Vortex Generator Jets Research Articles

Distortion Control in Intakes Subject to Strong Crosswinds Using Steady Vortex Generator Jets

Flow separation over the intake lip often occurs in gas turbine engines at off-design conditions such as crosswinds. The distortion transferred to the fan face detrimentally impacts the engine performance. The current study explores the efficacy of steady vortex generator jets (VGJ) to alleviate this flow distortion using high-fidelity implicit large-eddy simulations on a quasi-3D intake. The study reveals that VGJs, strategically placed on the windward side of the intake, induce coherent structures that include cylindrical jet shear layers, horseshoe vortices, and counter-rotating vortex pairs similar to transverse jets in crossflow. Parametric studies are carried out to identify the optimal VGJ location and blowing ratios. Superior flow control is achieved when the VGJs are placed on the windward side closer to the leading edge, reducing the distortion coefficient by ≈17% compared to the uncontrolled case. In contrast, when the VGJs are placed farther from the leading edge, the flow relaminarizes and the coherent structures decay rapidly due to severe acceleration over the intake lip. Consistent with experiments, our computations at higher blowing ratios (VR1.5 and VR2) show an improved pressure recovery decreasing the distortion coefficient by ≈40% due to deeper jet penetration and enhanced mixing.

Flow Control in Serpentine Inlet Duct Using Vortex Generator Jets

The objective of the present research is to study the effectiveness of steady and pulsed vortex generator jets in reducing inlet flow distortion and in improving pressure recovery by effective secondary flow control in uniform inflow serpentine duct diffuser. The measurements were carried out at a test Reynolds number of 6.5 x 105 based on the diffuser inlet width. Serpentine duct diffuser consisted of two main portions, namely, a square to circular constant area transition duct followed by a circular diffusing duct. Investigations show that the flow in the serpentine diffusing duct suffers from stall on the inner wall and consequently the outflow at AIP has considerable flow distortion due to the combined effect of secondary flow and the inner wall stall. It is observed that the use of vortex generator jets, both in steady and pulsed modes, improve the performance substantially. The number of jets, location of jets, velocity ratios and the pulse frequency are some of the variables that are studied. The results obtained so far suggest that use of pulsed jet not only gives better performance but also reduces the amount of air that is needed to be injected through the jets in comparison to steady jets for similar velocity ratios.

Control mechanism of vortex-generator jet on turbulent separation in a highly loaded compressor cascade

The active flow control technique of vortex-generator jet (VGJ) was used to control the turbulent separation of a highly loaded compressor cascade at a high incidence. VGJ schemes on suction surface with different jet locations, skewed angles, pitch angles were numerically performed and the control mechanism of VGJ parameters on the flow field of the cascade was revealed. For avoiding the effect of endwall boundary layer, both endwall surfaces of the cascade were set to translational periodicity boundary (TPB). Results show that VGJ significantly eliminates the turbulent separation and improves the performance of cascade. The overall loss coefficient of cascade is reduced by 52.3% at most. The optimal VGJ location in this study is not separation location but 7% axial chord downstream of it, which is probably due to the ultra-high loading of the cascade. The spanwise location and intensity of jet vortices are mainly affected by skewed angle, and will increase with the skewed angle. The VGJ case with a higher pitch angle features better control effect on suction surface but increases the pitchwise scale of the low-velocity region. In addition, as pitch angle increases, the mixing loss between mainstream and jet flow increases, which brings a negative effect on cascade performance. In order to enhance the momentum transporting between mainstream flow and separation flow, counter vortex-generator jet (CVGJ) schemes were designed and studied. Though CVGJ strengthens the jet vortices near the trailing edge and achieves minimum loss near TPB sections at 150% axial chord section, the interaction of jet vortices with opposite rotating direction brings extra loss, which leads to the control effect of CVGJ is weaker than that of VGJ.

Leading-Edge Active Flow Control Enabled by Curved Fluidic Oscillators

A new design of fluidic oscillator, in which the oscillator is curved along its primary flow direction, allows for a sweeping jet to be placed near the leading edge of a wing as an active flow control device. Previous studies of fluidic oscillator applications have shown their promise as an active flow control device by increasing the lift over a wing and preventing flow separation. However, the planar extent of the flat fluidic oscillators creates challenges when trying to optimally implement them in a confined geometry. The application of these new curved oscillators is experimentally investigated on the leading edge of an upswept NACA0018 airfoil full-span wing. Global load cell measurements of lift, drag, and pitching moment are presented and analyzed using suction surface static pressure taps, and particle image velocimetry data are presented. The effects of active flow control on lift, drag, and stall at a Reynolds number of 100,000 are documented for a variety of oscillator chordwise locations near the leading edge and compared to traditional vortex-generating jets. While further aft-positioned oscillators produced a larger increase in maximum lift, more forward locations resulted in better poststall performance and delayed flow separation over the wing.

