scholarly journals Influence of sub boundary layer vortex generator height and attack angle on cross-flows in the hub region of compressors

2021 ◽  
Author(s):  
Hao Fu ◽  
Ling Zhou ◽  
Lucheng Ji
Keyword(s):  
Boundary Layer ◽  
Vortex Generator ◽  
Attack Angle

scholarly journals On the formation of streamwise vortices by plasma vortex generators

2013 ◽  
Vol 733 ◽  
pp. 370-393 ◽  
Author(s):  
Timothy N. Jukes ◽  
Kwing-So Choi
Keyword(s):  
Boundary Layer ◽  
Flow Direction ◽  
Vortex Formation ◽  
Vortex Generator ◽  
Streamwise Vortex ◽  
Spanwise Direction ◽  
Formation Mechanisms ◽  
Wall Jet ◽  
Streamwise Vortices ◽  
Barrier Discharge Plasma

AbstractThe streamwise vortices generated by dielectric-barrier-discharge plasma actuators in the laminar boundary layer were investigated using particle image velocimetry to understand the vortex-formation mechanisms. The plasma vortex generator was oriented along the primary flow direction to produce a body force in the spanwise direction. This created a spanwise-directed wall jet which interacted with the oncoming boundary layer to form a coherent streamwise vortex. It was found that the streamwise vortices were formed by the twisting and folding of the spanwise vorticity in the oncoming boundary layer into the outer shear layer of the spanwise wall jet, which added its own vorticity to increase the circulation along the actuator length. This is similar to the delta-shaped, vane-type vortex generator, except that the circulation was enhanced by the addition of the vorticity in the plasma jet. It was also observed that the plasma vortex was formed close to the wall with an enhanced wall-ward entrainment, which created strong downwash above the actuator.

Reducing Low-Pressure Turbine Stage Blade Count Using Vortex Generator Jet Separation Control

2002 ◽  
Author(s):  
Rolf Sondergaard ◽  
Jeffrey P. Bons ◽  
Matthew Sucher ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
Vortex Generator ◽  
Separation Control ◽  
Surface Boundary ◽  
Freestream Turbulence ◽  
Skew Angle ◽  
Suction Surface ◽  
Simple Boundary ◽  
Design Value ◽  
Vortex Generator Jets

An experimental investigation has been conducted into the feasibility of increasing blade spacing (pitch) at constant chord in a linear turbine cascade. Vortex generator jets (VGJs) located on the suction surface of each blade in the cascade are employed to maintain attached boundary layers despite the increasing tendency to separate due to the increased uncovered turning. Tests were performed at low Mach numbers and at blade Reynolds numbers between 25,000 and 75,000 (based on axial chord and inlet velocity). The vortex generator jets (30 degree injection angle and 90 degree skew angle) were operated with steady flow with momentum blowing ratios between zero and five, and from two spanwise rows of holes located at 45% and 63% axial chord. In the absence of control, pitch-averaged wake losses increase up to 600% as the blade pitch is increased from its design value to twice the design value. With the application of VGJs, these losses were driven down to or below the losses at the design pitch. The effectiveness of VGJs was found to increase modestly with increasing Reynolds number up to the highest value tested, Re = 75,000. The fluid phenomenon responsible for this remarkable range of effectiveness is clearly more than a simple boundary layer transition effect, as boundary layer trips installed on the same blades without VGJ blowing had no beneficial effect on blade losses. Also, tests conducted at elevated levels of freestream turbulence (4% at the cascade inlet) where the suction surface boundary layer is generally turbulent, showed wake loss reduction comparable to tests conducted at the nominal 1% freestream turbulence. For all configurations, blowing from the upstream row had the greatest wake influence. These findings open the possibility that future LPT designs could take advantage of active separation control using integrated VGJs to reduce the turbine part count and stage weight without significant increase in pressure losses.

Improving Ships’ Efficiency Using Energy Saving Devices (ESDs)

2015 ◽  
Author(s):  
Charinda L. Perera ◽  
Ema Muk-Pavic
Keyword(s):  
Boundary Layer ◽  
Potential Energy ◽  
Energy Saving ◽  
Flow Pattern ◽  
Energy Savings ◽  
Vortex Generator ◽  
Wake Flow ◽  
Container Ship ◽  
Trapezoidal Shape ◽  
Before And After

This research paper describes the CFD work carried out by the authors to investigate the potential energy savings achieved by attaching a Vortex Generator to the hull of a container ship. This is done by computing the flow pattern at the propeller plane before and after the addition of a Vortex Generator, to determine if the addition of the mentioned device presents the propeller with a more favourable inflow. The Vortex Generator is a trapezoidal shape fin attached to the hull which works by inducing vorticity and deflecting streamlines within the boundary layer, thus diverting and equalizing wake flow into the propeller.

