient at the casing's first bend and upstream low momentum wakes caused the boundary layer to separate on the casing. The separated flow on the casing appears to reattach at the second bend. Counter-rotating and corotating vortex generators were installed on the casing. While both vortex generators significantly decreased the casing boundary layer separation with consequential reduction of overall pressure losses, the corotating configuration was found to be more effective.

Modeling Vortex Generators in a Navier-Stokes Code

A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.

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.

Direct numerical simulation of large-eddy-break-up devices in a boundary layer

Turbulent boundary layers create aerodynamic noise inside all vehicles, and especially inside jetliners. The objective of this project is to modify the turbulence in an attached boundary layer, not to reduce skin friction, but to weaken the wall pressure fluctuations, or to shift them to less damaging frequencies and wavelengths. In order to benefit an entire airliner windshield, the effect would be sustained over about 25 boundary-layer thicknesses, δ, which far exceeds the common rule that the relaxation of the turbulence takes about 10 δ. Various flow-control devices are studied by Direct Numerical Simulation, which is free of modeling and provides the full details of the pressure field. The Reynolds number is far lower than in the real flow, but this limitation of DNS is tolerable, because the focus is on the larger eddies. The multi-block implicit numerical method can represent fairly complex devices at a manageable cost. Inflow turbulence is provided by a recycling procedure derived from that of Lund, Wu and Squires, but much simpler. It occupies less than 5 δ in the streamwise direction. Flow visualizations, Reynolds stresses, and spectra are shown; the baseline spectra are within the experimental scatter. Co-rotating vortex generators are tried first. They reduce the turbulence intensity away from the wall, as hoped, but actually intensify the wall pressure fluctuations and were therefore abandoned. Large-eddy-break-up devices resembling a highway bridge are tried next, and succeed in reducing the wall fluctuations, but only over about 6 δ. Thus, the technology is not successful yet for a windshield, but it might be applied to other windows or other vehicles, and the simulation methodology appears to be well developed and of some interest particularly regarding inflow conditions.

Application of Vortex Generators in Flow Control of the Inlet

This paper introduces the features of using co-rotating vortex generators for controlling boundary layer and flow field in the inlet without flow separation. The principles of the arrangements of the blades and selection of constructional parameters of the generators that are applied to create the transverse flow between the high and low pressure regions and to reduce the secondary flow losses are analysed. The experimental results show that when the appropriate parameters of the co-rotating vortex generators are chosen for the inlet subsonic diffuser with apparent high and low pressure regions, not only the nonuniformity of the flow field is greatly improved but also the dynamic performance of the flow at exit is slightly improved.Copyright © 1985 by ASME