Swept-Wing Active Flow Control with a Streamwise Row of Vortex Generating Jets

A novel swept-wing active flow control (AFC) technique was developed and tested on a NACA wing with 30° leading-edge sweep. A streamwise row of 20 vortex generating jets (VGJs), pitched 30° from the wing surface and skewed 60° toward the wing root, was applied at three different spanwise locations. Performance was assessed using load-cell measurements and surface oil flow visualizations at a Reynolds number of 100,000. More inboard placement of the AFC produced higher values of , but further outboard placement resulted in a higher stall angle. With a momentum coefficient of only 2%, lift was enhanced up to 15% and stall was delayed up to 12°, depending on the AFC location. The number of jets used in the row was reduced, resulting in nearly the same performance benefits with half of the momentum coefficient required for the full row of jets. The performance enhancements of this active flow control technique are comparable to a passive boundary-layer fence without the 25% increase in drag caused by the fence. The mass flow cost of the streamwise row of VGJs is 75% lower than the mass flow required for a previously studied swept-wing active flow control technique involving a streamwise slot.

Effect of Jet Vortex Generators on Shock Wave Induced Separation on Gas Turbine Profile

The interaction between a shock wave and a boundary layer on a suction side of gas turbine profile, namely Transition Location Effect on Shock Wave Boundary Layer Interaction, was one of main objectives of TFAST project. A generic test section in a transonic wind tunnel was designed to carry out such investigations. The design criteria were to reproduce flow conditions on the profile in wind tunnel as the one existing on the suction side of the turbine guide vane. In this paper, the effect of film cooling and jet vortex generators on the shock wave boundary layer interaction and shock induced separation is presented. Numerical results for Explicit Algebraic Reynolds Stress Model with transition modeling are compared with experimental data.

The effects of minute vortex generator jet in a turbulent boundary layer with adverse pressure gradient.

Experimental and numerical analysis of active and passive flow control is an important topic of practical value in the study of turbulent flows. This paper numerically analyzed the effects of an air microjet on an adverse pressure gradient turbulent boundary layer over a flat plane. Experimental data were employed to verify the numerical modeling. Vortex formation and development were then studied by changing the microjet to inflow velocity ratio (VR) and microjet angles. According to the results, the best values of the angles and for various velocities were found to be 30° and from 60° to 90°, respectively. Moreover, at VRs = 1, 2, and 4, the values (the distance at which the complete vortex persisted in the flow) were 0.058, 0.078, and 0.18, respectively. Compared to VR = 1, the vortex strength for VRs = 2 and 4 grew by 3.5 and 6.8 times, respectively. When the microjet was added to the flow, the highest variation in the Reynolds stress along the x-direction from VR = 1-4 was 10%. The corresponding values along the y and z- directions were 15% and 2.7 times, respectively.

Optimization of the hole exit shape of the vortex generator jets in a compressor cascade

Vortex generator jets usually use a circular hole. The hole exit shape is also an important parameter, so the change of the shape will have a significant influence on the control effect of the compressor. In this article, the optimization design of the hole exit shape is studied in order to find the optimal geometry. The 2D hole exit shape is represented with a binary coded and initialized with the B-spline. The surrogate-based optimizer consists of a parametric design code, a computational fluid dynamics solver, a Kriging model, an infill sample criterion, and a genetic algorithm. First, the design of the symmetric hole is studied in a low ratio of the jet to inlet mass flow. The circumferential length of the designed hole is fixed. Second, both the symmetric hole and the asymmetric hole are studied. And the area of the hole exit shape is fixed. The results show that the optimal hole shape can enhance the strength of the jet vortex and reduce the total pressure loss of the compressor cascade. A better control effect can also be obtained in a high jet mass flow.