The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets

2001 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Rolf Sondergaard ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
Duty Cycle ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Skew Angle ◽  
Suction Surface ◽  
Duty Cycles ◽  
Wide Range ◽  
Vortex Generator Jets

The effects of pulsed vortex generator jets on a naturally separating low pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 degree pitch and 90 degree skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient vs. pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies (F+) well below unity and with low (10%) duty cycles. This unexpected low frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50% duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is 5–6 times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.

The Numerical Simulation Research on Heat Transfer Enhancement of the Interpolation-Tubular Air Pre-Heater with Semi-Elliptic Cylinder Shell Vortex Generator

2013 ◽  
Vol 397-400 ◽  
pp. 230-234
Author(s):  
De Fan Qing ◽  
Qing Feng Ai
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Vortex Generator ◽  
Elliptic Cylinder ◽  
Attack Angle ◽  
Width Ratio ◽  
Transfer Enhancement ◽  
Simulation Research ◽  
Number Range ◽  
Dip Angle

The semi-elliptic cylinder shell vortex generator set in the interpolation-tubular air pre-heater was studied. And by changing the high-width Ratiov, dip angleα, attack angleβ, spacingsof vortex generator to research the heat transfer and resistance properties under different working conditions, and the optimization structure of vortex generator was determined. The heating medium of the air pre-heater is the flue gas that passes across tube outside, and the cooling air as the cooling medium in the tube longitudinal scoured. The Reynolds number range is 25000 ~ 40000. The research shows that: semi-elliptic cylinder vortex generator can obviously improve the heat transfer performance, the optimization structure of the semi-elliptic cylinder vortex generator: high-width ratiov= 0.45, attack angleβ= 65 °, dip angleα= 15 °, spans= 90 mm, the heat transfer enhancement comprehensive effect raised about 43.2%~72.6%.

Turbine Separation Control Using Pulsed Vortex Generator Jets

2000 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Rolf Sondergaard ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
A Priori ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Order Of Magnitude ◽  
Flow Oscillations ◽  
Vortex Generator Jets

The application of pulsed vortex generator jets to control separation on the suction surface of a low pressure turbine blade is reported. Blade Reynolds numbers in the experimental, linear turbine cascade match those for high altitude aircraft engines and aft stages of industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets have a 30 degree pitch and a 90 degree skew to the freestream direction. Jet flow oscillations up to 100 Hz are produced using a high frequency solenoid feed valve. Results are compared to steady blowing at jet blowing ratios less than 4 and at two chordwise positions upstream of the nominal separation zone. Results show that pulsed vortex generator jets produce a bulk flow effect comparable to that of steady jets with an order of magnitude less massflow. Boundary layer traverses and blade static pressure distributions show that separation is almost completely eliminated with the application of unsteady blowing. Reductions of over 50% in the wake loss profile of the controlled blade were measured. Experimental evidence suggests that the mechanism for unsteady control lies in the starting and ending transitions of the pulsing cycle rather than the injected jet stream itself. Boundary layer spectra support this conclusion and highlight significant differences between the steady and unsteady control techniques. The pulsed vortex generator jets are effective at both chordwise injection locations tested (45% and 63% axial chord) covering a substantial portion of the blade suction surface. This insensitivity to injection location bodes well for practical application of pulsed VGJ control where the separation location may not be accurately known a priori.

Control of incident shock-induced boundary-layer separation using steady micro-jet actuators at M∞ = 3.5

2018 ◽  
Vol 233 (4) ◽  
pp. 1284-1306 ◽  
Author(s):  
Manisankar Chidambaranathan ◽  
Shashi B Verma ◽  
Ethirajan Rathakrishnan
Keyword(s):  
Boundary Layer ◽  
Pitch Angle ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Incident Shock ◽  
Skew Angle ◽  
Zero Crossing ◽  
Shock Generator ◽  
Jet Actuators ◽  
Injection Pressures