On the Importance of Transition Control at Transonic Compressor Blades

AbstractThe flow through a transonic compressor cascade is characterized by high unsteadiness and a high loss level. This results from the shock waves in the blade cascade and their interaction with the blade suction side boundary layer. In the case of a laminar shock wave boundary layer interaction, the loss level is higher due to the occurrence of a laminar separation bubble below the shock wave compared to the shock wave interaction with a turbulent boundary layer. In addition, the oscillation of the shock position in both cases influences the working range concerning the point of stall onset as well as leading to an unsteady interaction with the blade called buffeting. The reduction of losses and of unsteadiness in the shock wave oscillation, connected to a decrease of the blade buffeting effect, is the aim of the current investigation. Therefore, experimental investigations using a roughness patch as well as air jet vortex generators in order to control the transition in a transonic compressor cascade have been conducted at the transonic cascade wind tunnel of the German Aerospace Center (DLR) at Cologne. At an inflow Mach number of 1.21, a loss reduction for both transition control cases is achieved. In spite of a nearly uninfluenced fluctuation range of the passage shock wave compared to the reference cascade, the oscillation spectra of the transition control cases show a reduction of the shock movement amplitude at a frequency below 500 Hz and above 1 kHz. In the closing section of the paper, a detailed discussion on the reasons for the resulting flow behavior based on particle image velocimetry and high-speed shadowgraphy data is given. The resulting conclusion of the study is that the consideration of transition control at transonic compressor blades is very important in order to reduce losses and flow unsteadiness that directly influences blade buffeting and the numerical prediction quality of the stall onset.

Transient dynamical effects induced by single-pulse fluidic actuation over an airfoil

Flow control experiments on a NACA 0015 airfoil using pulsed vortex generator jets (PVGJs) are carried out at a chord-based Reynolds number of $$4.6 \times 10^5$$ . Configurations of partially separated flow over the airfoil are studied with a special focus on the transient effects induced by actuation. The main objective is the improvement of the rate of variation of the aerodynamic loads. The response to a single-pulse actuation, of duration smaller than the convective time over the airfoil, is compared with the response to the onset of steady blowing. We observe that the single-pulse actuation, if correctly tuned, induces a higher rate of loads variation (up to 50 $$\%$$ for the lift). By using Lagrangian analyzing tools (finite-time Lyapunov exponent—FTLE), we show that this improvement is due to dynamical effects at the scale of the airfoil, associated with the formation of a closed separation region during the initial transient phase after the end of actuation. Such load control could be effective in situations where a fast time response is needed to compensate unsteady aerodynamic effects, such as in gusting flows or during rapid maneuvers.

Combined Flow Control of Positively Bowed Blade and Vortex Generator Jet on a Compressor Cascade

Abstract A combined flow control method based on positively bowed blade and endwall vortex generator jet (VGJ) was performed to a compressor cascade under three kinds of inlet conditions. The results show that the endwall VGJ can further decrease the total losses in positively bowed cascades. At 0° incidence with zero inlet boundary layer, the separation type in the positively bowed blade is open, with the VGJ, the loss reduction is 2.7 %. As the inlet boundary layer thickens at 0° incidence, the separation region increases with the separation type keeping unchanged, the loss reduction increasing to 11.73 %. As the incidence rises to +7° with zero inlet boundary layer, the separation type converts into closed and the flow separation is the severest in the three cases, with the VGJ, however, the loss reduction is just 7.4 %, which means that the control effect of endwall VGJ not only depends on the size of separation region but also relies on the type of separation mode. If the separation type is open, as the size of separation region expands, the control effectiveness of endwall VGJ increases; if the separation type converts into closed with the further aggravation of flow field, that control effect will decrease.

An Experimental Study of a Passive Method of Attenuating a Transonic Buffet Phenomenon

The results of experimental studies of the physical pattern of the appearance of the buffet phenomenon at transonic speeds for a model supercritical profile are presented. A passive way of controlling this phenomenon is proposed that is connected with the organization of special jet vortex generators. It is experimentally found that the proposed approach leads to a delay in the appearance and weakening of the transonic buffet and, as a result, to an improvement in the aerodynamic characteristics of the profile.

The Effect of Steady and Pulsed Air Jet Vortex Generator Blowing on an Airfoil Section Model Undergoing Sinusoidal Pitching

Experimental results are reported on the assessment of steady and pulsed air jet vortex generators (AJVGs) for the suppression of dynamic stall on a sinusoidal pitching RAE9645 airfoil model. Tests at Rec of 1 million, at reduced pitching frequencies between 0.01 and 0.10 were performed with and without steady and pulsed AJVG blowing. The effect of jet momentum coefficient (0.0003< Cμ< 0.0046), jet duty cycle (0.25< DC< 1) and jet pulsing frequency (0.29< F+< 2.93) were investigated. Pulsed air jet blowing with F+ in the range 0.5–1.0 and with a duty cycle in the range 0.4–0.5, was found to be the most effective to achieve full suppression of dynamic stall vortex formation.