Experiments were carried out to control an incident shock-induced separation associated with 22° shock generator in a Mach 3.5 flow using an array of steady micro-jet actuators. Four micro-jet actuator configurations based on the variation in their pitch angle [Formula: see text], skew angle [Formula: see text] and span-wise spacing were used. Each of these configurations were placed 14 δ upstream of the interaction and operated with injection pressures ( Poj) varying from 140 to 643 kPa. While no major variations in separation characteristics were observed for Poj < 140 kPa, significant modifications were observed beyond [Formula: see text] of 140 kPa and until 208.5 kPa. Amongst all the four control configurations, micro-jet vortex generator 2 ([Formula: see text] showed the best control with a 2 δ downstream shift in separation point location relative to no-control. The shift is also accompanied with a change in maximum zero-crossing frequency towards higher frequency (almost twice), a reduction in the intermittency length and an increase in the correlation value between the boundary layer just upstream of the interaction and the intermittent region. These results indicate that the effectiveness of micro-jet vortex generator 2 is probably due to the improved entrainment levels in the shear layer induced by the micro-vortices which are generated downstream of these devices. The increase of the skew angle [Formula: see text] from 180° to 270° for the same pitch angle of β =  45° (micro-jet vortex generator 3) seems to have no major impact on the separation characteristics. The reduction in the span-wise spacing (micro-jet vortex generator 4) resulted in deterioration of the flow field due to the jet-to-jet interaction with increasing injection pressures.

Control of Separated Boundary-Layer on Subsonic Airfoil Using Vortex Generator Jet Devices

2006 ◽  
Author(s):  
A. Kourta ◽  
G. Petit ◽  
J. C. Courty ◽  
J. P. Rosenblum
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Three Dimensional ◽  
Vortex Generator ◽  
Leading Edge ◽  
Skin Friction Coefficient ◽  
Synthetic Jets ◽  
High Lift ◽  
Longitudinal Vortices

The control of subsonic high lift induced separation on airfoil may improve the flight envelope of current aircraft or even simplify the complex and heavy high-lift devices on commercial airframes. Until now, synthetic jets have proved a really interesting efficiency to delay or remove even leading-edge located separated areas on high-lift configuration but are not efficient for real scale aircrafts. In case of pressure-like separation (i.e. from trailing-edge), synthetic jets can be replaced by so the called “Vortex Generator Jets” which create strong longitudinal vortices that increase mixing in inner boundary layer and consequently the skin friction coefficient is increased to prevent separation. In this study, numerical simulations were undertaken on a generic three dimensional flat plate in order to quantify the effect of the longitudinal vortices on the natural skin friction coefficient. Both counter and co-rotative devices were tested at different exhaust velocities and distances between each others. Finally co-rotative vortex generators jets were tested on a three dimensional generic airfoil ONERA D. Results show a delay of the separation occurence but this solution does not seem to be as robust as synthetic jets. The study of jets spacing with respect to the efficiency of the devices shows a maximum for a given ratio of spacing to exhaust velocity.

Heat Transfer Augmentation and Flow Visualization With Delta Winglets in a Tube: A Numerical Approach

2020 ◽  
Author(s):  
Md. Islam ◽  
Liang Guangda ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Performance ◽  
Performance Enhancement ◽  
Swirling Flow ◽  
Circular Tube ◽  
Vortex Generator ◽  
Attack Angle ◽  
Maximum Enhancement ◽  
Longitudinal Vortices

Abstract In this research, heat transfer and pressure penalty from a circular tube with delta winglets insert are numerically investigated through Computational Fluid Dynamics (CFD) methodology. Numerical analysis with and without vortex generators (VGs) insert in a tube are done for a turbulent air flow, Reynolds number ranging from 6000 to 33000, under constant heat flux condition on the circular tube model surface. In our current research, we employed the shear stress transport (SST) k-omega model. The Nusselt number and friction factor results show the influence of the VGs insert on thermal performance. Effects of different winglet attack angles and blockage ratios on thermal performance enhancement were examined. Thermal performance is enhanced 5.1–30.7% using winglets in a tube. It is observed that small blockage ratio, B = 0.1 performed better than its counterpart of 0.2 and 0.3 for all the Reynolds number and for the same attack angle. The attack angle β = 15° and 30° showed better thermal performance enhancement at lower Re while at higher Re, β = 15° showed better performance. The maximum enhancement obtained for β = 30° and B = 0.1. Winglet vortex generator could create swirling flow when attack angle is 0 or 15°. When attack angle is increased, both swirling flow and longitudinal vortices appeared. At attack angle of 45°, large longitudinal vortices was found.

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