The Performance of the Self-Supplying Vortex Generator Jets on a High-Speed Compressor Cascade

Abstract The self-supplying vortex generator jet (SVGJ) is introduced to the separation control of a high-speed compressor cascade with an inlet Mach number of 0.67. A parametric investigation concerning the jet location and the injection angle is conducted numerically. The effect mechanisms of SVGJ on the cascade performance are analyzed in detail. The potentials of SVGJ at off-design points are also discussed. The vortex generated by the jet utilizing the pressure difference between the pressure surface and suction surface could enhance the fluid exchange between the boundary layer and the mainstream, thus weakening the flow separation and reducing the flow loss effectively. With a hole of diameter 0.5 mm and a jet-to-inflow mass flow ratio less than 0.3‰, the maximum loss reductions are 5.2 % at the design point and 8.0 % at the off-design point, validating the high efficiency of SVGJ. In this work, the optimum performance is obtained by the SVGJ located at xj /B=40 %, h/H=15 % with a skew angle of β=60°.

Experimental study on the control of turbulent wall jet by a vortex generator jet

Experimental study on the control of turbulent wall jet by a vortex generator jet

Экспериментальное исследование пассивного способа ослабления трансзвукового баффета

Experimental studies of buffeting onset phenomenon physical picture on a model of a supercritical airfoil at transonic speeds are presented. Passive control method of this phenomenon based on application of the special jet vortex generators is given. It is shown that application of this method leads to delaying of the onset and decreasing of buffeting phenomenon, and at the result – to improve aerodynamic characteristics of airfoil.

Numerical Investigation of Steady and Harmonic Vortex Generator Jets Flow Separation Control

Active flow control of canonical laminar separation bubbles by steady and harmonic vortex generator jets (VGJs) was investigated using direct numerical simulations. Both control strategies were found to be effective in controlling the laminar boundary-layer separation. However, the present results indicate that using the same blowing amplitude, harmonic VGJs were more effective and efficient at reducing the separated region than the steady VGJs considering the fact that the harmonic VGJs use less momentum than the steady case. For steady VGJs, longitudinal structures forming immediately downstream of the injection location led to the formation of hairpin-type vortices, causing an earlier transition to turbulence. Symmetric hairpin vortices were shown to develop downstream of the forcing location for the harmonic VGJs, as well. However, the increased control effectiveness for harmonic VGJs’ flow control strategy is attributed to the fact that the shear-layer instability mechanism was exploited. As a result, disturbances introduced by VGJs were strongly amplified, leading to the development of large-scale coherent structures, which are very effective at increasing the momentum exchange, thus limiting the separated region.

Application of Jets and Vortex Generators to Improve Air-Cooling and Temperature Uniformity in a Simple Battery Pack

Abstract In this paper, the problem of air cooling and temperature nonuniformity at the cell and pack level is addressed. Passive techniques are developed by integrating jet inlets and vortex generators (VGs) in a simple battery pack with the goal to achieve an effective cooling, and the desired temperature uniformity at the cell and pack level to less than 5 °C, without an increase in the required mass flow and power requirements. Moreover, various configurations of the developed techniques are assessed and compared. In order to achieve the objectives, computational fluid dynamics (CFD) is used to conduct numerical studies on the battery packs. The results concluded that by adding both the delta winglet (DW) vortex generator arrays and jet inlet arrays in the same configuration, improvements in temperature reduction and uniformity can be achieved. The results showed that the maximum temperature of the battery pack was reduced by ∼6% and the temperature uniformity at the pack level was increased by 24%. Additionally, a ∼37% improvement in the temperature uniformity at cell level was achieved.

Active Control of Cylinder Charge Motion Using Vortex Generating Jets (VGJs) on Generic Intake Port Geometries

Active Control of Cylinder Charge Motion Using Vortex Generating Jets (VGJs) on Generic Intake Port Geometries

Effect of the end-wall vortex generator jets on the performance of a high subsonic compressor cascade

This paper presents a numerical and experimental result of the end-wall vortex generator jets for controlling corner separation and enhancing the aerodynamic performance in a high subsonic (Ma = 0.7) compressor cascade. The experiments were carried out on a compressor cascade at design point ( i = 0°) and off-design points ( i = −2°, 2°, and 4°). At design point, the total pressure loss coefficient could be reduced up to 12.1%.With the increase in the incidence, the control effect is enhanced first and then reduced. The maximum total pressure loss reduction is up to 14.6% when the incidence is 2°. The numerical study is further conducted to analyze the flow pattern and the vortex structure. The jet vortex is formed downstream of the jet hole using the vortex generator jets, the cross flow on the end wall is also suppressed.